OBSERVATION OF A CINNABAR PHASE IN GAAS AT HIGH-PRESSURE

A previously unidentified high-pressure phase of GaAs has been found o n pressure decrease from GaAs-II. The new phase is hexagonal, with a f ourfold coordinated cinnabar structure very similar to that of ZnTe-II . The phase first appears on download from GaAs-II at 11.9(1) GPa, coe xists with GaAs-I below 11.2(3) GPa, and starts to transform to GaAs-I at 8.1(2) GPa. Although no evidence of the phase is seen on pressure increase, detailed comparisons with ZnTe suggest cinnabar GaAs is an e quilibrium phase.