Deformation and texture development in CaIrO₃ post-perovskite phase up to 6 GPa and 1300 K

At near ambient conditions, CaIrO₃ is isostructural with the high-pressure polymorph MgSiO₃ "post-perovskite" (pPv). MgSiO₃ pPv is thought to be a major phase in the earth's lowermost mantle. CaIrO₃ can thus serve as an analog for studying deformation of the pPv phase under conditions achievable with a multi-anvil deformation apparatus. Here we study the rheologic behavior of CaIrO₃ pPv at a variety of pressure and temperature conditions from 2 GPa to 6 GPa and 300 K to 1300 K and various strain rates. Sintered, polycrystalline CaIrO₃ pPv, cylindrical in shape, was deformed in the D-DIA multi-anvil press in several shortening cycles up to 20% axial strain at each temperature and pressure. Shortening cycles were followed by lengthening back to 0% strain. Quantitative texture information was obtained using in-situ synchrotron X-ray diffraction and the Rietveld method to analyze images. In all cases we find that (010) lattice planes align perpendicular to the compression direction upon shortening, and that there is little change in texture with temperature or pressure. This texture pattern is consistent with slip on (010)[100]. The texture observed here is different from that produced in room temperature diamond anvil cell (DAC) experiments on MgGeO₃ and MgSiO₃ pPv which both display textures of (100) and {110} lattice planes at high angles to the compression direction. This implies that CaIrO₃ pPv may not be a good analog for the plastic behavior of MgSiO₃ pPv.