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arXiv 1802.00784cond-mat.mtrl-sci
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钙钛矿氧化物中氧-八面体转动的第一性原理能量学

Energetics of oxygen-octahedra rotations in perovskite oxides from first principles

Peng Chen, Mathieu N. Grisolia, Hong Jian Zhao, Otto E. Gonzalez-Vazquez, L. Bellaiche, Manuel Bibes, Bang-Gui Liu, Jorge Iniguez

摘要:

我们使用第一性原理方法来研究ABO 3钙钛矿氧化物中的氧八面体旋转。我们专注于短周期,完全反相或同相,倾斜模式,表征大多数化合物和控制其物理(例如,导电、磁性)特性。基于相关的势能面的解析形式,我们讨论了呈现不同倾斜模式的多晶型物的稳定性条件,并获得了35种代表性材料的数值结果。我们的研究结果揭示了一种特殊结构频繁出现的机制,这种结构结合了反相和同相旋转,即,约一半的钙钛矿氧化物和许多非氧化钙钛矿显示出正交Pbnm相。Pbnm相受益于彼此竞争的反相和同相倾斜图案的同时发生,但不强烈到相互排斥。我们还发现,二次反极性模式,涉及A阳离子,有助于削弱不同的倾斜之间的竞争,并发挥关键作用,在他们的共存。因此,我们的结果证实并更好地解释了以前对特定化合物的观察。有趣的是,我们还发现,应变效应,这是已知的一个主要因素,在相关的阶段竞争(例如,铁电)钙钛矿氧化物,对于不同旋转多晶型物的相对稳定性不起重要作用。此外,我们讨论了为什么Pbnm结构停止的基态在两个相反的限制,大和小的A阳离子,显示非常不同的效果成为相关的在每种情况下。因此,我们的工作提供了一个全面的讨论这些所有重要的和丰富的材料,这将有助于更好地了解现有的化合物,以及确定新的战略材料工程。

英文摘要:

We use first-principles methods to study oxygen-octahedra rotations in ABO3 perovskite oxides. We focus on the short-period, perfectly antiphase or in-phase, tilt patterns that characterize most compounds and control their physical (e.g., conductive, magnetic) properties. Based on an analytical form of the relevant potential energy surface, we discuss the conditions for the stability of polymorphs presenting different tilt patterns, and obtain numerical results for a collection of thirty-five representative materials. Our results reveal the mechanisms responsible for the frequent occurrence of a particular structure that combines antiphase and in-phase rotations, i.e., the orthorhombic Pbnm phase displayed by about half of all perovskite oxides and by many non-oxidic perovskites. The Pbnm phase benefits from the simultaneous occurrence of antiphase and in-phase tilt patterns that compete with each other, but not as strongly as to be mutually exclusive. We also find that secondary antipolar modes, involving the A cations, contribute to weaken the competition between different tilts and play a key role in their coexistence. Our results thus confirm and better explain previous observations for particular compounds. Interestingly, we also find that strain effects, which are known to be a major factor governing phase competition in related (e.g., ferroelectric) perovskite oxides, play no essential role as regards the relative stability of different rotational polymorphs. Further, we discuss why the Pbnm structure stops being the ground state in two opposite limits, for large and small A cations, showing that very different effects become relevant in each case. Our work thus provides a comprehensive discussion on these all-important and abundant materials, which will be useful to better understand existing compounds as well as to identify new strategies for materials engineering.

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