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arXiv 0812.2175cond-mat.mtrl-sci
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SrBi $_2$ Ta $_2$ O $_9$温度驱动相变的第一性原理计算

Temperature-driven phase transitions in SrBi$_2$Ta$_2$O$_9$ from first-principles calculations

R. Machado, M. Sepliarsky, M. G. Stachiotti

摘要:

采用壳层模型研究了SrBi $_2$ Ta $_2$ O $_9$的相变序列,模型参数符合第一性原理计算.我们发现,极性和非极性不稳定性之间的复杂的相互作用导致两个相变的存在下,证实了存在一个中间正交顺电相。该相的特征在于TaO $_6$八面体围绕a轴的旋转。我们表明,这个阶段也可以检测到从材料的介电响应。本方法构成了一个强大的工具,理论预测的中间阶段,尚未观察到的实验,在其他Aurivillius化合物。

英文摘要:

The phase transition sequence of SrBi$_2$Ta$_2$O$_9$ is investigated using a shell model with parameters fitted to first-principles calculations. We show that the complex interplay between polar and nonpolar instabilities leads to the presence of two phase transitions, corroborating the existence of an intermediate orthorhombic paraelectric phase. This phase is characterized by the rotation of the TaO$_6$ octahedra around the a-axis. We show that this phase can be also detected from the dielectric response of the material. The present approach constitutes a powerful tool for a theoretical prediction of intermediate phases, not yet observed experimentally, in other Aurivillius compounds.

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