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, (C6H13NH3)2MCl4 (M = Cu2+, Mn2+, Cd2+), 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
Cu2+ and Cd2+ 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.