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  • Grain boundary driven mechanical properties of ZrB2 And ZrC-ZrB2 nanocomposite: A molecular simulation study
    J. Am. Ceram. Soc. (IF 2.841) Pub Date : 2018-01-19
    Md. Riaz Kayser, Ashfaq Adnan

    Abstract In this study, we report the grain boundary driven mechanical behavior of two polycrystalline ultra-high-temperature ceramics (UHTCs), zirconium diboride (ZrB2) and zirconium carbide (ZrC) with zirconium diboride (ZrC-ZrB2). These nanocomposites were investigated using large-scale molecular dynamics simulations. First, the atomistic models of the polycrystalline ZrB2 and ZrC-ZrB2 nanocomposites were subjected to tensile loading to determine their elastic constants and tensile strengths. It was found that the presence of nanoparticles imparts an insignificant effect on the mechanical properties of ZrB2. It has also been observed that the failure mechanisms of both the ZrB2 and ZrC-ZrB2 nanocomposite are driven by grain boundary deformation. At any instant during the applied load transfer, local tensile stress distribution data indicate that atomic stress becomes much higher near the grain boundaries compared to other locations. The authors performed additional sets of simulations to obtain tensile and shear properties of grain boundary material. When these properties were compared with the adjacent single crystal and overall polycrystalline material properties, it was found that the shear strength and stiffness of the grain boundary materials are significantly lower than the single crystal or polycrystal ZrB2. It is believed that the overall deformation and failure properties of ZrB2 and its composite are controlled by the properties of grain boundary. Hence, the addition of nanoparticles played an insignificant role on the mechanical properties of ZrB2. This article is protected by copyright. All rights reserved.

    更新日期:2018-01-19
  • Fabrication of dense polymer derived silicon carbonitride ceramic bulks by PIP processes without losing piezoresistivity
    J. Am. Ceram. Soc. (IF 2.841) Pub Date : 2018-01-19
    Baisheng Ma, Yiguang Wang

    Abstract Dense polymer-derived silicon carbonitride (SiCN) ceramic bulks were fabricated by powder consolidation following precursor infiltration and pyrolysis (PIP) densification. The density and open porosity of the ceramics varied from 1.42 g/cm3 and 32.75% before the PIP to 2.29 g/cm3 and 3.64% after the PIP, respectively. The electrical conductivity of the ceramics sharply increased from 6.26×10-10 S/cm before the PIP process to 3.20×10-7 S/cm after the 1st cycle of PIP and then gradually increased to 6.89×10-6 S/cm after four cycles of PIP. However, the piezoresistive coefficient did not change with the PIP. The Raman and electron paramagnetic resonance results show that the graphitization level of free carbon in ceramics derived from PIP was higher than the ceramics derived from powder consolidation. The high graphitization level of free carbon leads to a high conductivity, and thus the conductivity of ceramics increased significantly after the PIP process. The carbon cluster size, which is related to the gauge factor of piezoresistivity, did not change significantly after the PIP process; thus, the gauge factor did not change significantly. Dense, large-scale polymer-derived ceramics were fabricated by combined conventional powder consolidation and PIP without the loss of piezoresistivity. These ceramics have potential application as both structural and functional components that can bear loads as well as monitor variations in external stress. This article is protected by copyright. All rights reserved.

    更新日期:2018-01-19
  • Improving high power properties of PZT ceramics by external DC bias field
    J. Am. Ceram. Soc. (IF 2.841) Pub Date : 2018-01-19
    Anushka Bansal, Husain N. Shekhani, Maryam Majzoubi, Eberhard Hennig, Timo Scholehwar, Kenji Uchino

    Abstract This paper concludes that the deterioration of the mechanical quality factor Qm when operated under high power, can be recovered by externally applying positive DC bias field. Material constants for piezoelectric ceramics are generally characterized under low power conditions. However, high-power properties deviate significantly from the ones measured under low power conditions (Qm degrades by a factor of ~2). DC Bias field helps to recover the properties of the ceramic under high power conditions. The DC bias field of 200 V/mm exhibits an almost equivalent “opposite” change rate to the vibration velocity of 0.1 m/sec. It is also notable that the piezoelectric loss tan θ’ can be decreased most effectively under positive DC bias field (1.9% per 100 V/mm for the hard PZT and 3.1% per 100 V/mm for the soft PZT), in comparison with the elastic or dielectric losses. This report presents a comprehensive analysis on the low and high power piezoelectric properties of hard and soft Lead Zirconate Titanates (PZT's) under externally applied DC bias field in the k31 resonance mode (transverse extensional). This article is protected by copyright. All rights reserved.

    更新日期:2018-01-19
  • Low-temperature synthesis of uranium monocarbide by a Pechini-type in-situ polymerizable complex method
    J. Am. Ceram. Soc. (IF 2.841) Pub Date : 2018-01-19
    Hangxu Guo, Jieru Wang, Jing Bai, Shiwei Cao, Denglei Chen, Yalou Sun, Xiaojie Yin, Wei Tian, Cunmin Tan, Zhi Qin, Qihuang Deng

    Abstract Uranium monocarbide (UC) was successfully synthesized by the Pechini-type in-situ polymerizable complex technique (IPC) with the organic matter as the only carbon source. In the aqueous process, a mixture of citric acid (CA) and mannitol with UO22+ was polymerized to form a spongy-like organic polymeric precursor without any precipitations. The structural evolution and formation mechanism of the precursor were investigated using XRD, DSC-TG, SEM (EDX), TEM and FT-IR. XRD results demonstrated that UC was obtained with the UO22+/mannitol/CA molar ratios of 1.0/0.3/1.0 at a low temperature of 1400 °C. SEM and TEM analyses revealed that the UO2 nanoparticles were uniformly distributed in the carbon matrix to form UO2/C nanocomposites, and submicron-sized ellipsoidal UC particles cemented together. FT-IR showed that a UO22+-CA chelated structure was firstly obtained, achieving the molecular-scale mixing of uranium and C. Then the in-situ charring guaranteed the intimate contact of UO2 and C, leading to a low reaction temperature in carbothermal reduction owing to a short diffusion distance. This article is protected by copyright. All rights reserved.

    更新日期:2018-01-19
  • Structural dependence of crystallization in glasses along the nepheline (NaAlSiO4) - eucryptite (LiAlSiO4) join
    J. Am. Ceram. Soc. (IF 2.841) Pub Date : 2018-01-19
    José Marcial, Joey Kabel, Muad Saleh, Nancy Washton, Yaqoot Shaharyar, Ashutosh Goel, John S. McCloy

    Abstract Lithium and sodium aluminosilicates are important glass-forming systems for commercial glass ceramics, as well as being important model systems for ion transport in battery studies. Additionally, uncontrolled crystallization of LiAlSiO4 (eucryptite) in high-Li2O compositions, analogous to the more well-known problem of NaAlSiO4 (nepheline) crystallization, can cause concerns for long-term chemical durability in nuclear waste glasses. To study the relationships between glass structure and crystallization, nine glasses were synthesized in the LixNa1-xAlSiO4 series, from x = 0 to x = 1. Raman spectra, nuclear magnetic resonance (NMR) spectroscopy (Li-7, Na-23, Al-27, Si-29), and X-ray diffraction were used to study the quenched and heat-treated glasses. It was found that different LiAlSiO4 and NaAlSiO4 crystal phases crystallize from the glass depending on the Li/Na ratio. Raman and NMR spectra of quenched glasses suggest similar structures regardless of alkali substitution. Li-7 and Na-23 NMR spectra of the glass ceramics near the endmember compositions show evidence of several differentiable sites distinct from known LixNa1-xAlSiO4 crystalline phases, suggesting that these measurements can reveal subtle chemical environment differences in mixed-alkali systems, similar to what has been observed for zeolites. This article is protected by copyright. All rights reserved.

    更新日期:2018-01-19
  • Non-isothermal crystallization kinetics of Al2O3-YAG amorphous ceramic coating deposited via plasma spraying
    J. Am. Ceram. Soc. (IF 2.841) Pub Date : 2018-01-19
    Jian Rong, Kai Yang, Yin Zhuang, Xinghua Zhong, Huayu Zhao, Jinxing Ni, Shunyan Tao, Liang Wang, Chuanxian Ding

    Abstract Crystallization kinetics of the newly developed Al2O3-Y3Al5O12 (YAG) amorphous ceramic coating fabricated by atmospheric plasma spraying (APS) were investigated via differential scanning calorimetry (DSC) under non-isothermal conditions. The phase compositions and microstructure of the as-sprayed coating were characterized by X-ray diffraction (XRD) and Scanning electron microscopy (SEM). The glass transition temperature Tg, the onset temperature of crystallization Tc and the peak temperature of crystallization Tp presented heating rate dependence. The related kinetic parameters of activation energies (Eg, Ec, Ep) and Avrami exponents (n) were quantified using various methods including Kissinger, Augis-Bennett, Ozawa and Matusita-Sakka, etc, to understand the phase transition mechanism and crystallization process in depth. A series of parameters including devitrification interval ΔT, thermal stability (Tc、Ec), nucleation resistance Ec/RTg and fragility index F were quantified in order to evaluate the nucleation mechanism, crystallization behavior and thermal stability of Al2O3-YAG amorphous ceramic coating. Excellent thermal stability was witnessed in the studied coating. Furthermore, the YAG crystalline phases can be reasonably controlled and independently precipitated from the amorphous matrix via proper annealing. This article is protected by copyright. All rights reserved.

    更新日期:2018-01-19
  • Investigation of phase composition and microwave dielectric properties of MgO-Ta2O5 ceramics with ultra-high Qf value
    J. Am. Ceram. Soc. (IF 2.841) Pub Date : 2018-01-19
    Mingzhao Dang, Haishen Ren, Xiaogang Yao, Haiyi Peng, Tianyi Xie, Huixing Lin, Lan Luo

    Abstract Four MgO-Ta2O5 ceramics with the MgO/Ta2O5 mole ratio x=1, 2, 3 and 4 were prepared by traditional solid state reaction method, and the influence of x on the phase composition, microstructure and dielectric properties (the dielectric constant εr, the temperature coefficient of resonant frequency τf and the quality factor Qf) of the materials was investigated by using XRD, SEM, etc. The results indicated that the ceramics were composed of two crystalline phases MgTa2O6 and Mg4Ta2O9 in the composition range studied, and that the dielectric properties ln ε, 1/Qf and τf changed proportionally to the fraction of main crystal phases, which meet perfectly with the mixing model proposed in this study. It is obvious that the proportion of the two crystal phases could be precisely controlled by x, and thereby, the dielectric properties can be conveniently and precisely tailored. Our research provided a new microwave dielectric ceramic with the composition of 2MgO-Ta2O5, which has an ultra-high Qf value (211 000 GHz), low dielectric constant εr (19.9) and near zero temperature coefficient of resonant frequency τf (8 ppm/°C). This article is protected by copyright. All rights reserved.

    更新日期:2018-01-19
  • Cationic effect of charge compensation on the sulfide capacity of aluminosilicate slags
    J. Am. Ceram. Soc. (IF 2.841) Pub Date : 2018-01-19
    Joon Sung Choi, Youngjoo Park, Sunghee Lee, Dong Joon Min

    Abstract The effect of CaO on the sulfide capacity of CaO-Al2O3-SiO2 slags was studied from the viewpoint of the ionic structure of alumina in slag. The aluminum coordination number was analyzed using 27Al 500-MHz solid nuclear magnetic resonance spectroscopy and the results were compared with those of the sulfide capacity analysis. The sulfide capacity of slag, in the peralkaline region 1.0), exhibited a linear relationship with respect to basicity (a02-) as excess free Ca2+ formed a four-coordinated aluminum unit structure ([IV]Al; AlO45-) and stabilized the sulfide ions. However, sulfide capacity in the peraluminous region (Xcao/XA12os<1.0) exhibited a nonlinear relationship with respect to basicity (ao2-) owing to the structure of higher-coordinated aluminum units ([V]Al,[VI]Al; Al3+) and the relative lack of Ca2+. Therefore, the sulfide capacity of high Al2O3-bearing slags strongly depended on the basicity (ao2-) and stability of sulfide ions (γs2-), which depended on the competitive behavior of Ca2+ owing to the structural changes in Al2O3. The effect of the aluminum coordination number on the sulfide capacity was discussed in detail using an analysis of the slag structure and thermodynamics model. This article is protected by copyright. All rights reserved.

    更新日期:2018-01-19
  • Preparation of Homogeneous Mullite Based Fibrous Ceramics by Starch Consolidation
    J. Am. Ceram. Soc. (IF 2.841) Pub Date : 2018-01-19
    Wenjie Zang, Tao Jia, Xue Dong, Jiachen Liu, Haiyan Du, Feng Hou, Anran Guo

    Abstract Silica sol is one of the frequently-used binders in high-temperature resisting fibrous porous ceramics, but in the drying process, it can diffuse with water and influence the uniformity of ceramics. To solve this diffusion problem and fabricate homogeneous fibrous porous ceramics, cationic starch was firstly introduced in mullite fibrous system. The effects of starch content and high temperature binder content on microstructure, physical and mechanical properties were also investigated. The results indicate that starch consolidated mullite fibrous ceramics owned a homogeneous 3D skeleton structure, since the introduced starch can absorb both water and silica particles by gelatinization and ensure the even distribution of binders. Compared with the mullite fibrous ceramics fabricated without starch addition, starch consolidated ceramics owned better microstructure and higher interior compression strength. Furthermore, both the starch and silica sol content had great impact on the microstructure, density, porosity, thermal conductivity and compressive strength of the fibrous ceramic. This article is protected by copyright. All rights reserved.

    更新日期:2018-01-19
  • Influence of calcium additions on the compressive strength and microstructure of alkali-activated ceramic sanitary-ware
    J. Am. Ceram. Soc. (IF 2.841) Pub Date : 2018-01-19
    L. Reig, L. Soriano, M.M. Tashima, M.V. Borrachero, J. Monzó, J. Payá

    Abstract The ceramic sanitary-ware market generates large amounts of waste, both during the production process and due to construction and demolition practices. In this paper, the effect of different amounts and calcium sources (calcium hydroxide Ca(OH)2, calcium aluminate cement CAC, Portland cement PC) on the alkaline activation of ceramic sanitary-ware waste (CSW) was assessed. Blended samples were activated with NaOH and sodium silicate solutions and cured for 3 and 7 days at 65 °C. The maximum amount of calcium source-type added to the system varied according to its influence on the compactability of the mortars.CSW was physico-chemically characterized and the compressive strength development of activated samples was assessed on the mortars. The nature of the reaction products was analyzed in pastes, by X-ray diffraction, thermogravimetric analysis, infrared spectroscopy and microscopic studies. The results show a great positive influence with the addition of moderate amounts of Ca(OH)2, PC and CAC on the mechanical properties. Among the typical hydrates usually observed in plain water-hydrated PC or CAC, only AH3 and a small amount of C3AH6 were identified in the alkali-activated CSW/CAC blended pastes, which indicates that Al and Ca from PC, CAC and Ca(OH)2 are taken up in the newly-formed (N,C)-A-S-H or C-A-S-H gels. This article is protected by copyright. All rights reserved.

    更新日期:2018-01-19
  • Generation of Hydrogen under visible light irradiation with enhanced photocatalytic activity of Bi2WO6/Cu1.8Se for organic pollutants under Vis-NIR light reign
    J. Am. Ceram. Soc. (IF 2.841) Pub Date : 2018-01-16
    Li-Na Qiao, Huan-Chun Wang, Yi-Dong Luo, Hao-Min Xu, Junping Ding, Shun Lan, Yang Shen, Yuan-Hua Lin, Ce-Wen Nan

    Abstract To make better use of solar light, a new Bi2WO6 /Cu1.8Se photocatalyst active to visible and near-infrared light has been synthesized by a facile hydrothermal method. The composites were characterized by X-ray diffractometry (XRD), scanning electron microscopy (SEM), UV-vis diffuse reflectance spectroscopy (DRS) and photoluminescene (PL). The photocatalytic activities of Bi2WO6 /Cu1.8Se are evaluated by degrading Congo red solution and hydrogen generation from water. It was found that the molar percentage of Cu1.8Se had great effects on the morphology and photocatalytic property of the Bi2WO6/Cu1.8Se heterojunctions, and the composite with suitable molar amount of Cu1.8Se exhibits much enhanced photocatalytic activity for Congo red degradation under visible and near-infrared light irradiation and for hydrogen generation under visible light compared to Bi2WO6. The significant improvement photocatalytic activity of the composite could be attributed to its good light absorption, suitable band gap structure and effective separation of photogenerated electron–hole pairs of Bi2WO6/Cu1.8Se heterojunction. This work presents an efficient multifunction photocatalyst owning the activity both for water splitting under visible light and for organic contaminants decomposition under visible-near-infrared light. This article is protected by copyright. All rights reserved.

    更新日期:2018-01-17
  • Intriguing role of TiO2 in glass–ceramics: Bioactive and magneto-structural properties
    J. Am. Ceram. Soc. (IF 2.841) Pub Date : 2018-01-15
    Satwinder Singh Danewalia, K. Singh

    Abstract We report on the structural, magnetic and bioactive properties of TiO2 modified silicate glasses. Additions of TiO2 and heat treatment, shows remarkable and distinguishable effect on the properties of the glasses. Growth of titania–modified magnetic nanocrystals played effective role in the evolution of magnetic properties of the glass–ceramics. Some of the samples exhibit superparamagnetic nature, while others are found to be antiferromagnetic. Interestingly, after heat–treatment the magnetization trend of the samples reversed. The in–vitro bioactivity of these glass–ceramics was accessed by the formation of bone–like apatite structures on their surfaces after immersion in simulated body fluid (SBF). The magnetic properties along with the bioactivity of present glass–ceramics indicate their usefulness in the magnetically induced hyperthermia treatment of cancer. This article is protected by copyright. All rights reserved.

    更新日期:2018-01-15
  • Interaction of slip- and flame-spray coated carbon-bonded alumina filters with steel melts
    J. Am. Ceram. Soc. (IF 2.841) Pub Date : 2018-01-15
    Patrick Gehre, Anne Schmidt, Steffen Dudczig, Jana Hubálková, Christos G. Aneziris, Nick Child, Ian Delaney, Gilbert Rancoule, Duane DeBastiani

    Abstract Ceramic foam filters play an essential role in the quest for cleanliness of cast steel parts as they facilitate turbulence reduction during mold filling as well as removal of nonmetallic inclusions. A coating on these filters is able to increase their strength and filtration efficiency by improving the adhesion of inclusions to the filter strands. In this study, Al2O3-C filters were coated with an alumina slip via slip and flame spraying. The phase composition and the microstructure of the coatings were investigated before and after immersion into molten steel contained in a metal casting simulator. After contact with molten steel, Al2O3-C reference filter shows intense decarburization which often influence the quality of cast steel parts due to formation of gas bubbles. Slip-sprayed alumina coatings on such a filter promote the deposition of inclusions due to formation of a vitreous alumina layer but will also cause gas bubble formation as they exhibit a high porosity. Flame-spray coatings have low porosity and hence, prevent formation of gas bubbles. Furthermore, they showed the highest reactivity towards the steel melt and hence, are recommended for filtration of cast products with a high demand on cleanliness. This article is protected by copyright. All rights reserved.

    更新日期:2018-01-15
  • Combined experimental and ab initio based determination of the thermal expansion of La0.5Sr0.5Co0.25Fe0.75O3
    J. Am. Ceram. Soc. (IF 2.841) Pub Date : 2018-01-12
    X. Yin, A. Beez, N. H. Menzler, R. Spatschek

    Abstract The thermal expansion of La0.5Sr0.5Co0.25Fe0.75O3 (LSCF55) is investigated both by first principles phonon calculations combined with the quasi-harmonic approximation (QHA) and by experimental approaches. Within the framework of the QHA, the volumetric thermal expansion coefficient of rhombohedral LSCF55 is calculated as αV,GGA=50.34*10-6k-1. For comparison, the lattice expansion and the volume expansion of LSCF55 grain are measured by in-situ high temperature X-ray diffractometer (HT-XRD). An anisotropic thermal expansion of rhombohedral LSCF55 with αa,hex=10.89*10-6K-1 and α c,hex=21.18*10-6K-1 is obtained. The volumetric thermal expansion coefficient is measured as αV,HT-XRD=43.17*10-6K-1. Additionally, the effectively isotropic expansion coefficients of a polycrystalline LSCF55 bar specimen are measured using a vertical high-performance thermo-mechanical analyzer and yield αl,bar specimen=17.37*10-6K-1 and αV,bar specimen=52.11*10-6K-1. This article is protected by copyright. All rights reserved.

    更新日期:2018-01-12
  • Inversion Domain Network Stabilization and Spinel Phase Suppression in ZnO
    J. Am. Ceram. Soc. (IF 2.841) Pub Date : 2018-01-11
    Joshua Hoemke, Eita Tochigi, Tetsuya Tohei, Hidehiro Yoshida, Naoya Shibata, Yuichi Ikuhara, Yoshio Sakka

    AbstractThe development of inversion domain networks consisting of basal-plane and pyramidal-plane inversion domain boundary (b-IDB and p-IDB) interfaces within grains in Sn-Al dual-doped ZnO (Zn0.98Sn0.01Al0.01O) polycrystalline ceramics has been confirmed using transmission electron microscopy. The atomic structure of the b-IDB and p-IDB interfaces has been analyzed using atomic-resolution scanning transmission electron microscopy. The localization of Sn and Al at the respective sites of the b-IDBs and p-IDBs was confirmed by energy-dispersive X-ray spectroscopy. In contrast to Sn or Al single-dopant addition to ZnO, which results in the formation of spinel phase precipitates without the development of inversion domain networks, Sn-Al dual-doping caused the suppression of spinel phase formation and the formation of monophasic inversion domain networks composed of RMO3(ZnO)n homologous phase compound members, where R and M represent dopants substituting at the b-IDB and p-IDB sites, with a general formula of SnAlO3(ZnO)n. The results of this study demonstrate that the formation of inversion domain networks in ZnO-based ceramics can be stabilized via multiple-dopant addition. This finding has potential implications for the modification of the bulk or nanoscale properties based on the choice of the specific dopants, R and M, the control of the ratio R:M and the value of n in the RMO3(ZnO)n homologous phase compound members constituting the inversion domain networks.This article is protected by copyright. All rights reserved.

    更新日期:2018-01-11
  • Boron-dependent microstructural evolution, thermal stability and crystallization of mechanical alloying derived SiBCN
    J. Am. Ceram. Soc. (IF 2.841) Pub Date : 2018-01-11
    Daxin Li, Zhihua Yang, Dechang Jia, Delong Cai, Shengjin Wang, Qingqing Chen, Yu Zhou, Dongli Yu, Yongjun Tian

    AbstractAmorphous boron-rich SiBCN were prepared by high-energy ball milling of the mixtures of Si, graphite, h-BN and inorganic boron, which acted as extra boron source. The solid-state amorphization, thermal stability and crystallization of the boron-rich SiBCN were studied in detail. It was suggested that mechanical alloying can drive solid-state amorphization but also can be an initiation step for the nucleation of nanocrystals. The amorphous networks of Si-C, C-B, C-C, C-N, B-N and C-B-N bonds are detected by XPS; however, solid-state NMR further confirms the formation of a new chemical environment around B atoms, BC3. The increases in boron content improve the thermal stability of SiBCN ceramics but weaken their oxidation resistance. Nano-SiC crystallizes first while BN(C) forms subsequently. Boron promoting SiC crystallization may result from the reduced hindering effects of B-N-C nanodomains that retard SiC crystallization.This article is protected by copyright. All rights reserved.

    更新日期:2018-01-11
  • Powder Chemistry Effects on the Sintering of MgO-doped Specialty Al2O3
    J. Am. Ceram. Soc. (IF 2.841) Pub Date : 2018-01-11
    T. Frueh, C. Marker, E. R. Kupp, C. Compson, J. Atria, J. L. Gray, Z.-K. Liu, G. L. Messing

    AbstractIn this work we investigate the effects of powder chemistry on the sintering of MgO-doped specialty alumina. The stages at which MgO influences densification of Al2O3 were identified by comparing dilatometry measurements and the sintering kinetics of MgO-free and MgO-doped specialty alumina powders. MgO is observed to reduce the grain boundary thickness during densification using TEM. We show that MgO increases the solubility of SiO2 in alumina grains near the boundaries using EDS. First-principles DFT calculations demonstrate that the co-dissolution of MgO and SiO2 in alumina is thermodynamically favored over the dissolution of MgO or SiO2 individually in alumina. This study experimentally demonstrates for the first time that removal of SiO2 from the grain boundaries is a key process by which MgO enhances the sintering of alumina.This article is protected by copyright. All rights reserved.

    更新日期:2018-01-11
  • Chemical composition and temperature dependence of the energy storage properties of Ba1-xSrxTiO3 ferroelectrics
    J. Am. Ceram. Soc. (IF 2.841) Pub Date : 2018-01-11
    Bingcheng Luo, Xiaohui Wang, Enke Tian, Haimo Qu, Qiancheng Zhao, Ziming Cai, Hongxian Wang, Wei Feng, Baiwen Li, Longtu Li

    AbstractDielectric materials with high power and energy densities are desirable for potential applications in advanced pulsed capacitors. Computational material designs based on first-principles calculations provide a “bottom-up” method to design novel materials. Here, we present a first-principles effective Hamiltonian simulation of perovskite ferroelectrics, Ba1-xSrxTiO3, for energy storage applications. The effects of different chemical compositions, temperatures, and external electric fields on the ferroelectric hysteresis and energy storage density of Ba1-xSrxTiO3 were investigated. The Curie temperature was tuned from 400 K to 100 K by doping Sr in the BaTiO3 lattice. At a constant temperature, the ferroelectric hysteresis became slimmer as the Sr content increased, and the energy storage efficiency increased. For the same chemical composition, the energy storage density increased as the temperature increased. For the composition x=0.4, a discharged energy density of ~2.8 J/cm3 with a 95% efficiency was obtained in an external electric field of 350 kV/cm, and a discharged energy density of 30 J/cm3 with a 92% efficiency was obtained in an external electric field of 2750 kV/cm. The energy storage property predictions and new material designs have potential to create experimental and industrial products with higher energy storage densities.This article is protected by copyright. All rights reserved.

    更新日期:2018-01-11
  • Environmental resistance of Cr2AlC MAX phase under thermal gradient loading using a burner rig
    J. Am. Ceram. Soc. (IF 2.841) Pub Date : 2018-01-11
    J. Gonzalez-Julian, T. Go, D. Mack, R. Vaßen

    AbstractDense Cr2AlC materials were tested under a gradient loading for the first time using a burner rig. The severe thermal cycling conditions consist of 500 short cycles at 1200 °C, with an accumulative time at the maximal temperature of more than 58 29 h. The samples showed no visible damage under these conditions due to the formation of an outer protective α-Al2O3 layer, which shows a strong adhesion with the Cr2AlC substrate. No cracks, delamination or damage were observed at the interface between the different layers. This excellent response under cyclic loading shows the excellent potential of Cr2AlC compounds for high temperature applications.This article is protected by copyright. All rights reserved.

    更新日期:2018-01-11
  • Magnetocrystalline anisotropy in the Co/Fe co-doped aurivillius oxide with different perovskite layer number
    J. Am. Ceram. Soc. (IF 2.841) Pub Date : 2018-01-09
    Wen Gu, Xiaoning Li, Shujie Sun, Liuyang Zhu, Zhengping Fu, Yalin Lu

    Abstract Perpendicular magnetic anisotropic materials are of great interest for their huge potential to realize high-density non-volatile memory and logic chips. Designing such materials with lower cost and better magnetoelectric coupling still remains major challenges. In this work, aurivillius oxide ceramics with highly [00l]-oriented grains were prepared by a facile pressureless sintering method, and the perovskite layer number was modified by varying the cobalt content. Afterwards, the unique perpendicular magnetic anisotropy and the intriguing anisotropic ferroelectric properties have been observed. The magnetic properties of the aurivillius oxides with different layer numbers have been carefully investigated by field cooling, zero field cooling, and the magnetization with a varying field. The magnetic anisotropy in the oriented ceramics is demonstrated to be caused by the magnetocrystalline anisotropy with the easy magnetization direction along the c-axis, which possibly arises from the unquenched 3d orbitals combined with the special layered crystal structures. The magnetocrystalline anisotropy becomes weaker in the ceramics with lower-numbered perovskite layers, while the orientation degree of the ceramics and the ferroelectric anisotropy show quite opposite trends. Furthermore, the weak magnetoelectric coupling is also observed in the ceramics. This special anisotropic multiferroic properties may open up a new window for the aurivillius materials. This article is protected by copyright. All rights reserved.

    更新日期:2018-01-09
  • Polymer derived ceramic adsorbent for pollutant removal from water
    J. Am. Ceram. Soc. (IF 2.841) Pub Date : 2018-01-09
    Damla Zeydanli, Suleyman Akman, Cekdar Vakifahmetoglu

    Abstract Polymer derived ceramic components (SiOC, sample W) were produced from preceramic polymer mixture and a catalyst. After curing and pyrolysis, some of the samples etched by hydrofluoric acid to obtain carbonaceous SiOC (C-rich SiOC, sample W-HF). W and W-HF were tested as an adsorbent material to remove both heavy metals ions (Cr (III), Pb (III) and Cd (II)) and cationic dyes (Methylene Blue (MB), Rhodamine B (RB) and Crystal Violet (CV)) from aqueous solutions. HF treated high surface area SiOC samples had quite high adsorption affinity for cationic dyes. According the Langmuir isotherm model the maximum dye uptake values were found to be around to 50 mg/g for sample W whereas those for sample W-HF ranged from 104 to 186 mg/g. Regeneration studies were conducted both by heat treatment and leaching, high recovery yields (always above 97%) of MB adsorption were obtained. This article is protected by copyright. All rights reserved.

    更新日期:2018-01-09
  • Synthesis and color properties of the TiO2@CoAl2O4 blue pigments with low cobalt content applied in ceramic glaze
    J. Am. Ceram. Soc. (IF 2.841) Pub Date : 2018-01-09
    Xuanmeng He, Fen Wang, Hui Liu, Lijun Niu, Xinzhen Wang

    Abstract the TiO2@CoAl2O4 complex blue pigments with low cobalt content were synthesized through calcinations of the precursor obtained from co-precipitating Co2+ and Al3+ to form Co-Al LDHs (layered double hydroxides) on the surface of TiO2 particles. The structure and the properties of the synthesized pigments were characterized by XRD, SEM, TEM, UV-Vis spectroscopy, XPS and colorimeter. The precursors of the blue TiO2@CoAl2O4 complex pigments were consisted of LDHs shell layer encapsulated TiO2 microsphere. After calcinations at 1100°C, the LDHs shell layer were absolutely transformed to the spinel CoAl2O4, and the pigments presented a core-shell structure and uniform sphere morphology (the diameter of microsphere was about 780nm). The absorption bands at around 547, 584 and 624 nm in the Uv-Vis absorption spectra of the TiO2@CoAl2O4 complex pigments were corresponded to the characteristic absorption bands of the spinel CoAl2O4, revealed the pigments with a bright blue hue. Besides, as the mass ratio of CoAl2O4/TiO2 increased to 0.4, the blue component of the pigments reached to 27.89 and slight color variation with the increase of the CoAl2O4 content in a range, possessed low cobalt content and exhibited a stabile performance in commercial low-temperature ceramic glazes. The XGT results showed that the TiO2@CoAl2O4 complex pigments with low cobalt content presented bright color in ceramic glaze. Especially, the synthesized pigments reduced the usage and toxicity of cobalt, which were efficiency for economy and environmental protection. This article is protected by copyright. All rights reserved.

    更新日期:2018-01-09
  • Controllable wear behaviors of silicon nitride sliding against sintered polycrystalline diamond via altering humidity
    J. Am. Ceram. Soc. (IF 2.841) Pub Date : 2018-01-05
    Wenbo Qin, Wen Yue, Chengbiao Wang

    AbstractThe tribological behaviors of silicon nitride (Si3N4) sliding against sintered polycrystalline diamond (PCD) were investigated by varying the relative humidity (RH) in the testing atmosphere. The results indicated that higher RH corresponds to higher wear loss of Si3N4 and the wear loss of PCD almost fell close to zero. Especially in the case of 85% RH, both a maximum wear loss of Si3N4 and a maximum friction coefficient were achieved. Besides, this study revealed insights into the interface chemistry effects on the wear behavior of Si3N4 under humidity. When water molecules were introduced into the testing atmosphere, the hydrolysis reaction occurred on the Si3N4 surface with the formation of the Si-O-Si bond across the sliding interface. And then, the hydration reaction dominated the process, during which Si-OH was formed through the bond fracture of the Si-O-Si. The X-ray Photoelectron Spectroscopy (XPS) results showed that the ratios of Si-OH/Si-O and Si-N/Si-OH+Si-O bonds increased as the relative RH levels increased. As a consequence, the wear loss of Si3N4 significantly increased. Thus, due to the hydrolysis and hydration reactions, the tribological behaviors of Si3N4 against sintered polycrystalline diamond can be essentially controlled via varying RH levels.This article is protected by copyright. All rights reserved.

    更新日期:2018-01-05
  • Inorganic polymers made of fayalite slag: on the microstructure and behavior of Fe
    J. Am. Ceram. Soc. (IF 2.841) Pub Date : 2018-01-04
    Silviana Onisei, Alexios P. Douvalis, Annelies Malfliet, Arne Peys, Yiannis Pontikes

    Abstract The microstructure of inorganic polymers (IP) formed from fayalite slag was investigated as a function of the composition of different activating solutions. The starting slag was 80 wt% amorphous, and after activation using sodium silicate solutions with varying SiO2/Na2O molar ratios, the amorphous phase dissolved and a binder phase was formed. The morphology of this binder, including the population and size of remnant particles and pores, was dependent on the particular activating solution used, and became denser as the level of silicate rose. 57Fe Mössbauer spectroscopy revealed that the IP synthesis reaction is combined with the oxidation of Fe2+ from the fayalite slag to Fe3+ in the inorganic polymer binder. The reaction extent varied and could be quantified using the absorption areas of these ions. Data corroborate that the Fe2+ ions in the amorphous part of the fayalite slag and the Fe3+ ions in the new binder phase had an average oxygen-coordination number of 5. This article is protected by copyright. All rights reserved.

    更新日期:2018-01-04
  • Control of Ferroelectric and Linear Piezoelectric Response of PZT Films through Texture
    J. Am. Ceram. Soc. (IF 2.841) Pub Date : 2018-01-03
    Debashish Das, Luz Sanchez, Joel Martin, Brian Power, Steven Isaacson, Ronald G. Polcawich, Ioannis Chasiotis

    AbstractThe high and low field ferroelectric response of freestanding PbZr0.52Ti0.48O3 (PZT) films, with texture varying from 100% (001) to 100% (111) was investigated via 500 nm thick PZT unimorphs deposited on the same substrate. It is shown that the ferroelectric and piezoelectric properties depend strongly on texture, as the effective transverse strain and stress coefficients vary linearly with %(001) and %(111) texture factors. PZT films with 100% (001) orientation displayed 150%, 140%, and 80% larger linear piezoelectric strain coefficient, saturated strain coefficient, and saturated stress coefficient, respectively, compared to films with 100% (111) orientation. As a result, pure (001) textured PZT films with 20% higher dielectric constant showed 50% higher figure of merit in sensing than films with pure (111) texture. The piezoelectric and ferroelectric properties of all but one combinations of (001) and (111) texture were shown for the first time to be bounded by the values for 100% (001) and 100% (111) texture. A notable exception was PZT films comprised of 73% (001) and 27% (111) texture which showed stable piezoelectric coefficients at all electric fields, with major technological implication to low power microdevices. Finally, the coercive field was shown to decrease with (001) texture factor and excess-Pb in the PZT and the PbTiO3 seed layer.This article is protected by copyright. All rights reserved.

    更新日期:2018-01-03
  • Phase transition of Eu2Ti2O7 under high pressure and a new ferroelectric phase with perovskite-like layered structure
    J. Am. Ceram. Soc. (IF 2.841) Pub Date : 2018-01-02
    Zhipeng Gao, Yi Liu, Chengjia Lu, Yuanhua Xia, Leiming Fang, Yongjun Ma, Qiang He, Duanwei He, Sinuo Yang

    AbstractFerroelectrics with perovskite - like layered (PL) structure are well known for their high Tc and the application prospect of high-temperature-piezoelectric sensing. In this study, the PL-structure Eu2Ti2O7 was prepared by one-step high pressure sintering, which show the pyrochlore structure of Eu2Ti2O7 would change into PL structure at 11 GPa, 1300°C. The PL-structure Eu2Ti2O7 is metastable, which will change back to pyrochlore structure at about 900°C in the air. The PL-structure Eu2Ti2O7 was confirmed as a high temperature ferroelectric material for the first time. The ferroelectric domain switching was directly observed using piezoelectric force microscope. The piezoelectric constant of the PL Eu2Ti2O7 ceramic was measured as 0.7-0.9 pC/N and its thermal depoling temperature (Td) was determined as 800 °C, which is associated with the PL-pyrochlore transition.This article is protected by copyright. All rights reserved.

    更新日期:2018-01-02
  • Amorphization-induced volume change and residual stresses in boron carbide
    J. Am. Ceram. Soc. (IF 2.841) Pub Date : 2018-01-02
    Gregory Parsard, Ghatu Subhash, Phillip Jannotti

    AbstractThe residual pressure surrounding quasistatic and dynamic Vickers indentations in boron carbide was quantitatively mapped in three dimensions using Raman spectroscopy. These maps were compared against similar maps of amorphization intensity and optical micrographs of deformed regions to determine the roles of amorphization and damage upon indentation-induced residual stress. Stress relaxation was observed near radial cracks, spalled regions, and graphitic inclusions. A positive correlation was found between high levels of residual stress and the number of amorphized sites detected. Finite element simulations were conducted to model the indentation-induced residual stress fields in the absence of amorphization and cracking. The simulations underpredicted the average residual pressure observed through Raman spectroscopy, implying that amorphization contributes to increased pressure in the material. This pressure is interpreted as potential evidence of volumetric expansion of the amorphized material which is less ordered and hence exerts compressive forces on the surrounding crystalline matrix.This article is protected by copyright. All rights reserved.

    更新日期:2018-01-02
  • A phase diagram of Ba1-xCaxTiO3 (x=0-0.30) piezoceramics by Raman spectroscopy
    J. Am. Ceram. Soc. (IF 2.841) Pub Date : 2018-01-02
    Chang Shu, Daniel Reed, Tim W. Button

    AbstractPiezoelectric ceramics are widely used in sensors, actuators and ultrasonic transducers due to their ability to achieve efficient conversion between electric and mechanical energy. There is a current drive towards lead-free material systems capable of achieving comparable piezoelectric performance to environmentally hazardous, but commonly used, lead-based materials such as lead zirconate titanate.This work constructs an accurate phase diagram for barium calcium titanate (Ba1-xCaxTiO3 or BCTO). The substitution of Ca2+ on the Ba-site of BCTO is of much interest due to electric property improvements compared to BaTiO3. In this work, Ba1-xCaxTiO3 (x=0-0.30) samples have been made by solid-state methods and, following initial characterisation by XRD, evaluation of changes in the Raman spectra has allowed accurate determination of the phase transition temperatures and the construction of a phase diagram.This article is protected by copyright. All rights reserved.

    更新日期:2018-01-02
  • Ionic transport in AgI-HgS-As2S3 glasses: Critical percolation and modifier-controlled domains
    J. Am. Ceram. Soc. (IF 2.841) Pub Date : 2018-01-02
    Mohammad Kassem, Sohayb Khaoulani, Eugene Bychkov

    AbstractElectrical measurements, dc and ac, show that (AgI)x(HgS)0.5-x/2(As2S3)0.5-x/2 glasses, 0.0 ≤ x ≤ 0.6, exhibit drastic changes in ionic conductivity σi with silver iodide additions. The ionic transport increases by 13 orders of magnitude with increasing silver content from ~0.002 to ~ 23 at.%, and the activation energy decreases from 1.05 to 0.35 eV. Two distinctly different ion transport regimes above the percolation threshold concentration, xc ≈ 30 ppm, were distinguished. The critical-percolation regime at low silver content (≤ 2-5 at.% Ag) is characterized by a random distribution of silver-related entities and obeys a power-law composition dependence of σi. The ion transport parameters depend on the host network connectivity, represented by the average coordination number <n0>, via the critical fictive temperature T0; the calculated T0 value is comparable to the glass transition temperature for the glassy (HgS)0.5(As2S3)0.5 host matrix. In contrast, in the modifier-controlled domain, the silver-related entities are non-randomly distributed. The high Ag+ ionic mobility results from interconnected tetrahedral (AgI2/2S2/2)n chains in the silver iodide content range 0.2 < x ≤ 0.5, and from 2D layers (Ag3/3I3/3)n or 3D mixed tetrahedral sub-network (AgI3/3S1/2) in the range x > 0.5.

    更新日期:2018-01-02
  • Phase coexistence and large piezoelectricity in BaTiO3-CaSnO3 lead-free ceramics
    J. Am. Ceram. Soc. (IF 2.841) Pub Date : 2018-01-02
    Yang Yang, Yibei Zhou, Juan Ren, Qiaoji Zheng, Kwok Ho Lam, Dunmin Lin

    AbstractFerroelectric phase coexistence was constructed in (1-x)BaTiO3–xCaSnO3 lead-free ceramics, and its relationship with the piezoelectricity of the materials was investigated to ascertain potential factors for strong piezoelectric response. It is found that the addition of CaSnO3 caused a series of phase transitions in the (1-x)BaTiO3–xCaSnO3 ceramics, and a ferroelectric coexistence of rhombohedral, orthorhombic and tetragonal phases is formed at x = 0.08, where the ceramics exhibit the lowest energy barrier and consequently facilitate the polarization rotation and extension, resulting in the optimal piezoelectricity of d33 and kp values of 550 pC/N and 0.60, respectively. Our study provides an intuitive insight to understand the origin of high piezoelectricity in the ceramics with the coexistence of multi-ferroelectric phases.This article is protected by copyright. All rights reserved.

    更新日期:2018-01-02
  • High dielectric constant and high–Q in microwave ceramics of SrTiO3 co–doped with aluminum and niobium
    J. Am. Ceram. Soc. (IF 2.841) Pub Date : 2018-01-02
    Siliang Chen, Lingxia Li, Shihui Yu, Haoran Zheng, Zheng Sun

    AbstractAl/Nb co–doped SrTiO3 microwave ceramics with the composition of SrTi1–x(Al0.5Nb0.5)xO3 (x = 0.03, 0.05, 0.1 and 0.15) have been synthesized via a standard solid–state reaction method. The substitution of (Al0.5Nb0.5)4+ in B–site inhibits the reduction of Ti4+ ions and the growth of grain size, then the transport of mobile charge carriers is limited, and thus the Q value is improved. For the SrTi0.9(Al0.5Nb0.5)0.1O3 ceramics, in addition to their high dielectric constant (εr ~185), they exhibit correspondingly a high Qf value (~ 9077 GHz) at 2.9 GHz, making the microwave ceramics suitable for myriad device miniaturization and high performance wireless communication.This article is protected by copyright. All rights reserved.

    更新日期:2018-01-02
  • Cover Image, Volume 101, Issue 3
    J. Am. Ceram. Soc. (IF 2.841) Pub Date : 2018-01-02
    更新日期:2018-01-02
  • Cover Image, Volume 101, Issue 3
    J. Am. Ceram. Soc. (IF 2.841) Pub Date : 2018-01-02
    更新日期:2018-01-02
  • Temperature stability and electrical properties of MnO doped KNN-based ceramics sintered in reducing atmosphere
    J. Am. Ceram. Soc. (IF 2.841) Pub Date : 2017-12-29
    Zhenyong Cen, Xiaohui Wang, Yu Huan, Longtu Li

    Abstract Lead-free MnO doped 0.955K0.5Na0.5NbO3-0.045Bi0.5Na0.5ZrO3 (abbreviate as KNN-0.045BNZ) ceramics have been prepared by a conventional solid-state sintering method in reducing atmosphere. The MnO addition can suppress the emergence of the liquid phase and improve the homogenization of grain size. All ceramics sintered in reducing atmosphere show a two-phase coexistence zone composed of rhombohedral (R) and tetragonal (T) phase. MnO dopant results in the content increase of R phase and slight increase of Curie temperature TC. For KNN-0.045BNZ ceramics, Mn2+ ions preferentially occupy the cation vacancies in A-site to decrease oxygen vacancy concentration for 0.2-0.4% MnO content, while Mn2+ ions substitute for Zr4+ ions in B-site to form oxygen vacancies at x≥0.5. The defect dipole (Mn''Zr-Vo··) is formed at the moderate concentration from 0.5 to 0.6, which can provide a preserve force to improve the temperature stability of piezoelectric properties for kp and d33*. The ͘͘Mn0.4 ceramics show excellent electrical properties with quasi-static piezoelectric constant d33=300 pC/N, electromechanical coupling coefficient kp = 51.2%, high field piezoelectric constant d33* = 430 pm/V (at Emax = 25 kV/cm) and TC = ~345 °C, insulation resistivity ρ = 6.13 × 1011 Ω・cm. This article is protected by copyright. All rights reserved.

    更新日期:2017-12-31
  • New strategy to enhance the broadband NIR emission of bismuth-doped laser glasses
    J. Am. Ceram. Soc. (IF 2.841) Pub Date : 2017-12-29
    Jiangkun Cao, Xiaoman Li, Liping Wang, Ziyang Zhang, Shanhui Xu, Mingying Peng

    Abstract Bismuth-doped glasses and fibers with broadband near infrared (NIR) emission have garnered much attention on account of their potential applications in new fiber lasers and broadband amplifiers. Yet the realization of high gain from Bi-doped fibers and highly efficient NIR emission from Bi-doped glasses are still a stubborn puzzle. The enhancement of Bi NIR emission is normally based on modifying the glass composition and topology, which will change the structure of the glass over a wide range and alter the thermal or mechanical properties of the glass simultaneously, making it more complicated for the designing and fabricating of Bi fibers with good performance. Here, we find that a trace addition of Si3N4 can efficiently enhance the Bi NIR emission without changing the glass structure significantly, right followed by spectral and structural analysis. 27Al NMR measurement reveals that the short- to medium-range order of this glass is unchanged. The EPMA measurement confirms the homogeneity of fabricated glass. The great enhancement and red-shift under blue light excitation may originate from the conversion of Bi active centers to low valence. Our results indicate that the trace addition of nitride could be a facile and maneuverable way to control the valence of active ions in glasses, which may contribute to improving the performance of photonic glasses. This article is protected by copyright. All rights reserved.

    更新日期:2017-12-31
  • Revisiting the temperature-dependent dielectric permittivity of Ba(Ti1-xZrx)O3
    J. Am. Ceram. Soc. (IF 2.841) Pub Date : 2017-12-29
    Laijun Liu, Shaokai Ren, Jie Zhang, Biaolin Peng, Liang Fang, Dawei Wang

    Abstract It has been a challenge to provide a unified description of the dielectric response versus temperature for ferroelectrics with diffuse phase transition (DPT) and relaxor behaviors, which can be used to fit the dielectric response both below and above the peak temperature (Tm). Most of the available functions used in fitting experimental data only provide a description of the dielectric permittivity near and above Tm. In this work, employing a macroscopic and phenomenological statistical model and using Ba(Ti1-x, Zrx)O3 ceramics as an example, we revisit the dielectric permittivity's temperature dependence, analyzing their DPT and relaxor behaviors and providing a complete description over the whole temperature range. We show that good agreements between theoretical and experimental results can be achieved. To better understand how Ba(Ti1-x, Zrx)O3 ceramics changes from DPT to relaxor with increasing x, we also discuss the relation between the fitting parameters and Ba(Ti1-x, Zrx)O3′s composition and structure, which suggests that the parameters from the statistical model reflects the size of the correlated Ti ions (small clusters or polar nanoregions), which largely determine the behavior of Ba(Ti1-x, Zrx)O3 ceramics. This article is protected by copyright. All rights reserved.

    更新日期:2017-12-31
  • Nanostructured Mullite Steam Oxidation Resistant Coatings for Silicon Carbide Deposited via Atomic Layer Deposition
    J. Am. Ceram. Soc. (IF 2.841) Pub Date : 2017-12-28
    Amanda L. Hoskins, Aidan H. Coffey, Charles B. Musgrave, Alan W. Weimer

    Abstract Oxidation resistant, thin, pinhole-free, crystalline mullite coatings were deposited on zirconia and silicon carbide particles using atomic layer deposition (ALD). The composition of the films was confirmed with inductively coupled plasma optical emission spectroscopy (ICP OES), and the conformality and elemental dispersion of the films were characterized with transmission electron microscopy (TEM) and energy dispersive X-ray spectroscopy (EDS), respectively. The films are deposited on the particle surface with a deposition rate of ~1 Å/cycle. The elemental concentration of aluminum relative to silicon in the film was determined to be 2.68:1 which agrees closely with the ratio of stable 3:2 mullite (2.88:1). A high-temperature anneal for 5 hours at 1500°C was used to crystallize the films into the mullite phase. This work represents the first deposition of mullite films by ALD. The mullite and alumina coated particles were exposed to high temperature steam for 20 hours at 1000°C to assess the oxidation resistance of the films, which reduced the oxidation of silicon carbide by up to 62% relative to uncoated particles under these conditions. The activation energy of oxygen diffusion in the films was determined with density functional theory, and the computational results aligned well with the experimental outcomes. This article is protected by copyright. All rights reserved.

    更新日期:2017-12-29
  • 3D characterisation of porosity in an air plasma-sprayed thermal barrier coating and its effect on thermal conductivity
    J. Am. Ceram. Soc. (IF 2.841) Pub Date : 2017-12-28
    Xun Zhang, Justyna Kulczyk-Malecka, James Carr, Ping Xiao, Philip J. Withers

    Abstract Air plasma spray (APS) thermal barrier coatings (TBCs) contain pores, cracks and splat interfaces that are preferentially aligned normal to the heat flux direction. These significantly reduce (by as much as 50%) the thermal conductivity over a fully dense coating. Here the microstructures of APS thermal barrier coatings (TBCs) have been characterised in 3D using X-ray micro-computed tomography (μ-CT). Pores larger than 2.8 μm3 are resolved and their contribution to thermal conductivity reduction is evaluated using image-based microstructurally realistic numerical models. However, the models overestimate (by nearly 50%) the measured thermal conductivity of the as-deposited TBC sample. It is shown that this discrepancy is due to very fine (micron and sub-micron) cracks which readily sinter after short term exposure to temperatures representative of TBC operating conditions causing the measured thermal conductivity to rise to within 15% of that predicted. This suggests that under the realistic service conditions, the 3D image-based models based on CT images provide a good indicator of the likely long-term TBC performance. Virtual experiments showed that for the retained pores, the larger pores which are flatter and more oriented in the plane of the APS splats, contribute disproportionately to the beneficial reduction in thermal conductivity. Our results demonstrate that X-ray imaging is a useful tool in establishing APS process conditions that gives rise to a beneficial distribution of such pores. This article is protected by copyright. All rights reserved.

    更新日期:2017-12-29
  • Formation of Structural Defects and Strain in Electrodegraded Fe-doped SrTiO3 Crystals due to Oxygen Vacancy Migration
    J. Am. Ceram. Soc. (IF 2.841) Pub Date : 2017-12-28
    D. Ascienzo, O. Kurt, S. Greenbaum, T. J. M. Bayer, R. A. Maier, C. A. Randall, Y. H. Ren

    Abstract We report on our investigation of structural defect and strain formation in electrodegraded reduced and oxidized, Fe-doped SrTiO3 (Fe:STO) single crystals using optical second harmonic generation (SHG) and confocal Raman spectroscopy. SHG and Raman spectra reveal structural and electrochemical inhomogeneity resulting from the formation of Fe4+/oxygen ion and Fe3+/oxygen vacancy aggregation sites along the degraded anode and cathode interfaces, respectively. We show that mixed Fe3+/Fe4+ states and structural strain gradients are generated across the color fronts. These results, as well as oxygen sublattice differences between the anodic and cathodic bulk, present the color front as an interface between two dominant oxygen bonding distortions. The strain near the color front shows a strong dependence on oxygen vacancy concentration and diffusion within the crystals. Our characterization of structural and electrochemical changes due to electric field-induced strain and oxygen vacancy migration advances knowledge of electrodegradation in perovskite-based titanate single crystals. This article is protected by copyright. All rights reserved.

    更新日期:2017-12-29
  • First-principles and crystal field calculations of the electronic and optical properties of two novel red phosphors Rb2HfF6:Mn4+ and Cs2HfF6:Mn4+
    J. Am. Ceram. Soc. (IF 2.841) Pub Date : 2017-12-28
    D.-X. Liu, C.-G. Ma, P.-W. Hu, Z. Li, Y. Tian, P. Su, M. G. Brik, A. M. Srivastava, S. Tanabe

    Abstract The electronic, structural and optical properties of two red phosphors, Rb2HfF6:Mn4+ and Cs2HfF6:Mn4+, are evaluated using the first-principles and crystal field theory methods. The calculated trigonal splitting of the Mn4+ orbital triplets perfectly matches the experimental excitation spectra. The structural and electronic properties of the mixed compound RbCsHfF6 are also studied theoretically. In the mixed compound, the inversion center symmetry around the Hf site is removed. This symmetry lowering may result in an increase in the Mn4+ 2E4A2 zero phonon line (ZPL) intensity, which is very weak in the two end members. This finding may be of interest for increasing the phosphor luminosity. It is believed that such a mechanism of local site symmetry lowering by preparing solid solutions may be used for other systems as well, to gain ZPL intensity and perhaps to minimize thermal losses, eventually leading to improved phosphor materials. This article is protected by copyright. All rights reserved.

    更新日期:2017-12-29
  • Mechanical Activation and Cement Formation of Trimagnesium Phosphate
    J. Am. Ceram. Soc. (IF 2.841) Pub Date : 2017-12-27
    Theresa Brückner, Katrin Hurle, Anja Stengele, Jürgen Groll, Uwe Gbureck

    AbstractMagnesium phosphate cements have attracted increasing attention for biomedical applications in the past years due to their high mechanical performance and fast in vivo degradation at bony implantation sites. Cements are usually multicomponent mixtures of cement raw powders and setting regulators, whereas the latter may have a detrimental effect on biocompatibility. Here, we demonstrate that following prolonged grinding of trimagnesium phosphate (Mg3(PO4)2, farringtonite), a mechanically induced disordering reaction strongly altered farringtonite reactivity such that self-setting cements without further components were formed with a compressive strength of up to 11 MPa. Time-resolved X-ray diffraction analysis revealed that the formation of a nanocrystalline magnesium phosphate phase during grinding was responsible for cement setting to the highly hydrated magnesium phosphate mineral cattiite (Mg3(PO4)2∙22H2O), whereas crystalline farringtonite showed practically no setting reaction.This article is protected by copyright. All rights reserved.

    更新日期:2017-12-27
  • Y5Si2B8: a theoretically predicted new damage tolerant MAB phase with layered crystal structure
    J. Am. Ceram. Soc. (IF 2.841) Pub Date : 2017-12-27
    Yanchun Zhou, Huimin Xiang, Fu-Zhi Dai, Zhihai Feng

    AbstractLayer structured MAB phases (M=transition metal, A=IIIA or IVA group element, B is boron) are promising ternary borides for high and ultrahigh temperature applications. Herein, a new MAB phase Y5Si2B8 consisting of alternative stacking of YB4 and Y3Si2 slabs along the [001] direction is investigated. Density functional theory (DFT) calculations on the electronic structure and chemical bonding reveal that this new MAB phase has diverse chemical bonding and properties similar to MAX phases. The strong covalent bonds in the two dimensional B network on (001) plane in the YB4 slab and between Si atoms on (002) plane in the Y3Si2-slab warrant the high stiffness (Ex=288 GPa) of Y5Si2B8 in the ab plane and the weak Y2-Si and Y1-B2 bonds that connecting the YB4 and Y3Si2 slabs underpin the low Young's modulus in [001] direction (Ez=200 GPa). The low shear deformation resistance is due to the presence of the metallic bond and the weak bond within the B6 octahedral. The possible slip systems are {001}<100> and {110}<111>. Based on the low shear modulus (G =104 GPa) and Pugh's ratio G/B, Y5Si2B8 is predicted as a damage tolerant MAB phase. Y5Si2B8 is also predicted electrically conductive and the conductivity is higher in directions parallel to ab plane. In addition, temperature dependent phonon and electron heat capacity are predicted based on the electron and phonon density of states analysis.This article is protected by copyright. All rights reserved.

    更新日期:2017-12-27
  • Orientation dependent mechanical and thermal properties of plasma sprayed ceramics
    J. Am. Ceram. Soc. (IF 2.841) Pub Date : 2017-12-23
    Gregory M. Smith, Michael Resnick, Björn Kjellman, Jan Wigren, Gopal Dwivedi, Sanjay Sampath

    Abstract Due to droplet based assembly, microstructure anisotropy is expected in atmospheric plasma sprayed coatings (APS), with lamellar separations and interfaces having critical effects on properties. Quantitative determination of these anisotropic properties is difficult due to geometric test constraints. This has been overcome in the literature through a variety of indirect, local, or modeled evaluation, however direct measurement on like-dimensioned coatings is not available. In this work, 25 mm thick ceramic coating variants, deposited at two different feed rates, were obtained from industry and macroscopic mechanical and thermal properties were evaluated in both in-plane and out-of-plane orientations using identical specimen geometries. As expected, and confirming select past work, coating anisotropy has a direct influence on measured properties. The response of each property is microstructure dependent, highlighting the specific interaction: for instance, the fracture toughness is 120% higher in the through-thickness orientation versus in-plane after thermal aging, while the thermal conductivity was 24% lower in the through-thickness. The former benefits from the lamellar interfaces that provide obstacles to crack propagation while the latter sees these interfaces as efficient phonon scatters. The results provide insights for design through robust property measurements and into operational mechanisms in this class of highly defected ceramics. This article is protected by copyright. All rights reserved.

    更新日期:2017-12-27
  • Microwave Assisted Synthesis and Characterization of Single-Phase Tabular Hexagonal Newberyite, an Important Bioceramic
    J. Am. Ceram. Soc. (IF 2.841) Pub Date : 2017-12-23
    Prabaha Sikder, Sarit B. Bhaduri

    Abstract Magnesium phosphate compounds such as newberyite (MgHPO4.3H2O) and struvite (MgNH4PO4·6H2O) are becoming important alternatives to calcium phosphates in hard tissue replacements. So far, newberyite has received lesser attention with respect to struvite. Therefore, the broad aim of this paper is to report an easy synthesis technique and characterization of single-phase newberyite, which may have diverse uses as a bioceramic material. Specifically, we describe a simple and robust microwave-assisted process for the synthesis of single-phase newberyite in tabular hexagonal form. Second, we soak the newberyite powders in simulated body fluid, a solution which mimics the pH and ion concentration of human blood plasma, for 7 days and analyze the apatite formation on the crystals. Third, we report that single-phase newberyite, by itself, does not possess antibacterial property. This article is protected by copyright. All rights reserved.

    更新日期:2017-12-27
  • Defect Mechanisms in BaTiO3-BiMO3 Ceramics
    J. Am. Ceram. Soc. (IF 2.841) Pub Date : 2017-12-23
    Nitish Kumar, Eric A. Patterson, Till Frömling, Edward P. Gorzkowski, Peter Eschbach, Ian Love, Michael P. Müller, Roger A. De Souza, Julie Tucker, Steven R. Reese, David P. Cann

    Abstract Often, addition of BiMO3 to BaTiO3 (BT) leads to improvement in resistivity with a simultaneous shift to n-type conduction from p-type for BT. In considering one specific BiMO3 composition, i.e. Bi(Zn1/2Ti1/2)O3 (BZT), several prospective candidates for the origin of this n-type behavior in BT-BZT were studied—loss of volatile cations, oxygen vacancies, bismuth present in multiple valence states and precipitation of secondary phases. Combined x-ray and neutron diffraction, prompt gamma neutron activation analysis and electron energy loss spectroscopy suggested much higher oxygen vacancy concentration in BT-BZT ceramics (>4%) as compared to BT alone. X-ray photoelectron spectroscopy and x-ray absorption spectroscopy did not suggest presence of bismuth in multiple valence states. At the same time, using transmission electron microscopy, some minor secondary phases were observed, whose compositions were such that they could result in effective donor doping in BT-BZT ceramics. Using experimentally determined thermodynamic parameters for BT and slopes of Kröger-Vink plots, it has been suggested that an ionic compensation mechanism is prevalent in these ceramics instead of electronic compensation. These ionic defects have an effect of shifting the conductivity minimum in the Kröger-Vink plots to higher oxygen partial pressure values in BT-BZT ceramics as compared to BT, resulting in a significantly higher resistivity values in air atmosphere and n-type behavior. This provides an important tool to tailor transport properties and defects in BT-BiMO3 ceramics, to make them better suited for dielectric or other applications. This article is protected by copyright. All rights reserved.

    更新日期:2017-12-27
  • Thickness-induced anomalous angular dependent magnetoresistance of La2/3Sr1/3MnO3 thin films grown on SrTiO3
    J. Am. Ceram. Soc. (IF 2.841) Pub Date : 2017-12-23
    Xiaotian Li, Bin Liu, Yiqian Wang, Xuyan Xue, Guiju Liu, Huaiwen Yang, Jirong Sun

    Abstract In this paper the effect of thickness on angular dependent magnetoresistance (MR) of La2/3Sr1/3MnO3 (LSMO) thin films grown on SrTiO3 is systematically investigated. In films thinner than 8 nm, we observe an anomalous weak peak in the MR curves when the magnetic field is parallel to the film surface. In films thicker than 10 nm, however, the weak peak disappears and a novel MR valley appears when the magnetic field is perpendicular to the film surface. The weak peak is thought to be induced by the formation of two-dimensional electron gas (2DEG) at the interface, which is confirmed by density functional theory calculations. The disappearance of the peak and appearance of the valley in the films thicker than 10 nm is associated with the formation of misfit dislocations near the interface between film and substrate, which are clearly visible in high-resolution transmission electron microscopy images. Our work could shed significant light on the influence of film thickness on 2DEG formation. This article is protected by copyright. All rights reserved.

    更新日期:2017-12-27
  • Thermal barrier coatings with interface modified by 3D mesh patterns: Failure analysis and design optimization
    J. Am. Ceram. Soc. (IF 2.841) Pub Date : 2017-12-26
    Lirong Luo, Xiao Shan, Yi Guo, Chunshan Zhao, Xin Wang, Xiaofeng Zhao, Fangwei Guo, Ping Xiao

    Abstract Surface patterning of the bond coat using a three-dimensional mesh offers a promising approach to improve the durability of the thermal barrier coatings (TBCs), in which the geometry parameters of the mesh play a vital role. The objective of this work is to investigate the failure behavior of the air-plasma sprayed TBCs with mesh, and to identify the optimal mesh design. The study revealed that the failure sequence of the TBCs with mesh patterns consisted of (I) initiation of the interfacial and ridge cracks (around the top of the mesh); (II) cracks propagation and buckling of the YSZ layer; (III) interfacial cracks deflection and coalescence with ridge cracks, leading to final spallation. The critical parameters governing each step of the failure sequence were discussed and proposed. For a typical TBCs with YSZ thickness about 200 μm, the critical mesh height h and spacing length L is about 110 μm and 7 mm, respectively, when the mesh width w is fixed at about 480 μm.

    更新日期:2017-12-27
  • An oscillatory pressure sintering of zirconia powder: densification trajectories and mechanical properties
    J. Am. Ceram. Soc. (IF 2.841) Pub Date : 2017-12-21
    Yao Han, Shuang Li, Tianbin Zhu, Weiwei Wu, Di An, Feng Hu, Zunlan Hu, Jian Liu, Jingkun Xu, Zhipeng Xie

    Abstract The densification trajectories and mechanical properties of zirconia ceramics obtained by oscillatory pressure sintering (OPS) process were investigated, during the sintering process an oscillatory pressure was applied at three stages. Current results indicated that at intermediate stage the oscillatory pressure revealed a favorable improvement of mechanical properties compared with conventional hot pressing (HP) and pressureless sintering (PS) procedures, while the enhancement was not obvious at initial stage. When the oscillatory pressure was applied at final stage, the OPS specimens exhibited the highest bending strength and hardness of 1455±99MPa and 16.6±0.31GPa compared with the PS and HP specimens. Considering the high elastic modulus and Moiré patterns observed in the OPS specimen, the oscillatory pressure applied at intermediate and final stages was detected to facilitate the sliding of grain boundary, plastic deformation of monolithic grains, the removal of pores and the strengthening of atomic bonds. This article is protected by copyright. All rights reserved.

    更新日期:2017-12-21
  • Synthesis of Group IV and V Metal Diboride Nanocrystals via Borothermal reduction
    J. Am. Ceram. Soc. (IF 2.841) Pub Date : 2017-12-21
    Luca Zoli, Pietro Galizia, Laura Silvestroni, Diletta Sciti

    Abstract The synthesis of early transition nanocrystals using NaBH4 and the respective metal oxides at atmospheric pressure was studied at temperatures between 400 and 1000 °C. Reaction products were analysed by x-ray diffraction, the crystallite size was determined after Rietveld refinement of diffraction patterns, whilst the morphology was analysed by scanning and transmission electron microscopy. For all the investigated systems the lowest temperature to complete the synthesis was 700 °C and the reaction occurred in three subsequent steps: a) decomposition of NaBH4, b) formation of crystalline ternary species Na-M-O and Na-B-O, c) conversion of intermediary species to MB2 and NaBO2. Syntheses carried out at T>700 °C only caused coarsening of the powders. The synthetized boride powders had the morphology of highly agglomerated nanocrystals. TiB2 had a specific surface area of 33.5 m2/g and crystallite diameter of 12 nm. Both ZrB2 and HfB2 had a platelet-like morphology with crystallite diameter around 45 nm and specific surface area of 25.0 and 36.4 m2/g, respectively. Finally, NbB2 and TaB2 powders had a crystallite diameter around 5 nm with specific surface area of 21.1 and 11.4 m2/g, respectively. The goal of this synthesis is the use of cheap raw materials and moderate temperature conditions. This article is protected by copyright. All rights reserved.

    更新日期:2017-12-21
  • Dielectric relaxation induced internal electric field and its effect on magnetoelectric state in Co4Nb2O9
    J. Am. Ceram. Soc. (IF 2.841) Pub Date : 2017-12-21
    Y. M. Xie, H. Zang, W. D. Ceng, S. T. Wang, C. C. Wang

    Abstract Pyrocurrent and dielectric properties of magnetoelectric antiferromagnet Co4Nb2O9 have been investigated. The sample shows two thermally activated dielectric relaxations in the temperature range far above Néel temperature with the low- and high-temperature ones being a dipolar and Maxwell-Wagner relaxations, respectively. Two types of dipoles: relaxing dipoles and magnetic-field-induced dipoles were found in the sample. An internal electric field is formed due to the ordering of relaxing dipoles. Three current peaks were observed. The two higher temperature current peaks correspond to the dielectric relaxations. The lowest temperature current peak contains a positive tip and negative dip. The tip and dip are related to the depolarization of ferroelectricity induced by external and internal fields, respectively. This article is protected by copyright. All rights reserved.

    更新日期:2017-12-21
  • High Energy Conversion Efficiency in Mn-modified BCTZ Lead-Free Energy Harvester
    J. Am. Ceram. Soc. (IF 2.841) Pub Date : 2017-12-20
    Xiaodong Yan, Mupeng Zheng, Yudong Hou, Mankang Zhu, Hui Yan

    Abstract Extracting energy from environment vibration by piezoelectric effect to power wireless sensor nodes has been an attractive field of research, and the key challenge is to design environmentally-friendly piezoelectric materials with high power density. In order to alleviate this issue, lead-free Mn-modified Ba0.9Ca0.1Ti0.93Zr0.07O3 (BCTZ) ceramics were prepared, and the energy harvesting characteristics were optimized by addition of Mn ions. The results showed that the construction of R–O–T phase boundary and uniform dense microstructure boost the high energy harvesting characteristics at x = 0.1 specimen. In the mode of the cantilever-type energy harvester, a high power density of 1.2 μW/mm3 and efficiency of energy conversion of 7% were obtained at x = 0.1 specimen under an acceleration of 1.0 g. In addition, the BCTZ energy harvester possesses outstanding and stable performance after a 106 cycles, as well as strong toughness against severe vibration environments. This article is protected by copyright. All rights reserved.

    更新日期:2017-12-21
  • Role of silica nanoparticle in multi-component epoxy composites for electrical insulation with high thermal conductivity
    J. Am. Ceram. Soc. (IF 2.841) Pub Date : 2017-12-19
    Dae Ho Lee, Nakyung Lee, Hoyyul Park

    AbstractMulti-component epoxy micro/nano-composites containing micro-alumina, micro-quartz, and nano-silica were fabricated to develop electrical insulation materials with high thermal conductivity. Simply changing the ratio between the alumina and quartz microparticles caused a trade-off relationship between the thermal conductivity and electrical insulation. Increasing the alumina content in the epoxy-alumina/quartz micro-composites enhanced the thermal conductivity but deteriorated the dielectric strength. An increase in the thermal conductivity without incurring a loss in the dielectric strength was achieved by incorporating silica nanoparticles in the epoxy micro-composites. Adding silica nanoparticles to the epoxy micro-composites was found to be more efficient in improving the thermal conductivity compared to increasing the alumina ratio, especially at low alumina/quartz ratios. This behavior corresponded with theoretical models. Therefore, we provide a useful insight, both practical and theoretical, into the more advanced optimization of designing multi-component epoxy composites for electrical insulation with high thermal conductivity.This article is protected by copyright. All rights reserved.

    更新日期:2017-12-20
  • New Single-Component Multicolor Emission Na1-xAl1+2xSi1-2xO4:xBi3+/Eu3+ Phosphors via Energy Transfer
    J. Am. Ceram. Soc. (IF 2.841) Pub Date : 2017-12-19
    Chengyi Xu, Ye Sheng, Yanhua Song, Hongxia Guan, Xiangting Zhang, Deyue Meng, He Zhu, Zhan Shi, Haifeng Zou, Keyan Zheng

    AbstractA series of emission-tunable Na1-xAl1+2xSi1-2xO4:xBi3+/Eu3+ phosphors were synthesized via high temperature solid-state reaction method. The luminescence properties, energy transfer from Bi3+ to Eu3+ ions, color tuning, thermally stability and quantum efficiency (QE) were systematically investigated. Especially, in the host, a certain amount of Si4+ were replaced by Al3+ in order to remedy the charge compensating defect, so that, the emission intensity had been improved. The results of Rietveld refinements, the analysis of SEM mapping and the fourier transform infrared (FT-IR) indicated that this charge balance strategy was an effective method. Meanwhile, the energy transfer from Bi3+ to Eu3+ can be inferred and confirmed and the mechanisms were demonstrated to quadrupole−quadrupole interaction. The emission hue can be tuned from blue to pink, and finally to orange red light by properly varying the ratio of Bi3+ and Eu3+. Importantly, when the temperature was raised to 150 °C, the integrated emission intensity was 71.20% of the initial value for NAS:1%Bi3+,2%Eu3+ samples indicating that these phosphors had excellent thermal stability and stable color (no emission shift) .All these properties indicate that the developed phosphors may be potentially used as single-component color-tunable-emitting phosphors for UV light-emitting diodes.This article is protected by copyright. All rights reserved.

    更新日期:2017-12-20
  • Fundamental principles that govern the copper doping behavior in complex clinker system
    J. Am. Ceram. Soc. (IF 2.841) Pub Date : 2017-12-19
    Yong Tao, Wenqin Zhang, Neng Li, Dechen Shang, Zhongsheng Xia, Fazhou Wang

    AbstractUnderstanding the doping behavior of impurity ions in clinker phases is crucial for controlling the doping effect on clinker compounds, which, however, has not yet been fully demonstrated due to the composition complexity. Herein, we employ the state-of-the-art ab initio calculation to uncover the substitution mechanism of Cu ions in four dominant clinker crystals. The defect formation energies indicate Cu ions energetically prefer to substitute Fe ions in ferrite, which is in accord with the experiments. The bond order difference is innovatively postulated to interpret the energy barriers of Cu substitution in comparison with the ionic radius criterion. The high potential barriers of Cu substituting Ca, Si, and Al ions are ascribed to their bond order mismatch, while the tendency of Cu replacing Fe is due to their bond order similarity. Namely, the Cu doping in clinker phases follows the “bond order conformity” principle. In-depth electronic structure analysis reveals that the bond order is more effective than the ionic radius to estimate potential barriers of Cu substitution in complex clinker system mainly because the latter underestimates the influence of electronic structure differences while the bond order directly measures the bonding structure related to interatomic charge transfer.This article is protected by copyright. All rights reserved.

    更新日期:2017-12-20
  • Lead-free (K,Na)NbO3-based Ceramics with High Optical Transparency and Large Energy Storage Ability
    J. Am. Ceram. Soc. (IF 2.841) Pub Date : 2017-12-17
    Qizhen Chai, Dong Yang, Xumei Zhao, Xiaolian Chao, Zupei Yang

    Highly transparent lead-free (1-x)K0.5Na0.5NbO3-xSr(Zn1/3Nb2/3)O3 (KNN-xSZN) ferroelectric ceramics have been synthesized via a conventional pressureless sintering method. All samples are optically clear, showing high transmittance in the visible and near-infrared regions (~70% and ~80% at 0.5mm of thickness, respectively). This exceptionally good transmittance is due to the pseudo-cubic phase structure as well as the dense and fine-grained microstructure. In addition, a high energy storage density of 3.0 J/cm3 has been achieved for the 0.94K0.5Na0.5NbO3-0.06Sr(Zn1/3Nb2/3)O3 ceramics with submicron-sized grains (~ 136 nm). The main reason is likely to be the typical relaxor-like behavior characterized by diffuse phase transition, in addition to the dense and fine-grained microstructure. This study demonstrates that the 0.94K0.5Na0.5NbO3-0.06Sr(Zn1/3Nb2/3)O3 ceramic is a promising candidate of lead-free transparent ferroelectric ceramics for new areas beyond transparent electronic device applications. This article is protected by copyright. All rights reserved.

    更新日期:2017-12-18
  • Sodium Silicate Activated Slag-fly ash Binders: Part I – Processing, Microstructure and Mechanical Properties
    J. Am. Ceram. Soc. (IF 2.841) Pub Date : 2017-12-17
    Kaushik Sankar, Peter Stynoski, Ghassan K. Al-Chaar, Waltraud M. Kriven

    Alkali silicate activated slag and class F fly ash based binders are ambient curing, structural materials that are feasible replacements for ordinary Portland cement (OPC). They exhibit advantageous mechanical properties and less environmental impact than OPC. In this work, five sodium silicate activated slag-fly ash binder mixtures were developed and their compressive and flexural strengths were studied as a function of curing temperature and time. It was found that the strongest mixture sets at ambient temperature and had a Weibull average flexural strength of 5.7 (±) 1.5 MPa and Weibull average compressive strength of 60 (±) 8 MPa at 28 days. While increasing the slag/fly ash ratio accelerated the strength development, the cure time was decreased due to the formation of calcium silicate hydrate (C-S-H), calcium aluminum silicate hydrate (C-A-S-H) and (Ca,Na) based geopolymer. The density, microstructure and phase evolution of ambient-cured, heat-cured, and heat-treated binders were studied using pycnometry, scanning electron microscopy, energy dispersive x-ray spectroscopy (SEM-EDS), and x-ray diffraction (XRD). Heat-cured binders were more dense than ambient-cured binder. No new crystalline phases evolved through 28 days in ambient or heat-cured binders. This article is protected by copyright. All rights reserved.

    更新日期:2017-12-18
  • Temperature stable K0.5(Nd1-xBix)0.5MoO4 microwave dielectrics ceramics with ultra-low sintering temperature
    J. Am. Ceram. Soc. (IF 2.841) Pub Date : 2017-12-16
    Li-Xia Pang, Di Zhou, Da-Wei Wang, Jin-Xiong Zhao, Wei-Guo Liu, Zhen-Xing Yue, Ian M. Reaney

    K0.5(Nd1-xBix)0.5MoO4 (0.2 ≤ x ≤ 0.7) ceramics were prepared via the solid state reaction method. All ceramics densified below 720 °C with a uniform microstructure. As x increased from 0.2 to 0.7, relative permittivity (ɛr) increased from 13.6 to 26.2 commensurate with an increase in temperature coefficient of resonant frequency (TCF) from − 31 ppm/oC to + 60 ppm/oC and a decrease in Qf value (Q = quality factor; f = resonant frequency) from 23,400 GHz to 8,620 GHz. Optimum TCF was obtained for x = 0.3 (− 15 ppm/oC) and 0.4 (+ 4 ppm/oC) sintered at 660 and 620 °C with ɛr ~ 15.4, Qf ~19,650 GHz, and ɛr ~ 17.3, Qf ~ 13,050 GHz, respectively. Ceramics in this novel solid solution are a candidate for ultra low tempertaure co-fired ceramic (ULTCC) technology. This article is protected by copyright. All rights reserved.

    更新日期:2017-12-16
  • Effect of the densification of C-S-H on hydration kinetics of tricalcium silicate
    J. Am. Ceram. Soc. (IF 2.841) Pub Date : 2017-12-16
    Shiju Joseph, Shashank Bishnoi, Koen Van Balen, Özlem Cizer

    Effect of water to cement (w/c) ratio and temperature profiles on the densification of C-S-H (calcium silicate hydrate gel) and hydration kinetics of triclinic tricalcium silicate (C3S) is studied beyond the first day of hydration. Calorimetry and quantitative X-ray diffraction/Rietveld analysis show that degree of hydration is unaffected by w/c up to seven days and marginally thereafter. Coupling the degree of hydration with the portlandite content measured from thermal analysis indicate that C/S ratio of C-S-H decreases with increasing w/c. There is a clear increase in the portlandite content with increasing w/c, even though the degree of hydration is unchanged, due to the variations in C/S ratio of C-S-H. On the other hand, when C3S is initially cured at a lower temperature (20°C) and then at a higher temperature (40°C), there is a significant increase in the reactivity even until 28 days and vice versa. These experimental results were explained using the densified volumetric growth (DVG) hypothesis, which assumes that hydration kinetics are dependent on the internal surface area of C-S-H. This article is protected by copyright. All rights reserved.

    更新日期:2017-12-16
  • AC electric field-induced softening of alkali silicate glasses
    J. Am. Ceram. Soc. (IF 2.841) Pub Date : 2017-12-16
    Charles T. McLaren, William R. Heffner, Rishi Raj, Himanshu Jain

    Electric field-induced softening (EFIS) is a recently discovered phenomenon leading to significant reduction in the furnace temperature at which glass softens under the application of DC voltage. Unfortunately, it is accompanied by local compositional changes due to migration of ions that could limit its usefulness. To overcome this drawback, we have investigated the same phenomenon using AC voltage i.e. AC-EFIS on a sodium disilicate glass and a 50/50 mixed lithium-sodium disilicate glass of very different ionic resistivity yet similar network structure. The results show that the magnitude of EFIS temperature reduction is significantly greater for AC compared to DC for both glass compositions. The enhancement of EFIS under AC voltage appears to be due to a more uniform power dissipation and self-healing of changes than under DC voltage. This uniformity allows for the overall sample temperature to increase throughout the bulk and provides a better technique for practical applications than the DC case which produces potentially undesirable changes, especially in the anode region. This article is protected by copyright. All rights reserved.

    更新日期:2017-12-16
  • Reversible luminescence modulation of Ho doped K0.5Na0.5NbO3 piezoelectrics with high luminescence contrast
    J. Am. Ceram. Soc. (IF 2.841) Pub Date : 2017-12-16
    Yao Zhang, Jian Liu, Haiqin Sun, Dengfeng Peng, Ruihong Li, Chaoke Bulin, Xusheng Wang, Qiwei Zhang, Xihong Hao

    A significant luminescence modulation behavior based on photochromic reactions was observed in Ho3+ doped (Na0.52K0.48)0.92Li0.08NbO3 ceramics, fabricated by the conventional solid-state reaction method. Under visible light irradiation (407 nm) for 20 s, the samples changed pale gray from initial pale green, and returned to their original color by a thermal stimulus of 230 °C for 10 min, showing typical photochromic phenomenon. Under 453 nm excitation, the samples exhibited strong green emission at 551 nm. Interestingly, their green emission intensity can be effectively tailored by controlling photochromic reaction processes (irradiation wavelength and time), and the luminescent modulation ratio (ΔRt) reaches up to 77%. And, the ΔRt value has no any obvious degradation after 10 cycles by alternating visible light irradiation and thermal stimulus, showing excellent reversibility. These results make it potential applications in many fields as a kind of multifunctional material. This article is protected by copyright. All rights reserved.

    更新日期:2017-12-16
Some contents have been Reproduced with permission of the American Chemical Society.
Some contents have been Reproduced by permission of The Royal Society of Chemistry.
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