Pressure-induced symmetry breaking in tetragonal CsAuI3
  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. 
Shibing Wang, Shigeto Hirai, Maxwell C. Shapiro, Scott C. Riggs,   Theodore H. Geballe, Wendy L. Mao and Ian R. Fisher
cond-mat.str-el cond-mat.mtrl-sci