3D-to-2D Transition of Anion Mobility in CsPbBr$_{3}$ under Pressure

TL;DR

This study investigates how hydrostatic pressure affects anion mobility in CsPbBr₃ perovskite, revealing highly anisotropic changes in mobility tensor that could influence material performance.

Contribution

It provides the first detailed computational analysis of pressure-dependent anion migration pathways and anisotropic mobility in CsPbBr₃ perovskite.

Findings

Anion mobility increases in the (010) plane with pressure.

Mobility decreases in the direction normal to the (010) plane.

Pressure induces significant anisotropic effects on anion migration.

Abstract

We study the effects of hydrostatic pressure in the range 0.0--2.0 GPa on anion mobility in the orthorhombic $Pnma$ phase of CsPbBr$_{3}$. Using density functional theory and the climbing nudged elastic band method, we calculate the transition states and activation energies for anions to migrate both within and between neighbouring PbBr$_{3}$ octahedra. The results of those calculations are used as input to a kinetic model for anion migration, which we solve in the steady state to determine the anion mobility tensor as a function of applied pressure. We find that the response of the mobility tensor to increasing pressure is highly anisotropic, being strongly enhanced in the $(010)$ lattice plane and strongly reduced in the direction normal to it at elevated pressure. These results demonstrate the potentially significant influence of pressure and strain on the magnitude and direction of anion migration in lead--halide perovskites.