Crossover in the pressure evolution of elementary distortions in RFeO3 perovskites and its impact on their phase transition

TL;DR

This study investigates how pressure affects octahedral tilts and bond lengths in RFeO3 perovskites, revealing a crossover in tilt behavior that influences phase transitions but not the insulator-to-metal transition.

Contribution

It uncovers a pressure-induced crossover in octahedral tilt behavior across different RFeO3 compounds and links tilt compressibility to critical pressure, advancing understanding of phase transition mechanisms.

Findings

Crossover in tilt behavior occurs between larger and smaller rare-earth cations.

Tilt changes are minor in the insulator-to-metal phase transition.

Octahedra compressibility correlates with critical pressure.

Abstract

This work reports on the pressure dependence of the octahedra tilts and mean Fe-O bond lengths in RFeO3 (R=Nd, Sm, Eu, Gd, Tb and Dy), determined through synchrotron X-ray diffraction and Raman scattering, and their role on the pressure induced phase transition displayed by all of these compounds. For larger rare-earth cations (Nd-Sm), both anti- and in-phase octahedra tilting decrease as pressure increases, whereas the reverse behavior is observed for smaller ones (Gd-Dy). EuFeO3 stands at the borderline, as the tilts are pressure independent. For the compounds where the tilts increase with pressure, the FeO6 octahedra are compressed at lower rates than for those ones exhibiting opposite pressure tilt dependence. The crossover between the two opposite pressure behaviors is discussed and faced with the rules grounded on the current theoretical approaches. The similarity of the pressure-induced isostructural insulator-to-metal phase transition, observed in the whole series, point out that the tilts play a minor role in its driving mechanisms. A clear relationship between octahedra compressibility and critical pressure is ascertained.