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

The pressure- and photo-induced phase transition in mixed-valence gold comp lexes 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 t he mixed-valence (MV) state to the single-valence (SV) state. The electroni c 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 behav ior accompanying this phase transition is successfully interpreted by the A vrami model, indicating the three-dimensional character of the MV cluster g rowth.