Pressure-induced symmetry breaking in tetragonal CsAuI 3

Results of in situ high-pressure x-ray powder diffraction on the mixed-valence compound (Cs2AuAuI6)-Au-I-I-III (CsAuI3) are reported for pressures up to 21 GPa in a diamond-anvil cell under hydrostatic conditions. We find a reversible pressure-induced tetragonal-to-orthorhombic structural transition at 5.5-6 GPa and reversible amorphization at 12-14 GPa. Two alternative structures are proposed for the high-pressure orthorhombic phase and are discussed in the context of a possible Au valence transition. DOI: 10.1103/PhysRevB.87.054104