The coupling between the organic ${\mathrm{CH}}_3\mathrm{N}{{\mathrm{H}}_3}^{+}$ cations and inorganic perovskite $\mathrm{Pb}{{\mathrm{Br}}_3}^{\text{–}}$ framework in a large single crystal of $\left({\mathrm{CH}}_3{\mathrm{NH}}_3\right)\mathrm{Pb}{\mathrm{Br}}_3$ weighing 13 g was studied using neutron diffraction and inelastic neutron scattering. Two lattice incommensurate (ICM) phases were found; one at higher temperatures, marked $\mathrm{IC}{\mathrm{M}}_{\mathrm{HT}}$, appeared between 150 and 134 K. The second one, marked $\mathrm{IC}{\mathrm{M}}_{\mathrm{LT}}$, developed below 143 K and remained at 75 K. The transition from the $\mathrm{IC}{\mathrm{M}}_{\mathrm{LT}}$ to $\mathrm{IC}{\mathrm{M}}_{\mathrm{HT}}$ phase upon warming gave rise to extremely large lattice shrinking, followed by extremely large lattice expansion of the tetragonal basal plane of the $\mathrm{Pb}{\mathrm{Br}}_3$ lattice. There was a progressive decrease in the width of the diffuse peak at the Bragg position from the $\mathrm{Pb}{{\mathrm{Br}}_3}^{\text{–}}$ lattice upon warming, which can be described using a critical exponent to show complete ordering of the atoms into a $\left({\mathrm{CH}}_3{\mathrm{NH}}_3\right)\mathrm{Pb}{\mathrm{Br}}_3$ lattice at 200 K. $\left({\mathrm{CH}}_3{\mathrm{NH}}_3\right)\mathrm{Pb}{\mathrm{Br}}_3$ exhibits six definitive acousticlike phonon branches at 75 K. The six branches reconstruct into two at 200 K, with the frequencies of both the transverse and longitudinal modes greatly enhanced. The asymmetric structure of the ${\mathrm{CH}}_3{\mathrm{NH}}_3$ ions together with the indirect interactions between the ${\mathrm{CH}}_3{\mathrm{NH}}_3$ ions mediated through the Br ions are used to understand the observed behaviors.

中文翻译：

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光电(CH3NH3)PbBr3中的双晶格不可通约性和通过低温热退火增强晶格完美性


有机物之间的耦合 ${\mathrm{CH}}_3\mathrm{N}{{\mathrm{H}}_3}^{+}$ 阳离子和无机钙钛矿 $\mathrm{Pb}{{\mathrm{Br}}_3}^{\text{–}}$ 大型单晶框架 $\left({\mathrm{CH}}_3{\mathrm{NH}}_3\right)\mathrm{Pb}{\mathrm{Br}}_3$ 使用中子衍射和非弹性中子散射对重 13 克的物体进行了研究。发现了两个晶格不通约（ICM）相；一种在较高温度下，标记 $\mathrm{IC}{\mathrm{M}}_{\mathrm{HT}}$ ，出现在 150 到 134 K 之间。第二个，标记为 $\mathrm{IC}{\mathrm{M}}_{\mathrm{LT}}$ ，在 143 K 以下发展并保持在 75 K。 $\mathrm{IC}{\mathrm{M}}_{\mathrm{LT}}$ 到 $\mathrm{IC}{\mathrm{M}}_{\mathrm{HT}}$ 升温时的相引起极大的晶格收缩，随后四方基面发生极大的晶格膨胀。 $\mathrm{Pb}{\mathrm{Br}}_3$ 格子。布拉格位置处的扩散峰宽度从 $\mathrm{Pb}{{\mathrm{Br}}_3}^{\text{–}}$ 升温时的晶格，可以使用临界指数来描述，以显示原子的完整排序 $\left({\mathrm{CH}}_3{\mathrm{NH}}_3\right)\mathrm{Pb}{\mathrm{Br}}_3$ 200 K 时的晶格。 $\left({\mathrm{CH}}_3{\mathrm{NH}}_3\right)\mathrm{Pb}{\mathrm{Br}}_3$ 在 75 K 时表现出六个明确的声学声子分支。在 200 K 时这六个分支重构为两个，横模和纵模的频率都大大增强。的不对称结构 ${\mathrm{CH}}_3{\mathrm{NH}}_3$ 离子以及离子之间的间接相互作用 ${\mathrm{CH}}_3{\mathrm{NH}}_3$ 通过 Br 离子介导的离子用于理解观察到的行为。