Determination of indium melting curve at high pressure by picosecond acoustics

Picosecond acoustics combined with a diamond anvil cell is used to study liquid indium and to determine with high accuracy both the sound velocity and the melting curve over an extended pressure and temperature range. The sound velocities, determined by phonon surface imaging, complement previous inelastic x-ray scattering determinations and are in good agreement with estimations according to a thermodynamic model. Based on exact thermodynamic relations, the equation of state of the liquid phase is obtained using the isothermal bulk modulus B-T,B- 0 and its first pressure derivative B'(T). These quantities are derived from the precise experimental determination of the variation of the sound velocity as a function of pressure. Melting is determined via the detection of abrupt changes in the elastic properties between solid and liquid phases and through the monitoring of the solid-liquid coexistence. The melting curve constrained up to 6 GPa and 673 K is shown to be well described by the Simon-Glatzel equation in the full (p, T) range explored.