Observation of a wurtzite form of gallium arsenide.

After a pressure decrease to ambient, the high-pressure SC16 phase of GaAs is found to transform to the hexagonal wurtzite structure. This has been suggested for GaAs in calculations but never previously observed experimentally. Wurtzite-GaAs is found to be stable at ambient pressures at temperatures up to 473 K, with a structure that is only slightly distorted from ideal. On recompression, the ratio is constant with pressure and wurtzite-GaAs transforms to the orthorhombic phase at 18.7(9) GPa.