Pyrochlore-type oxide solid solutions: (Bi1-xGax)2-dTi2O7-3d/2
Pyrochlore-type oxide solid solutions: (Bi1-xGax)2-dTi2O7-3d/2
复制标题
烧绿石型氧化物固溶体：(Bi1-xGax)2-dTi2O7-3d/2
DOI：
10.1039/c9tc06074j
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发表时间：
2020
影响因子：
6.4
通讯作者：
Takahiro Yamada
中科院分区：
文献类型：
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作者：
Hisanori Yamane;Ryota Yagi;Takahiro Yamada
用二元氧化物混合物在1100℃空气中加热的方法制备了焦绿石型氧化物固溶体(Bi1−xGax)2−dTi2O7−3d/2((x=0.04，d=0.19)-(x=0.18，d=0))多晶样品。从1250°C熔化并冷却凝固的样品中获得了x=0.08，d=0.24(Bi1.62Ga0.14Ti2O6.64)固溶体单晶。在多晶固溶体和Bi1.62Ga0.14Ti2O6.64单晶的X射线衍射图中，观察到基点间有弥散条纹和拖尾的宽峰。基于对非中心对称空间群F4132的单晶结构分析，提出了一个统计平均模型，即具有四重配位的Ga位位于具有八重配位的Bi位附近。测量了(Bi1 δxGax)2−dTi2O7−−3d/2(x=0.06，d=0.15)烧结多晶样品在100 kHz和20°C下的相对介电常数和介电损耗分别为126和0.003。在1 MHz频率下，样品的相对介电常数为12 0~118，温度系数为−166ppm°C−1。用交流阻抗法和两端直流法分别测量了2.9×10−5 S cm−1和2.7×10−5 S cm−1在70 3℃和6 92℃的电阻率，表明高温时主要载流子是空穴和/或电子。由直接允许跃迁假设的漫反射光谱估算出的光学带隙能为2.90 eV，与由电导激活能计算出的2.96 eV接近。
Polycrystalline samples of pyrochlore-type oxide solid solutions, (Bi1−xGax)2−dTi2O7−3d/2 ((x = 0.04, d = 0.19) – (x = 0.18, d = 0)), were prepared by heating binary-oxide mixtures at 1100 °C in air. Single crystals of a solid solution with x = 0.08 and d = 0.24 (Bi1.62Ga0.14Ti2O6.64) were obtained from a sample melted at 1250 °C and solidified by cooling from this temperature. Broad peaks with tails and diffuse streaks between the fundamental spots were observed in X-ray diffraction patterns for the polycrystalline solid solutions and for a single crystal of Bi1.62Ga0.14Ti2O6.64. A statistical average model in which the Ga site having four-fold coordination is placed near the Bi site having eight-fold coordination was proposed based on the single-crystal structure analysis with the non-centrosymmetric space group F4132. The relative dielectric constant and dielectric loss (tan δ) measured at 100 kHz and 20 °C for a sintered polycrystalline sample of (Bi1−xGax)2−dTi2O7−3d/2 (x = 0.06, d = 0.15) were 126 and 0.003, respectively. Relative dielectric constants of 120–118 with a temperature coefficient of −166 ppm °C−1 were obtained between 20 and 160 °C at 1 MHz. Electrical resistivities of 2.9 × 10−5 S cm−1 at 703 °C and 2.7 × 10−5 S cm−1 at 692 °C were determined using the alternate current impedance and two-terminal direct current methods, respectively, indicating that the major carriers were holes and/or electrons at high temperature. The optical band gap energy estimated from the diffuse reflectance spectrum by postulating direct allowed transition was 2.90 eV, which was close to the value of 2.96 eV calculated from the activation energy for the conduction.