Liquid gallium in confined droplets under high-temperature and high-pressure conditions

Phase transitions and the local structure of micrometric droplets of liquid gallium under pressure were studied by combining extended x-ray absorption fine structure, single-energy x-ray absorption detection (SEXAD), and energy-scanning x-ray diffraction (ESXD). Measurements were performed in a range of pressures and temperatures of 0-6.7 GPa and 298-440 K, respectively. The samples for the high-pressure measurements were obtained by using an emulsion of gallium into epoxy resin, a procedure previously developed by the authors. The distribution of droplets was fully characterized by scanning electron microscopy. We found that the liquid can be kept in a metastable state well beyond the liquid-solid coexistence line (1.9 GPa at 300 K). Considering both the ESXD patterns and the SEXAD scans, we infer that the quantity of crystallized gallium droplets increases as a function of pressure, while no sign of crystallization is observed up to 2.7 GPa. The structural and crystallization properties of Ga emulsions, including the determination of the short-range radial distribution function, were measured by XAS in an extended range of pressures and temperatures, putting to a test the possible existence of different Ga-liquid polymorphs.