The pressure dependence of the average interatomic distances for the first Ga shell in bulk tetrahedral a- GaSb has been studied by Ga K-edge extended x-ray-absorption fine structure. We have found that the microscopic compressibility of the covalent bonds in the disordered network is less than in the crystalline zinc-blende structure. Comparison of the microscopic bond-bulk modulus (${\mathit{B}}_{\mathrm{bond}}$≊105±20 GPa) in a-GaSb with the macroscopic bulk modulus (${\mathit{B}}_{\mathrm{cr}}$=35 GPa) and with the bulk modulus of c-GaSb (${\mathit{B}}_{\mathrm{cr}}$=56 GPa) gives unambiguous evidence for a pressure-induced geometrical or topological distortion in the a-GaSb tetrahedral network. Physical reasons for the observed behavior of volume in the amorphous tetrahedral network under pressure, such as a bond-bending distortion mechanism and a nonlinear averaging for a system with heterogeneous compressibility, are discussed. © 1996 The American Physical Society.

• Received 16 August 1996

DOI:https://doi.org/10.1103/PhysRevB.54.R14242