The driving forces for the phase transitions of ABX₃ hybrid organic–inorganic perovskites have been limited to the octahedral tilting, order–disorder, and displacement. Now, a complex structural phase transition has been explored in a HOIP, [CH₃NH₃][Mn(N₃)₃], based on structural characterizations and ab initio lattice dynamics calculations. This unusual first‐order phase transition between two ordered phases at about 265 K is primarily driven by changes in the collective atomic vibrations of the whole lattice, along with concurrent molecular displacements and an unusual octahedral tilting. A significant entropy difference (4.35 J K⁻¹ mol⁻¹) is observed between the low‐ and high‐temperature structures induced by such atomic vibrations, which plays a main role in driving the transition. This finding offers an alternative pathway for designing new ferroic phase transitions and related physical properties in HOIPs and other hybrid crystals.

中文翻译：

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有机-无机杂化钙钛矿中振动熵变化驱动的异常相变

ABX ₃杂化钙钛矿有机-无机杂化钙钛矿的相变驱动力仅限于八面体倾斜，有序无序和位移。现在，基于结构表征和从头算晶格动力学计算，已经在HOIP [CH ₃ NH ₃ ] [Mn（N ₃）₃ ]中探索了复杂的结构相变。大约265 K时，两个有序相之间的这种异常的一阶相变主要是由整个晶格的集体原子振动的变化，同时发生的分子位移和异常的八面体倾斜引起的。显着的熵差（4.35 J K ^-1  mol ^-1在这种原子振动引起的低温和高温结构之间观察到），这在驱动过渡中起主要作用。这一发现为在HOIP和其他杂化晶体中设计新的铁性相变和相关的物理性质提供了另一种途径。