Structural ordering in liquid gallium under extreme conditions

The atomic-scale structure, melting curve, and equation of state of liquid gallium has been measured to high-pressure (p) and -temperature (T) up to 26GPa and 900K by in situ synchrotron x-ray diffraction. Ab initio molecular dynamics simulations up to 33.4GPa and 1000K are in excellent agreement with the experimental measurements, providing detailed insight at the level of pair distribution functions. The results reveal an absence of dimeric bonding in the liquid-state and a continuous increase in average coordination number nGaGa from 10.4(2) at 0.1 GPa approaching ~12 by 25 GPa. Topological cluster analysis of the simulation trajectories finds increasing fractions of five-fold symmetric and crystalline motifs at high-p-T. Although the liquid progressively resembles a hard-sphere structure towards the melting curve, the deviation from this simple description remains large (> 40 %) across all p-T-space, with specific motifs of different geometries strongly correlating with low local two-body excess entropy at high-p-T.