Pressure-induced phase transition in mixed-valence gold complexes Cs2Au2X6 (X=Cl and Br)

Effects of hydrostatic pressure on Raman spectra have been investigated in mixed-valence (MV) gold complexes Cs2Au2X6 (X=Cl and Br). We have observed pressure-induced deactivation of the Raman-active Au-X stretching modes at various temperatures, indicating a pressure-induced phase transition from the MV state to a single-valence (SV) state. The critical pressure at 300 K decreases from 10.6 GPa for X=Cl to 6.8 GPa for X=Br, perhaps due to reduced electron–phonon interaction in Cs2Au2Br6. We further derived comprehensive electronic phase diagrams of Cs2Au2X6 (X=Cl and Br) as a function of pressure and temperature.