Post-perovskite phase transition in CaRuO3

High-pressure phase relations in CaRuO3 were examined at 13–27 GPa and 900–1200 °C using a multi-anvil apparatus. At about 21–25 GPa at 900–1200 °C, CaRuO3 with orthorhombic perovskite structure transformed to CaIrO3-type post-perovskite structure. The phase boundary of the post-perovskite transition in CaRuO3 was determined as P (GPa) = 0.010 × T (°C) + 12.4. The post-perovskite phase of CaRuO3 was quenchable to ambient conditions like that of CaIrO3. Rietveld refinement confirmed that CaRuO3 post-perovskite and perovskite have the structures of CaIrO3-type post-perovskite (space group Cmcm) and GdFeO3-type orthorhombic perovskite (Pbnm), respectively. Lattice parameters and unit cell volume of CaRuO3 post-perovskite were determined to be a = 3.1150(1) Å, b = 9.8268(1) Å, c = 7.2963(1) Å and V = 223.34(1) Å3, and those of CaRuO3 perovskite a = 5.3635(2) Å, b = 5.5261(2) Å, c = 7.6668(2) Å and V = 227.24(1) Å3. The structural features of CaRuO3 post-perovskite and perovskite are similar to those of the polymorphs of CaIrO3 and MgSiO3. The post-perovskite transition in CaRuO3 is consistent with the general tendency that orthorhombic perovskites with relatively large tilting of the octahedral framework transform to post-perovskite structure at high pressure. CaRuO3 would be a low-pressure, quenchable analogue material suitable for investigation on the post-perovskite phase transition of MgSiO3.