The Disorder Origin of Raman Scattering In Perovskites Single Crystals

TL;DR

This paper introduces a model explaining the temperature-dependent Raman spectra in disordered perovskite crystals by linking anharmonic lattice dynamics to spectral features, enhancing understanding of their structural behavior.

Contribution

It presents a novel model for 2nd-order Raman scattering that accounts for temperature trends in disordered perovskites, supported by numerical simulations.

Findings

Reproduces Raman spectral line-shapes and intensity trends with temperature

Identifies a low-frequency anharmonic mode as a transition between minima

Model applicable to other disordered crystal phases

Abstract

The anharmonic lattice dynamics of oxide and halide perovskites play a crucial role in their mechanical and optical properties. Raman spectroscopy is one of the key methods used to study these structural dynamics. However, despite decades of research, existing interpretations cannot explain the temperature dependence of the observed Raman spectra. We demonstrate the non-monotonic evolution with temperature of the scattering intensity and present a model for 2nd-order Raman scattering that accounts for this unique trend. By invoking a low-frequency anharmonic feature, we are able to reproduce the Raman spectral line-shapes and integrated intensity temperature dependence. Numerical simulations support our interpretation of this low-frequency mode as a transition between two minima of a double-well potential surface. The model can be applied to other dynamically disordered crystal phases, providing a better understanding of the structural dynamics, leading to favorable electronic, optical, and mechanical properties in functional materials.