Hypersonic attenuation in cesium borate glasses: Relaxation and anharmonicity

The internal friction and the sound velocity in a cesium borate glass (Cs2O)0.14(B2O3)0.86 were measured at ultrasonic and hypersonic frequencies by Brillouin scattering measurements over the temperature range between 15 and 300 K. The analysis of the experimental results show that, in addition to thermally activated local motions of structural defects, the vibrational anharmonicity contributes substantially to the temperatures dependences of both the hypersonic loss and velocity. It has been also proved that above 150 K the vibrational anharmonicity appears to be governed by the Akhiezer mechanism of phonon viscosity.