3D microstructure-based modelling of the deformation behaviour of ceramic matrix composites J. Eur. Ceram. Soc. (IF 3.411) Pub Date : 2017-11-15 Tomasz Trzepieciński, Grażyna Ryzińska, Magdalena Gromada, Mojtaba Biglar
In this paper the experimental and numerical investigations of microstructure modelling of multilayer actuator are considered. BaTiO3 powder is manufactured using the solid-state technique. The main parameter influencing the possibility of application of BaTiO3 ceramics on actuators is the grain size of the sintered materials. Three kinds of pellets with different average grain sizes were considered. The adhesive joints of a BaTiO3 and Ag-based conducting electric current epoxy adhesive were used to fabricate the model of actuator. A 3D microstructure model of BaTiO3 and composites were generated using Digimat-FE software. The Mori–Tanaka and double inclusion homogenization models for representative volume elements of multilayer actuator were carried out using Digimat-MF software, in order to obtain the failure characteristics of the composite material. To investigate the failure of the ceramic matrix composite the Hashin-Rotem criterion was used.
Composition and poling-induced modulation on photoluminescence properties for NBT-xBT: Pr3+ ceramics J. Eur. Ceram. Soc. (IF 3.411) Pub Date : 2017-11-22 Xiang Xia, Xiangping Jiang, Chao Chen, Na Tu, Yunjing Chen, Xiaohong Li, Pengbing Wang, Gang Fan
In this work, the modulation of photoluminescence (PL) properties, which was realized by the composition and poling-induced structural evolution, for the Pr3+ doped (1-x)(Na1/2Bi1/2)TiO3-xBaTiO3 (NBT-xBT: Pr3+) piezoelectric ceramics was systematically investigated. Based on the Rietveld refinement structural analysis, there were two distinct composition ranges characterized by different structural features for NBT-xBT: Pr3+ ceramics at room temperature: (i) rhombohedral R3c + monoclinic Cc phases for the compositions of x ≤ 0.03, and (ii) tetragonal P4bm + monoclinic Cc phases for 0.04 ≤ x ≤ 0.07. It was interesting to notice that the PL emission intensity is positively correlated with the phase fraction of Cc, which is closely related to the crystal symmetry of NBT-xBT: Pr3+ ceramics. The compositions with x ≤ 0.06 underwent an irreversible phase transformation on the application of electric field. The dielectric and Raman measurement revealed a transition from a relaxor state to a normal ferroelectric for the x ≤ 0.06 compositions under an applied poling electric field, with not only the reduction in the in-phase octahedral tilting disorder but also the establishment of long-range ordering. These electric field-induced structural changes were responsible for poling-induced PL quenching behaviors as a result of the increased local structure symmetry around doped Pr3+ ions in the poled ceramics.
Comparison of residual strength behavior after indentation, scratching and grinding of zirconia-based ceramics for medical-technical applications J. Eur. Ceram. Soc. (IF 3.411) Pub Date : 2017-11-21 B. Denkena, A. Wippermann, S. Busemann, M. Kuntz, L. Gottwik
In this study, three methods of characterizing the damage tolerance of different zirconia-based ceramics for medical-technical applications are presented. The damage is inflicted statically, with Vickers hardness impressions and dynamically by scratching with a Rockwell diamond, as well as by means of a reproducible grinding process. The damage intensity is, in each case, successively increased. The measured strength values as a function of the inflicted damage thus provide information on the grinding robustness of the material. This permits the determination of critical grinding parameters above which the component quality is impaired and, ultimately, the patient is endangered. The continuing pressure to reduce production costs by shortening processing times makes damage tolerant behavior of materials extremely important. Ultimately, this permits the reduction of production costs while maintaining component quality and the guarantee of future patient safety.
Microstructure evolution and mechanical property of ZrC-SiC/Ti6Al4V joints brazed using Ti-15Cu-15Ni filler J. Eur. Ceram. Soc. (IF 3.411) Pub Date : 2017-11-21 J.M. Shi, L.X. Zhang, X.Y. Pan, X.Y. Tian, J.C. Feng
ZrC-SiC ceramic and TC4 alloy were successfully brazed using a self-prepared Ti-15Cu-15Ni filler. The microstructure and mechanical property of the joints obtained at different brazing temperatures were investigated. The results indicated that Ti from the Ti-15Cu-15Ni and the TC4 reacted with the ZrC-SiC to form TiC phase adjacent to the ZrC-SiC ceramic. In the brazing seam, Ti2(Ni, Cu) intermetallic compounds zone (IMCs Zone), Hypoeutectic Zone and Hypereutectoid Zone formed. The brazing temperature affected the dissolution of TC4 into the braze filler significantly, and then determined the microstructure of the joint. The formation of α-Ti in the brazing seam could decrease the hardness and the brittleness of the brazing seam, which was beneficial to the property of the brazed joint. The joint strength reached a maximum value of 43 MPa when the joint was brazed at 970 °C and cracks propagated in the ZrC-SiC substrate near the brazing seam.
The effect of a carbon layer on the microstructural and mechanical properties of porous BN/Si3N4 ceramic brazed with a titanium-silicon filler J. Eur. Ceram. Soc. (IF 3.411) Pub Date : 2017-11-21 Y.L. Zhuang, T.S. Lin, S.J. Wang, P. He, D.P. Sekulic, D.C. Jia
The Ti22Si78 (wt. %) braze was used to bond porous BN/Si3N4 ceramic. The results revealed that the joint strength was low. In order to improve the joint strength, a carbon coated modification of the porous BN/Si3N4 substrate, achieved by the pyrolysis of phenol-formaldehyde resin was suggested. The thickness of carbon layer was controlled by the volume ratio of phenol-formaldehyde resin and methyl alcohol (R/M). The effect of the carbon layer on the microstructure and mechanical properties of the joint was examined. It was established that the maximum joint strength was achieved at the level of 80 MPa (as opposed to the uncoated joint with only 30 MPa) when R/M was 1:2, at the given brazing temperature. The improvement of the joint strength is attributed mainly to the formation of a SiC infiltration reaction layer, a significant population of SiC nanowires, as well as TiN0.7C0.3 and TiB2 particles.
The damage evolution of He irradiation on Ti3SiC2 as a function of annealing temperature J. Eur. Ceram. Soc. (IF 3.411) Pub Date : 2017-11-21 Hongliang Zhang, Ranran Su, Liqun Shi, D.J. O'Connor, B.V. King, E.H. Kisi
The radiation damage response of Ti3SiC2 irradiated by 110 keV helium ions at room temperature (RT), the subsequent evolution of damage including helium bubble growth as a function of annealing temperatures are investigated using grazing incidence X-ray diffraction (GIXRD), Raman spectroscopy and transmission electronic microscopy (TEM). In addition to collision cascade effects leading to TiC nanocrystal formation near the surface of Ti3SiC2, He ion irradiation produces damage due to the growth of He bubbles, which cause a structural transformation into a large grain TiC crystalline phase at high temperatures. The displacement of matrix Si atoms adjacent to the He bubbles along the Si layer in Ti3SiC2 either via bubble growth or the production of inter-bubble fracture is the reason for the structural transformation. Depending on the He damage level, a significant recovery of the He irradiation damage can occur at moderate temperatures. This property may play a positive role in the damage resistance of Ti3SiC2, making it a potential candidate for future nuclear reactor applications.
Photocatalytic Ceramic Tiles: Challenges and Technological Solutions J. Eur. Ceram. Soc. (IF 3.411) Pub Date : 2017-11-20 Andre L. da Silva, Michele Dondi, Mariarosa Raimondo, Dachamir Hotza
Titania-functionalized ceramic tiles are gaining space on the market of the self-cleaning photocatalytic building materials after a decade of industrial attempts and investigation on different technological issues. The present paper overviews the latest research on photocatalytic ceramic tiles in terms of process parameters, durability, cleanability and photoactivity, addressing challenges and solutions reported by academic and industrial sources. A special attention is paid to the superhydrophilicity and photocatalytic performance achievable on ceramic surfaces and their complex dependence on several factors (titania crystalline phase, deposition technique; firing temperature; thickness, roughness, specific surface area of the photoactive film; and so on). In particular, the methods used to deposit the titania layer, its degree of adhesion and effects on tile appearance (color, brightness, and roughness) are reviewed. Moreover, manufacturing a photocatalytic ceramic tile with a single firing step is still a challenge. Despite the international standards available on photocatalytic performance, the experimental parameters from one research to another may be quite different, therefore a performance comparison becomes virtually impossible. Nevertheless, among the available commercial products declared as photocatalytic ceramic tiles, just some of them revealed to be photoactive. From the data available, superhydrophilicity of tiles corresponded to contact angles with water in the 10 − 15° range. Specific photoactivity measured as methylene blue (MB) degradation resulted typically in the 2.8 − 3.4 mol/m2h range; photonic efficiency was between 0.025 and 0.030%; while MB index was in the 15 − 20 range. Finally, the relationship of dye degradation with the self-cleaning property is also a question that remains unanswered.
Three-dimensional printed Yttria-stabilized Zirconia self-supported electrolytes for Solid Oxide Fuel Cell applications J. Eur. Ceram. Soc. (IF 3.411) Pub Date : 2017-11-15 S. Masciandaro, M. Torrell, P. Leone, A. Tarancon
Additive manufacturing represents a revolution due to its unique capabilities for freeform fabrication of near net shapes with strong reduction of waste material and capital cost. These unfair advantages are especially relevant for expensive and energy-demanding manufacturing processes of advanced ceramics such as Yttria-stabilized Zirconia, the state-of-the-art electrolyte in Solid Oxide Fuel Cell applications. In this study, self-supported electrolytes of yttria-stabilized zirconia have been printed by using a stereolithography three-dimensional printer. Printed electrolytes and complete cells fabricated with cathode and anode layers of lanthanum strontium manganite- and nickel oxide-yttria-stabilized zirconia composites, respectively, were electrochemical characterized showing full functionality. In addition, more complex configurations of the electrolyte have been printed yielding an increase of the performance entirely based on geometrical aspects. Complementary, a numerical model has been developed and validated as predictive tool for designing more advanced configurations that will enable highly performing and fully customized devices in the next future.
Influence of whisker-aspect-ratio on densification, microstructure and mechanical properties of Al2O3 whiskers-reinforced CeO2-stabilized ZrO2 composites J. Eur. Ceram. Soc. (IF 3.411) Pub Date : 2017-11-15 Fei Zuo, Fan Meng, Dong-Tao Lin, Jun-Jie Yu, Hong-Jian Wang, Shen Xu, Wei-Ming Guo, Carmen Cerecedo, Víctor Valcárcel, Hua-Tay Lin
A novel composite of 12 mol% CeO2-stablized tetragonal ZrO2 reinforced with Al2O3 whiskers (designated as Ce-TZP/Aw) has been prepared and studied in this work. The objective of this investigation was to systematically study the influence of whisker-aspect-ratio on the densification behaviors, microstructure evolution, and mechanical properties of Ce-TZP/Aw composite. Results showed that the sintered density of composite increased and the grain growth tended to diminish with the decrease in whisker aspect radio. Both the fracture toughness and flexural strength reached maximum values of 475 ± 12 MPa and 11.4 ± 0.2 MPa.m1/2, respectively at a whisker aspect ratio of about 12. It was also observed that the fracture toughness, flexural strength and tetragonal to monoclinic ZrO2 transformation of the dual-phase composite exhibited similar variation trend as a function of the whisker-aspect-ratio, which suggested that the stress-induced phase transformation should be the main toughening and strengthening mechanism in the Ce-TZP/Aw composite.
Synthesis, Characterization and Sintering of Si-C-N Nano-powders via Sodium Reduction in Liquid Ammonia J. Eur. Ceram. Soc. (IF 3.411) Pub Date : 2017-11-14 Qi Wang, Mei Yang, Jiusan Xiao, Shuqiang Jiao, Hongmin Zhu
Si-C-N nano-powders with tunable carbon content were synthesized through the reduction of silicon tetrachloride (SiCl4) and trichloromethylsilane (SiCl3CH3) solution by sodium in liquid ammonia. The nano-powders contain two domains of structure, Si-C-N amorphous or continuous random networks (CRNs), and free carbon. The carbon content in Si3+nCnN4 CRNs, is tunable from n = 0 to n = 1. Free carbon will appeared with the increase of the C/Si mole ratio when C/Si is higher than 1/4. The crystallization of amorphous Si-C-N powders occurs at temperatures ranging from 1300 °C to 1500 °C depending on the carbon content. The additive-free dense Si-C-N ceramics with relatively low porosity were fabricated by Spark Plasma Sintering (SPS).
Zirconia nano-colloids transfer from continuous hydrothermal synthesis to inkjet printing J. Eur. Ceram. Soc. (IF 3.411) Pub Date : 2017-11-14 M. Rosa, P.N. Gooden, S. Butterworth, P. Zielke, R. Kiebach, Y. Xu, C. Gadea, V. Esposito
Water dispersions of nanometric yttria stabilized zirconia (YSZ) particles synthesized by Continuous Hydrothermal Synthesis are transferred into nano-inks for thin film deposition. YSZ nanoparticles are synthesized in supercritical conditions resulting in highly dispersed crystals of 10 nm in size. The rheology of the colloid is tailored to achieve inkjet printability (Z) by using additives for regulating viscosity and surface tension. Inks with a wide range of properties are produced. A remarkable effect of nanoparticles on the ink printability is registered even at solid load < 1%vol. In particular, nanoparticles hinder the droplet formation at low values of the printability while suitable jetting is observed at high Z values, i.e. Z ≈ 20. For the optimized inks, we achieve high quality printing with lateral and thickness resolutions of 70 μm and ca. 250 nm respectively, as well as self-levelling effect with a reduction of the substrate roughness. Densification is achieved at sintering temperatures below 1200 °C.
Phase variation and thermophysical properties of La2Hf2O7 with alumina addition J. Eur. Ceram. Soc. (IF 3.411) Pub Date : 2017-11-13 Shengyue Gu, Shouyang Zhang, Bei Xue, Jinkai Yan, Wei Li, Leilei Zhang
La2O3-Al2O3-HfO2 ceramics were prepared by solid reaction of La2Hf2O7 ceramic powders which were synthesized by solution combustion and commercial alumina powders at 1600 °C in air for 10 h. Phase variation and thermophysical properties of La2O3-Al2O3-HfO2 ceramics were investigated. With the increase of alumina content, LaAlO3, HfO2 and LaAl11O18 phase structures appeared. The thermal expansion coefficients gradually increased with the increase of alumina content from 1000 °C to 1300 °C. The thermal conductivities of La2O3-Al2O3-HfO2 ceramics had nonlinear variation with the increase of alumina content and reached the lowest value around 1.1 W·m−1·K−1 when the ratio of La2Hf2O7 to Al2O3 was 1:0.25. Therefore, the La2O3-Al2O3-HfO2 ceramics with a proper content of alumina can be considered as a new thermal barrier materials. Meanwhile, as potential application as interface layer in TBC, La2O3-Al2O3-HfO2 ceramics are beneficial to improve the effectiveness of the thermal barrier coating.
Preparation of Highly Porous ZrB2/ZrC/SiC Composite Monoliths Using Liquid Precursors via Direct Drying Process J. Eur. Ceram. Soc. (IF 3.411) Pub Date : 2017-11-13 Fei Li, Xiao Huang
We developed a simple liquid precursor method for the syntheses of porous ZrB2/ZrC/SiC composite monoliths. Furfuryl alcohol (FA), zirconium n-butoxide, tetraethyl orthosilicate and boric acid are used as the raw materials. By combining the polymerization of FA and gelation of inorganic sols, porous hybrid monoliths are prepared by direct drying the wet gels. The inorganic and organic polymers possibly form interpenetrated network which provides the robustness for the wet gel to withstand the severe changes during dessication. When heat-treated at 1600 °C, hybrid gels are converted into porous ZrB2/ZrC/SiC monoliths. The microstructure of the ZrB2/ZrC/SiC monoliths can be easily tailored by controlling the synthesis conditions. The porosities of the ZrB2/ZrC/SiC monoliths can be tuned around 74.3 ∼ 81.6%, while the average pore diameters can be tuned ranging from 1.0 to 8.5 μm with pretty narrow distribution. The compressive strengths of such highly porous ceramics are in the range of 1.2 ∼ 1.9 MPa.
A Corrosion Mechanism of Titanium Diboride in KF−AlF3−Al2O3 Melt. J. Eur. Ceram. Soc. (IF 3.411) Pub Date : 2017-11-13 Martin Kontrík, František Šimko, Dagmar Galusková, Martin Nosko, Valéria Bizovská, Michal Hičák, Dušan Galusek, Aydar Rakhmatullin, Michal Korenko
TiB2 samples were exposed to molten KF−AlF3−Al2O3: 54.8-42.1-3.1 mol % salt, at 680 °C for 50, 100 and 200 h. The corroded samples of TiB2 were investigated by SEM-EDX, EBSD, XRD, FT-IR and MAS NMR analysis. Corrosion was noted to occur predominantly as pitting attacks on the surface of the investigated materials. An inter-crystal and trans-crystal corrosion were identified on the cross-sections of the samples. A perturbation of Ti<img border="0" alt="single bond" src="https://cdn.els-cdn.com/sd/entities/sbnd">B bonds was detected (SEM-EDX and NMR analysis), at which a formation of orthorhombic TiO2 was also identified (EBSD analysis). The subsequent NMR, XRD and FT-IR analysis of the behaviour of TiB2 powder in molten KF−AlF3−Al2O3 supports the statement about the formation of orthorhombic TiO2 and mullite type of aluminium borates.
α-Alumina Membrane Having a Hierarchical Structure of Straight Macropores and Mesopores Inside the Pore Wall J. Eur. Ceram. Soc. (IF 3.411) Pub Date : 2017-11-13 Hideki Hashimoto, Sumire Kojima, Takashi Sasaki, Hidetaka Asoh
We prepared a through-hole α-alumina membrane with a hierarchical porous structure from an anodic porous alumina membrane prepared using phosphoric acid electrolyte as the starting material. By heating the anodic porous alumina membrane to 1400 °C, aluminum phosphate nanoparticles were segregated in the α-alumina matrix at the anion-incorporated outer layer and the high-purity alumina layer forming a cell boundary band sintered as a high-density α-alumina layer at the central core of the pore wall. When the heat-treated membrane was immersed in concentrated hydrochloric acid, a unique hierarchical porous α-alumina membrane structure was formed with straight macropores and mesopores inside the pore wall due to the dissolution of aluminum phosphate nanoparticles. The developed α-alumina membrane can be ultimately used as a multifunctional filter because of its unique hierarchical porous structure and extremely high chemical and thermal durability.
Joining and testing of alumina fibre reinforced YAG-ZrO2 matrix composites J. Eur. Ceram. Soc. (IF 3.411) Pub Date : 2017-11-13 Muhammad Yasir Akram, Monica Ferraris, Valentina Casalegno, Milena Salvo, Georg Puchas, Stefan Knohl, Walter Krenkel
Alumina (Nextel™ 610) fibre reinforced YAG-ZrO2 matrix composites were successfully joined by using different brazing alloys, metallic interlayers and a glass-ceramic. All joints were mechanically stable and free of cracks. Three commercial brazing alloys and a new alloy based on Ti/Cu/Al interlayers were selected to join these composites for applications in a non-oxidizing environment. A glass-ceramic based on SiO2-Al2O3-CaO-MgO was developed in case the joined component needs to be oxidation resistant. To evaluate the thermal stability, all joined composites were aged up to 100 h in air at 550 °C for brazing joints or 850 °C and 930 °C for glass-ceramic joints. The mechanical strength was measured using single lap and four point bending tests before and after ageing. Four point bending tests on glass-ceramic joined samples showed an average joint strength of about 70 MPa which is 35% of as-received composites.
A Composition Des ign Rule for Crystal Growth of Centimeter Scale by Normal Sintering Process in Modified Potassium Sodium Niobate Ceramics J. Eur. Ceram. Soc. (IF 3.411) Pub Date : 2017-11-12 Attaur Rahman, Kyung-Hoon Cho, Cheol-Woo Ahn, Jungho Ryu, Jong-Jin Choi, Jong-Woo Kim, Woon-Ha Yoon, Joon-Hwan Choi, Dong-Soo Park, Byung-Dong Hahn
It has been reported that single crystals could be grown by normal sintering process, without the addition of a seed, in (K,Na)NbO3 (KNN)-based ceramics. The growth of huge grains (approximately 5–30 mm) is due to the donor effect on abnormal grain growth (AGG) in KNN-based ceramics. In this study, a composition design rule is suggested to obtain the large single crystal without the seed addition in KNN-based ceramics. In addition, it is also identified by the microstructure observation that the huge grains can be due to the donor effect on the abnormal grain growth which is found in perovskite materials. The donor ratio must be designed to be located at the range between 0.7% and 0.9% compared to that of Na+ ions, in order to obtain the large single crystals in KNN-based ceramics. This range of the donor ratio is narrower than that in BaTiO3 (or SrTiO3) ceramics.
Tailoring microstructure and photovoltaic effect in multiferroic Nd-substituted BiFeO3 ceramics by processing atmosphere modification J. Eur. Ceram. Soc. (IF 3.411) Pub Date : 2017-11-12 Chi-Shun Tu, Pin-Yi Chen, Cheng-Sao Chen, Chun-Yen Lin, V.H. Schmidt
This study highlights significant effects of processing atmosphere ratio (O2/N2) on microstructure, impurity phases, atomic hybridization, band gap, and photovoltaic properties in (Bi0.93Nd0.07)FeO3 (BFO7Nd) ceramics. A Rietveld-refinement analysis indicates increased oxygen and bismuth vacancies in the specimens processed in the O2-rich atmosphere (hereafter called O2-rich-atmosphere specimens). In the matrix containing mainly Fe3+ ions, Fe4+ cations were identified with O2 concentration decreasing in the atmosphere by Fe K/L-edges synchrotron X-ray absorption. Oxygen K-edge absorption reveals reduced hybridizations of the O 2p–Fe 3d and the O 2p–Bi 6sp orbitals in the O2-rich-atmosphere specimens. Photovoltaic effects in the ITO/BFO7Nd/Au heterostructures under near-ultraviolet irradiation (λ = 405 nm) exhibit strong dependences on O2/N2 ratio. A p-n-junction model was used to describe open-circuit voltage and short-circuit current density as functions of irradiation intensity. The calculated carrier densities (in BFO7Nd ceramics) and p-n-junction widths (in the dark) are ∼1023 m−3 and a few hundred nanometers, respectively.
Microwave Dielectric Properties of Low-Temperature Sinterable α-MoO3 J. Eur. Ceram. Soc. (IF 3.411) Pub Date : 2017-11-11 Jobin Varghese, Tuomo Siponkoski, Mikko Nelo, Mailadil Thomas Sebastian, Heli Jantunen
The α-MoO3 ceramics were prepared by uniaxial pressing and sintering of MoO3 powder at 650 °C and their structure, microstructure, densification and sintering and microwave dielectric properties were investigated. The sintering temperature of α-MoO3 was optimized based on the best densification and microwave dielectric properties. After sintering at 650 °C the relative permittivity was found to be 6.6 and the quality factor was 41,000 GHz at 11.3 GHz. The full-width half-maximum of the A1g Raman mode of bulk α-MoO3 at different sintering temperatures correlated well with the Qf values. Moreover, the sintered samples showed a temperature coefficient of the resonant frequency of −25 ppm/°C in the temperature range from −40 to 85 °C and they exhibited a very low coefficient of thermal expansion of ±4 ppm/°C. These microwave dielectric properties of α-MoO3 will be of great benefit in future MoO3 based materials and their applications.
Transparent Sub-mircon Gd2Zr2O7 Ceramic Prepared by Spark Plasma Sintering Using Nanocrystalline Powders J. Eur. Ceram. Soc. (IF 3.411) Pub Date : 2017-11-11 Jianqi Qi, Zhangyi Huang, Mao Zhou, Shuting Peng, Nannan Ma, Tiecheng Lu
In this work, transparent sub-mircon Gd2Zr2O7 (GZO) ceramic was successfully sintered for the first time by spark plasma sintering (SPS) using nanocrystalline powders synthesized via a solvothermal assisted co-precipitation route. With the aids of fast heating and cooling rate and high pressure, the GZO transparent sample with an average grain size of about 205 nm was obtained at 1400 °C for 5 min. The maximum transmittance of about 70% was achieved at a wavelength of 2000 nm.
Effect of nanowires in microporous structures on the thermoelectric properties of oxidized Sb-doped ZnO film J. Eur. Ceram. Soc. (IF 3.411) Pub Date : 2017-11-11 Guojian Li, Lin Xiao, Shiying Liu, Huimin Wang, Yang Gao, Qiang Wang
Sb-doped ZnO thermoelectric films with microporous structures are fabricated by oxidizing evaporated Zn-Sb thin films in a leaf-like surface. High magnetic field (HMF) and Sb are employed to tune the formation of nanowires and nanorods in the microporous films and conduction type. Nanowire is formed in the film with Sb content of 3.0% and nanorod is formed with 4.6% Sb with the absence of HMF. P-type ZnO films with a wuterzite are formed. The resistivity of the films decreases by two orders of magnitude by increasing Sb content. The resistivity of films decreases 45% and 80% by forming nanowires and nanorods, respectively. The power factor of the nanorod structures increases by two orders of magnitude by comparison with others and reaches to 52.6 μW/m K2. This indicates that the nanorod structures with a higher Sb content are easy to obtain stable p-type semiconductor with a higher power factor.
Oxidation behavior of ZrB2-SiC-ZrC in oxygen-hydrogen torch environment J. Eur. Ceram. Soc. (IF 3.411) Pub Date : 2017-11-11 Yuki Kubota, Mamoru Yano, Ryo Inoue, Yasuo Kogo, Ken Goto
The oxidation behavior of four ZrB2-SiC-ZrC compositions with varying ZrC contents (20, 34, 50, and 64 vol.%) was compared to that of ZrB2-SiC. The ceramics were oxidized at 1700 °C in an oxygen-hydrogen torch environment. The liquid oxide on the ZrB2-SiC sample came off from the surface under such an environment. In contrast, the all ZrB2-SiC-ZrC samples maintained the convex oxide on the surface, which consisted of ZrO2 and SiO2. The convex oxide of ZSZ with higher ZrC content was thicker, with the exception of ZrB2-SiC-64vol.%ZrC sample. The ZrB2-SiC-64vol.%ZrC sample formed a ZrO2-rich layer, which was clearly denser than the ZrO2-SiO2. This densification was caused by ZrO2-sintering, and it was specific behavior under the dynamic pressure.
Texturing behaviours of (K0.47Na0.51Li0.02)(Nb0.8Ta0.2)O3 piezoelectric ceramics produced using NaNb1-xTaxO3 templates J. Eur. Ceram. Soc. (IF 3.411) Pub Date : 2017-11-10 Hyun Ae Cha, Jae-Ho Jeon
Textured (K0.47Na0.51Li0.02)(Nb0.8Ta0.2)O3 (KNLNT20) piezoelectric ceramics were prepared using NaNb1-xTaxO3 templates. The highest degree of grain orientation (97%) and piezoelectric constant (342 pC/N) were obtained upon adding 3 wt% of the NaNb0.8Ta0.2O3 (NNT20) template and sintering at 1150 °C for 1 h. Back-scattered scanning electron micrographs of the textured KNLNT20 samples sintered at 1150 °C for 1 h indicated the presence of templates similar in size to the original ones within the cores of the textured grains. The peak value of the dielectric constant corresponding to the NNT20 core decreased after prolonged holding at 1150 °C, owing to a decrease in the size of the NNT20 core because of the interdiffusion of K, Na, and Li ions between the NNT20 core and KNLNT20 shell. This interdiffusion also decreased the piezoelectric constant, d33 value of the textured KNLNT20 samples by inducing a change in the chemical composition of the shell region.
Fabrication of dye-sensitized solar modules based on a prototyping pilot line and their integration into energy storage microsystems J. Eur. Ceram. Soc. (IF 3.411) Pub Date : 2017-11-10 Giacomo Gorni, Isabella Zama, Christian Martelli, Luigi Armiento
We successfully developed a prototyping pilot line for dye-sensitized solar modules up to 23 × 23 cm2. Dedicated ceramic materials were studied for large area application: we formulated a lead-free glass frit sealant with low softening point based on the ternary system Bi2O3-B2O3-ZnO and a TiO2 anatase screen-printable paste for semi-transparent photoanodes. Alongside traditional screen-printing, specific machines among which a thermal press, a dye injection equipment and an automatic electrolyte filler were designed and realized. A silver-free layout was adopted and the solar modules reached an efficiency close to 2%. Photovoltaic glass panels composed by interconnected DSSC modules were interfaced with custom integrated circuits to realize energy storage microsystems for two self-powered prototypes: a USB solar table for recharging of portable devices and a novel LED glass parapet for active night lighting are here presented.
Ferroelastic domain structure and phase transition in single-crystalline [PbZn1/3Nb2/3O3]1-x[PbTiO3]x observed in situ via x-ray microbeam J. Eur. Ceram. Soc. (IF 3.411) Pub Date : 2017-11-10 Tao Li, Zehui Du, Nobumichi Tamura, Mao Ye, Saikumar Inguva, Wei Lu, Xierong Zeng, Shanming Ke, Haitao Huang
(1-x)Pb(Zn1/3Nb2/3)O3-xPbTiO3 ((1-x)PZN-xPT in short) is one of the most important piezoelectric materials. In this work, we extensively investigated (1-x)PZN-xPT (x = 0.07-0.11) ferroelectric single crystals using in-situ synchrotron μXRD, complemented by TEM and PFM, to correlate microstructures with phase transitions. The results reveal that (i) at 25 °C, the equilibrium state of (1-x)PZN-xPT is a metastable orthorhombic phase for x = 0.07 and 0.08, while it shows coexistence of orthorhombic and tetragonal phases for x = 0.09 and x = 0.11, with all ferroelectric phases accompanied by ferroelastic domains; (ii) upon heating, the phase transformation in x = 0.07 is Orthorhombic → Monoclinic → Tetragonal → Cubic. The coexistence of ferroelectric tetragonal and paraelectric cubic phases was in-situ observed in x = 0.08 above Curie temperature (TC), and (iii) phase transition can be explained by the evolution of the ferroelectric and ferroelastic domains. These results disclose that (1-x)PZN-xPT are in an unstable regime, which is possible factor for its anomalous dielectric response and high piezoelectric coefficient.
Tunable thermal properties in yttrium silicates switched by anharmonicity of low-frequency phonons J. Eur. Ceram. Soc. (IF 3.411) Pub Date : 2017-11-10 Yixiu Luo, Luchao Sun, Jiemin Wang, Zhilin Tian, Hongqiang Nian, Jingyang Wang
Coordinated modulation of thermal resistance and thermal expansion compatibility has become a chief concern in designing reliable environmental/thermal barrier coating candidates for Si-based ceramics. This study reports phonon behaviors and thermal properties of prototypical silicates X2-Y2SiO5 and γ-Y2Si2O7. The nature of anharmonicity for low-frequency phonons is analyzed, and the finding is discussed with respect to specific crystal structures and interatomic force constants. Low lattice thermal conductivities (κL) basically derive from the giant phonon anharmonicity enhanced by interactions between low-frequency optic and acoustic phonons. γ-Y2Si2O7 is predicted with considerably lower thermal expansion coefficient (αV) than Y2SiO5. The mechanism is disclosed as an effect of the extensive number of low-frequency phonons with negative Grüneisen constants (contributing to negative thermal expansion) in γ-Y2Si2O7, together with its higher elastic stiffness against internal thermal pressure at elevated temperature. A guideline for simultaneously approaching low κL and low αV is proposed for searching promising E/TBC candidates.
Fracture toughness of silicon nitride balls via thermal shock J. Eur. Ceram. Soc. (IF 3.411) Pub Date : 2017-11-10 Stefan Strobl, Franz-Alois Adlmann, Peter Supancic, Tanja Lube, Robert Danzer, Oskar Schöppl
A new method for fracture toughness determination of ceramic balls is presented. The starter crack is introduced into the surface of the ball by a Knoop indentation followed by grinding off the deformed zone. The loading through surface tensile stresses is realized by water quenching, i.e. dropping the heated ball into water. The temperature difference is stepwise increased to find the critical temperature difference for the initiation of crack growth. The geometric factor is calculated in a parametric finite element study, whereas the temperature distribution in the ball was previously determined by using the Biot concept.
Significantly enhanced breakdown field in Ca1-xSrxCu3Ti4O12 ceramics by tailoring donor densities J. Eur. Ceram. Soc. (IF 3.411) Pub Date : 2017-11-08 Zhuang Tang, Yuwei Huang, Kangning Wu, Jianying Li
Significantly enhanced breakdown field of 24.52 kV cm−1 as well as noteworthy nonlinear coefficient of 8.11 and low dielectric loss of 0.077 were obtained in Ca0.6Sr0.4Cu3Ti4O12 ceramic. It was proved from impedance spectra that improved breakdown field was attributed to enhanced grain boundary resistance and elevated Schottky barrier height, which was further found resulting from reduced donor densities in C-V measurements. In addition, it was found that the activation energy originated from oxygen vacancies was increased, indicating the generation of oxygen vacancies was suppressed. Since oxygen vacancies acted as donors in depletion layers, it is reasonable to deduce that the reduced donor density was mainly ascribed to the decreased oxygen vacancies. In conclusion, maximum integrated action of strong solid solution effect and weak Sr-stretching effect was achieved when Sr/Ca ratio is 40/60, leading to greatly elevated potential barrier height and enhanced breakdown field consequently.
Sintering behavior, microstructure and thermoelectric properties of calcium cobaltite thick films for transversal thermoelectric multilayer generators J. Eur. Ceram. Soc. (IF 3.411) Pub Date : 2017-11-08 Thomas Schulz, Timmy Reimann, Arne Bochmann, Andre Vogel, Beate Capraro, Björn Mieller, Steffen Teichert, Jörg Töpfer
The sintering behavior and the thermoelectric performance of Ca3Co4O9 multilayer laminates were studied, and a multilayer thermoelectric generator was fabricated. Compacts and multilayer samples with anisotropic microstructure and residual porosity were obtained after conventional sintering at 920 °C, whereas dense and isotropic multilayer samples were prepared by firing at 1200 °C and reoxidation at 900 °C. A hot-pressed sample has a dense and anisotropic microstructure. Samples sintered at 920 °C exhibit low electrical conductivity due to the low density, whereas the Seebeck coefficient is not sensitive to preparation conditions. However, thermal conductivity of multilayers is very low, and, hence acceptable ZT values are obtained. A transversal multilayer thermoelectric generator (TMLTEG) was fabricated by stacking layers of Ca3Co4O9 green tapes, AgPd conductor printing, and co-firing at 920 °C. The TMLTEG has a power output of 3 mW at ΔT = 200 K in the temperature interval of 25 °C to 300 °C.
Characteristics of LaCo0.4Ni0.6-xCuxO3-δ ceramics as a cathode material for intermediate-temperature solid oxide fuel cells J. Eur. Ceram. Soc. (IF 3.411) Pub Date : 2017-11-08 Yi-Xin Liu, Sea-Fue Wang, Yung-Fu Hsu, Hung-Wei Kai, Piotr Jasinski
In this study, the effects of Cu-ion substitution on the densification, microstructure, and physical properties of LaCo0.4Ni0.6-xCuxO3-δ ceramics were investigated. The results indicate that doping with Cu ions not only enhances the densification but also promotes the grain growth of LaCo0.4Ni0.6-xCuxO3-δ ceramics. The Cu substitution at x ≤ 0.2 can suppress the formation of La4Ni3O10, while the excess Cu triggers the formation of La2CuO4.032 phase. The p-type conduction of LaCo0.4Ni0.6O3-δ ceramic was significantly raised by Cu substitution because the acceptor doping (<img height="44" border="0" style="vertical-align:bottom" width="58" alt="View the MathML source" title="View the MathML source" src="http://origin-ars.els-cdn.com/content/image/1-s2.0-S0955221917307586-si1.gif">CuNi') triggered the formation of hole carriers; this effect was maximized in the case of LaCo0.4Ni0.4Cu0.2O3-δ composition (1480 S cm−1 at 500 °C). Thermogravimetric data revealed a slight weight increase of 0.29% for LaCo0.4Ni0.4Cu0.2O3-δ compact up to 871 °C; this is due to the incorporation of oxygen that creates metal vacancies and additional <img height="39" border="0" style="vertical-align:bottom" width="43" alt="View the MathML source" title="View the MathML source" src="http://origin-ars.els-cdn.com/content/image/1-s2.0-S0955221917307586-si2.gif">h•carriers, partially compensating the conductivity loss due to the spin-disorder scattering. As the temperature of the LaCo0.4Ni0.4Cu0.2O3-δ compacts rose above 871 °C, significant weight loss with temperature was observed because of the release of lattice oxygen to the ambient air as a result of Co (IV) thermal reduction accompanied by the formation of oxygen vacancies. A solid oxide fuel cell (SOFC) single cell with Sm0.2Ce0.8O2-δ (electrolyte) and LaCo0.4Ni0.4Cu0.2O3-δ (cathode) was built and characterized. The Ohmic (0.256 Ω cm2) and polarization (0.434 Ω cm2) resistances of the single cell at 700 °C were determined; and the maximum power density was 0.535 W cm−2. These results show that LaCo0.4Ni0.4Cu0.2O3-δ is a very promising cathode material for SOFC applications.
Fabrication and H2 flux measurement of asymmetric La27W3.5Mo1.5O55.5-δ − La0.87Sr0.13CrO3-δ membranes J. Eur. Ceram. Soc. (IF 3.411) Pub Date : 2017-11-08 Marie-Laure Fontaine, Christelle Denonville, Zuoan Li, Wen Xing, Jonathan M. Polfus, Jannicke Kvello, Joachim Seland Graff, Paul Inge Dahl, Partow P. Henriksen, Rune Bredesen
Novel asymmetric hydrogen permeable membranes consist of a dense ceramic-ceramic (cercer) composite layer of La0.87Sr0.13CrO3-δ and La27W3.5Mo1.5O55.5-δ deposited on a tubular porous support of the latter composition. The membranes were produced by extrusion and dip-coating with various thermal cycles required for adjusting the thermal shrinkage of the different layers and obtaining gas tight membrane layers. The produced asymmetric membranes have a dense cercer layer thicknesses ranging from 25 to 50 microns on supports exhibiting a porosity of up to 40 vol%. The effect of processing parameters, such as volume of pore former, coating steps, sintering temperature and soaking time on the microstructure of the membranes is discussed to highlight critical steps in the manufacturing protocol. Hydrogen fluxes were measured as a function of temperature with both wet and dry Ar sweep gas. Results are discussed with respect to membrane architectures and materials properties.
Enhancement of piezoelectric and ferroelectric performances in (Na0.85K0.15)0.5Bi0.5TiO3 films with BaTiO3 interlayers J. Eur. Ceram. Soc. (IF 3.411) Pub Date : 2017-11-08 Yunyi Wu, Xiaohui Wang, Caifu Zhong, Longtu Li
In this work, in order to optimize the electrical performance of (Na0.85K0.15)0.5Bi0.5TiO3 (NKBT) thin films, 20 nm-thick BaTiO3 (BTO) layer was utilized by deliberately coating in the NKBT film-substrate interface or in the NKBT film, i.e., BTO layers coated in sequence with NBKT layers. The BTO layer, especial coated in the NKBT film, was beneficial for crystallization process and more preferable to form a denser film morphology. The BTO-coated NKBT composite films exhibited much enhancement in electrical properties compared to the films without BTO layer. Accordingly, a high effective piezoelectric coefficient d33* of 75 pm/V and remnant polarization Pr of 22.1 μC/cm2, as well as a low leakage current density of 1.2 × 10−5 A/cm2 were obtained in the 460 nm-thick composite film with BTO layers coated in the NBKT film. It meant that this kind of BTO-coated NKBT composite film could perform as a potential candidate for the lead-free piezoelectric applications. The observed enhancement in the electrical properties with the introduction of BTO layer could be mainly explained by the weakened influence of domain pinning in the film-electrode interface and grain boundaries due to the decreased strain in the film-electrode interface and better crystallinity in the highly (110)-oriented NKBT films, thereby enhancing motion of domain-walls.
Effects of Deformation Rate on Properties of Nd,Y-codoped CaF2 transparent ceramics J. Eur. Ceram. Soc. (IF 3.411) Pub Date : 2017-11-08 Yiguang Jiang, Benxue Jiang, Nan Jiang, Pande Zhang, Shuilin Chen, Xu Hu, Ge Zhang, Jintai Fan, Liangbi Su, Jiang Li, Long Zhang
Different deformation rates of Nd,Y-codoped CaF2 transparent ceramics were prepared by ceramization of single crystals. The deformation rate effects on the crystallization behaviors, microstructures, mechanical properties, and optical performances were investigated for the first time. The results indicate that the comprehensive performances of Nd,Y-codoped CaF2 ceramic (△a = 62%) are the most optimal compared with other ceramics having different deformation rates (△a = 34%, 40%, 50%, and 75%). In further investigations of the optical properties, the Nd,Y-codoped CaF2 ceramic (△a = 62%) sample exhibited a high transparency (Ta > 91%, 3-mm thick，250 ∼ 1200 nm), low light scattering, superior fracture toughness (K1c ∼0.71 MPa·m1/2), strong fluorescence emission, long lifetime (τ = 348.72 μs), and broad FWHM (29.2 nm), promising a good candidate for high-power laser material.
Positron annihilation exploration of voids in zinc zirconium borate glass ceramics entrenched with ZnZrO3 perovskite crystal phases J. Eur. Ceram. Soc. (IF 3.411) Pub Date : 2017-11-07 A. Siva Sesha Reddy, M. Kostrzewa, A. Ingram, N. Purnachand, P. Bragiel, V. Ravi Kumar, I.V. Kityk, N. Veeraiah
Origin of atomic-deficient free-volume structure in ZnO–ZrO2–B2O3 glass ceramic versus ZrO2 concentration was explored by positron annihilation lifetime spectroscopy (PAL) technique. XRD and SEM studies, on the titled samples indicated that the samples consist of tetragonal ZnZrO3 perovskite crystal phases. The IR studies suggested that Zr4+ ions prevailingly occupy octahedral positrons and play crucial role in formation of positron trapping holes in the samples. The PAL studies using 0.1 MBq 22Na positron source indicated a significant variation in the positron annihilation life time with increasing ZrO2 for both positron- and positronium (Ps) trapping channels. The intensity of the longest positron annihilation component I3 is decreased from 4.45 to 3.07%, whereas o-Ps decay lifetime τ3 is enhanced from 1.18 to 1.34 ns with increase of ZrO2 from 0 to 5.0 mol%. These results suggested that the glass ceramic CZ5 contains the maximum free space or void expansion and void agglomeration.
Improving the thermal stability of phosphor in a white light-emitting diode (LED) by glass-ceramics: Effect of Al2O3 dopant J. Eur. Ceram. Soc. (IF 3.411) Pub Date : 2017-11-07 Hongbin Su, Yu Nie, Hsiwen Yang, Dian Tang, Kongfa Chen, Teng Zhang
In this work, a phosphor for white light-emitting diode (LED) application, Ce3+-doped yttrium aluminum garnet (YAG:Ce3+), was successfully packaged using a P2O5-ZnO-Na2O-Al2O3 glass-ceramic system, through a vertical deposition method. Here, we found that white light can be achieved by combining the packaged phosphor with a blue chip (e.g. InGaN). The specimen doped with 4 mol% Al2O3 showed a luminous efficacy (LE) of 125.8 lm W−1, at a correlated color temperature (CCT) of 5769 K, with a color rendering index (CRI) of 68. In addition, the LE loss of the specimen doped with 4 mol% Al2O3 was only 3.6% after heat treatment at 150 °C for 1200 h, which is significantly lower than that of traditional resin (19.3%). Moreover, a possible mechanism for reducing the LE loss using glass-ceramics was proposed.
Young’s modulus and hardness of multiphase CaZrO3-MgO ceramics by micro and nanoindentation J. Eur. Ceram. Soc. (IF 3.411) Pub Date : 2017-11-06 Abílio P. Silva, Fernando Booth, Liliana Garrido, Esteban Aglietti, Pilar Pena, Carmen Baudín
The aim of this work is to determine the values of the hardness and elastic modulus of the phases present in CaZrO3-MgO-ZrO2 composites and to analyse their contribution to the composite properties. Two materials previously developed with the same major phases (CaZrO3, MgO and c-ZrO2) present in different volume fractions and grain size have been analysed. The hardness and Young’s modulus of each phase determined by nanoindentation are independent from the specific composite and coincident with nanoindentation values for single phase bulk materials. The contribution of the individual phases to Young’s modulus of the multiphase materials is in agreement with calculations using the nanoindentation values and the Voight upper limit of the “rule of mixtures”. Scale effect due to microcracking has been observed for micro-hardness values of the composites and differences between calculations and experimental values are related to this effect.
Quantitative Differences in the Y Grain Boundary Excess at Boundaries Delimiting Large and Small Grains in Y Doped Al2O3 J. Eur. Ceram. Soc. (IF 3.411) Pub Date : 2017-11-06 Hadas Sternlicht, Stephanie A. Bojarski, Gregory S. Rohrer, Wayne D. Kaplan
The chemical excess at high angle grain boundaries in yttrium doped alumina was characterized using transmission electron microscopy and energy dispersive spectroscopy. The sample had a bimodal microstructure and one explanation for the fast growth of some grains was that they were surrounded by boundaries with a different yttrium grain boundary excess than the smaller grains. The amount of yttrium at boundaries between grains of similar and different sizes was quantified. Boundaries between smaller grains and between small grains bonded to sapphire had a mean Y excess of 1.3 atoms/nm2. The grain boundary excess of Y for boundaries delimiting large grains had either a lower Y content of 0.5 atoms/nm2 and 0.9 atoms/nm2, or a higher Y content of 1.6 atoms/nm2, consistent with the idea that these boundaries had a different composition and thus different complexions.
Temporal Stability of Oxygen-ion Conductivity in 1Nb2O5-10Sc2O3-89ZrO2 J. Eur. Ceram. Soc. (IF 3.411) Pub Date : 2017-11-06 Vandana, Shashwat Singh, Abhishek Jaiswal, Kantesh Balani, Anandh Subramaniam, Shobit Omar
A slight Nb2O5 co-doping in 11Sc2O3-89ZrO2 was earlier reported to stabilize the high-symmetry cubic phase completely and enhances the conductivity significantly. The present work looked at the temporal stability of conductivity in 1Nb2O5-10Sc2O3-89ZrO2 (1Nb10ScSZ) for the electrolyte application in solid oxide fuel cells. In-situ conductivity measurement was done using impedance spectroscopy at 650 °C in the air for 2000 h. A substantial conductivity loss (29%) was observed in the first 1000 h. Following which, conductivity remained relatively stable for the last 1000 h. Impedance analysis showed that the main contribution to the conductivity degradation was from grain conductivity. Phase analysis performed using XRD, TEM and Raman spectroscopy revealed that both the unaged and aged 1Nb10ScSZ samples consisted of metastable t″-phase. However, the extent of tetragonality was found to increase after ageing. The formation of low-symmetry phase was suggested to be the reason for the grain conductivity loss in 1Nb10ScSZ.
Field induced metastable ferroelectric phase in Pb0.97La0.03(Zr0.90Ti0.10)0.9925O3 ceramics J. Eur. Ceram. Soc. (IF 3.411) Pub Date : 2017-11-06 I.V. Ciuchi, C.C. Chung, C.M. Fancher, C. Capiani, J.L. Jones, L. Mitoseriu, C. Galassi
Pb0.97La0.03(Zr0.9Ti0.1)0.9925O3 (PLZT 3/90/10) ceramics prepared by solid-state reaction with the compositions near the antiferroelectric/ferroelectric (FE/AFE) phase boundary were studied. From the polarization–electric field P(E) dependence and ex situ X-ray study, an irreversible electric field induced AFE-to-FE phase transition is verified at room temperature. Dielectric and in situ temperature dependent X-ray analysis evidence that the phase transition sequence in PLZT 3/90/10-based ceramics can be readily altered by poling. A first order antiferroelectric-paraelectric (AFE-to-PE) transition occurred at ∼190 °C in virgin sample and at ∼180 °C in poled sample. In addition, a FE-to-AFE transition occurs in the poled ceramic at much lower temperatures (∼120 °C) with respect to the Curie range (∼190 °C). The temperature-induced FE-to-AFE transition is diffuse and takes place in a broad temperature range of 72–135 °C. The recovery of AFE is accompanied by an enhancement in the piezoelectric properties.
Influence of processing on stability, microstructure and thermoelectric properties of Ca3Co4-xO9+δ J. Eur. Ceram. Soc. (IF 3.411) Pub Date : 2017-11-06 Nikola Kanas, Sathya Prakash Singh, Magnus Rotan, Mohsin Saleemi, Michael Bittner, Armin Feldhoff, Truls Norby, Kjell Wiik, Tor Grande, Mari-Ann Einarsrud
Due to high figure of merit, Ca3Co4-xO9+δ (CCO) has potential as p-type material for high-temperature thermoelectrics. Here, the influence of processing including solid state sintering, spark plasma sintering and post-calcination on stability, microstructure and thermoelectric properties is reported. By a new post-calcination approach, single-phase materials were obtained from precursors to final dense ceramics in one step. The highest zT of 0.11 was recorded at 800 °C for CCO with 98 and 72% relative densities. In situ high-temperature X-ray diffraction in air and oxygen revealed a higher stability of CCO in oxygen (∼970 °C) than in air (∼930 °C), with formation of Ca3Co2O6 which also showed high stability in oxygen, even at 1125 °C. Since achievement of phase pure high density CCO by post-calcination method in air is challenging, the phase stability of CCO in oxygen is important for understanding and further improvement of the method.
Reverse manipulation of intrinsic point defects in ZnO-based varistor ceramics through Zr-stabilized high ionic conducting βIII-Bi2O3 intergranular phase J. Eur. Ceram. Soc. (IF 3.411) Pub Date : 2017-11-04 Jinqiang He, Shengtao Li, Jiajun Lin, Le Zhang, Kai Feng, Lei Zhang, Wenfeng Liu, Jianying Li
Intrinsic point defect structure plays a crucial role in functional ceramics with a grain-grain boundary microstructure. In the present study, a novel method of reversely manipulating intrinsic point defects (oxygen vacancy, Vo and zinc interstitial, Zni) in ZnO-based varistor ceramics is proposed, which makes use of Zr-stabilized high ionic conducting βIII-Bi2O3 intergranular phase. It is found that Zr-doping not only modifies the grain growth by the formation of secondary Zr-rich phase, but also influences the intrinsic point defect structure via the stabilized βIII-Bi2O3 phase, resulting in reduced Vo density but increased Zni density. The reverse manipulation is unambiguously demonstrated by broadband dielectric spectroscopy and further confirmed by the accelerated ageing experiment. The proposed intrinsic point defect dynamics unveil an important but usually neglected function of the dopant that has little solid solubility in ZnO grains, which opens up a promising way to tailor the material property.
Shifting Lu2SiO5 crystal to eutectic structure by laser floating zone J. Eur. Ceram. Soc. (IF 3.411) Pub Date : 2017-11-04 F. Rey-García, N. Ben Sedrine, A.J.S. Fernandes, T. Monteiro, F.M. Costa
Starting from stoichiometric mixtures of lutetium and silicon oxides, Lu2SiO5 (LSO) crystals to eutectic ceramic rods were obtained using the laser floating zone (LFZ) technique in air at growth rates ranging from 200 to 5 mm/h. The newly obtained eutectic is formed by Lu2O3 fibrils and/or lamellae into a LSO matrix being its formation induced by a SiO2 evaporation process during the LFZ growth.Scanning electron microscopy (SEM) and Raman spectroscopy studies allowed observing how growth rate affects microstructural evolution, namely the transition from single crystal to eutectic. SEM observations show that the eutectics present alternated monophasic oxyorthosilicate regions with biphasic Lu2SiO5/Lu2O3 ones identified by X-Ray diffraction as C2/c monoclinic Lu2SiO5 and Ia<img height="31" border="0" style="vertical-align:bottom" width="23" alt="View the MathML source" title="View the MathML source" src="http://origin-ars.els-cdn.com/content/image/1-s2.0-S0955221917307422-si1.gif">3¯ cubic lutetium oxide.While the luminescence phenomena were found to be only dependent on the excitation energy, a pronounced UV light-induced reversible photochromic effect was observed in the samples grown at slower rates.
0-3 type magnetoelectric 0.94Na0.5Bi0.5TiO3-0.06BaTiO3:CoFe2O4 composite ceramics with a deferred thermal depolarization J. Eur. Ceram. Soc. (IF 3.411) Pub Date : 2017-11-04 Anmeng Deng, Laihui Luo, Weiping Li, Feifei Wang, Yaojin Wang
Developing Na0.5Bi0.5TiO3-based magnetoelectric (ME) coupling composites with higher depolarization temperature is highly valuable for the environment-friendly smart electronic devices. We have developed a new kind of 0-3 type 0.94Na0.5Bi0.5TiO3-0.06BaTiO3:xCoFe2O4 (NBTBT:xCFO, x = 0, 0.1, 0.2, 0.3) composite ceramics with a deferred depolarization temperature, together with an additional strong ME coupling of 9.2 mV/cm·Oe for the NBTBT:0.2CFO. The basic structure, ferroelectric/ferromagnetic properties, and the depolarization temperature of the NBTBT:xCFO composite ceramics were investigated. It was found that an enhancement of depolarization temperature (>25 °C) was obtained in these 0-3 type composites relative to the pure NBTBT ones (115 °C vs 90 °C). The mechanism of the enhanced depolarization temperature of the composites is discussed. The present results demonstrate that NBTBT:xCFO composites have great potential for ME devices.
Novel mullite ceramic foams with high porosity and strength using only fly ash hollow spheres as raw material J. Eur. Ceram. Soc. (IF 3.411) Pub Date : 2017-11-04 Wenlong Huo, Xiaoyan Zhang, Yugu Chen, Yuju Lu, Jingjing Liu, Shu Yan, Jia-Min Wu, Jinlong Yang
A novel approach to fabricate mullite ceramic foams with high porosity and mechanical strength using fly ash hollow spheres (FAHSs) as the only raw material was reported for the first time, in which FAHSs served as both matrix and pore-forming agent. It was demonstrated that uniform FAHS ceramic foams without cracks could be fabricated by both direct stack sintering method and gel-casting route. The effect of sintering temperature on linear shrinkage, porosity, phase composition and mechanical properties was investigated. With the increase of sintering temperature from 1200 °C to 1350 °C, the fracture mechanism changed from fracturing along FAHSs to fracturing across FAHSs, and the compressive strength of the FAHS ceramic foams increased from 4.4 MPa to 33.4 MPa. The FAHS ceramic foams exhibited high porosity in the range of 73–81% and high mechanical strength, which benefited from the dense assembling of small FAHSs with natural diameter distribution and excellent wall-thickness uniformity.
Calcium-magnesium-alumino-silicate induced degradation and failure of La2(Zr0.7Ce0.3)2O7/YSZ double-ceramic–layer thermal barrier coatings prepared by electron beam-physical vapor deposition J. Eur. Ceram. Soc. (IF 3.411) Pub Date : 2017-11-04 Xin Zhou, Jinshuang Wang, Jieyan Yuan, Junbin Sun, Shujuan Dong, Limin He, Xueqiang Cao
Calcium-magnesium-alumino-silicate (CMAS) induced degradation of the La2(Zr0.7Ce0.3)2O7/YSZ double-ceramic-layer thermal barrier coatings (TBCs) prepared by electron beam-physical vapor deposition (EB-PVD) was investigated in this study. CMAS reacted with La2(Zr0.7Ce0.3)2O7 to form a dense crystalline layer composed of apatite and fluorite phases, while the penetration was not arrested in the double-ceramic-layer coating due to the formation of vertical cracks during heat-treatment. In fact, the vertical cracks in the LZ7C3 layer inevitably provided efficient infiltration paths for molten CMAS to attack the bottom YSZ layer. Since the formation of Ca2(La1-xCex)8(SiO4)6O26 apatite phase during CMAS reactions led to CaO enrichment in the melt, the YSZ buffer layer of the double-ceramic-layer coating even suffered a severer CMAS attack than the single YSZ coating.
Multiferroic and magnetoelectric properties of Pb0.99[Zr0.45Ti0.47(Ni1/3Sb2/3)0.08]O3–CoFe2O4 multilayer composites fabricated by tape casting J. Eur. Ceram. Soc. (IF 3.411) Pub Date : 2017-10-31 Giorgio Schileo, Cristina Pascual-Gonzalez, Miguel Alguero, Ian M. Reaney, Petronel Postolache, Liliana Mitoseriu, Klaus Reichmann, Michel Venet, Antonio Feteira
A 2-2 type multiferroic composite device encompassing three CoFe2O4 (CFO) layers confined between four Pb0.99[Zr0.45Ti0.47(Ni1/3Sb2/3)0.08]O3 (PZT) layers was fabricated by tape casting. X-ray diffraction data showed good chemical compatibility between the two phases, whereas Scanning Electron Microscopy imaging also revealed an intimate contact between CFO and PZT layers. Under an applied electric field of 65 kV/cm, this multilayer device shows a saturated polarisation of 7.5 μC/cm2 and a strain of 0.12%, whereas under a magnetic field of 10 kOe it exhibits a typical ferromagnetic response and a magnetic moment of 33 emu/g. These devices can be electrically poled, after which they exhibit magnetoelectric coupling.
Electrosteric colloidal stabilization for obtaining SrTiO3/TiO2 heterojunction: Microstructural evolution in the interface and photonics properties J. Eur. Ceram. Soc. (IF 3.411) Pub Date : 2017-10-31 Rafael A.C. Amoresi, Vinicius Teodoro, Guilhermina F. Teixeira, Maximo S. Li, Alexandre Z. Simões, Leinig A. Perazolli, Elson Longo, Maria A. Zaghete
Researches on solids heterojunctions has proven to be an important field for technological applications due to synergism achieved by interface phenomena. In this work, we present an understanding of SrTiO3/TiO2 interface and its effects on structural and microstructural characteristics, and relate them to photoluminescence properties of heterojunctions obtained by a simple method. It was observed that SrTiO3 proportion directly influences the structural order-disorder, as observed by X-Ray diffraction, Raman spectroscopy and Transmission electron microscopy. Photoluminescence behavior of heterojunction with 1% of SrTiO3 showed a shift to blue emission region compared to TiO2, and enhanced of emission intensity compared to SrTiO3, resulted from defects generated by interface effects, attracting possible applications on selective color emitter. Therefore, we conclude that in same materials phases, nature and concentration of structural defects has strong dependence of SrTiO3 concentration, which leads to different photoluminescence properties.
Polarity effects on the wettability and interfacial chemistry at Cu–YSZ interface by applying a direct current J. Eur. Ceram. Soc. (IF 3.411) Pub Date : 2017-10-29 Lian-Teng Yu, Ping Shen, Bo Yang, Rui-Fen Guo, Ni Zhang, Qi-Chuan Jiang
The application of a direct current, regardless of its polarity, can significantly improve the wettability of ZrO2–8 mol% Y2O3 (YSZ) by molten Cu at 1373 K, and this effect was more pronounced when YSZ was connected to cathode. The mechanisms for the wetting improvement varied with the change in the current polarity. When YSZ was connected to the cathode, the oxygen ions in the YSZ body driven by the external electric power moved to the solid–liquid interface and dissolved into liquid Cu, forming O<img border="0" alt="single bond" src="https://cdn.els-cdn.com/sd/entities/sbnd" class="glyphImg">Cu clusters. As a consequence, the solid–liquid interfacial energy and liquid surface tension were greatly reduced and wettability improved. On the other hand, when YSZ was connected to anode, the improvement in the wettability was mainly driven by the formation of nonstoichiometric zirconia and metallic Zr at the interface. Nevertheless, the newly formed ZrO2 at the triple line region inhibited further spreading of liquid front.
Impact of sandblasting on the mechanical properties and aging resistance of alumina and zirconia based ceramics J. Eur. Ceram. Soc. (IF 3.411) Pub Date : 2017-10-29 Carlos Francisco Caravaca, Quentin Flamant, Marc Anglada, Laurent Gremillard, Jérôme Chevalier
Bioinert zirconia and alumina ceramic devices are widely used, both in orthopaedics and in dentistry. In order to improve their bonding with bone tissues or dental resin cements, their surfaces are often roughened at different scales. In this work, we have investigated the effects of the same sandblasting treatment on alumina, zirconia and a zirconia-toughened alumina, focusing on their mechanical performance and the interplay between surface defects and residual stresses. Additionally, we explored the impact of the treatment on the hydrothermal aging of the two zirconia-containing materials. Residual stresses generated during sandblasting were always predominant over surface defects but their effect varied with the material: while they had a weakening effect on alumina, they reinforced both zirconia-containing materials. Finally, we found that the monoclinic grains at the surface of sandblasted zirconia recrystallized into tetragonal nanograins after annealing and this led to an increased resistance to aging.
Interactions between mullite saggar refractories and Li-ion battery cathode materials during calcination J. Eur. Ceram. Soc. (IF 3.411) Pub Date : 2017-10-28 Pengtao Zhai, Liugang Chen, Yiming Yin, Suping Li, Dafei Ding, Guotian Ye
Used mullite-based saggars from a Li(NixCoyMnz)O2 (LNCM) materials-making plant were collected to characterize the degradation occurring during application. Based on the post-mortem analysis, laboratory scale experiments were designed using mixtures of mullite powders and commercial Li-ion battery cathode precursors. The mixtures were calcined at temperatures ranging from 800 °C to 1100 °C, and characterized with X-ray diffraction and scanning electron microscopy. The influence of temperature on the interactions between mullite and LNCM materials was determined. The combination of the post-mortem study and the laboratory scale tests allowed a more comprehensive understanding of the evolution of the saggar microstructure during degradation.
Y2O3 doped Ba0.9Ca0.1Ti0.9Sn0.1O3 ceramics with improved piezoelecrtric properties J. Eur. Ceram. Soc. (IF 3.411) Pub Date : 2017-10-28 Zhi-hui Chen, Zhi-wei Li, Jian-hua Qiu, Tian-xiang Zhao, Jian-ning Ding, Xu-guang Jia, Wei-qin Zhu, Jiu-jun Xu
Lead-free Ba0.90Ca0.10Ti0.90Sn0.10O3-xY2O3 (BCTSY, x=0-0.09) ceramics were prepared by traditional solid-state sintering method. All the BCTSY samples showed pure perovskite structures without detectable impurity. Orthorhombic/tetragonal phase coexisted in the sample of x = 0.03 to 0.07. Remarkable enhancement of the electric properties were achieved at x = 0.03 with d33 of 650 pC/N, Kp of 59.6%, and the remnant polarization Pr of 10.2 μC/cm2. The strengthened temperature stability of piezoelectricity is beneficial to the application of the piezoceramics.
Crystal structure and microwave dielectric behaviors of scheelite structured (1-x)BiVO4-xLa2/3MoO4 (0.0 ≤ x ≤ 1.0) ceramics with ultra-low sintering temperature J. Eur. Ceram. Soc. (IF 3.411) Pub Date : 2017-10-27 Li-Xia Pang, Di Zhou, Wei-Guo Liu, Ze-Ming Qi, Zhen-Xing Yue
Sintering behaviour and microwave dielectric properties of BaAl2−2x(ZnSi)xSi2O8 ceramics J. Eur. Ceram. Soc. (IF 3.411) Pub Date : 2017-10-27 Xiao-Qiang Song, Wen-Zhong Lu, Xiao-Chuan Wang, Xiao-Hong Wang, Gui-Fen Fan, Raz Muhammad, Wen Lei
BaAl2−2x(ZnSi)xSi2O8 (x = 0.2–1.0) ceramics were prepared using the conventional solid-state reaction method. The sintering behaviour, phase composition and microwave dielectric properties of the prepared compositions were then investigated. All compositions showed a single phase except for x = 0.8. By substituting (Zn0.5Si0.5)3+ for Al3+ ions, the optimal sintering temperatures of the compositions decreased from 1475 °C (x = 0) to 1000 °C (x = 0.8), which then slightly increased to 1100 °C (x = 1.0). Moreover, the phase stability of BaAl2Si2O8 was improved. A novel BaZnSi3O8 microwave dielectric ceramic was obtained at the sintering temperature of 1100 °C. This ceramic possesses good microwave dielectric properties with εr = 6.60, Q × f = 52401 GHz (at 15.4 GHz) and τf = −24.5 ppm/°C.
Microstructure and properties of dense Tyranno-ZMI SiC/SiC containing Ti3Si(Al)C2 with plastic deformation toughening mechanism J. Eur. Ceram. Soc. (IF 3.411) Pub Date : 2017-10-27 Xiaokang Ma, Xiaowei Yin, Xiaomeng Fan, Xinnan Sun, Lingwei Yang, Fang Ye, Laifei Cheng
In this paper, Ti3Si(Al)C2 was introduced into dense SiC/SiC to improve the mechanical and electromagnetic interference (EMI) shielding properties. In order to reveal the effect of Ti3Si(Al)C2, dense SiC/SiC-Ti3Si(Al)C2 and dense SiC/SiC without Ti3Si(Al)C2 were fabricated. Owing to the plastic deformation toughening mechanism of Ti3Si(Al)C2, SiC/SiC-Ti3Si(Al)C2 performs a new damage mode characterized by matrix/matrix (m/m) debonding. High interfacial shear strength (IFSS) due to large thermal residual stress (TRS) is weakened by m/m debonding. This new mode also brings high effective volume fraction of loading fibers and long path of crack propagation. Hence SiC/SiC-Ti3Si(Al)C2 exhibits higher flexural strength (503 MPa) and fracture toughness (23.7 MPa·m1/2) than the dense SiC/SiC without Ti3Si(Al)C2. In addition, dense SiC/SiC-Ti3Si(Al)C2 shows excellent electromagnetic interference shielding effectiveness (EMI SE, 43.0 dB) in X-band, revealing great potential as thermo-structural and functional material.
Production of transparent yttrium oxide ceramics by the combination of low temperature spark plasma sintering and zinc cation-doping J. Eur. Ceram. Soc. (IF 3.411) Pub Date : 2017-10-27 Hidehiro Yoshida, Koji Morita, Byung-Nam Kim, Kohei Soga, Takahisa Yamamoto
1 mol% Zn2+-doped Y2O3 powder was consolidated utilizing spark plasma sintering (SPS) by systematically varying the heating schedule, sintering temperature, heating rate, holding time at the sintering temperature, and loading stress. Transparent, Zn2+-doped Y2O3 polycrystals were successfully produced at the heating rate of 2 °C/min, sintering temperature of 890 °C, holding time of 30 min, and loading stress of 150 or 170 MPa. The highest transmittance in the Zn2+-Y2O3 bodies at a wavelength of longer than 600 nm was comparable to those in the undoped SPSed Y2O3 in the literature. Employing a sintering temperature and loading stress higher than the optimum values led to coarsened pore and grain sizes, resulting in a decreased transparency. Low heating rate at temperatures above 700 °C was desirable for the attainment of high transparency. The grain boundary segregation of Zn2+ cations effectively contributed to the reduction of the sintering temperature required for attainment of transparency in the Y2O3 by SPS.
Ferroelectric phase transition and electrical properties of high-TC PMN-PH-PT ceramics prepared by partial oxalate route J. Eur. Ceram. Soc. (IF 3.411) Pub Date : 2017-10-26 Rongfeng Zhu, Bijun Fang, Xiangyong Zhao, Shuai Zhang, Dun Wu, Jianning Ding
The high-Curie temperature (TC) 0.15Pb(Mg1/3Nb2/3)O3-0.38PbHfO3-0.47PbTiO3 (PMN-PH-PT) piezoelectric ceramics were prepared by the partial oxalate route via the B-site oxide mixing method. The obtained uniform nm-sized PMN-PH-PT precursor powders provide high calcining and sintering activity for synthesizing ceramics, based on which the synthesis conditions were tailored as calcining at 775 °C and sintering at 1245 °C. The partial oxalate route synthesized PMN-PH-PT ceramics are far superior to the counterparts synthesized by the columbite precursor method and exhibit excellent thermal stability of the piezoelectric properties under TC (∼292 °C), ensuring the potential application in transducers under elevated environmental temperatures. The temperature dependent Raman spectroscopy not only proves the occurrence of the ferroelectric to paraelectric phase transition around TC, but also confirms the successive phase symmetry transitions, which correlate with the polar nanoregions (PNRs) and/or the coexistence of multiple ferroelectric phases, revealing the origin of the enhanced electrical properties in the PMN-PH-PT ceramics.
Sliding-wear resistance of pure near fully-dense B4C under lubrication with water, diesel fuel, and paraffin oil J. Eur. Ceram. Soc. (IF 3.411) Pub Date : 2017-10-25 Angel L. Ortiz, Victor M. Candelario, Oscar Borrero-López, Fernando Guiberteau
The sliding-wear resistance of pure near fully-dense B4C is investigated, and the wear mode/mechanisms identified, under lubrication with water, diesel fuel, and paraffin oil. It is found that the wear is mild in the three cases, with specific wear rates (SWRs) of 10−16–10−17 m3/N m. Nonetheless, the wear resistance of the B4C ceramic is one order of magnitude greater under oil lubrication (1016 N m/m3) than under water lubrication (1015 N m/m3), and twice as great for the specific case of paraffin oil than diesel fuel, attributable to the lubricant’s viscosity. It is also found that the wear mode is always abrasion, and that the wear mechanisms are plastic deformation and localized fracture with grain pullout. However, in agreement with the macro-wear data, the severity of the wear damage is lower under lubrication with paraffin oil, followed by diesel fuel, and lastly water. Finally, microstructural considerations are discussed with a view to enhancing the sliding-wear resistance of B4C triboceramics.
Low-temperature preparation of Si3N4 whiskers bonded/reinforced SiC porous ceramics via foam-gelcasting combined with catalytic nitridation J. Eur. Ceram. Soc. (IF 3.411) Pub Date : 2017-10-24 Lei Han, Junkai Wang, Faliang Li, Huifang Wang, Xiangong Deng, Haijun Zhang, Shaowei Zhang
Kinetic and thermodynamic effects of manganese as a densification aid in yttria-stabilized zirconia J. Eur. Ceram. Soc. (IF 3.411) Pub Date : 2017-10-24 Hui Li, Flavio L. Souza, Ricardo H.R. Castro
This work demonstrates the role of Mn as an effective sintering aid in Yttria-Stabilized-Zirconia (YSZ) is a result of the concomitant reduction of activation energies and change of interfacial energies caused by Mn segregation. Kissinger analyses of the heat of sintering showed a decrease in activation energy from 219.9 kJ/mol for YSZ to 103.4 kJ/mol for YSZ containing 3-mol% Mn. Direct microcalorimetry analyses showed that the average surface and grain boundary energies of YSZ decreased from 0.94 and 0.71 J/m2, respectively, to 0.70 and 0.17 J/m2 for 3-mol% Mn doped YSZ. The decrease in the ratio between surface and grain boundary energies indicates an increase in dihedral angle from 137.5° to 166.6°, meaning an increase in sintering stress. Segregation of manganese to grain boundaries was experimentally observed and is discussed to be responsible for both kinetic and thermodynamic changes in the system while suggesting interconnection by the thermodynamic extremal principle.
Nacre-like ceramic refractories for high temperature applications J. Eur. Ceram. Soc. (IF 3.411) Pub Date : 2017-10-24 Pedro I.B.G.B. Pelissari, Florian Bouville, Victor C. Pandolfelli, Davide Carnelli, Finn Giuliani, Ana P. Luz, Eduardo Saiz, André R. Studart
High-temperature ceramics, so-called refractories, are widely used for the manufacturing of metals, for energy generation and aerospace applications. Refractories are usually strong and stiff but fragile due to the lack of plastic deformation and other intrinsic toughening mechanisms. This inherent brittleness limits their use in applications where catastrophic failure is not tolerated. The present work reports the design and fabrication of refractories with a bio inspired nacre-like microstructure comprising aligned alumina platelets, separated by an aluminium borate interphase, obtained through transient liquid phase sintering. The bioinspired composites exhibit high strength, 672 MPa, toughness, 7.4 MPa m1/2, and stable crack propagation at high temperatures, above 600 °C, due to the aluminium borate interlayer. This makes nacre-like ceramic refractories sintered with a transient liquid phase good candidate for high temperature applications, competing favourably with ceramic matrix composites and following a simpler and cheaper processing route.
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