Stability of the sc16 polymorph of GaAs

The occurrence of the high-pressure simple cubic sc16 polymorph in GaAs has been experimentally confirmed, but whether it is a stable polymorph of the octet compound remains controversial. Using a laser-heated diamond anvil cell and x-ray microdiffraction techniques, we document the emergence of sc16-GaAs at 13.6 GPa upon heating the ambient-pressure zincblende phase. The single-crystal structural refinement of a selected micro-grain provides a detailed description of the coordination geometry in sc16-GaAs. The transition from zincblende to sc16 is associated with a change from ideal tetrahedral coordination to distorted tetrahedral coordination and a slight increase in bond lengths but similar tetrahedral volume. The 7.6% volume decrease is accomplished by a more compact arrangement of the tetrahedra, rather than an increase in coordination number, while relaxing the bond length. The results of first-principles calculations complement the structural experimental study and confirm the stability of the sc16 phase. The distortion in the tetrahedral coordination present in the high-pressure sc16 phase with respect to the ideal tetrahedral coordination of the low-pressure zincblende phase is not associated with a change in the bonding character as shown by our ELF analysis.