By slow cooling of the melt, large Bi₂Ti₂O₇ single crystals with a composition close to stoichiometric were grown. No traces of impurity phases were found on the X-ray diffraction patterns. A structural model with the space group Fd3m and displacive disorder in Bi-sublattice was proposed based on X-ray single crystal diffraction data. The dielectric properties of Bi₂Ti₂O₇ single crystals as a function of temperature at different frequencies were studied for the first time. As in the case of ceramic samples, a step-like frequency-dependent anomaly was detected at a temperature of about 220 K at a frequency of 1 kHz. It was found that attempts to describe the dielectric relaxation using the Arrhenius equation do not lead to physically significant values of the fitting parameters. However, the relaxation behavior is well described by the empirical Vogel–Fulcher relation, which is typical for many dipole and spin glasses, as well as relaxor ferroelectrics. Based on the value of fitting parameters, Bi₂Ti₂O₇ occupies an intermediate position between the canonical relaxor PbMg_1/3Nb_2/3O₃ on one hand and lead-free weakly coupled relaxors based on BaTiO₃ on the other one. Possible mechanisms of the observed relaxor-like behavior of the Bi₂Ti₂O₇ single crystal are discussed in terms of correlated hopping of bismuth cations and geometric frustration of the pyrochlore lattice.

中文翻译：

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Bi ₂ Ti ₂ O ₇烧绿石单晶的弛豫样行为和结构特征

通过缓慢冷却熔体，生长出具有接近化学计量组成的大的Bi ₂ Ti ₂ O ₇单晶。在X射线衍射图上未发现杂质相的痕迹。基于X射线单晶衍射数据，提出了空间空间群Fd 3 m，双亚晶格位移无序的结构模型。Bi ₂ Ti ₂ O ₇的介电性能首次研究了在不同频率下随温度变化的单晶。与陶瓷样品一样，在温度约为220 K，频率为1 kHz的情况下，检测到阶梯状的频率相关异常。已经发现，尝试使用阿伦尼乌斯（Arrhenius）方程描述介电弛豫并不会导致拟合参数的物理显着值。但是，弛豫行为可以通过经验Vogel-Fulcher关系很好地描述，该关系对于许多偶极子玻璃和自旋玻璃以及弛豫铁电体都是典型的。根据拟合参数的值，Bi ₂ Ti ₂ O ₇处于规范松弛器PbMg _1/3 Nb _2/3之间的中间位置一方面是O ₃，另一方面是基于BaTiO ₃的无铅弱耦合弛豫器。根据铋阳离子的相关跃迁和烧绿石晶格的几何受阻，讨论了Bi ₂ Ti ₂ O ₇单晶所观察到的弛豫样行为的可能机理。