Phase diagram of GaAs

Optical measurements in the diamond anvil cell (DAC) as well as thermodynamics, show cubic GaAs I to be unstable at 300 K, at 13 GPa. The thermodynamic phase line from GaAs I to the high pressure (H.P.) form(s) is at 11 ± 2 GPa. Large hyteresis makes the actual I→II transition observable only at 17.5 ± 1 GPa.