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Theory of prospective perovskite ferroelectrics with double rocksalt order

机译：双岩盐阶准钙钛矿铁电理论

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摘要

Using first-principles methods, we predict the energy landscape and ferroelectric states of double perovskites of the form AA'BB'O_6 in which the atoms on both the A and B sites are arranged in rocksalt order. While we are not aware of compounds that occur naturally in this structure, they might be realizable by directed synthesis, as has recently been demonstrated experimentally. The high-symmetry structure formed by this arrangement belongs to the tetrahedral F43m space group. If a ferroelectric instability occurs, the energy landscape will tend to have minima with the polarization along tetrahedral directions, leading to a rhombohedral phase, or along Cartesian directions, leading to an orthorhombic phase. We find that the latter scenario applies to CaBaTiZrO_6 and KCaZrNbO_6, which are weakly ferroelectric, and the former one applies to PbSnTiZrO6, which is strongly ferroelectric. The results are modeled with a fourth- or fifth-order Landau-Devonshire expansion, providing good agreement with the first-principles calculations. Computations of zone-center soft modes are also carried out in order to characterize the polar and octahedral-rotation instabilities in more detail.
机译：使用第一性原理方法，我们预测了AA'BB'O_6形式的双钙钛矿的能量态势和铁电态，其中A和B位上的原子都按岩盐顺序排列。虽然我们不知道自然存在于该结构中的化合物，但如最近通过实验证明的那样，可以通过定向合成实现它们。通过这种布置形成的高对称结构属于四面体F43m空间群。如果发生铁电不稳定性，则能量格局将趋于具有极小值，其极化沿四面体方向（导致菱形相）或沿笛卡尔方向（导致正交晶相）极化。我们发现，后一种情况适用于弱铁电的CaBaTiZrO_6和KCaZrNbO_6，前一种情况适用于强铁电的PbSnTiZrO6。用四阶或五阶Landau-Devonshire展开对结果进行建模，这与一阶原理计算具有很好的一致性。为了更详细地描述极坐标和八面体旋转的不稳定性，还进行了区域中心软模的计算。

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