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  • Multiscale design of high-voltage multilayer energy-storage ceramic capacitors
    J. Am. Ceram. Soc. (IF 2.841) Pub Date : 2017-11-20
    Ziming Cai, Xiaohui Wang, Bingcheng Luo, Wei Hong, Longwen Wu, Longtu Li

    Multilayer energy-storage ceramic capacitors (MLESCCs) are studied by multiscale simulation methods. Electric field distribution of a selected area in a MLESCC is simulated at a macroscopic scale to analyze the effect of margin length on the breakdown strength of MLESCC using a finite element method. Phase field model is introduced to analyze the dielectric breakdown mechanism of MLESCC at a mesoscopic scale. The microstructure of selected area is generated through voronoi tessellation random construction routine containing core-shell-structured dielectric materials. The effects of margin length, shell permittivity, and shell volume fraction on the breakdown strength of MLESCC are respectively studied. Results indicate that the breakdown strength of MLESCC can be enhanced by adopting larger margin lengths, or by increasing the shell permittivity or volume fraction.

    更新日期:2017-11-20
  • Effect of topological structure on photoluminescence of PbSe quantum dot-doped borosilicate glasses
    J. Am. Ceram. Soc. (IF 2.841) Pub Date : 2017-11-20
    Zhousu Xu, Xiaofeng Liu, Chun Jiang, Dewei Ma, Jinjun Ren, Cheng Cheng, Jianrong Qiu

    Borosilicate glasses doped with PbSe quantum dots (QDs) were prepared by a conventional melt-quenching process followed by heat treatment, which exhibit good thermal, chemical, and mechanical stabilities, and are amenable to fiber-drawing. A broad near infrared (NIR) photoluminescence (PL) emission (1070-1330 nm) band with large full-width at half-maximum (FWHM) values (189-266 nm) and notable Stokes shift (100-210 nm) was observed, which depended on the B2O3 concentration. The PL lifetime was about 1.42-2.44 μs, and it showed a clear decrease with increasing the QDs size. The planar [BO3] triangle units forming the two-dimensional (2D) glass network structure clearly increased with increasing B2O3 concentration, which could accelerate the movement of Pb2+ and Se2− ions and facilitate the growth of PbSe QDs. The tunable broadband NIR PL emission of the PbSe QD-doped borosilicate glass may find potential application in ultra-wideband fiber amplifiers.

    更新日期:2017-11-20
  • Highly porous Y2SiO5 ceramic with extremely low thermal conductivity prepared by foam-gelcasting-freeze drying method
    J. Am. Ceram. Soc. (IF 2.841) Pub Date : 2017-11-20
    Zhen Wu, Luchao Sun, Jingjing Pan, Jingyang Wang

    Foam-gelcasting-freeze drying method is developed to fabricate porous Y2SiO5 ceramic with ultrahigh porosity of 92.2%-95.8% and isotropous multiple pore structures. As prepared porous samples have quite low shrinkages of 0.8%-1.9% during demolding and drying processes, lightweights of 0.19-0.35 g/cm3, and extremely low thermal conductivities of 0.054-0.089 W·(m·K)−1. Our approach combines the merits of foam-gelcasting method and freeze drying method. It is a simple and effective method to fabricate porous ceramics with very high porosity and extremely low thermal conductivity through low shrinkage of green body and near net complex shape forming.

    更新日期:2017-11-20
  • Highly porous mullite ceramics from engineered alkali activated suspensions
    J. Am. Ceram. Soc. (IF 2.841) Pub Date : 2017-11-20
    Acacio Rincón Romero, Hamada Elsayed, Enrico Bernardo

    Air may be easily incorporated by vigorous mechanical stirring, with the help of surfactants, of activated geopolymer-yielding suspensions. The cellular structure is stabilized by the viscosity increase caused by curing reactions, configuring an “inorganic gel casting”. The present paper is aimed at extending this approach to mullite foams, obtained by the thermal treatment of engineered alkali activated suspensions. “Green” foams were first obtained by gel casting of a suspension for Na-geopolymer enriched with reactive γ-Al2O3 powders. Sodium was later extracted by ionic exchange with ammonium salts. In particular, the removal of Na+ ions was achieved by immersion in ammonium nitrate solution overnight, with retention of the cellular structure. Finally, the ion-exchanged foams were successfully converted into pure mullite foams by application of a firing treatment at 1300°C, for 1 hour. Preliminary results concerning the extension of the concept to mullite three-dimensional scaffolds are presented as well.

    更新日期:2017-11-20
  • Valence state and ionic conduction in Mn-doped MgO partially stabilized zirconia
    J. Am. Ceram. Soc. (IF 2.841) Pub Date : 2017-11-20
    Buyoung Kim, Heesoo Lee

    The mechanism of the enhancement in the ionic conductivity resulting from cubic phase stabilization in MgO partially stabilized zirconia (MgPSZ) by Mn doping was studied by examining the local Zr-O structure. Cubic phase (14 vol%) in MgPSZ was increased with the addition of MnO2, and 10 mol% Mn-doped MgPSZ exhibited the highest cubic phase fraction (98.72%), which was analyzed by Rietveld refinement. In addition, only the cubic phase, not the monoclinic and tetragonal phases, was observed in the TEM-SAED pattern of 10 mol% Mn-doped MgPSZ. Doped Mn exhibited a high Mn2+/Mn4+ ratio, which was identified by X-ray photoelectron spectroscopy (XPS). In addition, it indicates that oxygen vacancy formation by substitution of Mn2+ in the Zr4+ site in MgPSZ increased cubic phase fraction. Ionic conductivity of MgPSZ was improved by the cubic phase increase attributed to Mn doping, and 10 mol% Mn-doped MgPSZ exhibited higher ionic conductivity than MgPSZ. To investigate the mechanism of the ionic conductivity improvement, Zr-O local structure in Mn-doped MgPSZ was analyzed by Zr K-edge EXAFS of MgPSZ, and the number of bonding of the Zr-O first shell decreased with increased Mn substitution. Therefore, it was considered that the oxygen vacancy generation led to an increase in the cubic phase and the number of ionic conduction sites.

    更新日期:2017-11-20
  • Radio-frequency negative permittivity in the graphene/silicon nitride composites prepared by spark plasma sintering
    J. Am. Ceram. Soc. (IF 2.841) Pub Date : 2017-11-20
    Chuanbing Cheng, Runhua Fan, Zhongyang Wang, Peitao Xie, Chuanxin Hou, Guohua Fan, Yanhua Lei, Liqiong An, Yao Liu

    Graphene/silicon nitride (GR/Si3N4) ceramic composites with uniformly dispersed GR sheets were prepared using spark plasma sintering. The effects of GR content on the microstructure and electrical properties of the composites were investigated in detail. With the GR content rising, the conductive GR network was formed in the composites, leading to the appearance of a percolation phenomenon, and the conductive mechanism also changed from hopping conductivity to metal-like conductivity. When the GR content reached the percolation threshold, the composites showed a negative permittivity behavior, which resulted from the low frequency plasmonic state generated by the formative conducting GR networks. The increasing GR content resulted in a higher plasma frequency and larger magnitude of negative permittivity, which was consistent with the analysis of Drude model. A relatively high dielectric loss was observed in the composites and mainly induced by the high leakage current among GR sheets. Our work is beneficial to expound the regulation mechanism of negative permittivity, and the obtained ceramic composites present some potential applications in microwave absorption, shielding and capacitors.

    更新日期:2017-11-20
  • Creation of 3D terahertz photonic crystals by the direct writing technique with a TiO2 sol-gel ink
    J. Am. Ceram. Soc. (IF 2.841) Pub Date : 2017-11-19
    Rong Wang, Weiyi Yang, Pengfei Zhu, Shuang Gao, Bo Li, Qi Li

    This article is protected by copyright. All rights reserved.

    更新日期:2017-11-20
  • Crystal Structure, Defect Relaxation and Microwave Dielectric Properties of Ba[(Mg1/3Nb2/3)1-xHfx]O3 Solid Solutions
    J. Am. Ceram. Soc. (IF 2.841) Pub Date : 2017-11-19
    Jie Zhang, Zhenxing Yue, Longtu Li

    This article is protected by copyright. All rights reserved.

    更新日期:2017-11-20
  • The production of a lead glaze with galena: thermal transformations in the PbS-SiO2 system
    J. Am. Ceram. Soc. (IF 2.841) Pub Date : 2017-11-19
    Roberta Di Febo, Judit Molera, Trinitat Pradell, Joan Carles Merlgarejo, Josep Madrenas, Oriol Vallcorba

    This article is protected by copyright. All rights reserved.

    更新日期:2017-11-20
  • Carbon-content dependent phase composition, microstructural evolution and mechanical properties of SiBCN monoliths
    J. Am. Ceram. Soc. (IF 2.841) Pub Date : 2017-11-17
    Daxin Li, Zhihua Yang, Dechang Jia, Xiaoming Duan, Yu Zhou, Dongli Yu, Yongjun Tian, Zihuan Wang, Yinglong Liu

    This article is protected by copyright. All rights reserved.

    更新日期:2017-11-17
  • Origin of dielectric loss in Ba(Co1/3Nb2/3)O3 microwave ceramics
    J. Am. Ceram. Soc. (IF 2.841) Pub Date : 2017-11-17
    Ahmad Sayyadi-Shahraki, Ehsan Taheri-Nassaj, Hassan Sharifi, Justin Gonzales, Taras Kolodiazhnyi, Nathan Newman

    This article is protected by copyright. All rights reserved.

    更新日期:2017-11-17
  • A novel approach to improve flexural strength of Al2O3-20 wt% ZrO2 composites by oscillatory pressure sintering
    J. Am. Ceram. Soc. (IF 2.841) Pub Date : 2017-11-17
    Tianbin Zhu, Zhipeng Xie, Yao Han, Shuang Li, Yawei Li, Di An, Xudong Luo

    This article is protected by copyright. All rights reserved.

    更新日期:2017-11-17
  • A model delineating the dielectric spectra of a relaxor PLZT obtained by impedance analyzer
    J. Am. Ceram. Soc. (IF 2.841) Pub Date : 2017-11-17
    Chang-Hyo Hong, Wook Jo

    This article is protected by copyright. All rights reserved.

    更新日期:2017-11-17
  • Fast preparation of (111)-oriented β-SiC films without carbon formation by laser chemical vapor deposition from hexamethyldisilane without H2
    J. Am. Ceram. Soc. (IF 2.841) Pub Date : 2017-11-17
    Qingfang Xu, Peipei Zhu, Qingyun Sun, Rong Tu, Song Zhang, Meijun Yang, Qizhong Li, Ji Shi, Haiwen Li, Lianmeng Zhang, Takashi Goto, Mingxu Han, Jiasheng Yan, Shusen Li, Hitoshi Ohmori

    (111)-oriented β-SiC films were prepared by laser chemical vapor deposition using a diode laser (wavelength: 808 nm) from a single liquid precursor of hexamethyldisilane (Si(CH3)3–Si(CH3)3, HMDS) without H2. The effects of laser power (PL), total pressure (Ptot) and deposition temperature (Tdep) on the microstructure, carbon formation and deposition rate (Rdep) were investigated. β-SiC films with carbon formation and graphite films were prepared at PL ≥ 170 W and Pto ≥ 1000 Pa, respectively. Carbon formation strongly inhibited the film growth. β-SiC films without carbon formation were obtained at Ptot = 400-800 Pa and PL = 130-170 W. The maximum Rdep was about 50 μm·h−1 at PL = 170 W, Ptot = 600 Pa and Tdep = 1510 K. The investigation of growth mechanism shows that the photolytic of laser played an important role during the depositions.

    更新日期:2017-11-17
  • Effect of interfacial energy on microstructure of a directionally solidified Al2O3/YAG eutectic ceramic
    J. Am. Ceram. Soc. (IF 2.841) Pub Date : 2017-11-17
    Xu Wang, Yujie Zhong, Dong Wang, Luchao Sun, Bailing Jiang, Jingyang Wang

    An Al2O3/Y3Al5O12 eutectic ceramic was prepared with a c-axis sapphire seed by an optical floating zone furnace. The crystallographic relationships in the initial and the steady growth sections of the as-grown eutectic ceramic were investigated by electron backscattering diffraction and transmission electron microscopy. The corresponding results were: <111 > {101}Y3Al5O12 || <0001 > {}Al2O3 and <110 > {}Y3Al5O12 || < > {0001}Al2O3, respectively. The steady orientation of the latter one shows smaller planar disregistry. Interfacial strain played the decisive role in affecting the solidification behavior of the Al2O3/Y3Al5O12 eutectic ceramic. The stability of interfaces with minimum interfacial strain and better ionic charge balance in irregular microstructure prevail upon the constraint of the seed. These results might cast light for the interfacial design of the Al2O3/Y3Al5O12 binary eutectic ceramic.

    更新日期:2017-11-17
  • Pyroelectric properties of Mn-doped Aurivillius ceramics with different pseudo-perovskite layers
    J. Am. Ceram. Soc. (IF 2.841) Pub Date : 2017-11-17
    Yanxue Tang, Zong-Yang Shen, Xiangyong Zhao, Feifei Wang, Wangzhou Shi, Dazhi Sun, Zhiyong Zhou, Shujun Zhang

    The pyroelectric properties of Mn-doped Aurivillius ceramics with different pseudo-perovskite layers were investigated. The pyroelectric coefficients for 0.2 wt% Mn-doped two-layer CaBi2Nb2O9 (CBN–Mn), three-layer Bi4Ti2.85Nb0.15O12 (BTN–Mn), and four-layer CaBi4Ti3.95Nb0.05O15 (CBTN–Mn) ferroelectric ceramics were found to be on the order of 26.0, 54.4, 84.4 μC/m2K at room temperature, respectively. These values were closely associated with the number of octahedral layers in the pseudo-perovskite blocks. The high pyroelectric coefficient, together with low dielectric permittivity and loss (tan δ < 0.003), results in to high figures of merit for the current responsivity, voltage responsivity, and detectivity. The excellent pyroelectric properties and high Curie temperatures (TC > 660°C) make the Aurivillius ceramics potential candidates for pyroelectric devices over a broad temperature range.

    更新日期:2017-11-17
  • Exact identification of migrating ion species in scandium tungstate solid electrolyte
    J. Am. Ceram. Soc. (IF 2.841) Pub Date : 2017-11-17
    Nobuhito Imanaka, Naoyoshi Nunotani, Ken-ichiro Araki, Megumi Yamane

    The Sc3+ ion migration in the scandium tungstate solid was qualitatively demonstrated. For clarifying the exact migrant quantitatively, modified Tubandt electrolysis was performed for the Sc2(WO4)3 solid. As a result of the strict compensation, that is, vaporization and adherence compensations, a weight increase at the cathodic side and a weight decrease at the anodic side were reproducibly observed after the electrolysis. In addition, the Sc concentration at the cathodic side was increased and a corresponding decrease at the anodic side was observed. Therefore, the Sc3+ ion conduction in the Sc2(WO4)3 solid was quantitatively demonstrated.

    更新日期:2017-11-17
  • A critical comparison of 3D experiments and simulations of tricalcium silicate hydration
    J. Am. Ceram. Soc. (IF 2.841) Pub Date : 2017-11-16
    Jeffrey W. Bullard, John Hagedorn, M. Tyler Ley, Qinang Hu, Wesley Griffin, Judith E. Terrill

    Advances in nano-computed X-ray tomography (nCT), nano X-ray fluorescence spectrometry (nXRF), and high-performance computing have enabled the first direct comparison between observations of three-dimensional nanoscale microstructure evolution during cement hydration and computer simulations of the same microstructure, using HydratiCA. nCT observations of a collection of triclinic tricalcium silicate () particles reacting in a calcium hydroxide solution are reported and compared to simulations that duplicate, as nearly as possible, the thermal and chemical conditions of those experiments. Particular points of comparison are the time dependence of the solid phase volume fractions, spatial distributions, and morphologies. Comparisons made at 7 hours of reaction indicate that the simulated and observed volumes of consumed by hydration agree to within the measurement uncertainty. The location of simulated hydration product is qualitatively consistent with the observations, but the outer envelope of hydration product observed by nCT encloses more than twice the volume of hydration product in the simulations at the same time. Simultaneous nXRF measurements of the same observation volume imply calcium and silicon concentrations within the observed hydration product envelope that are consistent with Ca(OH)2 embedded in a sparse network of calcium silicate hydrate (C–S–H) that contains about 70% occluded porosity in addition to the amount usually accounted as gel porosity. An anomalously large volume of Ca(OH)2 near the particles is observed both in the experiments and in the simulations, and can be explained as originating from the hydration of additional particles outside the field of view. Possible origins of the unusually large amount of observed occluded porosity are discussed.

    更新日期:2017-11-16
  • MgO nanoparticles synthesized starting from an innovative one-step process
    J. Am. Ceram. Soc. (IF 2.841) Pub Date : 2017-11-16
    Giuliana Taglieri, Valeria Daniele, Claudia Mondelli

    Nanosized MgO is a functional material showing a great promise as destructive adsorbent for toxic chemical agents, unique optical electronic, magnetic, thermal, and mechanical properties, as well as in good bactericidal performance in aqueous environments and in the cancer therapy. In this study, MgO nanoparticles are obtained by thermal decomposition of nanosized Mg(OH)2, which are synthesized by means of an innovative, time and cost-effective, scalable, and patented method. The nanoparticles are characterized by means of several techniques such as thermal analyses, X-ray diffraction analysis, infrared spectroscopy, transmission electron microscopy, atomic force microscopy, and surface area measurements (BET). After a pseudomorphic decomposition of the hydroxide precursor, pure and crystalline MgO nanoparticles are obtained. These nanoparticles are roughly spherical, monodispersed, and monocrystalline, having size ≤10 nm. Moreover, they exhibited a surface area up to 178 m2/g, revealing a bimodal mesoporous distribution with the important part of the pores with dimensions peaked at 4.87 nm.

    更新日期:2017-11-16
  • Oxygen diffusion mechanisms during high-temperature oxidation of ZrB2-SiC
    J. Am. Ceram. Soc. (IF 2.841) Pub Date : 2017-11-16
    Kathleen S. Cissel, Elizabeth Opila

    Oxygen diffusion mechanisms during oxidation of ZrB2-30 vol% SiC were explored at temperatures of 1500°C and 1650°C using an 18O tracer technique. Double oxidation experiments in 16O2 and 18O2 were performed using a modified resistive heating system. A combination of scanning electron microscopy, energy-dispersive spectroscopy, and time-of-flight secondary ion mass spectrometry was used to characterize the borosilicate and ZrO2 oxidation products. Oxygen exchange with the borosilicate network was observed to occur quickly at the oxygen-borosilicate surface at both 1500°C and 1650°C, while evidence of oxygen permeation was only observed at 1650°C for short time (<1 min) exposures. At longer times, >5-9 min, complete oxygen exchange throughout both the borosilicate glass and ZrO2 was observed at both temperatures preventing identification of the oxygen transport mechanisms, but demonstrating that oxygen transport is rapid in both oxide phases.

    更新日期:2017-11-16
  • Chemical modification at and within nanopowders: Synthesis of core-shell Al2O3@TiON nanopowders via nitriding nano-(TiO2)0.43(Al2O3)0.57 powders in NH3
    J. Am. Ceram. Soc. (IF 2.841) Pub Date : 2017-11-16
    Fei You, Kai Sun, Eongyu Yi, Eitaro Nakatani, Noritsugu Umehara, Richard M. Laine

    Here, we demonstrate the potential utility of using chemical modification to reorganize metastable nanoparticles into nanostructured nanoparticles without coincidentally inducing extensive necking/sintering. The motivation for this effort derives from the concept that chemical reduction in a single component in a mixed-metal nanoparticle will create segregated islands of a second immiscible phase. Given the very high chemical energies inherent in nanoparticles, the formation of even smaller islands of a second phase can be anticipated to lead to extremely high interfacial energies that may drive these islands to diffuse to cores or surfaces to form core-shell structures that minimize such interfacial energies. Thus, ammonolysis of (TiO2)0.43(Al2O3)0.57 composition nanopowders where both elements are approximately uniformly mixed at atomic length scales, under selected conditions (1000°C) for various periods of time at constant NH3 flow rates leads primarily to the reduction in the Ti species to form TiN or TiON which then appears to diffuse to the surface of the particles. The final products consist of Al2O3@TiON core-shell nanopowders that remain mostly unaggregated pointing to a new mechanism for modifying nanopowder chemistries and physical properties.

    更新日期:2017-11-16
  • Optical properties, thermal stability, and forming region of high refractive index La2O3–TiO2–Nb2O5 glasses
    J. Am. Ceram. Soc. (IF 2.841) Pub Date : 2017-11-16
    Zhaozhao Mao, Chaoyue Wang, Xiaojie Zheng, Jianding Yu, Liangming Xiong

    The high refractive index La2O3–TiO2–Nb2O5 glasses were prepared by containerless processing, and the glass-forming region was determined. The refractive index showed the range from 2.20 to 2.32, and the values were much higher than those of most optical glasses. The completely miscible 30LaO3/2–(70−x)TiO2–xNbO5/2 (0 ≤ x ≤70) system was fabricated to study the compositional dependence of refractive index and optical transmittance. The crucial determinants of the refractive index of oxide glasses, oxygen molar volume, and electronic polarizability of oxygen ions were calculated. The principle of additivity of glass properties was suitable for the calculation of refractive index between glass and compositional oxides. All the glasses were colorless and transparent in the visible to 6.5 μm middle infrared (MIR) region. These results are useful for designing new optical glasses with high refractive index and low wavelength dispersion in wide optical window.

    更新日期:2017-11-16
  • Aluminum-enhanced alkali diffusion from float glass to PVD-sputtered silica thin films
    J. Am. Ceram. Soc. (IF 2.841) Pub Date : 2017-11-15
    Jean-Thomas Fonné, Ekaterina Burov, Emmanuelle Gouillart, Sergey Grachev, Hervé Montigaud, Damien Vandembroucq

    This article is protected by copyright. All rights reserved.

    更新日期:2017-11-15
  • New methodology for determining the dielectric constant of a piezoelectric material at the resonance frequency range
    J. Am. Ceram. Soc. (IF 2.841) Pub Date : 2017-11-15
    Hossein Daneshpajooh, Husain N. Shekhani, Minkyu Choi, Kenji Uchino

    This article is protected by copyright. All rights reserved.

    更新日期:2017-11-15
  • CO2-driven synthesis of monodisperse barium titanate microspheres
    J. Am. Ceram. Soc. (IF 2.841) Pub Date : 2017-11-15
    Nianqi Liu, Wei Zhao, Jiacheng Rong

    This article is protected by copyright. All rights reserved.

    更新日期:2017-11-15
  • Continuous flash sintering
    J. Am. Ceram. Soc. (IF 2.841) Pub Date : 2017-11-15
    Emanuele Sortino, Jean-Marie Lebrun, Andrea Sansone, Rishi Raj

    We develop an algorithm that relates the incubation time for flash initiation to the workpiece velocity as it is pulled through stationary electrodes in a continuous flash sintering experiment. Experiments with a whiteware green body that is sintered in this way are compared with the model. A processing map when the workpiece is drawn at a constant velocity is developed. The parameter space for the map is given by the speed and the current flowing through the workpiece. It distinguishes between the regimes for uniform and inhomogeneous sintering. All experiments were carried out at a furnace temperature of 900°C. The study shows the viability of continuous flash sintering of ceramics at speeds of up to 3 mm s−1 with electrodes that form a line contact with the workpiece. Remarkably, higher velocities and higher currents yield better sintering.

    更新日期:2017-11-15
  • Effect of ZnO/MgO ratio on the crystallization and optical properties of spinel opaque glazes
    J. Am. Ceram. Soc. (IF 2.841) Pub Date : 2017-11-15
    Jingpei Cai, Ming Lu, Kang Guan, Weixiong Li, Fan He, Peng Chen, Cheng Peng, Pinggen Rao, Jianqing Wu

    The effect of the ZnO/MgO ratio on the crystallization and optical properties of glass-ceramic glazes from the SiO2–Al2O3–ZnO–MgO–CaO–K2O–Na2O–B2O3 system was studied. The glazes with different ZnO/MgO ratios were characterized by differential scanning calorimetry, X-ray powder diffraction, Raman spectroscopy, scanning electron microscopy, energy dispersive spectroscopy analysis and a spectrophotometer. The results reveal that the A glaze without ZnO content contains forsterite and sapphirine. The B and C glazes with intermediate ZnO/MgO ratio contain enstatite and spinel solid solution. The D to F glazes with higher ZnO/MgO ratio crystallize spinel solid solution as the only crystalline phase. The amount of spinel solid solution, lightness values (L*), gloss values and the reflectance of the studied glazes increase with the ZnO/MgO ratio.

    更新日期:2017-11-15
  • Determination of crystal size distributions in alumina ceramics by a novel X-ray diffraction procedure
    J. Am. Ceram. Soc. (IF 2.841) Pub Date : 2017-11-15
    Sigmund H. Neher, Helmut Klein, Werner F. Kuhs

    A novel X-ray diffraction based method is presented, capable of determining volume-based crystal size distribution (CSD) of polycrystalline materials and crystalline powders with unprecedented sampling statistics; the method is named fast X-ray diffraction crystal size distribution analysis (FXD-CSD). FXD-CSD can be performed with standard laboratory X-ray diffractometers equipped with a position sensitive detector and uses a software package written in Python for the data analysis. FXD-CSD is a destruction-free and generally applicable method to establish CSDs of polycrystalline materials as well as powders for sizes well below 1 μm up to about 100 μm; it even allows for studies of samples enclosed in complex environments, e.g., for in situ measurements in a furnace or in a pressure cell. To show the capability of the method the microstructural evolution of four alumina substrates with different time-spans of sintering (4, 8, 16, and 24 hour at 1600°C) is investigated via FXD-CSD and SEM imaging. The corresponding CSDs and average grain sizes are determined, results obtained by FXD-CSD and the line-intersection methods are compared and clear evidence for the presence of abnormal grain growth (AGG) during sintering is shown. From three tested probability density functions (PDF) describing the CSDs a log-normal PDF fits best to the volume based CSDs; the method provides size distributions with unprecedented precision opening the way to a systematic and meaningful comparison between theoretically predicted and observed CSDs.

    更新日期:2017-11-15
  • Strength of brittle materials in moderately corrosive environments
    J. Am. Ceram. Soc. (IF 2.841) Pub Date : 2017-11-15
    Robert F. Cook

    The strengths of four brittle materials―cordierite glass ceramic, fused silica, silicon, and polycrystalline alumina were measured after exposure to weakly corrosive water and moderately corrosive buffered HF (BHF) solution. Exposure to water did not alter the strengths in subsequent inert strength tests and decreased the strengths in reactive strength tests. Exposure to BHF increased the strengths in both tests, but only after an incubation exposure time. Prior to the incubation time, the BHF had the same effect as water, suggesting that the bond rupture kinetics were unaffected. Examination of strength-controlling indentation flaws after the incubation time showed clear corrosive effects on the flaw geometry indicative of reductions in the indentation residual stress fields. The implication is that moderately corrosive environments increase the strength or lifetime of a brittle component by reducing the crack driving force via flaw alteration and do not, as perhaps expected, decrease the strength or lifetime through enhanced chemical reactivity.

    更新日期:2017-11-15
  • Static Fatigue and Compressive Stress Generation in an Aged Crack
    J. Am. Ceram. Soc. (IF 2.841) Pub Date : 2017-11-13
    Peter J. Lezzi, Jared H. Seaman

    This article is protected by copyright. All rights reserved.

    更新日期:2017-11-13
  • Slag Corrosion Mechanism of Lightweight Al2O3-MgO Castable in Different Atmospheric Conditions
    J. Am. Ceram. Soc. (IF 2.841) Pub Date : 2017-11-13
    Yang Zou, Huazhi Gu, Ao Huang

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    更新日期:2017-11-13
  • Enhancing emission intensity and thermal stability by charge compensation in Sr2Mg3P4O15:Eu3+
    J. Am. Ceram. Soc. (IF 2.841) Pub Date : 2017-11-10
    Shiqi Liu, Yujun Liang, Yingli Zhu, Haoran Li, Jiahui Chen, Mengyuan Wang, Wenjian Li

    This article is protected by copyright. All rights reserved.

    更新日期:2017-11-11
  • Valence state and ionic conduction in Mn-doped MgO partially stabilized zirconia
    J. Am. Ceram. Soc. (IF 2.841) Pub Date : 2017-11-10
    Buyoung Kim, Heesoo Lee

    This article is protected by copyright. All rights reserved.

    更新日期:2017-11-11
  • Coupling copper and hydrogenated TiO2 to bare TiO2 structures for improved photocatalytic performance
    J. Am. Ceram. Soc. (IF 2.841) Pub Date : 2017-11-10
    Yeong Gyeong Kim, Wan-Kuen Jo

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    更新日期:2017-11-11
  • Binary oxide ceramics for enhanced phenols degradation under simulated Solar light
    J. Am. Ceram. Soc. (IF 2.841) Pub Date : 2017-11-10
    Milica V. Carević, Nadica D. Abazović, Tatjana D. Savić, Tatjana B. Novaković, Dejan J. Pjević, Mirjana I. Čomor

    Solvothermal synthesis of ZrO2–TiO2 binary oxides and pure counterparts at 150°C in water/isopropanol media is presented. Titanium (IV) isopropoxide and zirconium (IV) propoxide were used as precursors. XRD and TEM techniques were used for structural and morphological characterization of obtained samples. XPS spectra of mixed oxide samples were compared in order to correlate composition of samples with surface properties and presence of defects. Relative positions of defect states within band-gaps of semiconductors were estimated from UCPL spectra. UV-Vis DRS spectra revealed that both pure oxides experienced red shift of absorption thresholds compared to reference data. Photocatalytic activities of all samples were probed under simulated Solar light on three model compounds: phenol, 4-chlorophenol (4-CP) and 2, 4, 6-trichlorphenol (TCP). Pure TiO2 showed the highest photocatalytic activity in the case of phenol. However, pure ZrO2 and binary oxides showed higher photoactivity in degradation of 4-CP and TCP. The activity of wide band-gap semiconductors under simulated Solar light in photodegradation of phenol and its derivatives is most probably the consequence of formation of charge transfer complexes between pollutant molecules and semiconductors surface.

    更新日期:2017-11-11
  • Fabrication and properties of CNT/Ni/Y/ZrB2 nanocomposites reinforced in situ
    J. Am. Ceram. Soc. (IF 2.841) Pub Date : 2017-11-10
    Hua Jin, Zhewen Li, Liuwei Wang, QinXuan Zeng

    Carbon nanotubes (CNTs) were synthesized in situ by chemical vapor deposition of methane over nano-ZrB2 matrix using Ni/Y catalysts. Well-grown CNTs with tangled and long bodies and mainly composed of well-crystallized graphite were obtained when the Ni content reaches 10 wt%. The CNT/ZrB2 nanocomposites obtained by spark plasma sintering at 1400°C exhibited full density and optimal mechanical properties. The flexural strength and fracture toughness of the nanocomposites were 1184 ± 52 MPa and 10.8 ± 0.3 MPa·m1/2, respectively. Results indicated that the dispersion of CNTs in situ can improve composite performance, rendering the mechanical properties of the CNT/ZrB2 nanocomposites synthesized in situ considerably superior to those of monolithic ZrB2 nanoceramics and CNT/ZrB2 nanocomposites synthesized using the traditional method. The toughening mechanisms included crack deflection, crack bridging, CNT debonding, pull-out, and fracture.

    更新日期:2017-11-11
  • Transformation of stainless steel slag toward a reactive cementitious binder
    J. Am. Ceram. Soc. (IF 2.841) Pub Date : 2017-11-10
    Lubica Kriskova, Massimiliano Eroli, Remus I. Iacobescu, Silviana Onisei, Franco Vecchiocattivi, Yiannis Pontikes

    Argon oxygen decarburization (AOD) slag represents more than 50 wt% of the slag from stainless steel production. Although some applications are available, e.g., as aggregates for road constructions or fertilizers, they are characterized by low economic value and limited applicability. In order to increase the economic value of AOD slag, alternative applications have been proposed, e.g., as partial or full replacement for Ordinary Portland Cement (OPC). The work presented here investigates whether the adaptation of the AOD slag chemistry within a high temperature process leads to an improvement of its hydraulic properties and thereby can demonstrate its potential to be converted into a hydraulic binder suitable for OPC replacement. For this purpose, three synthetic AOD slags with basicities (CaO/SiO2) of 2.0, 2.2, and 2.4 were synthesized, and the effect of the CaO/SiO2 ratio on the material stability, the amount of tricalcium silicate formed, and their hydraulic properties investigated. X-ray diffraction, scanning electron microscope (SEM), and isothermal calorimetry analysis were used to characterize the microstructure and the hydraulic activity. The results show that the proposed method is indeed a promising way to stabilize a stainless steel AOD slag and convert it into a hydraulic binder.

    更新日期:2017-11-11
  • Enhanced and stable strain memory in Mn-doped Pb(Mn1/3Sb2/3)O3–Pb(Zr,Ti)O3 ceramics realized by sesquipolar loading
    J. Am. Ceram. Soc. (IF 2.841) Pub Date : 2017-11-10
    Caiyun Chen, Zhiyong Zhou, Zhen Liu, Ruihong Liang, Wenbin Zhang, Xianlin Dong

    The negative electric field, field cycling and frequency dependence of strain memory effect in poled and aged Mn-doped Pb(Mn1/3Sb2/3)O3–Pb(Zr,Ti)O3 (PMS–PZT) piezoceramics under sesquipolar loading were investigated. The strain memory effect of Mn-doped PMS–PZT is especially sensitive to the applied negative electric field. Maximum strain memory of 0.32% is achieved when the negative electric field is around negative coercive field of ~2.1 kV/mm, which can be ascribed to the partially depoled state with randomized domains. And this strain memory shows very good cycling stability, varying less than 5% up to 104 cycles, while almost 40% degradation is found under bipolar signal. In addition, due to the stabilized defect dipoles, the strain memory exhibits stable characteristic over a broad frequency range from 0.01 Hz to 20 Hz. The results may shed new insights into designing the novel strain memory actuators where stable strain state could be realized after the removal of electric field.

    更新日期:2017-11-11
  • Transparent glass ceramics containing Lu6O5F8:Tb3+ nano-crystals: Enhanced photoluminescence and X-ray excited luminescence
    J. Am. Ceram. Soc. (IF 2.841) Pub Date : 2017-11-10
    JiangKun Cao, WeiPing Chen, DengKe Xu, XiaoMan Li, RongFei Wei, LiPing Chen, XinYuan Sun, Hai Guo

    The development of scintillators is of fundamental and industrial meaning for their diverse applications. Despite the great advance in scintillating mono-crystals, challenge remains to search for novel scintillating materials with low cost, large volume, and high efficiency. Here, Tb3+-doped glass ceramics (GC) with crystallized Lu6O5F8 nano-crystals were prepared and characterized as potential X-ray scintillators. Their structural, optical, and luminescent properties were explored systematically. After thermal treatment, X-ray excited luminescence (XEL) intensity from Lu6O5F8:Tb3+ GC is greatly increased and the relative intensity is about 64% of commercial BGO scintillator, benefiting from preferential enrichment of Tb3+ ions into Lu6O5F8 nano-crystals with low phonon energy. Moreover, unusual decay behaviors of Tb3+ emissions in GC sample are observed and discussed. Our results indicate that rare earth doped GC may offer a novel platform for designing and fabricating new scintillating materials in the future.

    更新日期:2017-11-11
  • Effect of topological structure on photoluminescence of PbSe quantum dot-doped borosilicate glasses
    J. Am. Ceram. Soc. (IF 2.841) Pub Date : 2017-11-09
    Zhousu Xu, Xiaofeng Liu, Chun Jiang, Dewei Ma, Jinjun Ren, Cheng Cheng, Jianrong Qiu

    This article is protected by copyright. All rights reserved.

    更新日期:2017-11-09
  • Relaxor Nature in Ba5RZr3Nb7O30 (R=La, Nd, Sm) Tetragonal Tungsten Bronze New System
    J. Am. Ceram. Soc. (IF 2.841) Pub Date : 2017-11-09
    Wen Bin Feng, Xiao Li Zhu, Xiao Qiang Liu, Mao Sen Fu, Xiao Ma, Shu Jing Jia, Xiang Ming Chen

    This article is protected by copyright. All rights reserved.

    更新日期:2017-11-09
  • Highly porous Y2SiO5 ceramic with extremely low thermal conductivity prepared by foam-gelcasting-freeze drying method
    J. Am. Ceram. Soc. (IF 2.841) Pub Date : 2017-11-09
    Zhen Wu, Luchao Sun, Jingjing Pan, Jingyang Wang

    This article is protected by copyright. All rights reserved.

    更新日期:2017-11-09
  • MgO nanoparticles synthesized starting from an innovative one-step process
    J. Am. Ceram. Soc. (IF 2.841) Pub Date : 2017-11-08
    Giuliana Taglieri, Valeria Daniele, Claudia Mondelli

    This article is protected by copyright. All rights reserved.

    更新日期:2017-11-09
  • Enhancement of the oxygen desorption/absorption property of BaFe1−xInxO3−δ by In substitution for Fe site
    J. Am. Ceram. Soc. (IF 2.841) Pub Date : 2017-11-08
    Fumito Fujishiro, Minako Izaki, Takuya Hashimoto

    This article is protected by copyright. All rights reserved.

    更新日期:2017-11-09
  • Highly Porous Mullite Ceramics from Engineered Alkali Activated Suspensions
    J. Am. Ceram. Soc. (IF 2.841) Pub Date : 2017-11-08
    Acacio Rincón Romero, Hamada Elsayed, Enrico Bernardo

    This article is protected by copyright. All rights reserved.

    更新日期:2017-11-09
  • Properties and structures of nonstoichiometric (K, Na)NbO3-based lead free ceramics
    J. Am. Ceram. Soc. (IF 2.841) Pub Date : 2017-11-07
    Jie Xing, Zhi Tan, Lixu Xie, Laiming Jiang, Jing Yuan, Qiang Chen, Jiagang Wu, Wen Zhang, Dingquan Xiao, Jianguo Zhu

    This article is protected by copyright. All rights reserved.

    更新日期:2017-11-08
  • Modeling environmentally-induced property degradation of SiC/BN/SiC Ceramic Matrix Composites
    J. Am. Ceram. Soc. (IF 2.841) Pub Date : 2017-11-07
    Triplicane A Parthasarathy, Brian Cox, Olivier Sudre, Craig Przybyla, Michael K Cinibulk

    This article is protected by copyright. All rights reserved.

    更新日期:2017-11-08
  • Melting behavior and superheating capacity of REBa2Cu3Oy films with nano-layer buffered structures
    J. Am. Ceram. Soc. (IF 2.841) Pub Date : 2017-11-08
    Wei Wang, Hui Xiang, Ghulam Hussain, Dejing Yu, Yisha Zhu, Letian Zhang, Sergey V. Samoilenkov, Andrey R. Kaul, Xin Yao

    Using high temperature-optical microscopy, in situ investigations were conducted on melting and superheating behaviors of REBa2Cu3O7−δ (RE123, RE = Nd, Gd) films, which were grown on nano-layer buffered substrates. The results demonstrate that all buffered RE123 films have improved crystallinity and in-plane alignments, leading to the higher superheating capability. In the first case, due to its good lattice match with the buffer material of Y123, the Nd123 film with the minimal extrinsic property grew from the superior interface. In the second circumstance, because of its stronger chemical bonding with the buffer layer of Gd2O3, the pure c-axis oriented Gd123 film was fabricated. Moreover, the optimized thickness of buffer layer plays an important role in reducing interface energy of RE123 films and enhancing its superheating capacity.

    更新日期:2017-11-08
  • Deep-red photoluminescence and long persistent luminescence in double perovstkite-type La2MgGeO6:Mn4+
    J. Am. Ceram. Soc. (IF 2.841) Pub Date : 2017-11-08
    Xiaowen Zhang, Jianmin Nie, Shanshan Liu, Yang Li, Jianrong Qiu

    A novel non-rare-earth doped phosphor La2MgGeO6:Mn4+ (LMG:Mn4+) with near-infrared (NIR) long persistent luminescence (LPL) was successfully synthesized by solid-state reaction. The phosphors can be effectively excited using ultraviolet light, followed by a sharp deep-red emission peaking at 708 nm, which is originated from 2Eg  4A2g transition of Mn4+ ions. The luminescent performance was analyzed by photoluminescence (PL) and photoluminescence excitation (PLE) spectra. The crystal field parameters were calculated to describe the environment of Mn4+ in LMG host. The LPL behaviors as well as the mechanisms were systematically discussed. This study suggests that the phosphors will broaden new horizons in designing and fabricating novel NIR long phosphorescent materials.

    更新日期:2017-11-08
  • Ferroelectric-quasiferroelectric-ergodic relaxor transition and multifunctional electrical properties in Bi0.5Na0.5TiO3-based ceramics
    J. Am. Ceram. Soc. (IF 2.841) Pub Date : 2017-11-08
    Changrong Zhou, Qingning Li, Jiwen Xu, Ling Yang, Weidong Zeng, Changlai Yuan, Guohua Chen

    A-site substituted 0.88(Bi0.5Na0.5)1−x(Li0.5Nd0.5)xTiO3–0.12BaTiO3 (BNTLNx–BT12) ceramics were synthesized using a conventional solid-state reaction route. The structural transformation and miscellaneous electrical properties were systematically investigated. The A-site modification induced two sequence transitions from ferroelectric tetragonal (T) to quasi-ferroelectric pseudocubic (PC) phase, followed closely by the second transition from non-ergodic to ergodic relaxor (NR-ER), and finally to dynamic polar nanoregions (PNRs). The significant enhancement in piezoelectric activity, strain response, broad plateau-like maximum dielectric permittivity over a large temperature range and energy-storage level at different compositions may be attributed to the compositionally-induced T-PC to NR-ER transition and the alignment of dynamically-fluctuating PNRs, respectively. The evolution of multifunctional electrical properties, associated with the variations in structure/microstructure, might provide a new insight to investigate the underlying mechanism of structure-electrical properties relationship in ferroelectric solid solutions.

    更新日期:2017-11-08
  • Highly porous barium strontium titanate (BST) ceramic foams with low dielectric constant from particle-stabilized foams
    J. Am. Ceram. Soc. (IF 2.841) Pub Date : 2017-11-08
    Wenlong Huo, Yugu Chen, Zaijuan Zhang, Jingjing Liu, Shu Yan, Jia-Min Wu, Xiaoyan Zhang, Jinglong Yang

    A novel method for fabrication of highly porous barium strontium titanate (BST) ceramic foams based on particle-stabilized foaming method was developed for the first time, in which propyl gallate (PG) was employed as BST particle modifier. The results showed that the stability of wet BST foams closely depends on the pH value and PG concentration, which could be explained by the adsorption behavior of PG on BST particle surface. BST ceramic foams with dense, uniform, and closed pore and defect-free wall were obtained. The pore size and porosity can be well controlled by adjusting solid loading and sintering temperature. It was revealed that not only sintering temperature but also solid loading significantly influenced the growth of BST grain. The BST ceramic foams exhibited high porosity in the range of 81%-95%, low dielectric constant in the range of 47-150, and low dielectric loss below 0.0025. The BST ceramic foams with higher porosity presented a tendency of lower dielectric constant and the fitting results indicated that the natural logarithm of dielectric constant was linear correlated with porosity.

    更新日期:2017-11-08
  • Size effects of electrocaloric cooling in ferroelectric nanowires
    J. Am. Ceram. Soc. (IF 2.841) Pub Date : 2017-11-08
    Houbing Huang, Guangzu Zhang, Xingqiao Ma, Deshan Liang, Jianjun Wang, Yang Liu, Qing Wang, Long-Qing Chen

    Considering finite size effect, ferroelectric nanowires may show novel phenomena compared to ferroelectric thin film and bulk. Here we investigated the effect of width and surface compressive stress on electrocaloric cooling in ferroelectric nanowire by using thermodynamic calculations and phase-field simulations. It was found that the isothermal entropy change and adiabatic temperature change in nanowire are 50% larger than that in thin film due to different mechanical boundary conditions of nanowire and thin film. The largest electrocaloric temperature changes were shown to increase significantly either with the decrease in nanowire width or the increase with the surface compressive stress. It was also revealed that the largest intrinsic entropy changes are almost the same for different nanowires with different widths and various stresses. The present study therefore contributes to the understanding of size effects of electrocaloric cooling and provides guidance for experiments to design high-efficiency cooling devices using ferroelectric nanosystems.

    更新日期:2017-11-08
  • Ultralight and resilient Al2O3 nanotube aerogels with low thermal conductivity
    J. Am. Ceram. Soc. (IF 2.841) Pub Date : 2017-11-08
    Chencheng Xu, Haolun Wang, Jianan Song, Xiaopeng Bai, Zhenglian Liu, Minghao Fang, Yongshuai Yuan, Junyuan Sheng, Xiaoyan Li, Ning Wang, Hui Wu

    This report describes a novel method to produce fluffy and resilient nanotube aerogels by combining solution blow spinning and Atom Layer Deposition (ALD). Polyvinylpyrrolidone (PVP) sponges obtained by blow spinning are used as templates and are deposited in ALD. After removal of template, semitransparent aerogels whose density can be as low as 0.68 mg/cm3 were obtained. The product is heat-stable, with the ability to retain original shape and keep elastic after being kept at 900°C for 2 hours. It is also heat-insulated, with a thermal conductivity of 0.022 W/K∙m at room temperature. Additionally, when compressed to 60% of the original height for 100 cycles during in-situ mechanical test, the sponges recovered to around 80% of the original shape, further indicating excellent mechanically elasticity of the aerogel.

    更新日期:2017-11-08
  • Synthesis and microwave dielectric properties of new high quality Mg2NdNbO6 ceramics
    J. Am. Ceram. Soc. (IF 2.841) Pub Date : 2017-11-08
    Shaobo Zhang, Liwei Shi, Lanyang Zhang, Haiyan Zhu, Wangsuo Xia

    New high-quality microwave dielectric ceramics Mg2NdNbO6 were prepared by conventional solid-state sintering method. The phases, micro-structures and microwave dielectric properties of Mg2NdNbO6 ceramics were investigated at sintering temperature in the range of 1275°C-1400°C. The X-ray diffraction patterns showed that the peaks of the compounds were attributed to two phases, including the main crystalline phase of NdNbO4 that was indexed as the monoclinic phase and MgO as the second phase. Well-developed microstructures of Mg2NdNbO6 ceramics can be achieved, and the grain size reached the maximum value (1.63 μm) at 1375°C. As the sintering temperature increased, the dielectric constant, temperature coefficient of resonant frequency and apparent density remained almost unchanged, however, the significant change in the quality factor was observed. At 1375°C, Mg2NdNbO6 ceramics possessed excellent microwave dielectric properties: εr = 16.22, Q × f = 116 000 GHz and τf = −30.96 ppm/°C.

    更新日期:2017-11-08
  • Self-propagating mechanosynthesis of HfB2 nanoparticles by a magnesiothermic reaction
    J. Am. Ceram. Soc. (IF 2.841) Pub Date : 2017-11-08
    Maisam Jalaly, Francisco J. Gotor, María J. Sayagués

    A mechanically induced self-sustaining reaction (MSR) was used to synthesize hafnium diboride nanoparticles. Along this route, magnesium was selected as a robust reducing agent for co-reduction in boron and hafnium oxides in a combustive manner. Combustion occurred after a short milling period of 12 minutes. The hafnium diboride nanoparticles had a polygonal faceted morphology and were 50-250 nm in diameter. The assessment of the processing mechanism revealed that the initial combustive reduction in B2O3 to elemental B by Mg was the major step for progressing the overall reaction. After that, HfO2 can be reduced to elemental Hf, followed by the synthesis of HfB2 phase.

    更新日期:2017-11-08
  • A novel method for preparing dense diffusion barrier limiting current oxygen sensor
    J. Am. Ceram. Soc. (IF 2.841) Pub Date : 2017-11-08
    Tao Liu, Hongbin Jin, Lin Li, Jingkun Yu

    A novel method for preparation of a dense diffusion barrier limiting current oxygen sensor is presented. The dense thin-layer with the nominal composition Sr-, Mg- and Fe-doped lanthanum gallate (LSGMF) was prepared over La0.8Sr0.2Ga0.8Mg0.2O3–δ (LSGM) electrolyte by a thermal diffusion method. The crystal structure, morphology, elemental distribution, conductivity, and sensing performance of the prepared sample were investigated. X-ray diffraction (XRD) analysis shows a highly crystalline perovskite. SEM-EDS analysis shows that the dense thin-layer with about 40 μm thickness is well attached to the solid electrolyte. Electrical conductivity measurement shows that the dense thin-layer has high conductivity of 8.73 S·cm−1 at 800°C. The oxygen sensor exhibits good sensing performance. The variations of the limiting current (IL) vs oxygen content (x(O2)) can be obtained as follows:

    更新日期:2017-11-08
  • Dielectric nonlinear behavior of (Ba0.95Ca0.05)(Ti0.83Zr0.17)O3-based multi-layer ceramic capacitor
    J. Am. Ceram. Soc. (IF 2.841) Pub Date : 2017-11-08
    Seok-Hyun Yoon, Mi-Yang Kim

    The influence of temperature on the variation in dielectric nonlinearity and domain structures was investigated for the (Ba0.95Ca0.05)(Ti0.83Zr0.17)O3 (BCTZ)-based multilayer ceramic capacitor that shows a diffuse phase transition. Whereas the dielectric constant (εr) vs temperature shows a broadened maximum peak at low ac driving field, such a peaked behavior disappears at high ac driving field due to an abrupt increase in dielectric constants at low temperatures. Such low temperature effect can be associated with an enhanced spontaneous polarization (PS) and a significant increase in irreversible domain wall contribution to polarization representing normal ferroelectric behavior based on the Preisach analysis. No ferroelectric domain contrasts were observed at room temperature through transmission electron microscopy. However, they appeared and became more and more distinct with the decrease in temperature, and the crystal structure also changed from cubic to rhombohedral with increased lattice constants. It demonstrates that the dramatic increase in the dielectric nonlinearity with decreasing temperatures originates from the corresponding changes in domain and crystal structure, where the polar-micro-regions of BCTZ at room temperature change to normal ferroelectric domains at low temperatures.

    更新日期:2017-11-08
  • Crack propagation in silica from reactive classical molecular dynamics simulations
    J. Am. Ceram. Soc. (IF 2.841) Pub Date : 2017-11-08
    Jessica M. Rimsza, Reese E. Jones, Louise J. Criscenti

    Mechanistic insight into the process of crack growth can be obtained through molecular dynamics (MD) simulations. In this investigation of fracture propagation, a slit crack was introduced into an atomistic amorphous silica model and mode I stress was applied through far-field loading until the crack propagates. Atomic displacements and forces and an Irving–Kirkwood method with a Lagrangian kernel estimator were used to calculate the J-integral of classical fracture mechanics around the crack tip. The resulting fracture toughness (KIC), 0.76 ± 0.16 MPa√m, agrees with experimental values. In addition, the stress fields and dissipation energies around the slit crack indicate the development of an inelastic region ~30Å in diameter. This is one of the first reports of KIC values obtained from up-scaled atomic-level energies and stresses through the J-integral. The application of the ReaxFF classical MD force field in this study provides the basis for future research into crack growth in multicomponent oxides in a variety of environmental conditions.

    更新日期:2017-11-08
  • Coupled experimental phase diagram study and thermodynamic optimization of the Li2O–MgO–SiO2 system
    J. Am. Ceram. Soc. (IF 2.841) Pub Date : 2017-11-08
    Bikram Konar, Dong-Geun Kim, In-Ho Jung

    A coupled key phase diagram study and critical evaluation and optimization of all available experimental data of the Li2O–MgO–SiO2 system was performed to obtain a set of Gibbs energy functions to reproduce all the reliable phase equilibria and thermodynamic data. Differential scanning calorimetry measurements and equilibration/quenching experiments were performed in the Li2SiO3–MgO and Li4SiO4–Mg2SiO4 sections, respectively, using sealed Pt capsules to prevent the volatile loss of Li. According to the present experimental results, Li2MgSiO4 is the only compound present in the Li4SiO4–Mg2SiO4 isopleth, which shows a peritectic melting at 1465 ± 6°C (1738 ± 6 K). The Modified Quasichemical Model, which considers short-range ordering in the melt, was employed to describe the thermodynamic properties of the liquid phase. The Li4SiO4–Li2MgSiO4 and Mg2SiO4-rich solid solutions were modeled using the Compound Energy Formalism.

    更新日期:2017-11-08
  • Effect of interfacial energy on microstructure of a directionally solidified Al2O3/YAG eutectic ceramic
    J. Am. Ceram. Soc. (IF 2.841) Pub Date : 2017-11-05
    Xu Wang, Yujie Zhong, Dong Wang, Luchao Sun, Bailing Jiang, Jiangyang Wang

    This article is protected by copyright. All rights reserved.

    更新日期:2017-11-06
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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