Raman scattering investigation of the pressure induced structural phase transition in LaCrO3

TL;DR

This study uses Raman scattering to explore how pressure affects structural phase transitions in LaCrO3 and related RCrO3 compounds, revealing a crossover in tilt behavior linked to R-ion size and bond distortions.

Contribution

It uncovers the pressure-induced crossover in octahedral tilt distortions in RCrO3 compounds and relates it to R-ion size and polyhedral distortions, providing new insights into structural transitions.

Findings

Tilt distortions are suppressed in LaCrO3 under pressure.

A crossover in tilt behavior occurs at R-ion radius of 1.20 Å.

Polyhedral distortions influence pressure-dependent structural evolution.

Abstract

We report the pressure dependence of perovskite distortions in rare-earth (R) orthochromites (RCrO3) probed using Raman scattering in order to investigate the origin of structural transition from orthorhombic Pnma to rhombohedral R-3C phase in LaCrO3. The pressure induced changes in octahedral tilt modes demonstrates that tilt distortions are suppressed in LaCrO3 and are enhanced in the remaining members of RCrO3 family. This crossover between the two opposite pressure behaviors occurs at a critical R-ion radius of 1.20 {\AA}. We attempted to establish the relation between this unusual crossover and compressibility at Cr- and R-sites by probing Raman phonon modes sensitive to the mean bond strength of Cr-O and R-O respectively. Finally, we study the bond-length splitting of both CrO6 and RO12 polyhedra to ascertain the role of polyhedral self distortion in determining the pressure dependent evolution of perovskite distortions.