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Keisuke Kobayashi Minoru Ryu Yutaka Doshida Youichi Mizuno Clive A. Randall 《Journal of the American Ceramic Society》2013,96(2):531-537
The (1?x)NaNbO3–(x)NaTaO3 solid solution was investigated for x ≤ 0.4 in terms of new high‐temperature and high‐permittivity dielectric system that is suitable for base metal inner electrode capacitor applications. The addition of Ta significantly enhanced the resistivity of the dielectric, resulting in superior resistivity than the dielectrics‐formulated BaTiO3 systems that dominate the multilayer ceramic capacitor dielectric devices. The voltage dependence of the permittivity was also superior to BaTiO3‐based materials, providing higher capacitance at higher temperatures. A transmission electron microscopy study illustrated that the grains had so‐called core‐shell structure. According to the electron diffraction analysis, the core region had an inhomogeneous structure between antiferroelectric and ferroelectric phases, and shell region had an incommensurate ferroelectric‐like structure. The core and shell region had Nb‐ and Ta‐rich composition, respectively, and their interface was compositionally sharp, implying that shell region was formed via a liquid phase during the sintering process with an incongruent Ta dissolution reprecipitation. We anticipate that these or similar materials based on the alkali‐niobate perovskites can be further enhanced to provide capacitor solutions from 150°C to 250°C, which is an important range for a number of new AC–DC invertor and engine control units. 相似文献
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High‐Temperature Multilayer Ceramic Capacitors Based on 100−x(94Bi1/2Na1/2TiO3–6BaTiO3)–xK0.5Na0.5NbO3
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Claudia Groh Keisuke Kobayashi Hiroyuki Shimizu Yutaka Doshida Youichi Mizuno Eric A. Patterson Jürgen Rödel 《Journal of the American Ceramic Society》2016,99(6):2040-2046
The potential high‐temperature dielectric materials 100?x(94Bi1/2Na1/2TiO3–6BaTiO3)–xK0.5Na0.5NbO3 with x = 12, 18, and 24 were processed as bulk samples in order to examine the reduction of sintering temperature by means of CuO as sintering aid. Due to the successful reduction of sintering temperature, low cost Ag:Pd could be used as a co‐fired electrode material for multilayer ceramic capacitors (MLCCs). Fabrication of 8 μm thick, dense MLCCs with self‐contained, nonreactive electrodes is reported for a wide range of compositions of Bi1/2Na1/2TiO3–BaTiO3–K0.5Na0.5NbO3. Among the manufactured MLCCs, those with compositions x = 24 showed the most promising dielectric properties for applications where high operating temperatures are needed. The temperature‐dependence of permittivity was quite low, revealing a change of less than ±10% compared to its 150°C‐value in the range of 40°C–225°C. For samples sintered at 1000°C, an RC constant of about 300 s was obtained at 150°C. Furthermore, these x = 24 MLCCs exhibited the finest microstructures among the compositions examined; making it a suitable candidate for further miniaturization of layer thickness as required for state‐of‐the art devices. 相似文献
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The small signal gain coefficients were measured in Tm3+,Ho3+ co-doped alumino-zirco-fluoride glass. A gain of 15%/cm at 2.05 μm was obtained for pump power density of 42 kW/cm2. The temperature increase of the glass was found to be more than 150 K with this pump power, which was estimated from a comparison between fluorescence intensities of Tm3+ 3 F4-3H6 and Ho3+ 5 I7-5I8. An upconversion rate constant of 12.5×10-17 cm3 sec-1 from a coupled (Tm3+ 3F4, Ho3+ 5I7) level to a coupled (Tm3+ 3H5, Ho3+ 5I6) level was determined by fitting the experimentally obtained gain coefficients to the calculated one which takes into consideration any temperature increase 相似文献
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Satoshi Tanaka Yusuke Tomita Ryoichi Furushima Hiroyuki Shimizu Yutaka Doshida Keizo Uematsu 《Science and Technology of Advanced Materials》2009,10(1)
High magnetic field was applied to fabricate novel lead-free piezoelectric ceramics with a textured structure. A compact of crystallographically oriented grains was prepared by dry forming in a high magnetic field from a mixed slurry of bismuth titanate and barium titanate powders. Bismuth titanate particles with a size of about 1 μ m were used as the host material. In the forming process, the slurry was poured into a mold and set in a magnetic field of 10 T until completely dried. Bismuth titanate particles were highly oriented in the slurry under the magnetic field. The dried powder compact consisted of highly oriented bismuth titanate particles and randomly oriented barium titanate particles. Barium bismuth titanate ceramics with a- and b-axis orientations were successfully produced from the dried compact by sintering at temperatures above 1100 ° C. 相似文献
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Tamiko Kinoshita Mamoru Senna Yutaka Doshida Hiroshi Kishi 《Ceramics International》2012,38(3):1897-1904
From a core–shell structured precursor, comprising Nb2O5 core enveloped by KHCO3 in an equimolar proportion, phase pure KNbO3 (KN) fine particles were obtained by calcining in air at 600 °C for 1 h. Disintegrating the large agglomerated particles of KHCO3 prior to the precursor preparation enabled the micronization of the KN particle size down to 240 nm, close to that of the starting Nb2O5, due to increased mixing homogeneity and consequent thorough enveloping of individual Nb2O5 particles. Based on these findings, together with the known coupling diffusion mechanism of potassium and oxygen into Nb2O5, it was concluded that the core–shell particles in the precursor serve as a separated reaction space to complete the formation of KN without appreciable coalescence or local sintering, as far as the firing temperature is low enough like those employed in the present study. Superiority of KHCO3 over K2CO3 or KNO3 as a potassium source was also discussed. 相似文献
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The numbers of lattice defects formed by applying cyclic prestress with/without hydrogen for various numbers of cycles and strain rates during cyclic prestress were compared for tempered martensitic steel. A tensile test was also carried out to evaluate hydrogen embrittlement susceptibility following the application of cyclic prestress. The results showed that when cyclic prestress was applied without hydrogen, the number of cycles and strain rate had no apparent effect on mechanical properties and fracture morphology at the time of the subsequent tensile test. In contrast, when cyclic prestress was applied with hydrogen, the fracture strain and fracture stress decreased with an increasing number of prestress cycles and a decreasing strain rate, and the fracture morphology exhibited brittle fracture, signifying an increase in hydrogen embrittlement susceptibility at the time of the tensile test. The number of hydrogen-enhanced lattice defects also increased with increasing number of cycles and a decreasing strain rate was found when cyclic prestress was applied with hydrogen. These results indicate a correlation between hydrogen embrittlement susceptibility and the number of hydrogen-enhanced lattice defects. The kinds of increased hydrogen-enhanced lattice defects were probably vacancies and vacancy clusters formed by the interactions between hydrogen and dislocation movement during the application of cyclic prestress. The vacancies and vacancy clusters formed during the application of cyclic prestress with hydrogen presumably caused intergranular fracture and increased hydrogen embrittlement susceptibility. 相似文献
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