Structure of liquid GaSb at pressures up to 20 GPa

We have investigated the structure of liquid GaSb up to 20 GPa by a high-pressure and high-temperature x-ray-diffraction technique. With increasing pressure, the hump at high-Q side of the first peak in the structure factor, $S(Q),$ reflecting an anisotropic local structure becomes smaller and the ratio of the wave number of the second peak to that of the first one, Q₂/Q₁, decreases. Simultaneously, the coordination number CN increases in correspondence to the elongation of the nearest-neighbor distance compared to that expected from a uniform contraction model. These findings suggest that the liquid GaSb contracts nonuniformly and the local structure changes with pressure. Analysis of the pair distribution function $g(r)$ by a distorted-crystalline model shows that the liquid consists of two parts similar to the β-Sn and body-centered cubic (bcc) structures which are realized in the high-pressure crystalline phases, rather than the zinc-blende structure in an ambient phase. The fraction of the bcc-like local structure increases continuously from 0.08±0.05 to 0.43±0.05 as the pressure is raised from 1.7 GPa to 20 GPa. The pressure dependence can be explained quantitatively by Rapoport's two-species model [J. Chem. Phys. 46, 2891 (1967)]. The observed elongation of the nearest-neighbor distance and the increase of CN would be attributed to the continuous change of the local structure from the β-Sn-like one into the bcc-like one under pressure.