Revisiting the melting curve of H 2 O by Brillouin spectroscopy to 54 GPa

The melting curve of H O was investigated up to 54 GPa and ∼2000 K by Brillouin scattering spectroscopy in a diamond anvil cell. A CO laser was used for heating the H O sample directly in order to reduce the risk of chemical reactions. The melting was identified based on the appearance of the Brillouin peaks derived from the liquid phase. The longitudinal wave velocity (V ) of the liquid phase along the melting curve exhibits a smooth increase with pressure. The melting temperature of H O shows no kink previously reported but a monotonic increase between 26 and 54 GPa. Present melting data suggest that the melting occurs from body-centered-cubic superionic phase in the pressure-temperature range investigated.