High-pressure synthesis and physical properties of perovskite and post-perovskite Ca_1-xSr_xIrO₃

The post-perovskite (pPv) is the high-pressure phase of some highly distorted perovskites. The pPv phase of MgSiO₃ stabilized under 125 GPa and 2000 K cannot be quenched to ambient pressure. In contrast, the pPv CaIrO₃ can be synthesized under a modest pressure or even at ambient pressure. However, the pPv CaIrO₃ has not been fully characterized. We report here systematic structural studies, measurements of transport and magnetic properties including critical phenomena, specific heat, and thermal conductivity in a series of samples Ca_1-xSr_xIrO ₃ synthesized under high pressure. The Ca_1-xSr _xIrO₃ samples exhibit an evolution from the pPv phase to the perovskite phase. We have also prepared the perovskite (Pv phase) CaIrO ₃ with the wet chemical method. Rietveld refinements of the pPv and Pv phase CaIrO₃ have been made based on high-resolution synchrotron diffraction. In comparison with effects of the chemical substitution on the crystal structure and physical properties, we have studied the structure and magnetic properties of the pPv CaIrO₃ under hydrostatic pressure. Results have been discussed in the context of orbital ordering biased on the intrinsic structural distortion and the strong spin-orbit coupling that is much enhanced in these 5d oxides with the pPv structure.