Consequences of pressure-instigated spin crossover in R FeO 3 perovskites; a volume collapse with no symmetry modification

High-pressure X-ray diffraction, Mossbauer, and Raman studies in the antiferromagnetic insulators RFeO3 orthorhombic perovskites (R = Pr, Eu, Lu) disclose an unusual phenomena of a reversible first-order isostructural phase transition around 50 GPa concurring with an abrupt ~ 5% volume decrease. It is shown experimentally that this transformation concurs with, and is driven by, a high-to-low-spin transition taking place in Fe3+; a manifestation of a new kind of isostructural phase transition. These studies suggest that the RFeO3 perovskite is a rather sturdy oxide-structure, maintaining its original structural symmetry beyond 125 GPa.