Bi0.5K0.5TiO3–CaTiO3 ceramics: Appearance of the pseudocubic structure and ferroelectric-relaxor transition characters

In this study, solid solution ceramics of (1−x)Bi_0.5K_0.5TiO₃–xCaTiO₃ (BKT-CT, x = 0, 0.12, 0.15, 0.18, 0.21, and 0.25) were prepared. A phase transition from the tetragonal symmetry to the pseudocubic symmetry is discovered near x = 0.25. The reasons for the appearance of the pseudocubic phase were discussed. The compositions of x ≤ 0.21 show the ferroelectric ordering at room temperature. The remnant polarization (P_r) is 22.4 μC/cm² for the x = 0.15 composition. The temperature dependence of the relative permittivity suggests two dielectric anomalies for x ≤ 0.18. The dielectric anomaly in the low-temperature range is related to a spontaneous transition between the ferroelectric and relaxor states. The temperature (T_F-R) for the transition decreases with the CT addition, falling from 211°C for x = 0.12-134°C for x = 0.18. Only one relaxor-like dielectric anomaly was observed for x ≥ 0.21. The thin double ferroelectric hysteresis loops have been observed during the ferroelectric-relaxor transition process for x ≥ 0.21. The maximum electrostrain (S_m) reaches 0.155% at 100°C for x = 0.21. The low-temperature Raman measurement suggests the intrinsic tetragonal distortions for x = 0.25.     

Reduced leakage current and enhanced piezoelectricity of BNT–BT–BMO thin films

BiMeO₃ (where Me denotes a transition metal) is often used as a chemical modifier to form the Bi_0.5Na_0.5TiO₃-based solid solutions and to improve the electromechanical properties of the materials. In this study, BiMnO₃ was selected as a chemical modifier, and (1 − x)(0.94Bi_0.5Na_0.5TiO₃-0.06BaTiO₃)–xBiMnO₃ thin films with x = 0, 0.005, 0.01, and 0.015 were fabricated using the metal organic decomposition method to study the contributions of the third end-member BiMnO₃ to the reduction in the leakage current and the enhancement of the piezoelectric properties of Bi_0.5Na_0.5TiO₃-BaTiO₃ thin films. Thin films with 1 mol% BiMnO₃ exhibit a lower leakage current, and a better piezoelectricity and ferroelectricity, whose S_max/E_max, P_max, 2E_c, and ε_r are 100.4 pm/V, 48.0 μC/cm², 54.9 kV/cm, and 942, respectively.     

从昆明公交专用道探讨公交站台的设置

通过调研昆明公交专用道和内侧式公交站台的现状,对比深圳等大城市公交站台,分析昆明的内侧式公交站台设置问题,并探讨公交专用道与之相适应的公交站台,以在公交优先的背景下体现以人为本。     

Solid state synthesis and sintering of solid solutions of BNT–xBKT

Various compositions of the solid solution system (100 − x) Bi_0,5Na_0,5TiO₃–xBi_0,5K_0,5TiO₃ (x = 0, 10, 25, 50, 75, 90, 100) were prepared by the mixed oxide route. The formation reaction was analyzed by thermogravimetry coupled with mass spectroscopy and differential scanning calorimetry. In situ high temperature X-ray diffraction up to 770 °C indicated emerging and vanishing of phases during the calcination. Intermediate phases such as alkalipolytitanate (Na/K)₂Ti₆O₁₃ and bismuth titanate Bi₂Ti₂O₇ were identified as forming the perovskite phase. The formation reactions were proposed based on the data obtained. Furthermore the microstructure and the dielectric behavior of the sintered samples were observed by scanning electron microscopy, impedance spectrometry and polarization measurements.     

无铅BaTiO_3系热敏电阻及其PTC性能的研究进展

通常在BaTiO3中固溶PbTiO3来提高BaTiO3系PTCR的居里温度,但是铅的毒性和挥发性限制了BaTiO3系PTCR的应用,因此需要研制出高居里点的无铅PTCR陶瓷。随着BNT、BKT含量增加,BaTiO3系PT-CR的居里点升高,但同时室温电阻快速增大。若在提高居里点的同时抑制室温电阻率的增大,就能制备出有实用价值的无铅高居里点的PTC材料。综述了BNT、BKT的含量对居里温度的影响及其机理,通过加入还原剂或在还原气氛下烧结并制定合理的烧结制度可以得到低室温电阻率和性能较好的PTC材料。     

Enhanced piezoelectricity and energy storage performances of Fe-doped BNT–BKT–ST thin films

Fe-doping is an effective way to improve physical performances of piezoelectric and ferroelectric materials. Under such circumstances, x mol% (x?=?0.0, 1.0, 1.5, 2.5) Fe-doped 0.72Bi_0.5Na_0.5TiO₃–0.18Bi_0.5K_0.5TiO₃–0.10SrTiO₃ (BNT–BKT–ST–xFe) thin films were prepared by sol-gel method and the relationships between the content of Fe and electromechanical properties of the films were studied. The BNT–BKT–ST–1.0Fe thin films exhibit the best electromechanical properties, whose S_max/E_max, W_rec, η, P_max, P_rem and ε_r of are 68.00?pm/V, 20.34?J/cm³, 65.17%, 71.5?μC/cm², 14.8?μC/cm², 868 respectively. These results indicate that BNT–BKT–ST–1.0Fe thin films are promising for applications for advanced piezoelectric materials and capacitors with high energy-storage density.