Departamento de Ciencias de la Tierra y Física de la Materia Condensada, Universidad de Cantabria, Cantabria Campus Internacional, Santander, Spain.
Phys Rev Lett. 2011 Nov 18;107(21):217601. doi: 10.1103/PhysRevLett.107.217601. Epub 2011 Nov 15.
We report first-principles calculations on the coupling between epitaxial strain, polarization, and oxygen octahedra rotations in monodomain (PbTiO(3))(n)/(SrTiO(3))(n) superlattices. We show how the interplay between (i) the epitaxial strain and (ii) the electrostatic conditions can be used to control the orientation of the main axis of the system. The electrostatic constrains at the interface facilitate the polarization rotation and, as a consequence, we predict large piezoelectric responses at epitaxial strains smaller than those required considering only strain effects. In addition, ferroelectric (FE) and antiferrodistortive (AFD) modes are strongly coupled. Usual steric arguments cannot explain this coupling and a covalent model is proposed to account for it. The energy gain due to the FE-AFD coupling decreases with the periodicity of the superlattice, becoming negligible for n ≥ 3.
我们报告了在单晶畴 (PbTiO(3))(n)/(SrTiO(3))(n) 超晶格中，外延应变、极化和氧八面体旋转之间的耦合的第一性原理计算。我们展示了（i）外延应变和（ii）静电条件之间的相互作用如何用于控制系统主轴的方向。界面处的静电约束促进了极化旋转，因此，我们预测在比仅考虑应变效应所需的应变还小的外延应变下，会产生较大的压电响应。此外，铁电 (FE) 和反铁电畸变 (AFD) 模式强烈耦合。常见的空间位阻论点无法解释这种耦合，因此提出了一个共价模型来解释它。由于 FE-AFD 耦合而获得的能量增益随超晶格的周期性减小，对于 n ≥ 3 时变得可以忽略不计。
