Pressure- and photo-induced phase transition in mixed-valence gold complexes

The pressure- and photo-induced phase transition in mixed-valence gold complexes of Cs2Au2X6 (X = Cl, Br, and I) has been investigated by means of the Raman scattering. The Raman-active Au-X stretching modes were deactivated by the pressure, which indicates a pressure-induced phase transition from the mixed-valence (MV) state to the single-valence (SV) state. The electronic phase diagrams Of Cs2Au2X6 (X = Cl and Br) as a function of pressure and temperature have been derived. A photoinduced phase transition from the MV state to the SV state has been found for Cs2Au2Br6. The observed time behavior accompanying this phase transition is successfully interpreted by the Avrami model, indicating the three-dimensional character of the MV cluster growth.