  Results of in situ high pressure x-ray powder diffraction on the mixed
valence compound Cs2Au(I)Au(III)I6 (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.
