Crystal structure of CaRhO3 polymorph: High-pressure intermediate phase between perovskite and post-perovskite

A high-pressure phase of CaRhO3 stable between perovskite and post-perovskite in P-T space was synthesized at 17 GPa and 1650 °C using a multi-anvil apparatus. The crystal structure of CaRhO3 was solved by the structure prediction evolutionary algorithm and was refined by Rietveld analysis of the synchrotron powder X-ray diffraction pattern, along with transmission electron microscopy observations. The structure is monoclinic with lattice parameters of a = 12.5114(1) Å, b = 3.1241(1) Å, c = 8.8579(1) Å, β = 103.951(1)°, V = 336.01(1) Å3 with space group P21/m. The structure contains edge-sharing RhO6 octahedral chains along the b-axis. The six RhO6 octahedral chains make a unit, which stacks up alternatively with the CaO8 polyhedral layer along the [101] direction to form the structure of CaRhO3 intermediate phase.