# Lattice dynamics and Raman spectrum of BaZrO3 single crystals

## TL;DR

This study investigates the unexpected Raman spectrum of BaZrO3 single crystals across a wide temperature range, combining experimental data with first-principle calculations to explain the spectral features without evidence of nanoscale domains.

## Contribution

It provides a detailed analysis of BaZrO3's Raman spectrum, demonstrating that second-order scattering explains the features and offering phonon mode assignments based on lattice dynamics calculations.

## Key findings

- Raman spectrum shows no evidence of nanoscale domains.
- Spectral features are explained by classical second-order Raman scattering.
- High-frequency spectrum reflects phonon density of states of oxygen octahedra modes.

## Abstract

BaZrO3 is a perovskite that remains in the simple cubic phase at all temperatures, hence with no first-order Raman-active phonon mode allowed by symmetry. Yet, it exhibits an intense Raman spectrum with sharp and well-defined features. Here, we report the evolution of the Raman spectrum of BaZrO3 single crystals in a broad temperature range (4--1200~K) and discuss its origin with the support of detailed first-principle calculations of the lattice dynamics. Phonon calculations are performed not only for the cubic phase of BaZrO3, but also for the low-symmetry phases with octahedra tilts that have been suspected to exist at the nanoscale. We show that the Raman spectrum shows no direct evidence for these nanodomains, but can instead be explained by classical second-order Raman scattering. We provide an assignment of the dominant features to phonon modes combinations. In particular, we show that the high frequency range of the spectrum is dominated by overtones and shows an image of the phonon density of states corresponding to the stretching modes of the oxygen octahedra.