Reversible Medium-Dependent Solid–Solid Phase Transformations in Two-Dimensional Hybrid Perovskites

The thermodynamically favored phases in a family of two-dimensional (2D) hybrid perovskites, (C 6 H 13 NH 3 ) 2 MCl 4 (M = Cu 2+, Mn 2+, Cd 2+ ), can be reversibly switched by changing the medium in which particles are immersed. Differential scanning calorimetry and X-ray diffraction show that the temperature of a known solid–solid phase transition in the series of layered perovskites shifts to lower temperature when exposing the particles to organic solvents. For the Cu 2+ and Cd 2+ members of the series, the shift in transition temperature changes the thermodynamically favored phase at room temperature. Interactions between the solvent and the particle surface alter the surface stress, thereby reducing the effective pressure, leading to a change in transition temperature. The mechanism likely explains some anomalous behavior in related 2D perovskites and could factor into potential applications of hybrid perovskite-based materials.