ELASTIC BEHAVIOR UNDER HYDROSTATIC-PRESSURE AND ACOUSTIC-MODE VIBRATIONAL ANHARMONICITY OF SINGLE-CRYSTAL GALLIUM PHOSPHATE (GAPO4)

The hydrostatic pressure derivatives of the complete set of the second -order elastic constants have been obtained up 3 10(8) Pa for the rhom bohedral single-crystal gallium phosphate (GaPO4) using the ultrasonic pulse-echo overlap technique. experimental data have been compared wi th available ones concerning an other derivative of isoelectronic quar tz (SiO2), (AlPO4), and quartz itself. The overall pattern of the elas tic constants and their pressure derivatives far these crystals discus sed In addition, the compression V(P)/V-0 (the ratio of volume at a pr essure P to that V-0 at atmospheric pressure) has treated using the Mu rnaghan equation, due to its central influence in the understanding of the behavior of gallium under volumetric stress. In other respects, t he acoustic-mode Gruneisen parameters have been derived in the approxi mation to quantify the vibrational anharmonicity.