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

Abstract

The nuclear and magnetic structure of PrCrO 3 has been investigated using neutron and X-ray powder diffraction as a function of pressure and temperature. The orthorhombic symmetry (space group P b n m ) 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 ( T N ≈ 240  K) with P b ′ n ′ m symmetry, with a maximum moment of 2.34 ( 2 ) μ b on the Cr 3 + 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 PrCrO 3 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)’.