Microscopic pathways of structural phase transitions in metal halide perovskites are difficult to probe because they occur over disparate time and length scales and because electron-based microscopies typically used to directly probe nanoscale dynamics of phase transitions often damage metal halide perovskite materials. Using in situ nanoscale cathodoluminescence microscopy with low electron beam exposure, we visualize nucleation and growth in the thermally driven transition to the perovskite phase in hundreds of non-perovskite phase nanowires. In combination with molecular dynamics simulations, we reveal that the transformation does not follow a simple martensitic mechanism, but proceeds despite a substantial energy barrier via ion diffusion through a liquid-like interface between the two structures. While cations are disordered in this liquid-like region, the halide ions retain substantial spatial correlations. This detailed picture not only reveals how phase transitions between disparate structures can proceed, but also opens the possibility to control such processes.

金属卤化物钙钛矿中结构相变的微观路径很难探测，因为它们发生在不同的时间和长度范围内，并且因为通常用于直接探测相变纳米级动力学的基于电子的显微镜检查通常会破坏金属卤化物钙钛矿材料。原位使用纳米级阴极发光显微镜在低电子束曝光下，我们可以观察到成百上千的非钙钛矿相纳米线在热驱动过渡到钙钛矿相中的成核和生长。与分子动力学模拟相结合，我们揭示了这种转变并不遵循简单的马氏体机制，而是尽管通过离子扩散通过两个结构之间的液体状界面而产生了很大的能垒，但仍进行了转变。尽管阳离子在该液体状区域中是无序的，但卤化物离子仍保留了重要的空间相关性。这张详细的图片不仅揭示了不同结构之间的相变如何进行，而且还为控制此类过程提供了可能。