# Liquid-Like Interfaces Mediate Structural Phase Transitions in Lead Halide Perovskites

## TL;DR

This study visualizes and analyzes the nanoscale pathways of phase transitions in lead halide perovskites, revealing a liquid-like interface mechanism that influences nucleation and growth, with implications for material design.

## Contribution

It uncovers a liquid-like interface mechanism mediating phase transitions in lead halide perovskites, combining nanoscale imaging and simulations to advance understanding of nanoscale phase control.

## Key findings

- Phase transition involves ion diffusion through a liquid-like interface.
- Nucleation occurs faster at nanowire ends due to anisotropic structure.
- Transformation does not follow a simple martensitic mechanism.

## Abstract

Microscopic pathways of structural phase transitions are difficult to probe because they occur over multiple, disparate time and length scales. Using $in$ $situ$ nanoscale cathodoluminescence microscopy, we visualize the thermally-driven transition to the perovskite phase in hundreds of non-perovskite phase nanowires, resolving the initial nanoscale nucleation and subsequent mesoscale growth and quantifying the activation energy for phase propagation. In combination with molecular dynamics computer simulations, we reveal that the transformation does not follow a simple martensitic mechanism, and proceeds 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. We find that the anisotropic crystal structure translates to faster nucleation of the perovskite phase at nanowire ends and faster growth along the long nanowire axis. These results represent a significant step towards manipulating structural phases at the nanoscale for designer materials properties.