Unraveling the Hidden Martensitic Phase Transition in BaClF and PbClF under High Pressure Using an Ab Initio Evolutionary Approach.
Unraveling the Hidden Martensitic Phase Transition in BaClF and PbClF under High Pressure Using an Ab Initio Evolutionary Approach.
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DOI：
10.1021/acs.inorgchem.9b00243
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发表时间：
2019-04
影响因子：
4.6
通讯作者：
N. Yedukondalu;M. Davari Esfahani
中科院分区：
文献类型：
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作者：
N. Yedukondalu;M. Davari Esfahani
我们通过在常压和高压下进行从头算进化模拟来预测 MClF（M = Ba 和 Pb）化合物的晶体结构。我们提出了 MClF 化合物的结构转变顺序如下：P4/ nmm → Pmcn → P63/ mmc 低于 100 GPa。预测的环境相和中间相与 X 射线和拉曼光谱测量一致，而新提出的高压 P63/ mmc 相在热力学上比之前提出的单斜 (P21/ m) 相更有利。研究发现，P4/ nmm → Pmcn 转变本质上是一级相变，而 Pmcn → P63/ mmc 转变是马氏体相变，伴随着轻微的体积变化，具有位移性质。奥氏体和马氏体相在很宽的压力范围内共存，特别是对于 PbClF。马氏体相变主要由以下驱动：(1) MCl6 扭曲七面体向五面体环境的倾斜和转变，导致负面积压缩性；(2) F-离子的协同位移运动，在金属阳离子周围形成三角锥体 (MF5) 结构。总体而言，高压下金属阳离子配位从 9 (MF4Cl5- P4/ nmm) 增加到 10 (MF4Cl6- Pmcn)，并进一步增加到 11 (MF5Cl6- P63/ mmc)。预测的环境压力和高压阶段在研究的压力范围内机械和动态稳定。使用 Tran Blaha 修正 Becke Johnson 势的新参数化计算和讨论电子结构、键合和光学特性。我们发现几乎各向同性的光学特性（除了 PbClF 的环境相），尽管所有预测的环境和高压相在结构上都是各向异性的。
We predict crystal structures of MClF (M = Ba and Pb) compounds by performing an ab initio evolutionary simulation at ambient as well as high pressure. We propose a structural transition sequence in MClF compounds as follows: P4/ nmm → Pmcn → P63/ mmc below 100 GPa. The predicted ambient and intermediate phases are consistent with X-ray and Raman spectroscopic measurements, while the newly proposed high pressure P63/ mmc phase is thermodynamically more favorable than the previously proposed monoclinic ( P21/ m) phase. It is found that the P4/ nmm → Pmcn transition is first order in nature, while the Pmcn → P63/ mmc transition is a martensitic phase transition, which is accompanied by a slight volume change and is of a displacive nature. The austenite and martensite phases coexist in a wide pressure range, especially for PbClF. The martensite phase transition is mainly driven by (1) tilting and transformation of distorted heptahedron to pentahedron environment of MCl6, which leads to negative area compressibility, and (2) cooperative displacive movement of F- ions to form a trigonal bypyramidal (MF5) structure around a metal cation. Overall, the metal cation coordination increases from 9 (MF4Cl5- P4/ nmm) to 10 (MF4Cl6- Pmcn) and, further, to 11 (MF5Cl6- P63/ mmc) under high pressure. The predicted ambient and high pressure phases are mechanically and dynamically stable under the studied pressure range. Electronic structure, bonding, and optical properties are calculated and discussed using new parametrization of Tran Blaha modified Becke Johnson potential. We find nearly isotropic optical properties (except for the ambient phase of PbClF), even though all the predicted ambient and high pressure phases are structurally anisotropic.