Acoustic velocities in polycrystalline NaCl at 300°K measured at static pressures from 25 to 270 kbar

The room temperature longitudinal and shear acoustic velocities in polycrystalline NaCl have been measured at static pressures in the range of 25–270 kbar (2.5–27.0 GPa). The measurements were made by ultrasonic interferometry in a variable lateral support Bridgeman anvil device. The velocity data are developed with the aid of the Decker equation of state. Previous measurements of acoustic velocities made in the range of 0–100 kbar are in agreement with the data. At higher pressures the shear mode velocity is approximately constant or slowly increasing with increasing pressure. This is in agreement with predictions made with next nearest neighbor interatomic force calculations. Nearest neighbor only and fourth order finite strain theory calculations which use the assumption that the elastic parameter c44 goes to zero at the 292-kbar phase transition are determined to be inaccurate near the transition. It is suggested that the ratio of the acoustic velocities of polycrystalline NaCl can be used in the future as a parameter for calibration of ultrahigh-pressure devices.