High-pressure synthesis and physical properties of perovskite and post-perovskite Ca1−xSrxIrO3

Abstract

The post-perovskite (pPv) is the high-pressure phase of some highly distorted perovskites. The pPv phase of MgSi${O}_{3}$ stabilized under 125 GPa and 2000 K cannot be quenched to ambient pressure. In contrast, the pPv CaIr${O}_{3}$ can be synthesized under a modest pressure or even at ambient pressure. However, the pPv CaIr${O}_{3}$ 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${}_{1\ensuremath{-}x}$Sr${}_{x}$Ir${O}_{3}$ synthesized under high pressure. The Ca${}_{1\ensuremath{-}x}$Sr${}_{x}$Ir${O}_{3}$ samples exhibit an evolution from the pPv phase to the perovskite phase. We have also prepared the perovskite (Pv phase) CaIr${O}_{3}$ with the wet chemical method. Rietveld refinements of the pPv and Pv phase CaIr${O}_{3}$ 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 CaIr${O}_{3}$ 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 5$d$ oxides with the pPv structure.