A Complete Solid Solution with Rutile‐Type Structure in SiO 2 –GeO 2 System at 12 GPa and 1600°C

High pressure and temperature synthesis of compositions made of (Si 1− x ,Ge x )O 2 where x is equal to 0, 0.1, 0.2, 0.5, 0.7, and 1 was performed at 7–12 GPa and 1200–1600°C using a Kawai‐type high‐pressure apparatus. At 12 GPa and 1600°C, all the run products were composed of a single phase with a rutile structure. The lattice constants increase linearly with the germanium content ( x ), which indicates that the rutile‐type phases in the SiO 2 –GeO 2 system form a complete series of solid solutions at these pressure and temperature conditions. Our experimental results show that thermodynamic equilibrium state was achieved in this system at 12 GPa and 1600°C, but not at 1200°C. At lower pressures (7 and 9 GPa) and 1600°C, we observed the decomposition of (Si 0.5 ,Ge 0.5 )O 2 into SiO 2 ‐rich coesite and GeO 2 ‐rich rutile phases. The silicon content in the rutile structure increases sharply with pressure in the vicinity of the coesite–stishovite phase transition pressure in SiO 2 .