Zhang Rong, Cai Weizhao, Bi Tiange, Zarifi Niloofar, Terpstra Tyson, Zhang Chuang, Verdeny Z Valy, Zurek Eva, Deemyad Shanti
Department of Physics and Astronomy, University of Utah , 115S 1400E, Salt Lake City, Utah 84112, United States.
Department of Chemistry, State University of New York at Buffalo , Buffalo, New York 14260-3000, United States.
J Phys Chem Lett. 2017 Aug 3;8(15):3457-3465. doi: 10.1021/acs.jpclett.7b01367. Epub 2017 Jul 13.
We report synchrotron X-ray diffraction, photoconductivity, and photoluminescence investigations of methylammonium-lead-bromide (MAPbBr) under various stress conditions, supported by density-functional-theory (DFT) calculations. The properties of MAPbBr show substantial dependence on the hydrostatic conditions. While nonhydrostatic compression of MAPbBr leads to amorphization above 2.4 GPa, under quasi-hydrostatic (Ar) and hydrostatic (He) pressure, the sample remains in crystalline phases. A sequence of phase transitions between two cubic phases and orthorhombic Pnma phase is observed when using Ar, or no pressure-transmitting-medium (PTM). In helium-PTM only transitions between the two cubic structures and a new isostructural phase transition with a large volume collapse to a third cubic-phase at 2.7 GPa was observed. The photoluminescence measurements indicate a pressure-induced band gap-narrowing in the cubic phase I, and a blue-shift in the orthorhombic structure. DFT calculations illustrate that the dynamics of the organic molecules and the inorganic lattice, coupled via the N-H···Br hydrogen-bonding interactions, affect the Pb-Br distance and the bandgap evolution under pressure.
我们报告了在密度泛函理论（DFT）计算的支持下，对甲基溴化铅（MAPbBr）在各种应力条件下进行的同步加速器X射线衍射、光电导率和光致发光研究。MAPbBr的性质显示出对静水条件的显著依赖性。虽然MAPbBr的非静水压缩在2.4 GPa以上会导致非晶化，但在准静水（Ar）和静水（He）压力下，样品仍保持晶相。当使用Ar或不使用压力传递介质（PTM）时，观察到两个立方相和正交Pnma相之间的一系列相变。在氦-PTM中，仅观察到两个立方结构之间的转变以及在2.7 GPa时发生的具有大体积塌缩到第三个立方相的新的同构相变。光致发光测量表明，立方相I中存在压力诱导的带隙变窄，而正交结构中存在蓝移。DFT计算表明，通过N-H···Br氢键相互作用耦合的有机分子和无机晶格的动力学，会影响压力下的Pb-Br距离和带隙演化。
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