A structural study of PrCrO 3 under extreme conditions: A comparison with the effects of doping

The nuclear and magnetic structure of PrCrO3 has been investigated using neutron and X-ray powder diffraction as a function of pressure and temperature. The orthorhombic symmetry (space group Pbnm) remains stable up to the highest temperature (1500 K) and pressure (approx. 6 GPa) considered. There is a crossover in the magnitude of the a- and b-lattice parameters at approximately 1135 K, caused by competing effects of octahedral tilting and distortion. The material is antiferromagnetic (TN≈240 K) with Pb′n′m symmetry, with a maximum moment of 2.34(2)μb on the Cr3+ sites aligned along the direction of the a-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 12 GPa, with discontinuous mode behaviour further suggesting the existence of a transition above 7 GPa. The measured structural changes in PrCrO3 are compared extensively in the wider context of other lanthanide orthochromites, and the comparative effects of A- and B-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)'.