A structural study of PrCrO under extreme conditions: a comparison with the effects of doping.

The nuclear and magnetic structure of [Formula: see text] has been investigated using neutron and X-ray powder diffraction as a function of pressure and temperature. The orthorhombic symmetry (space group [Formula: see text]) remains stable up to the highest temperature (1500 K) and pressure (approx. [Formula: see text]) considered. There is a crossover in the magnitude of the and -lattice parameters at approximately 1135 K, caused by competing effects of octahedral tilting and distortion. The material is antiferromagnetic ([Formula: see text] K) with [Formula: see text] symmetry, with a maximum moment of [Formula: see text] on the [Formula: see text] sites aligned along the direction of the [Formula: see text]-axis. The application of pressure shows an abnormal softening in the unit-cell volume, which is suggestive of a continuous approach to a second-order phase transition. Raman spectroscopy measurements at ambient temperature were collected as a function of pressure up to approximately [Formula: see text] GPa, with discontinuous mode behaviour further suggesting the existence of a transition above 7 GPa. The measured structural changes in [Formula: see text] are compared extensively in the wider context of other lanthanide orthochromites, and the comparative effects of - and -site substitution on the polyhedral tilts and distortion are discussed. This article is part of the theme issue 'Exploring the length scales, timescales and chemistry of challenging materials (Part 1)'.