Elastic properties of a-SiO2 up to 2300 K from Brillouin scattering measurements

The velocities of the transverse and longitudinal acoustic modes of silica glass and liquid have been measured by Brillouin spectroscopy from 300 to 2300 K. Elastic properties of liquid SiO2 could thus be studied over an interval of 800 K above the standard glass transition temperature. The velocity of the transverse mode, and thus the shear modulus, first increases with temperature and then decreases after reaching a maximum near the glass transition temperature. The velocity of the longitudinal mode and the bulk modulus, in contrast, continuously increase up to the maximum temperatures investigated. This unusual increase of the bulk modulus with temperature becomes less strong above 900 K. The vibrational (high frequency) contribution to the compressibility of the liquid, which is about three times smaller than the configurational (static) part, is thus insensitive to the configurational state of the liquid.