First principles prediction of new high-pressure phase of InOOH

We have predicted a new high-pressure phase of InOOH by first principles density functional calculations, which stabilizes at similar to 15 GPa under the static 0 K condition. The structure obtained at 15 GPa has a pyrite-type InO2 framework with the interstitial asymmetric hydrogen bonds, which is assigned to the space group P2(1)3 (No. 198). The cell parameters and internal atomic coordinates optimized at 15 GPa are a = 5.265 angstrom, In-x = 0.005, O1(x) = 0.367, O2(x) = 0.633, and H-x = 0.487. Relative enthalpies also indicate that the dehydration of this phase into In2O3 + H2O is unlikely to occur at least up to 50 GPa under the static condition. To our knowledge, this is the first report on the high-pressure isochemical phase transition of oxyhydroxide compounds to the pyrite-type structure. The new phase of InOOH has been identified in an experiment, as reported in detail in a separate paper. We have also found that the low-pressure-type asymmetric hydrogen bond in the new pyrite-type phase changes to the symmetric hydrogen bond over 30 GPa. The present results suggest that a similar phase relation is expected in other group IIIB oxyhydroxides such as AIOOH and GaOOH.