Yangui Aymen, Sy Mouhamadou, Li Liang, Abid Younes, Naumov Panče, Boukheddaden Kamel
Groupe d'Etudes de la Matière Condensée, Université de Versailles, CNRS UMR 8635, 45 Avenue des Etats Unis, 78035 Versailles, France.
Laboratoire de Physique Appliquée, Faculté des Sciences de Sfax, Route de Soukra km 3.5 3000 Sfax, Tunisia.
Sci Rep. 2015 Nov 16;5:16634. doi: 10.1038/srep16634.
The dynamics of the thermally induced first-order structural phase transition in a high-quality single crystal of the organic-inorganic perovskite (C12H25NH3)2PbI4 was investigated by optical microscopy. The propagation of the straight phase front (habit plane) during the phase transition along the cooling and heating pathways of the thermal hysteresis was observed. The thermochromic character of the transition allowed monitoring of the thermal dependence of average optical density and aided the visualization of the interface propagation. The thermal hysteresis loop is 10 K wide, and the interface velocity is constant at V ≈ 1.6 mm s(-1). The transition is accompanied with sizeable change in crystal size, with elongation of ~6% along the b axis and compression of ~ -2% along the a axis, in excellent agreement with previously reported X-ray diffraction data. The progression of the habit plane is at least 160 times faster than in spin-crossover materials, and opens new prospects for organic-inorganic perovskites as solid switching materials. Moreover, the crystals of (C12H25NH3)2PbI4 are unusually mechanically robust and present excellent resilience to thermal cycling. These hitherto unrecognized properties turn this and possibly similar hybrid perovskites into perspective candidates as active medium for microscopic actuation.
通过光学显微镜研究了高质量有机-无机钙钛矿（C12H25NH3）2PbI4单晶中热诱导的一级结构相变动力学。观察到在相变过程中，沿着热滞回线的冷却和加热路径，直相前沿（惯习面）的传播情况。转变的热致变色特性使得能够监测平均光密度的热依赖性，并有助于直观显示界面的传播。热滞回线宽10 K，界面速度恒定，约为V ≈ 1.6 mm s-1。该转变伴随着晶体尺寸的显著变化，沿b轴伸长约6%，沿a轴压缩约-2%，这与先前报道的X射线衍射数据高度吻合。惯习面的推进速度至少比自旋交叉材料快160倍，为有机-无机钙钛矿作为固体开关材料开辟了新前景。此外，（C12H25NH3）2PbI4晶体具有异常高的机械强度，并且对热循环具有出色的恢复能力。这些迄今未被认识到的特性使这种以及可能类似的混合钙钛矿成为微观驱动活性介质的潜在候选材料。
