Ruddlesden–Popper strontium titanates with composition Sr_n+1Ti_nO_3n+1, RP-n-STO, n = 1, 2, ..., ∞, are prototypical layered perovskites from which many crystal-chemistry principles can be assessed. In addition, their phase stabilities and lattice thermal expansions are essential factors for their usage in realistic devices. In this work, we use first-principles electronic structure methods to determine the n-layer dependent phase stabilities, including thermodynamic energies and pressure–critical temperature (P–T_c) phase diagrams and coefficients of thermal expansion. We correlate these properties with the perovskite (SrTiO₃)_n·SrO block thickness, n, to show that a change in materials behavior occurs at a critical thickness n_c = 3, which we ascribe to the presence (absence) of octahedral layers exhibiting antiferrodistortions at n ≥ 3 (n < 3). Last, we attribute the absence of quasi-two-dimensional lattice anharmonicity in the layered RP titanates to the stiff (SrTiO₃)_n intrablock Ti–O bonds and strong interblock bonding. The layer dependent properties studied here will be useful for the design and application of related quasi-2D materials and devices.

中文翻译：

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Ruddlesden-Pop锶钛酸盐的结构依赖性相稳定性和热膨胀

具有组成Sr _{n +1} Ti _n O _{3 n +1}，RP- n -STO，n = 1、2，...，∞的Ruddlesden-Popper钛酸锶是典型的层状钙钛矿，可以从中获得许多晶体化学原理。评估。另外，它们的相稳定性和晶格热膨胀是在实际设备中使用它们的必要因素。在这项工作中，我们使用第一性原理电子结构方法来确定n层相关的相稳定性，包括热力学能量和压力-临界温度（P – T _c）相图和热膨胀系数。我们将这些性质与钙钛矿（SrTiO ₃）_n ·SrO嵌段厚度n相关联，以表明材料行为的变化在临界厚度n _c = 3处发生，这归因于存在（不存在）八面体层antiferrodistortions在ñ ≥3（ñ <3）。最后，我们将层状RP钛酸盐中缺少准二维晶格失谐归因于刚性（SrTiO ₃）_n嵌段内Ti-O键和牢固的嵌段间键合。此处研究的层相关属性将对相关的准2D材料和设备的设计和应用很有用。