Porosification Behaviour of LTCC Substrates with Potassium Hydroxide J. Eur. Ceram. Soc. (IF 3.411) Pub Date : 2018-01-17 Ali Hajian, Michael Stöger-Pollach, Michael Schneider, Doruk Müftüoglu, Frank K. Crunwell, Ulrich Schmid
The demand to meet advanced substrate requirements in terms of electrical, mechanical, thermal, and dielectric properties has led to an increasing interest in low temperature co-fired ceramics (LTCC). However, LTCC materials suffer from high permittivity. We recently showed that the wet-chemical porosification under acidic conditions allows the reduction of the permittivity of LTCCs in the as-fired state. In the present study, potassium hydroxide solution was employed as an alternative etchant which features a suitable bearing plane for further metallization lines. Various characterization techniques, including scanning and transmission electron microscopy, energy-dispersive X-ray spectroscopy, X-ray diffraction analysis, and electron energy loss spectroscopy were used for investigation of the morphology and chemical composition of the substrates. Three-dimensional information of the surface topography was acquired by means of MeX® Alicona software and the obtained roughness parameters confirmed the advantage of the proposed approach over acid treatment when targeting an enhanced surface quality.
Oxygen Vacancies as a Link between the Grain Growth and Grain Boundary Conductivity Anomalies in Titanium-rich Strontium Titanate J. Eur. Ceram. Soc. (IF 3.411) Pub Date : 2018-01-12 Alexander Tkach, Luís Amaral, Paula M. Vilarinho, Ana M.R. Senos
Titanium-rich (Sr/Ti = 0.995) strontium titanate (ST) ceramics, air-sintered in a temperature range of 1400-1625 °C, were reported to possess anomalies in the grain growth and analogous anomalies in the grain boundary (GB) conductivity activation energy. However, these two interface-related phenomena, occurring at GBs, could not be associated with each other using a simple “brick-layer” model. In this work we revise the topic and advocate that the deviation from the model comes from the oxygen vacancies localized at GBs of the rapidly-cooled ST ceramics. To verify this, we annealed the ceramics in oxygen and performed their systematic and comparative analysis using impedance spectroscopy. A levelling-off in the GB conductivity activation energy, which increases for ≤1.2 eV, and a four-fold decrease in the GB permittivity are observed after annealing. Thus, we confirm a key role of oxygen vacancies in relation between the grain growth and GB conductivity anomalies of as-sintered Ti-rich ST ceramics.
Tribological Behavior of αı/βı-SiAlON-TiN Composites J. Eur. Ceram. Soc. (IF 3.411) Pub Date : 2018-01-12 Nurcan Calis Acikbas
There are limited studies on the tribological properties of SiAlON-TiN composites. Therefore, in the present study, tribology tests were conducted on a number of αı/βı-SiAlON-TiN composites with different αı/βı-SiAlON phase ratio and TiN content, fabricated with unique compositional design. The influence of αı/βı-SiAlON phase ratios, microstructure, mechanical properties and TiN content on friction and wear behavior was investigated and wear mechanisms were explained. Tribology tests were conducted on computer controlled tribometer under dry unlubricated ambient conditions with a linear reciprocating movement in a ball-on-disc sliding wear configuration and test parameters kept as constant. It was observed that TiN addition (17 wt.%) did not change the friction (CoF) of SiAlON and wear rate and wear volume were observed to increase. Wear mechanisms showed differences with αı:βı-SiAlON phase ratio. Fracture toughness had very pronounced effect on wear resistance.
Thermal-stability of electric field-induced strain and energy storage density in Nb-doped BNKT-ST piezoceramics J. Eur. Ceram. Soc. (IF 3.411) Pub Date : 2018-01-11 Rizwan Ahmed Malik, Ali Hussain, Matias Acosta, John Daniel, Hyoung-Su Han, Myong-Ho Kim, Jae Shin Lee
In this work, the relationship between the structural mechanisms and macroscopic electrical properties of the Nb-modified 0.96(Bi0.5Na0.84K0.16TiO3)–0.04SrTiO3 (BNKT–ST) system were elucidated by using temperature dependent and in situ synchrotron X-ray diffraction (XRD) techniques. For the composition x = 0.0175, a large-signal piezoelectric coefficient (Smax/Emax = d33*) of 735 pm V−1 at 6 kV mm−1 was observed at room temperature. Interestingly, at a higher temperature of 110°C, the sample still showed a large d33* of 570 pm V−1. Furthermore, the temperature-invariant electrostrictive coefficient for this sample was found to be 0.0285 m4 C−2 over the temperature range of 25–170 °C. Moreover, the energy density for x = 0.030 sample was ~1.0 J cm−3 with an energy storage efficiency of ˃70% in the temperature range of 25–135 °C. These results suggest that the synthesized Nb-modified BNKT–ST system is promising for the design of ceramic actuators as well as capacitor applications.
Formation and leachability of hexavalent chromium in the Al2O3-CaO-MgO-Cr2O3 system J. Eur. Ceram. Soc. (IF 3.411) Pub Date : 2018-01-11 Yingjiang Wu, Shengqiang Song, Andrie M. Garbers-Craig, Zhengliang Xue
Aqueous suspension processing of multicomponent submicronic Y-TZP/Al2O3/SiC particles for suspension plasma spraying J. Eur. Ceram. Soc. (IF 3.411) Pub Date : 2018-01-10 V. Carnicer, C. Alcazar, E. Sánchez, R. Moreno
In order to obtain thermal barrier coatings by Suspension Plasma Spraying (SPS) process with potential new self-healing ability multicomponent submicronic Y-TZP/Al2O3/SiC suspensions were prepared. For this purpose, concentrated aqueous suspensions of individual components, as well as the multicomponent mixture were studied and characterised, in terms of colloidal stability and rheological behaviour to determine the best conditions for processing and preparation of the coatings. In the study, different dispersant contents and sonication times were tested. Subsequently, low concentrated suspensions were prepared to obtain preliminary thermal barrier coatings with the optimised feedstock. Thus, ceramic coatings were deposited by SPS and then characterised in order to assess the microstructure and phase distribution, in particular, the degree of preservation of the sealing agent, SiC, in the final coating as a previous indicator of its self-healing ability.
Effects of spark plasma sintering on ferroelectricity of 0.8Bi3.15Nd0.85Ti3O12-0.2CoFe2O4 composite ceramic J. Eur. Ceram. Soc. (IF 3.411) Pub Date : 2018-01-10 Hongjun Zhang, Hua Ke, Huijiadai Lu, Pengkang Guo, Bin Yan, Dechang Jia, Yu Zhou
The 0.8Bi3.15Nd0.85Ti3O12 (BNdT)-0.2CoFe2O4 (CFO) composite multiferroic ceramics have been fabricated by spark plasma sintering (SPS) at 850 °C. The relative density of as-sintered SPS ceramic reaches 97.4 (±0.3)%. The composites are composed of pure BNdT and CFO phases without any preferred c-orientation. The a-orientation preference is more obvious perpendicular to the pressure direction. The average grain-sizes of BNdT and CFO are 163 and 146 nm, respectively. The BNdT phase has more grains below 100 nm (~20%). The super energy-dispersive X-ray analyses suggest no serious reaction between BNdT and CFO. The Raman spectrum verifies the nano-structure of the SPS ceramic via the broadening bands and peak shifts. The Curie temperature of the SPS ceramic declines to 560 °C with stabilized dielectric loss. The grain boundary resistance plays a dominant role on impedance above 700 °C. The remanent polarization approaches to 15.2 μC/cm2 (300 kV/cm) with lower coercive fields (−89/+95kV/cm).
Glass-ceramic oxidation protection of higher manganese silicide thermoelectrics J. Eur. Ceram. Soc. (IF 3.411) Pub Date : 2018-01-09 M. Salvo, F. Smeacetto, F. D’Isanto, G. Viola, P. Demitri, F. Gucci, M.J. Reece
A higher manganese silicide (HMS) thermoelectric, with composition MnSi1.74, densified by spark plasma sintering, was successfully coated with a glass-ceramic, in order to be used at temperatures higher than 500 °C.Compositional changes in both the HMS substrate and the glass-ceramic coating are reviewed and discussed with respect to the electrical properties of the uncoated and coated HMS before and after thermal cycles from RT to 600 °C in air. The formation of a Si-deficient layer (MnSi) on the uncoated HMS surface is due to the reaction between the HMS and oxygen at 600 °C, thus contributing to a lower power factor in comparison with the as-sintered HMS. Coated HMS samples (after thermal cycles RT-600 °C) show a lower electrical resistivity and a significantly higher power factor in comparison with the uncoated ones. The glass-ceramic coating is self-reparable at 600 °C, as demonstrated by the complete sealing of an induced scratch on its surface.
A novel application of alumina fiber mats as TBC protection for CFRP/epoxy laminates – laboratory tests and numerical modeling J. Eur. Ceram. Soc. (IF 3.411) Pub Date : 2018-01-09 Przemysław Golewski, Tomasz Sadowski
A novel method is proposed to create a TBC on the CFRP/epoxy laminate surface in a single technological process by formation of one additional layer made of a commercially available alumina fiber mat. Both materials: the CFRP/epoxy laminate made of four layers and the ceramic mat were joined during prepreg curing. The quick thermal heating tests of the TBC system were conducted for different times with a propane-butane torch. Changes of material strains due to temperature influence are determined experimentally in uniaxial tensile tests via the Digital Image Correlation (DIC) method. A numerical model corresponding to the experimental quick heating test is built in Abaqus standard finite element software to determine temperature distribution in the CFRP/epoxy laminate. The experimental and numerical investigations lead to a conclusion that the alumina fiber mat is an effective protection of the CFRP/epoxy laminate against temperature degradation and can be used in industrial practice.
A validation procedure for numerical models of ceramic powder pressing J. Eur. Ceram. Soc. (IF 3.411) Pub Date : 2018-01-09 C.C. Melo, A.L.I. Moraes, F.O. Rocco, F.S. Montilha, R.B. Canto
This paper describes an experimental procedure to validate numerical models used to simulate powder pressing. It consists mainly of two steps: closed die uniaxial pressing followed by isostatic pressing. The uniaxial pressing causes a non-homogeneous density distribution in the pressing direction as a consequence of friction between die walls and powder. In the isostatic pressing, less compacted regions have a larger volumetric strain, resulting in a non-trivial shape of the re-compacted part, which computes indirectly the previous density distribution. Experimental data from both steps are compared to the results from finite element models. The Drucker-Prager/Cap constitutive model was used to represent the compaction of alumina powder. Several simulations covering a range of parameters obtained from the literature were performed to calibrate the model, through an inverse analysis. The developed procedure sheds a light in the methods to calibrate and/or validate constitutive models used for powder pressing.
Rigid-Resilient Transition in Calcium Borosilicate Sealing Glass–Ceramics: Effect of Preferred Orientation J. Eur. Ceram. Soc. (IF 3.411) Pub Date : 2018-01-08 Jiajia Yan, Ruiguo Chen, Baisheng Sa, Dewei Lin, Lihua Hong, Rui Xiong, Yukun Wu, Hande Chen, Hongbin Su, Qingming Huang, Hsiwen Yang, Kongfa Chen, Teng Zhang
At present, the insufficient thermo-mechanical stability of sealing glass presents a challenge for solid oxide fuel cells (SOFCs). In this work, we report for the first time that a rigid-resilient transition occurs in a calcium borosilicate sealing glass upon heating at 700°C for different durations. The elastic modulus increases from 28.1–40.0 GPa for 24 h to 92.3–105.1 GPa for 100 h, while the corresponding hardness increases from 2.5–3.1 GPa to 8.1–9.2 GPa. In addition, a possible mechanism for the rigid-resilient transition has been proposed. The reported results provide a new approach to solve the sealing problem of SOFCs.
Effects of Crystallization Temperature on Phase Evolution and Energy Storage Properties of BaO-Na2O-Nb2O5-SiO2-Al2O3 Glass-Ceramics J. Eur. Ceram. Soc. (IF 3.411) Pub Date : 2018-01-04 Jingran Liu, Ke Yang, Jiwei Zhai, Bo Shen
Barium sodium niobate (BNN) glass ceramics were successfully fabricated with controllable crystallization by technology for heating processing and the effects of crystallization temperatures on phase evolution, microstructure, dielectric properties and breakdown strength were investigated systematically. In addition, the empirical power-law dependence of breakdown strength on thickness (Eb∝d-n E b ∝ d - n ) was confirmed in BNN glass-ceramic system with an exponent n of 0.21. Based on the results, the BNN glass ceramic crystallized at 800 °C presents a remarkable breakdown strength (BDS) of 2322 kV/cm with the tested thickness of 30 μm, and the highest energy density of 16.6 J/cm3 was achieved.
A new method for bonding alumina to the alloy titanium-zirconium-molybdenum J. Eur. Ceram. Soc. (IF 3.411) Pub Date : 2018-01-04 Réda Berkouch, Stéphane Valette, Joseph Absi, Pierre Lefort
Assemblies of TZM alloy with alumina were obtained with a two-step process, much shorter than moly-manganese brazing methods. This new process involves, first, the preoxidation of the alloy in air at 795 °C, followed by hot-pressing in flowing argon, at 1700 °C under 22 MPa. The adherence of the joints, higher than 45 MPa, was explained by two complementary reasons: i) a mechanical contribution, of “tenon and mortise” type and ii) the penetrations of secondary phases (MoO2 and minor phases coming from alumina additives) into both materials that play the role of nails joining the alloy and the ceramics.
Induction plasma spheroidization of ZrB2-SiC powders for plasma-spray coating J. Eur. Ceram. Soc. (IF 3.411) Pub Date : 2018-01-04 Shijie Sun, Zhuang Ma, Yanbo Liu, Ling Liu, Fuchi Wang, Jiayi Guo
To improve the microstructure and properties of ZrB2-SiC (ZrB2-30vol%SiC, Z7S3) coatings, a facile synthesis route involving induction plasma spheroidization (IPS) has been proposed, and the morphologies, particle size distributions, and phase compositions of the feedstock powders were analysed by scanning electron microscopy and focused ion beam techniques. The obtained results showed that the surfaces of the produced powders contained eutectic-like and granular zones. Owing to the existence of a temperature gradient, the internal microstructure of the IPS-treated powder exhibited a three-layered structure consisting of a’ surface shell’, a’ transition layer’, and a’ porous core’. Additionally, the properties of the IPS-treated samples were compared with those of the spray-dried (SD) powders. The former exhibited good plastic deformation properties, and their single splats contained flattened structures, while the single splats of the SD powder melted only partially retaining some of their original characteristics.
Preparation and mechanical behaviors of SiOC-modified carbon-bonded carbon fiber composite with in-situ growth of three-dimensional SiC nanowires J. Eur. Ceram. Soc. (IF 3.411) Pub Date : 2018-01-04 Du Bin, Changqing Hong, Xinghong Zhang, Jiazhi Wang, Qu Qiang
Carbon-bonded carbon fiber (CBCF) composites are novel and important high-temperature insulation materials owing to their light weight, low thermal conductivity and high fracture tolerance. To further improve the mechanical property of CBCF composite, we propose a three-dimensional (3D) SiC nanowires structure, which is in situ grown on a CBCF matrix via directly annealing silicon oxycarbide (SiOC) ceramic precursor. The synthesized multiscale reinforcements including microscale SiOC ceramics and nanoscale SiC nanowires are mainly attributed to the initial phase separation of SiOC phase and subsequent solid-phase reaction of SiO and C phases. Compared to SiOC/CBCF composite, the resulting 3D SiC nanowires/SiOC/CBCF hybrid structure exhibited high flexural/tensile strength and fractured strain due to the pull-out and bridging behavior of SiC nanowires. This one-step process supplied a feasible way to synthesize 3D SiC nanowires to reinforce and toughen SiOC-modified CBCF composite.
Anodic polarization induced performance loss in GdBaCo2O5+δ oxygen electrode under solid oxide electrolysis cell conditions J. Eur. Ceram. Soc. (IF 3.411) Pub Date : 2018-01-03 Bo Wei, Jiebing Feng, Lin Zhu, Zhihong Wang, Xingbao Zhu, Xiqiang Huang, Yaohui Zhang, Lingling Xu, Hong Gao, Zhe Lü
Double perovskite oxide GdBaCo2O5+δ (GBCO) is widely investigated as promising cathode for solid oxide fuel cells (SOFCs), but it remains unclear whether GBCO is suitable for application in solid oxide electrolysis cells (SOECs) anode. In this study, the effect of anodic polarization on electrochemical activity and microstructure of GBCO electrode are investigated under SOECs operation conditions. Both polarization and impedance spectra results clearly demonstrate that anodic bias treatment leads to substantial performance degradation and higher anodic current passage causes more serious activity loss. The deactivation behavior can be mainly ascribed to the formation of surface BaO precipitates in harsh oxidation atmosphere, as revealed by microstructural observation. Our study suggests that GBCO oxide is not suitable for SOECs anode application, but significant change of surface chemistry enables it a good model electrode for segregation related studies.
Study of the relationships among the crystal structure, phase transition behavior and macroscopic properties of modified (K,Na)NbO3-based lead-free piezoceramics J. Eur. Ceram. Soc. (IF 3.411) Pub Date : 2018-01-02 Laiming Jiang, Zhi Tan, Lixu Xie, Yueyi Li, Jie Xing, Jiagang Wu, Qiang Chen, Dingquan Xiao, Jianguo Zhu
Although phase boundary engineering has made notable progress in improving the electrical properties of (K,Na)NbO3-based piezoceramics, lattice distortion and spontaneous polarization of multiphase coexisting systems are a few of the remaining concerns. Here, new research employing XRD Rietveld refinement was performed to explore crystal structures, phase fractions and atomic parameters of Fe2O3-added (0.995-x)K0.48Na0.52NbO3-xBi0.5Na0.5ZrO3-0.005BiScO3 ceramics. The distortion of the oxygen octahedron and the spontaneous polarization were presented. Central cation displacement provides a much larger contribution to polarization and the electric dipole moment in orthorhombic phase is much larger than that in tetragonal phase. Benefiting from tetragonal-orthorhombic phase coexistence and lattice distortion, optimized ferroelectric and piezoelectric properties (d33 ~ 381 pC/N, Pr ~ 20.47 μC/cm2) were obtained. The ceramic still holds a large d33 (313 pC/N) after up to 300 ℃ of thermal annealing. A series of material constants was also calculated and compared to lead-based ones.
Influence of K0.5Bi0.5TiO3 on the structure, dielectric and ferroelectric properties of (Ba,Ca)(Zr,Ti)O3 ceramics J. Eur. Ceram. Soc. (IF 3.411) Pub Date : 2018-01-02 Mohammed N. Al-Aaraji, David A. Hall
A new lead-free ferroelectric solid solution between (Ba,Ca)(Zr,Ti)O3 (BCZT) and K0.5Bi0.5TiO3 (KBT) has been systematically investigated in terms of its phase transformations, microstructure, dielectric and ferroelectric properties. The incorporation of KBT into BCZT was found to enhance the sintering behavior, although secondary phases of K4Ti3O8 and BaBi4Ti4O15 were detected at high KBT contents. Chemical heterogeneity was also observed in the form of core-shell grain structures comprising tetragonal ferroelectric BCZT-rich cores with pseudo-cubic relaxor ferroelectric KBT-rich shell regions. Temperature-dependent dielectric property measurements revealed that the BCZT-KBT ceramics exhibited both normal and relaxor ferroelectric behaviour simultaneously, associated directly with the core-shell structure. Ferroelectric hysteresis measurements indicated that the remanent polarisation and coercive field were strongly dependent on KBT content. In common with other lead-free relaxor ferroelectrics, increasing temperature led to the formation of constricted polarisation-electric field hysteresis loops, indicating the occurrence of a reversible electric field-induced nanopolar to long-range ordered ferroelectric state.
Yttrium doping of Ba0.5Sr0.5Co0.8Fe0.2O3-δ part I: Influence on oxygen permeation, electrical properties, reductive stability, and lattice parameters J. Eur. Ceram. Soc. (IF 3.411) Pub Date : 2017-12-30 Lana-Simone Unger, Christian Niedrig, Stefan F. Wagner, Wolfgang Menesklou, Stefan Baumann, Wilhelm A. Meulenberg, Ellen Ivers-Tiffée
Ba0.5Sr0.5Co0.8Fe0.2O3-δ (BSCF) exhibits a very high oxygen permeability in its cubic perovskite phase, making it a promising candidate for high-temperature energy-related applications such as oxygen-transport membranes. It suffers, however, from a pronounced phase instability at application-relevant temperatures below 840 °C which is presumed to result from a valence change of B-site cobalt. In an attempt to stabilize the cubic BSCF phase, monovalent Y3+ was doped in small concentrations (1–10 mol-% yttrium) onto its B-site. The influence of this doping on the physico-chemical properties (electrical conductivity, reductive stability, lattice constant), on the sintering behavior, and on the oxygen permeation of BSCF has been systematically investigated. Despite a slightly adverse effect to permeability (decrease in oxygen permeation by about 20–30%), a doping concentration of 10 mol-% Y is found to completely suppress secondary-phase formation and, hence, stabilize the cubic BSCF system at 800 °C. These findings are extremely promising with regard to a long-term operation of BSCF in atmospheres free of acidic impurity gases.
Polymer-derived ceramic/graphene oxide architected composite with high electrical conductivity and enhanced thermal resistance J. Eur. Ceram. Soc. (IF 3.411) Pub Date : 2017-12-29 Benito Román-Manso, Juan J. Moyano, Domingo Pérez-Coll, Manuel Belmonte, Pilar Miranzo, M. Isabel Osendi
A low temperature method for the fabrication of architected graphene containing ceramic composites is developed based on the infiltration of lightweight graphene oxide (GO) micro-lattices with a preceramic polymer. Self-supported highly porous three-dimensional (3D) GO structures fabricated by direct ink writing are infiltrated with a liquid organic-polysilazane (a compound of Si, C, H, N), and subsequently pyrolyzed at temperatures of 800-1000 ºC to favor the ceramic conversion. These ceramic composites replicate the patterned GO skeleton and, whereas the graphene network provides the conductive path for the composite (electrical conductivity in the range 0.2- 4 S cm-1), the ceramic wrapping provides a protective barrier against atmosphere, temperature (up to 900 ºC in air) and even direct flame. These structured composites also show hydrophobicity (wetting angle above 120º) and better load bearing capacity than the corresponding 3D GO lattice. The process is very versatile and could be applied for different liquid precursors.
High efficiency synthesis of Nd:YAG powder by a spray co-precipitation method for transparent ceramics J. Eur. Ceram. Soc. (IF 3.411) Pub Date : 2017-12-28 Wei Jing, Fang Li, Shengquan Yu, Xiangbo Ji, Tao Xu, Jian Zhang, Zhongben Pan, Zerui Yuan, Bin Kang, Jianguo Deng, Wenlong Yin, Hui Huang
A spray co-precipitation method was developed to efficiently synthesize Nd:YAG nano-powders. The effects of spray speeds and solution concentrations on the crystallization processes of calcined precursors have been studied. The results indicated that the pure phase of YAG could be obtained by three different crystallization processes owing to different homogeneity levels of Y and Al mixing. Pure YAG powder was obtained at 850°C and the phase purity persisted to 1600°C. Using the obtained powders, transparent ceramics with the in-line transmittance up to 80.2%@400 nm and 83.1%@1064 nm were fabricated by gel-casting method and hot isostatic pressing sintering. Furthermore, the microstructure and laser properties of the transparent ceramics have been measured. The maximum laser output of 7.015 W has been obtained with an oscillation threshold and a slope efficiency of 0.235 W and 59.4%, respectively.
Advanced Crystallographic Study of the Columnar Growth of YZS Coatings Produced by PS-PVD J. Eur. Ceram. Soc. (IF 3.411) Pub Date : 2017-12-27 Wenting He, Georg Mauer, Alexander Schwedt, Olivier Guillon, Robert Vaßen
In the Plasma Spray-Physical Vapor Deposition (PS-PVD) process, columnar structured coatings are deposited mainly from the vapor phase due to the intensive evaporation of the feedstock powder. This paper highlights the application of electron backscatter diffraction (EBSD) for the characterization of columnar structured ceramic PS-PVD coatings. The growth processes of PS-PVD coatings could be elucidated, developing from small equiaxed crystals to large columnar crystals. Furthermore, the main effect of the torch swing on coating deposition could be the interruption of crystal growth and thus repeated nucleation. This may have a similar effect as slowly rotating the substrate in Electron Beam-Physical Vapor Deposition (EB-PVD).
Structural phase transition, electrical and photoluminescent properties of Pr3+-doped (1-x)Na0.5Bi0.5TiO3-xSrTiO3 lead-free ferroelectric thin films J. Eur. Ceram. Soc. (IF 3.411) Pub Date : 2017-12-27 Wenhua Huang, Shuai He, Aize Hao, Ni Qin, Muhammad Ismail, Jiang Wu, Dinghua Bao
Lead-free ferroelectric Pr3+-doped (1-x)Na0.5Bi0.5TiO3-xSrTiO3 (x = 0–0.5) (hereafter abbreviated as Pr-NBT-xSTO) thin films were prepared on Pt/Ti/SiO2/Si and fused silica substrates by a chemical solution deposition method combined with a rapid thermal annealing process at 700 °C, and their structural phase transition, dielectric, ferroelectric, and photoluminescent properties were investigated as a function of STO content. Raman analysis shows that with increasing STO content, the phase structures evolve from rhombohedral phase to coexistence of rhombohedral and tetragonal phases (i.e. morphotropic phase boundary), and then to tetragonal phase. The structural phase transition behavior has been well confirmed by temperature- and frequency- dependent dielectric measurements. Meanwhile, the variation in photoluminescence intensity of Pr3+ ions with different STO content in the NBT-xSTO thin films also indicates that there exists a clear structural phase transition when the film composition is close to the morphotropic phase boundary. Superior dielectric and ferroelectric properties are obtained in the Pr-NBT-0.24STO thin films due to the formation of morphotropic phase boundary. Our study suggests that Pr-NBT-xSTO thin films be promising multifunctional materials for optoelectronic device applications.
Effect of calcia co-doping on ceria-stabilized zirconia J. Eur. Ceram. Soc. (IF 3.411) Pub Date : 2017-12-27 Miquel Turon-Vinas, Fei Zhang, Jef Vleugels, Marc Anglada
Ceria-stabilized zirconia ceramics are characterised by excellent hydrothermal stability and high fracture toughness, but the fracture strength and hardness are lower than that of conventional 3Y-TZP, which is sensitive to low temperature degradation in humid environments. In the present work, the influence of small concentrations of calcia on the microstructure, mechanical properties and hydrothermal ageing resistance of 10 and 12 mol% CeO2 stabilised ZrO2 has been assessed. The addition of only 1 mol% of CaO had a strong refining effect on the microstructure resulting in an increased hardness and strength but reduced stress activated tetragonal-to-monoclinic transformability. The addition of 3 mol% CaO however enhanced the transformability with respect to 1 mol% CaO and preserved the high resistance to hydrothermal degradation of Ce-TZP.
Rare earth and transition metal based entropy stabilised perovskite type oxides J. Eur. Ceram. Soc. (IF 3.411) Pub Date : 2017-12-27 Abhishek Sarkar, Ruzica Djenadic, Di Wang, Christina Hein, Ralf Kautenburger, Oliver Clemens, Horst Hahn
Multicomponent oxides with perovskite type of structure containing up to 10 different cations in equiatomic amounts have been synthesised for the first time. Out of eleven systems synthesised, only six systems crystallised as single phase perovskite type compounds with random and homogenous cation distribution on the respective sites. The formation of phase pure 10-cationic system, (Gd0.2La0.2Nd0.2Sm0.2Y0.2)(Co0.2Cr0.2Fe0.2Mn0.2Ni0.2)O3, in contrast to the multiphase mixtures observed in five of the lower entropy systems (containing 6 cations) indicates a possible role of entropy in the stabilisation of a single phase crystal structure. The entropy driven structural stabilisation effect is further supported by the reversible phase transformation, from single phase to multiple phase upon cyclic heat treatment, observed in the (Gd0.2La0.2Nd0.2Sm0.2Y0.2)MnO3 system. This type of entropic signature has been observed in rocksalt based multicomponent equiatomic oxide systems. However, it has not been reported before for perovskite based compounds, as shown in this study.
High-temperature compressive creep of novel fine-grained orthorhombic ZrO2 ceramics stabilized with 12 mol% Ta doping J. Eur. Ceram. Soc. (IF 3.411) Pub Date : 2017-12-27 Gabriele Sponchia, Bibi Malmal Moshtaghioun, Pietro Riello, Alvise Benedetti, Diego Gómez-García, Arturo Domínguez-Rodríguez, Angel L. Ortiz
A novel fine-grained orthorhombic ZrO2 ceramic stabilized with 12 mol% Ta doping was fabricated by spark-plasma sintering from home-made powders, and its high-temperature mechanical properties evaluated for the first time by compressive creep tests in both Ar and air. It was found that the high-temperature plasticity of the ceramic deformed in Ar, under which the Ta-doped orthorhombic ZrO2 is a black suboxide with abundant oxygen vacancies in its crystal structure, is controlled by grain boundary sliding (stress exponent ~2, and activation energy ~780‒800 kJ/mol). However, the high-temperature plasticity of the ceramic deformed in air, under which the Ta-doped orthorhombic ZrO2 is a white oxide due to the elimination in situ of oxygen vacancies, is controlled by recovery creep (stress exponent ~3, and activation energy ~750 kJ/mol). It was also observed that black Ta-doped orthorhombic ZrO2 is more creep resistant than its white counterpart with the same grain size, and that the former deforms as the more conventional Y2O3-stabilized ZrO2 does.
Microwave-assisted solution synthesis, microwave sintering and magnetic properties of cobalt ferrite J. Eur. Ceram. Soc. (IF 3.411) Pub Date : 2017-12-27 J.C. Fariñas, R. Moreno, A. Pérez, M.A. García, M. García-Hernández, M.D. Salvador, A. Borrell
A simple, soft, and fast microwave-assisted hydrothermal method was used for the preparation of nanocrystalline cobalt ferrite powders from commercially-available Fe(NO3)3∙9H2O, Co(NO3)2∙6H2O, ammonium hydroxide, and tetrapropylammonium hydroxide (TPAH). The synthesis was conducted in a sealed-vessel microwave reactor specifically designed for synthetic applications, and the resulting products were characterized by XRD, FE-SEM, TEM, and HR-TEM. After a systematic study of the influence of the microwave variables (temperature, reaction time and nature of the bases), highly crystalline CoFe2O4 nanoparticles with a high uniformity in morphology and size, were directly obtained by heating at 130°C for 20 min using the base TPAH. Dense ceramics of cobalt ferrite were prepared by non-conventional, microwave sintering of synthesized nanopowders at temperatures of 850-900ºC. The magnetic properties of both the nanopowders and the sintered specimens were determined in order to establish their feasibility as a permanent magnet.
Effect of molten zone ablated by femtosecond laser on fracture toughness of oxide ceramics J. Eur. Ceram. Soc. (IF 3.411) Pub Date : 2017-12-27 Jinping Cui, Zhenyuan Gong, Pinggen Rao
In this paper, an ultra-sharp V-notch was produced by femtosecond laser on the green bodies of 3Y-TZP, Al2O3 and 8Y-FSZ, respectively. After sintering, the fracture toughness of those ceramic samples was tested by single-edge V-notched beam (SEVNB) method. For comparison, the fracture toughness of ceramic samples with an ultra-sharp V-notch ablated by femtosecond laser directly on the sintered test bars was also determined as a regular testing route. The results reveal that the two different preparation methods of ultra-sharp V-notches can obtain the actual fracture toughness of 3Y-TZP, Al2O3 and 8Y-FSZ. It proves that the influence of thermal effect of ablation process caused by femtosecond laser in front of the notch tip on the fracture toughness can be negligible.
Thermal properties of Cf/HfC and Cf/HfC-SiC composites prepared by precursor infiltration and pyrolysis J. Eur. Ceram. Soc. (IF 3.411) Pub Date : 2017-12-27 Niranjan Patra, Nasrin Al Nasiri, Daniel D. Jayaseelan, William E. Lee
Ultra-high temperature ceramic infiltrated carbon-fibre composites were prepared by precursor infiltration and pyrolysis (PIP) using a laboratory synthesized precursor. Microstructures and thermal properties including thermal expansion, thermal diffusivity, specific heat capacity and oxidative stability are correlated. XRD reveals the presence of Cf-HfC and Cf-HfC-SiC phases without formation of oxides. The CTE observed at 1200 °C is slightly higher for Cf-HfC (3.36×10-6 K-1) compared to Cf-HfC-SiC (2.95×10-6 K-1) composites. Lower thermal diffusivity of the Cf-HfC-SiC compared to Cf-HfC composites is attributed to a thermal barrier effect and cracks in the composites which formed due to the CTE mismatch between carbon fibre and the matrix as well as CO generated during graphitization. The thermal conductivity of Cf-HfC (4.18±0.14 Wm-1K-1) is higher than that of Cf-HfC-SiC composite (3.33±0.42 Wm-1K-1). Composites microstructures were coarse with some protruding particles (5 µm) with a homogeneous dense (~70%) matrix (HfC and HfC-SiC) for both composites.
Yttrium Doping of Ba0.5Sr0.5Co0.8Fe0.2O3-δ Part II: Influence on Oxygen Transport and Phase Stability J. Eur. Ceram. Soc. (IF 3.411) Pub Date : 2017-12-26 Lana-Simone Unger, Rian Ruhl, Matthias Meffert, Christian Niedrig, Wolfgang Menesklou, Stefan F. Wagner, Dagmar Gerthsen, Henny J.M. Bouwmeester, Ellen Ivers-Tiffée
Ba0.5Sr0.5Co0.8Fe0.2O3-δ (BSCF) in its cubic perovskite phase has attracted much interest for potential use as oxygen transport membrane (OTM) due to its very high oxygen permeability at high temperatures. However, performance degradation due to a sluggish phase decomposition occurs when BSCF is operated below 840 °C. Partial B-site substitution of the transition metal cations in BSCF by larger and redox-stable cations has emerged as a potential strategy to improve the structural stability of cubic BSCF. In this study, the influence of yttrium doping (0…10 mol-%) on oxygen transport properties and stability of the cubic BSCF phase is assessed by in situ electrical conductivity relaxation (ECR) and electrical conductivity measurements during long-term thermal annealing both at 700 °C and 800 °C. Detailed phase analysis is performed by scanning electron microscopy (SEM) after long-term annealing of the samples in air at different temperatures.
Damage development of sintered SiC ceramics with the depth variation in Ar ion-irradiation at 600℃ J. Eur. Ceram. Soc. (IF 3.411) Pub Date : 2017-12-26 Bizhe Su, Hanqin Liang, Guiling Liu, Zhengren Huang, Xuejian Liu, Zhongming Chen, Denis Y.W. Yu
Irradiation damage of the materials depends on the irradiation dose and the intrinsic property of the material. In this paper, the high purity hot pressing sintered SiC ceramics with very few second phase and excellent crystallinity were prepared as the target materials, and the high irradiation dose up to 0.95 and 3.16dpa respectively were chosen. The as-sintered SiC ceramics were irradiated with a 160 keV Ar ion beam at 600 °C. X-ray photoelectron spectroscopy, Raman spectrum, transmission electron microscopy and nanoindentation tests were utilized to analyze the microstructure variations on the surface of irradiated SiC, and it was found that the irradiated crystals kept crystallinity, although amorphization of SiC was generated with 10-25nm depth, following with a mixture of point defect clusters and extended defects. Furthermore, it is also evident that there is a balance between irradiated-induced damages buildup and dynamic annealing of defects in high temperature.
Shear crack growth in brittle materials modeled by constrained Cosserat elasticity J. Eur. Ceram. Soc. (IF 3.411) Pub Date : 2017-12-26 Panos A. Gourgiotis
The propagation of in-plane shear cracks is investigated in brittle microstructured materials modeled by the constrained Cosserat elasticity. This theory introduces characteristic material lengths in order to describe the scale effects that emerge from the underlying microstructure and has proved to be very effective for modeling complex microstructured materials. An exact solution is obtained based on integral transforms and the Wiener-Hopf technique. Numerical results are presented illustrating the dependence of the stress intensity factor and the energy release rate upon the loading profile, the propagation velocity, and the characteristic material lengths of Cosserat elasticity. It is shown that depending on the Cosserat microstructural lengths the limiting crack propagation velocity can be significantly lower than the classical Rayleigh limit. Moreover, strengthening effects are observed when the characteristic material lengths become comparable to the geometrical lengths of the problem, a behavior that has been experimentally verified in fracture of ceramics.
Thermal cycling behavior of the plasma-sprayed coating of lanthanum hexaaluminate J. Eur. Ceram. Soc. (IF 3.411) Pub Date : 2017-12-26 Junbin Sun, Jinshuang Wang, Xin Zhou, Yu Hui, Shujuan Dong, Lifen Li, Longhui Deng, Jianing Jiang, Xueqiang Cao
Amorphous phase is commonly found in plasma-sprayed LaMgAl11O19 coating. In this work, LaMgAl11O19 coatings were deposited by atmospheric plasma spraying with powders synthesized at the temperatures range from 1300°C to 1600°C. The melting degree of the feedstock was influenced by the amount of the second phase LaAlO3 and density of the powders, which was dependent on the synthesis temperature. Therefore, LaMgAl11O19 coatings with different amorphous phase contents and microstructures were produced. Results showed that the lower the amorphous contents, the lower the volume shrinkage of the coating during the recrystallization process and the longer the thermal cycling lifetime. However, when the amorphous contents were in the same level, the thermal cycling lifetime differences of these coatings seemed to be dependent on the grain size. LMA coating sprayed with powders synthesized at 1450°C had relatively low amorphous content and moderate grain size, showing the longest thermal cycling lifetime.
Advanced microstructural study of solution precursor plasma sprayed Zn doped hydroxyapatite coatings J. Eur. Ceram. Soc. (IF 3.411) Pub Date : 2017-12-26 Rolando T. Candidato Jr., Rachele Sergi, Jenny Jouin, Olivier Noguera, Lech Pawłowski
Hydroxyapatite is a bioceramic material known as orthopedic implant due to its excellent biocompatibility. From a crystallographic aspect, HA is flexible and can accommodate different ions in its structure. Zinc (Zn) is essential in the human body due to its role in many biological functions and is known to have antibacterial properties. In this work, Zn doped hydroxyapatite coatings were developed by solution precursor plasma spraying using different zinc ion concentrations. It was found that zinc addition does not modify the morphology of coatings. X-ray diffraction analysis showed that Zn concentration greater than 10 mol% inhibits the formation of HA and favors the formation of calcium zinc phosphate. Rietveld refinement showed that the unit cell parameters were not substantially changed upon Zn addition. In general, the structural analysis revealed that Zn ions were highly likely inserted at the hydroxyl column formed by the dehydroxylation of HA under high-temperature plasma environment.
Aero-thermo-chemical characterization of Ultra-High-Temperature Ceramics for aerospace applications J. Eur. Ceram. Soc. (IF 3.411) Pub Date : 2017-12-24 Raffaele Savino, Luigi Criscuolo, Giuseppe Daniele Di Martino, Stefano Mungiguerra
Ultra-High-Temperature Ceramic (UHTC) materials, because of their high temperature resistance, are suitable as thermal protection systems for re-entry vehicles or components for space propulsion. Massive UHTC materials are characterized by poor thermal shock resistance, which may be overcome using C or SiC fibers in a UHTC matrix (UHTCMC). The University of Naples “Federico II” has a proven experience in the field of material characterization in high-enthalpy environments. A hypersonic arc-jet facility allows performing tests in simulated atmospheric re-entry conditions. The Aerospace Propulsion Laboratory is employed for testing rocket components in a representative combustion environment. Ad-hoc computational models are developed to characterize the flow field in both facilities and perform thermal analysis of solid samples. Current research programs are related to a new-class of UHTCMC materials, for rocket nozzles and thermal protection systems. The activities include design of the prototypes for the test campaign, numerical simulations and materials characterizations.
Crystal structure, impedance and broadband dielectric spectra of ordered scheelite-structured Bi(Sc1/3Mo2/3)O4 ceramic J. Eur. Ceram. Soc. (IF 3.411) Pub Date : 2017-12-24 Di Zhou, Li-Xia Pang, Da-Wei Wang, Huan-Huan Guo, Fan Yang, Ze-Ming Qi, Chun Li, Biao-Bing Jin, Ian M. Reaney
Self-Propagating High-Temperature Synthesis of Refractory Boride Ceramics (Zr,Ta)B2 with Superior Properties J. Eur. Ceram. Soc. (IF 3.411) Pub Date : 2017-12-24 V.V. Kurbatkina, E.I. Patsera, E.A. Levashov, A.N. Timofeev
Microstructural characterization and robust comparison of ceramic porous orbital implants J. Eur. Ceram. Soc. (IF 3.411) Pub Date : 2017-12-24 Francesco Baino, Giuseppe Falvo D’Urso Labate, Giovanna Gautier di Confiengo, Maria G. Faga, Chiara Vitale-Brovarone, Gerardo Catapano
This research work tackles the challenge of developing an objective and reliable criterion to score porous bioceramic orbital implants with different microstructural characteristics. We produced porous glass-ceramics by the foam replica method and characterized their 3D micro-architecture through non-destructive X-ray micro-computed tomography. Six key features were estimated influencing their clinical performance, i.e. total porosity, pore interconnectivity, pore size distribution, surface-to-volume ratio, connectivity density and degree of anisotropy. Surface roughness was also characterized by profilometry. A multiparametric score accounting for all the estimated features was developed and used to evaluate the similarity between the produced porous bioceramics and commercial orbital implants. The clinical use of such a global score could make the selection of orbital implants less arbitrary and less dependent on the skills and personal experience of the ophthalmic surgeon. The approach presented in this study could be extended to other areas of ceramics science and technology.
Self-organized nano-scale multilayer coating on SiC fibers obtained by phosphating J. Eur. Ceram. Soc. (IF 3.411) Pub Date : 2017-12-24 S. Mazerat, R. Pailler
Ceramic matrix composites (CMC) combine refractory and structural properties, with a damage-tolerant behavior ensured by an interphase material, usually deposited on fibers. Unfortunately, surface deposition does not prevent contacts between fibers, which are responsible for the premature collective failure of fiber clusters and therefore for limited lifetime. Recently, a workaround has been proposed by transforming the surface of the fibers itself into a continuous monolayer coating. Here we describe an SiC fiber etching process by phosphoric acid vapors at atmospheric pressure and intermediate temperature (600-700°C), leading to an in situ multilayer transformation into a (carbon/silicophosphate)n coating, n ranging from unity to tens and layers thickness from 100 to 300 nm. The carbon layers are micro/mesoporous carbide-derived carbon (CDC) tubes with micrometric radii. This one-step etching process gives opportunity to create layered materials containing CDC even on complex geometries such as fabrics.
Permittivity of polycrystal: laminar structure J. Eur. Ceram. Soc. (IF 3.411) Pub Date : 2017-12-24 I. Rychetsky, A. Klic
A simple model of the laminar polycrystal is constructed that can be solved analytically and it also provides various mixing formulas. The polycrystal structure is composed of the layers, which represent rotated anisotropic crystallites. The dielectric response of such structure is much more complex comparing with the response of the layered structure built up of the isotropic materials. The general formal expressions for the effective permittivity were derived. The micro-geometry is determined by the distribution function of the crystal orientations. The effective permittivity can be controlled by variation of the distribution function. By discussing three examples it was shown that the uniform distribution of 2D rotations, as well as uniform 3D rotations, leads to the logarithmic-like mixing law of the effective permittivity.
Simulation of thermal shock cracking in ceramics using bond-based peridynamics and FEM J. Eur. Ceram. Soc. (IF 3.411) Pub Date : 2017-12-23 Ilias N. Giannakeas, Theodosios K. Papathanasiou, Hamid Bahai
The effects of moderate intensity ‘hot’ or ‘cold’ shock in brittle solids have been extensively studied, while much less is known about thermal shock response during large temperature variations. In this study, a combined finite element – peridynamics numerical procedure is proposed for the simulation of cracking in ceramic materials, undergoing severe thermal shock. Initially, Finite Element nonlinear heat transfer analysis is conducted. The effects of surface convection and radiation heat exchange are also included. Subsequently, the interpolated temperature field is used to formulate a varying temperature induced action for a bond-based peridynamics model. The present model, which is weakly coupled, is found to reproduce accurately previous numerical and experimental results regarding the case of a ‘cold’ shock. Through several numerical experiments it is established that ‘cold’ and ‘hot’ shock conditions give rise to different failure modes and that large temperature variations lead to intensified damage evolution.
Enhanced high-temperature strength of HfB2–SiC composite up to 1600°C J. Eur. Ceram. Soc. (IF 3.411) Pub Date : 2017-12-23 Shuqi Guo, Tianwei Liu, De-Hai Ping, Toshiyuki Nishimura
Using B4C and C additives, a HfB2–SiC composite with an enhanced strength up to 1600 °C was prepared using high-energy ball milling followed by hot pressing. The composite microstructure comprised equiaxed large HfB2 and fine SiC grains and an intergranular amorphous phase. The mechanical behaviour of the composite was evaluated up to 1600 °C via a four-point bending test. At or below 1500 °C, only a linear stress–strain response was observed. At 1600 °C, however, the initial linear response was followed by nonlinear deformation behaviour. The flexural strength was constant between room temperature and 1400 °C; subsequently, the flexural strength significantly increased with increasing temperature up to 1600 °C, with strengths in the range of 650–750 MPa.
Creep behavior of porous La0.6Sr0.4Co0.2Fe0.8O3-δ substrate material for oxygen separation application J. Eur. Ceram. Soc. (IF 3.411) Pub Date : 2017-12-23 Ying Zou, Falk Schulze-Küppers, María Balaguer, Jürgen Malzbender, Manja Krüger
Advanced oxygen transport membrane designs consist of a thin functional layer supported by a porous substrate material that carries mechanical loads. Creep deformation behavior is to be assessed to warrant a long-term reliable operation at elevated temperatures. Aiming towards an asymmetric composite, the current study reports and compares the creep behavior of La0.6Sr0.4Co0.2Fe0.8O3-δ (LSCF) perovskite porous substrate material with different porosity and pore structures in air for a temperature range of 800 to 1000 °C. A porosity and pore structure independent average stress exponent and activation energy is derived from the deformation data, both being representative for the LSCF material. To investigate the structural stability of the dense layer in an asymmetric membrane, sandwich samples of Ba0.5Sr0.5Co0.8Fe0.2O3-δ (BSCF) and La0.6Sr0.4Co0.2Fe0.8O3-δ (LSCF) with porous substrate and dense layers on both side were tested by three-point bending with respect to creep rupture behavior of the dense layer. Creep rupture cracks were observed in the tensile surface of BSCF, but not in the case of LSCF.
Modeling of Young’s modulus and thermal conductivity evolution of partially sintered alumina ceramics with pore shape changes from concave to convex J. Eur. Ceram. Soc. (IF 3.411) Pub Date : 2017-12-22 Tereza Uhlířová, Vojtěch Nečina, Willi Pabst
Numerical calculations of the effective (relative) Young’s modulus and thermal conductivity have been performed for porous model materials on computer-generated digital microstructures with a transition from concave to convex pore shape. The results are compared to the case of purely concave and convex pores (isolated or overlapping). It is shown that the Pabst-Gregorová cross-property relation for isotropic porous materials with isometric pores gives an excellent prediction of effective (relative) properties for materials with a transition from concave to convex pore shape. With accuracy better than 0.010 relative property units (RPU) this prediction is far better than the prediction by any other cross-property relation currently known. For the intermediate (concave-convex) microstructures the accuracy of this cross-property relation is better than that for microstructures with purely concave pores (accuracy better than 0.034 RPU) and, surprisingly, even better than for purely convex pores (accuracy better than 0.011–0.013 RPU).
Temperature-Stable Dielectric Ceramics based on Na0.5Bi0.5TiO3 J. Eur. Ceram. Soc. (IF 3.411) Pub Date : 2017-12-21 Aurang Zeb, Saeed ullah Jan, Faith Bamiduro, David A. Hall, Steven J. Milne
Multiple ion substitutions to Na0.5Bi0.5TiO3 give rise to favourable dielectric properties over the technologically important temperature range -55 °C to 300 °C. A relative permittivity, εr, = 1300 ± 15 % was recorded, with low loss tangent, tanδ ≤ 0.025, for temperatures from 300°C to 0°C, increasing to 0.05 at -55 °C (1 kHz) in the targeted solid solution (1–x)[0.85Na0.5Bi0.5TiO3–0.15Ba0.8Ca0.2Ti1-yZryO3]–xNaNbO3: x = 0.3, y= 0.2. The εr-T plots for NaNbO3 contents x < 0.2 exhibited a frequency-dependent inflection below the temperature of a broad dielectric peak. Higher levels of niobate substitution resulted in a single peak with frequency dispersion, typical of a normal relaxor ferroelectric. Experimental trends in properties suggest that the dielectric inflection is the true relaxor dielectric peak and appears as an inflection due to overlap with an independent broad dielectric peak. Process-related cation and oxygen vacancies and their possible contributions to dielectric properties are discussed.
Li2AGeO4 (A = Zn, Mg): Two novel low-permittivity microwave dielectric ceramics with olivine structure J. Eur. Ceram. Soc. (IF 3.411) Pub Date : 2017-12-21 Chunchun Li, Huaicheng Xiang, Minyu Xu, Ying Tang, Liang Fang
Two low-permittivity dielectric materials Li2AGeO4 (A = Zn, Mg) were prepared via the solid-state reaction method. X-ray diffraction analysis and Rietveld refinement indicated that both ceramics crystallize in an orthorhombic olivine structure with a space group Pmn21. Dense ceramics with high relative density and homogeneous microstructure were obtained. Li2ZnGeO4 densified at 1200 °C possessed a relative permittivity εr = 6.5, a quality factor Q×f = 35,400 GHz, and a temperature coefficient of resonant frequency. Li2MgGeO4 exhibited εr = 6.1, Q×f = 28,500 GHz, and τf = –74.7 ppm/°C when sintered at 1220 °C. Additionally, the large negative τf values of Li2AGeO4 (A = Zn, Mg) ceramics were successfully adjusted compensated by forming composite ceramics with CaTiO3 and near-zero τf values of +2.9 ppm/°C and +5.8 ppm/°C were achieved in 0.92Li2ZnGeO4-0.08CaTiO3 and 0.90Li2MgGeO4-0.10CaTiO3, respectively.
On the search for nucleation agents in BaO-SrO-ZnO-SiO2 glasses: The influence of P2O5 J. Eur. Ceram. Soc. (IF 3.411) Pub Date : 2017-12-21 Katrin Thieme, Tilman Zscheckel, Christian Thieme, Thomas Höche, Christian Rüssel
Glasses in the system BaO-SrO-ZnO-SiO2 from which a phase with the composition Ba1-xSrxZn2Si2O7 can be precipitated possess a strong tendency towards surface crystallization and due to the high anisotropy of the coefficient of thermal expansion of this crystal phase, the obtained glass-ceramics often show micro cracking. The present article deals with the effect of P2O5 on the crystallization behavior of BaO-SrO-ZnO-SiO2 glasses. The phase formation and the microstructure of the glass-ceramics are studied using thermal analyses, X-ray diffraction, optical microscopy, as well as scanning electron microscopy. While the stoichiometric glass melt spontaneously crystallizes upon cooling, the P2O5 addition leads to a stabilization of the glass enabling the preparation of a glass without any crystals. The appearance of stresses and micro cracks during crystallization can be assigned to certain crystallographic directions using electron backscatter diffraction. Moreover, it is possible to achieve volume crystallization in this otherwise solely surface crystallizing glass system.
Comparison between sinter forging and X-ray microtomography methods for determining sintering stress and bulk viscosity J. Eur. Ceram. Soc. (IF 3.411) Pub Date : 2017-12-21 Gaku Okuma, Jesus Gonzalez-Julian, Olivier Guillon, Fumihiro Wakai
The macroscopic sintering parameters, sintering stress, bulk viscosity, and shear viscosity, were measured by the discontinuous sinter forging experiment for viscous sintering of calcium aluminosilicate (CAS) glass. The calculated results were compared with experimental values from the microstructural evolution during viscous sintering of spherical soda lime glass particles by X-ray microtomography. The sintering stress of CAS glass normalized by surface energy and the initial particle size was in good agreement with values estimated from the microtomography data of soda lime glass, despite the differences in particle shape and chemical composition. The bulk viscosity obtained by discontinuous sinter forging agreed fairly well with that estimated by X-ray microtomography observation, when they were normalized by glass viscosity.
Mechanical property degradation of high crystalline SiC fiber–reinforced SiC matrix composite neutron irradiated to ~100 displacements per atom ☆ J. Eur. Ceram. Soc. (IF 3.411) Pub Date : 2017-12-20 Takaaki Koyanagi, Takashi Nozawa, Yutai Katoh, Lance L. Snead
For the development of silicon carbide (SiC) materials for next-generation nuclear structural applications, degradation of material properties under intense neutron irradiation is a critical feasibility issue. This study evaluated the mechanical properties and microstructure of a chemical vapor infiltrated SiC matrix composite, reinforced with a multi-layer SiC/pyrolytic carbon–coated Hi-NicalonTM Type S SiC fiber, following neutron irradiation at 319 and 629°C to ~100 displacements per atom. Both the proportional limit stress and ultimate flexural strength were significantly degraded as a result of irradiation at both temperatures. After irradiation at 319°C, the quasi-ductile fracture behavior of the nonirradiated composite became brittle, a result that was explained by a loss of functionality of the fiber/matrix interface associated with the disappearance of the interphase due to irradiation. The specimens irradiated at 629°C showed increased apparent failure strain because the fiber/matrix interphase was weakened by irradiation-induced partial debonding.
Disturbance and recovery in high speed (110) cleavage in single crystalline silicon J. Eur. Ceram. Soc. (IF 3.411) Pub Date : 2017-12-20 Lv Zhao, Meng Wang, Anne Maynadier, Daniel Nelias
Stress perturbations and material defects can significantly affect the fracture initiation and propagation behaviors in brittle materials. In this work, we show that (110) cleavage in silicon deflects onto (111) plane in the presence of contact stresses. The deflection is however not permanent as the crack returns to the (110) plane after a certain length of propagation, even in the case where the crack velocity is up to 78% of the Rayleigh wave speed. The recovery behavior indicates that the (110) cleavage is invariably prevailing when perpendicular to the maximum stress. Following this indication, it can be concluded that the observed (110)–(111) deflection in previous literature is most likely driven by the external disturbance rather than the crack velocity induced toughness evolution. We also highlight that the extra energy for the (110) recovery is minimized at the expense of a large propagation distance upon the plane switch.
Inert atmosphere processing of hydroxyapatite in the presence of lithium iron phosphate J. Eur. Ceram. Soc. (IF 3.411) Pub Date : 2017-12-19 Miodrag J. Lukić, Maja Kuzmanović, Meltem Sezen, Feray Bakan, Adela Egelja, Ljiljana Veselinović
The present study describes sintering behaviour of hydroxyapatite (HAp) upon addition of lithium iron phosphate (LFP) (1-10 wt. %) system in inert (Ar) atmosphere. The interaction between materials and melting of LFP influenced early and intermediate stages of HAp sintering, shifting the densification curves towards low-temperature side. Analysis of densification process indicated significant differences upon LFP addition. The reaction mechanism that assumes the initial interaction between phosphates from LFP and calcium from HAp was proposed, generating calcium vacancies and contributing to HAp densification. Cross-sections of sintered samples showed changes in microstructural properties, with uniform atomic distribution and presence of Li2Fe3O4 spherical inclusions (200 nm) located at grain boundaries of calcium phosphate matrix. The Rietveld refinement analysis indicated changes in structural and microstructural parameters like crystallite size, anisotropy and microstructural strain of HAp upon LFP addition. Mechanical characterisation indicated improvements in fracture behaviour upon LFP addition.
A Critique of Master Sintering Curve Analysis of Sintering Processes J. Eur. Ceram. Soc. (IF 3.411) Pub Date : 2017-12-19 T. Frueh, I.O. Ozer, S.F. Poterala, Haijoon Lee, E.R. Kupp, C. Compson, J. Atria, G.L. Messing
In this work, we explore factors affecting the accuracy of the master sintering curve (MSC) approach for analyzing the complete sintering profile of ceramic powders. We show that the instantaneous anisotropic shrinkage must be accounted for to develop an accurate MSC. The MSC diverges at >90% density because of basic assumptions that oversimplify the analysis of the densification process. We also show that powder chemistry and forming techniques can affect the fitting parameter Q. Q should not be interpreted as the sintering activation energy, or used to interpret mechanistic differences since it is comprised of several mechanisms that influence densification throughout the sintering cycle. Despite these limitations, the MSC is a useful and practical tool for predicting thermal load (i.e. time and temperature) effects on the densification of a ceramic part fabricated from a singular powder that is fabricated by a singular forming process.
COMPARATIVE STUDY OF STATIC AND CYCLIC FATIGUE OF ZrB2-SiC CERAMIC COMPOSITES J. Eur. Ceram. Soc. (IF 3.411) Pub Date : 2017-12-19 M. Lugovy, N. Orlovskaya, V. Slyunyayev, E. Mitrentsis, M. Neumann, C.G. Aneziris, H. Jelitto, G.A. Schneider, J. Kuebler
Room temperature static and cyclic fatigue of ZrB2-32 vol% SiC and ZrB2-45 vol% SiC particulate ceramic composites has been studied. It was established that the presence of grain bridging plays an important role in the lifetime and time dependent mechanical performance of ZrB2-SiC composites. It was also established that the cohesive strength of grain boundaries of the composites was a determining factor if grain bridging would occur during crack growth, as the grain boundaries strength would determine the pathway of the moving crack. Grain bridging was limited in ZrB2-32 vol% SiC leading to the absence of a cyclic fatigue effect, while grain bridging indeed occurred in ZrB2-45vol%SiC contributing to a cyclic fatigue effect which limits the lifetime of the composite. Such differences were responsible for the occurrence of R-curve behavior in ZrB2-SiC ceramic composites.
Ferroelectric P4mm to Relaxor P4bm Transition and Temperature-Insensitive Large Strains in Bi(Mg0.5Ti0.5)O3-Modified Tetragonal 0.875Bi0.5Na0.5TiO3-0.125BaTiO3 Lead-Free Ferroelectric Ceramics J. Eur. Ceram. Soc. (IF 3.411) Pub Date : 2017-12-19 Ling Li, Mankang Zhu, Qiumei Wei, Mupeng Zheng, Yudong Hou, Jigong Hao
Tetragonal phase (1–x)(0.875Bi0.5Na0.5TiO3–0.125BaTiO3)–xBi(Mg0.5Ti0.5)O3 lead-free ferroelectrics were designed and fabricated by a conventional solid state route. All the specimens exhibit a tetragonal perovskite structure, and undergo a phase evolution from ferroelectric P4mm to antiferroelectric relaxor P4bm as the BMT addition increases. The critical composition x=0.04 makes a bridge between the both tetragonal phases, and gives a large field-induced strain of 0.30% and an adequately-large electrostrictive coefficient Q33 of 0.0254 m4/C2. To be highlighted, the field-induce strain of the composition x=0.04 shows an almost constant value over the temperature range of 18-100 °C, illustrating a temperature-insensitive behavior, which could be attributed to the widened gap between TR–E and TF–R. The temperature-insensitive large strain of the tetragonal BNT–BT–BMT composition give a promising potential for application in precision position actuators.
A Combined Structural, Microstructural and Dilatometric Analysis of MgPSZ J. Eur. Ceram. Soc. (IF 3.411) Pub Date : 2017-12-18 A.I.B. Rondão, M.R. Soares, D.M. Tobaldi, A. Ferreira, J.A. Labrincha, F.M.B. Marques
Spark plasma sintering of titanium nitride in nitrogen: Does it affect the sinterability and the mechanical properties? J. Eur. Ceram. Soc. (IF 3.411) Pub Date : 2017-12-18 Bibi Malmal Moshtaghioun, Diego Gómez-García, Arturo Domínguez-Rodríguez
Titanium nitride ceramics have an intrinsic interest due to its optical and structural applications. However, the conditions for sintering of dense pieces are not still clarified. This research work is focused on the spark plasma sintering (SPS) of near-fully dense fine-grained TiN. The main goal is giving a response to a longstanding debate: can the external atmosphere favor sintering? Different sintering atmospheres, either vacuum or a nitrogen flow, have been used during SPS heating to this purpose. X ray diffraction analysis has showed the presence of TiN as the main phase with traces of Ti4O7 in optimal SPS conditions (1600 °C, one minute dwell time). Our results show that the use of a nitrogen flow while heating can improve sinterability very slightly, but mechanical properties are essentially unaltered within the experimental uncertainty. The hardness reaches values as high as 20GPa whereas fracture toughness can be evaluated around 4 MPam1/2.
Amorphous fine-diameter SiC-based fiber from a boron-modified polytitanocarbosilane precursor J. Eur. Ceram. Soc. (IF 3.411) Pub Date : 2017-12-18 Guomei He, Baojie Zhang, Bowei Wang, Danni Xu, Siwei Li, Zhaoju Yu, Jiangxi Chen
An amorphous SiC-based fiber was successfully prepared by the preceramic polymer route from a boron-modified polytitanocarbosilane. It was found that the addition of titanium and boron had adverse effect on melt-spinning, while the tensile strength of the obtained SiC-based fibers increased with the contents of titanium and boron increasing. It is worth mentioning that the decomposition of Si-C-O phase and the resultant β-SiC crystallization were retarded by the incorporation of titanium and boron into the SiC-based fiber.
Temperature-dependent fracture strength and the effect of oxidation for ZrB2-SiC ceramics J. Eur. Ceram. Soc. (IF 3.411) Pub Date : 2017-12-17 Hailong Wang, Jianyong Chen, Pengfei Yu, Shengping Shen
Using the stress distribution of the body containing a spherical inclusion, the stress intensity factor at the tip of the annular flaw emanating from the inclusion isformulized. Since the thermal expansion coefficient of matrix and inclusion is not matched, the residual stress is also taken into account. Introducing into the proposed temperature-dependent fracture surface energy or fracture toughness, the temperature-dependent fracture strength for ZrB2-SiC is obtained. The influence of oxidation on the fracture strength is also discussed and the analysis reveals that the oxidation has significant effect on the fracture strength under some circumstances. The calculated results are compared with the experimental data and they have very good consistency.
Holmium doped yttria transparent ceramics for 2-μm solid state lasers J. Eur. Ceram. Soc. (IF 3.411) Pub Date : 2017-12-15 Jun Wang, Yongguang Zhao, Danlei Yin, Peng Liu, Jie Ma, Ying Wang, Deyuan Shen, Zili Dong, Ling Bing Kong, Dingyuan Tang
0.7 at.% Ho:Y2O3 transparent ceramics were fabricated by using vacuum sintering plus hot isostatic pressing (HIPing) process. Vacuum sintered at 1500 °C for 12 h followed by HIPing at 1450 °C for 4 h, the Ho:Y2O3 ceramics showed excellent in-line transmission and uniform grain size, with an average grain size of about 1 μm. The Ho:Y2O3 ceramics showed good thermal conductivity thanks to the identical effective ionic radius between Ho3+ and Y3+. For the first time, room temperature laser oscillation from Ho:Y2O3 transparent ceramics was demonstrated. The uncoated 0.7 at.% Ho:Y2O3 ceramic slabs were in-band pumped by a Tm:fiber laser at 1941 nm, and a maximum output power of 1.3 W at 2116.8 nm was achieved with a slope efficiency of 31.2%. It indicates that Ho:Y2O3 transparent ceramics could be excellent laser gain medias for 2 μm solid-state laser applications.
Fabrication and spectral properties of Dy: Y2O3 transparent ceramics J. Eur. Ceram. Soc. (IF 3.411) Pub Date : 2017-12-15 Zongwen Hu, Xiaodong Xu, Jun Wang, Peng Liu, Dongzhen Li, Xiaodan Wang, Jian Zhang, Jun Xu, Dingyuan Tang
Dy3+-doped Y2O3 ceramics were fabricated by Spark Plasma Sintering method. The effect of sintering temperature on the microstructure and the optical transmittance of the ceramics was studied. The maximum in-line transmittance of Dy:Y2O3 ceramics with thickness of 1 mm was 74.5% at 574 nm when sintering temperature was 1550 ℃. The spectroscopic parameters were determined by Judd-Ofelt theory based on the room temperature absorption spectra. The peak emission cross section for the 4F9/2→6H13/2 transition was calculated to be 0.569×10-20 cm2. The fluorescence decay curve and quantum efficiency of the 4F9/2 multiplet were measured to be 269.2 µs and 37.1%, respectively.
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