Pyrochlore-type oxide solid solutions: (Bi1−xGax)2−dTi2O7−3d/2†,Journal of Materials Chemistry C

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Pyrochlore-type oxide solid solutions: (Bi1−xGax)2−dTi2O7−3d/2†
Journal of Materials Chemistry C ( IF 5.7 ) Pub Date : 2019-12-05 , DOI: 10.1039/c9tc06074j
Hisanori Yamane _{1,

2,

3,

4,

5} , Ryota Yagi _{1,

2,

3,

4,

5} , Takahiro Yamada _{1,

2,

3,

4,

5}

Affiliation

Polycrystalline samples of pyrochlore-type oxide solid solutions, (Bi_1−xGa_x)_2−dTi₂O_7−3d/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 (Bi_1.62Ga_0.14Ti₂O_6.64) 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 Bi_1.62Ga_0.14Ti₂O_6.64. 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 (Bi_1−xGa_x)_2−dTi₂O_7−3d/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.

中文翻译：

烧绿石型氧化物固溶体：（Bi _{1- x} Ga _x）_{2- d} Ti ₂ O _{7-3 d / 2}†

烧绿石型氧化物固溶体的多晶样品，（Bi _{1- x} Ga _x）_{2- d} Ti ₂ O _{7-3 d / 2}（（x = 0.04，d = 0.19）–（x = 0.18，d = 0））是通过在空气中1100°C下加热二元氧化物混合物来制备的。x = 0.08和d = 0.24的固溶体单晶（Bi _1.62 Ga _0.14 Ti ₂ O _6.64）是从在1250°C下熔化并从该温度冷却而固化的样品中获得的。对于多晶固溶体和Bi _1.62 Ga _0.14 Ti ₂ O _6.64的单晶，在X射线衍射图中观察到基本点之间存在带有尾巴和弥散条纹的宽峰。基于具有非中心对称空间群F 4 ₁ 32的单晶结构分析，提出了一种统计平均模型，其中具有四重配位的Ga位被置于具有八重配位的Bi位附近。常数和介电损耗（tanδ δ）在100 kHz和20°C下测得的（Bi _{1- x} Ga _x）_{2- d} Ti ₂ O _{7-3 d / 2}（x = 0.06，d = 0.15）的多晶烧结样品分别为126和0.003 。在20 MHz和160°C之间以1 MHz的频率获得的相对介电常数为120-118，温度系数为-166 ppm°C ^-1。703°C和2.9×10 ^-5 S cm ^-1时的电阻率为2.9 ×10 ^-5 S cm ^-1分别使用交流阻抗和两端直流法确定了692°C时的温度，这表明高温下主要的载流子为空穴和/或电子。通过假设直接允许的跃迁从漫反射光谱估计的光学带隙能量为2.90 eV，接近于从传导的激活能计算得出的2.96 eV的值。

更新日期：2020-01-08

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