Organic-inorganic hybrid metal-halide perovskite (OIHP) materials provide a tunable platform for engineering their opto-electronic properties. Although several high pressure studies have been conducted from the OIHP family of single crystals and films, the exact nature of the dynamic coupling of the CH${}_3$NH${}_3$ (MA) cation with the octahedral lattice framework and the mechanisms responsible for the structural phase transformation under pressure are not well captured. By combined photoluminescence (PL), synchrotron-based X-ray diffraction (XRD), and Raman scattering studies as a function of pressure from methylammonium lead bromide (MAPbBr${}_3$), we shed light on an isostructural phase transition due to the coupling of the MA cation and the PbBr${}_6$ lattice through hydrogen bonding. The sharp discontinuities at $\sim$ 1 GPa and $\sim$ 3 GPa in the PL peak positions correlate with the structural changes observed in high pressure XRD and Raman scattering studies. The electronic band-edge as a function of pressure is calculated within density-functional theory. The PL peak position, intensity, and width of the excitonic peak show significant changes at 2 GPa, which corroborate the changes observed in high pressure Raman scattering studies. The frequencies of the lattice modes and the C-H/N-H bending and stretching modes of the MA cation show anomalous changes and other nuances at 2 GPa. The suppression of rotational and orientational disorder of the organic moiety is initiated at 2 GPa and the ordering is completed by 3.0 GPa, leading to an order-disorder type cubic II ($Im\bar{3}$) to orthorhombic ($Pnma$) phase transition. Along with the revelation of an isostructural transformation at 2 GPa, this study highlights the impact of molecular vibrations on the electronic properties of MAPbBr${}_3$ under pressure.

中文翻译：

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甲基铵卤化铅钙钛矿中有机阳离子和无机晶格的耦合：压力诱导的同构相变的见解

有机-无机杂化金属卤化物钙钛矿（OIHP）材料为工程化其光电性能提供了可调平台。尽管已经从OIHP单晶和薄膜家族中进行了一些高压研究，但CH动态耦合的确切性质${}_3$NH${}_3$（MA）具有八面体晶格骨架的阳离子以及负责在压力下进行结构相变的机理均未得到很好的体现。通过结合光致发光（PL），基于同步加速器的X射线衍射（XRD）和拉曼散射研究甲基溴化铅（MAPbBr）的压力${}_3$），由于MA阳离子和PbBr的耦合，我们揭示了同构相变${}_6$通过氢键形成晶格。尖锐的不连续点$〜$ 1 GPa和 $〜$PL峰位置的3 GPa与高压XRD和拉曼散射研究中观察到的结构变化相关。电子带边沿作为压力的函数是在密度泛函理论中计算的。PL峰的位置，强度和激子峰的宽度在2 GPa处显示出显着变化，这证实了在高压拉曼散射研究中观察到的变化。MA阳离子的晶格模态频率和CH / NH弯曲和拉伸模态在2 GPa时显示出异常变化和其他细微差别。在2 GPa时开始抑制有机部分的旋转和取向紊乱，并在3.0 GPa时完成有序化，从而形成有序无序类型的立方II（$\mathrm{一世}米\stackrel{〜}{3}$）至斜方（$Pñ米\mathrm{一种}$）相变。伴随着同构结构在2 GPa时的揭示，这项研究突出了分子振动对MAPbBr电子性质的影响${}_3$ 在压力之下。