Semiconductor-to-metal and metal-to-metal transitions in the three-dimensional mixed-valence compound Cs2Au2I6 under high pressures

Electrical resistivity of three-dimensional Au mixed-valence compound Cs2Au2I6 was investigated under hydrostatic pressures up to 7.0 GPa and temperatures between room temperature and 480 K, where a semiconductor-to-metal transition (P=4.5 GPa, T=room temperature) and a metal-to-metal transition (P=6.5 GPa, T≈330 K) were observed. The metallic phase appeared at P=6.5 GPa and T⪆ 330 K could be obtained at room temperature and ambient pressure as a metastable phase, whose structure was found to be a cubic perovskite structure from the X-ray diffraction pattern. In connection with these results, the Au valence state of Cs2Au2I6 under high pressures was discussed.