In situ Brillouin scattering study of water in high pressure and high temperatureconditions

Abstract

Experimental studies of liquid water are of particular interest because of the unusualbehavior of most of its physical properties. The in situ high pressure and high temperatureBrillouin scattering technique has been used to examine the sound velocity and elasticproperties of water; we present experimental data for the velocities of liquid water underthese conditions. The velocity dispersion with pressure and temperature is presented;besides the discontinuous behavior in density dependence of the elastic constantbelow 353 K revealed before, which was located at the domain where the lowdensity water transforms to the high density water, the pressure evolution ofvelocity at higher temperatures above 453 K also exhibits different change behaviorsduring compression; a velocity descent with increasing temperature at pressuresbelow about 2.0 GPa was observed, but no obvious drop was seen in the higherpressure region. The elastic constants were calculated based on the velocities and asimilar trend of changes with pressure was found. The temperature dependences ofvelocities measured along the quasi-isobaric lines give a consistent result. Withanalysis of the local structure of liquid water, it is suggested that these observationsdenote a reflection of the density changes which are induced by hydrogen bondingconfiguration modifications under high pressure and high temperature conditions. Wediscuss details of the experimental observations and analyze the mysterious physicalproperties of liquid water, combining other experiments and theory calculations.