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.
B. Lavina, E. Zanardi, A. Mujica, H. Cynn, S. Tkachev, Journal of Physics and Chemistry of Solids, 2021, Journal of Physics and Chemistry of Solids, DOI : 10.1016/j.jpcs.2021.110233. abstract
