High-pressure and high-temperature synthesis of a cubic IrO2 polymorph

We report on in situ observations of a new cubic iridium dioxide (IrO2) polymorph. Experiments were performed using a laser-heated diamond anvil cell, and high-pressure data were collected using the synchrotron X-ray diffraction method. The new high-pressure IrO2 phase has a pyrite-type structure with space group Pa-3 and cubic symmetry. The phase was stable at pressures up to 50 GPa. The pyrite-type IrO2 structure is the same as that exhibited by other AO2 compounds at high pressure, such as SiO2, GeO2, and SnO2. The new high-pressure phase was not preserved on decompression to ambient pressure. The Birch-Murnaghan equation of state for this new cubic phase was determined from the experimental unit cell parameters, with K0=306 (±7) GPa when the value of K0′ was set to K0′=4. The compressibility of the cubic IrO2 phase was in agreement with the compressibilities of other AO2 compounds reported in the literature.