Structural evolution in liquid GaIn eutectic alloy under high temperature and pressure

Abstract

The structural evolution of a liquid GaIn eutectic alloy under high temperature and high pressure is investigated by combining in situ X-ray diffraction (XRD) and ab initio molecular dynamics simulations. Both experimental and theoretical results confirm that no pressure-induced sudden structural changes are detected in the liquid state along different isotherms below 700 K. The XRD patterns indicate that the liquids at 400 and 673 K both crystallize into a tetragonal crystalline phase under high pressure, whose structure is locally face centered cubic (fcc)-like. The theoretical simulations successfully describe the atomic-scale structural evolution from disordered liquid to ordered solid phases during the isothermal compression at different temperatures, revealing a strong competition between the body-centered cubic (bcc)-like and fcc-like local atomic packings at the early stage of nucleation. The liquid can directly solidify into the bcc-like atomic packing at temperatures above 650 K, whereas this bcc-like structure becomes transient and metastable below 600 K and finally transforms into a stable fcc-like atomic packing with increasing pressure. Furthermore, a high-pressure and high-temperature "phase diagram" of the GaIn eutectic alloy is roughly constructed, providing new insight into atomic-scale disorder-to-order transition of the liquid GaIn eutectic alloy in extreme conditions.