Origin of Rayleigh scattering and anomaly of elastic properties in vitreous and molten GeO2

The vibrational dynamics of GeO2at the glass transition: a Raman and Brillouin scattering study

“…In the framework of the possible connection between the BP and the elastic properties of the system, we have evaluated the longitudinal and transverse sound velocities, taking properly into account the temperature variation of the refractive index. The results are reported in Figure 2 together with the available literature data [22,23]. The comparison of the data shows a good agreement both in the temperature behavior and in the absolute values at high T (4400 K), while some differences are observed in the low-temperature range.…”

“…Temperature evolution of the longitudinal and transverse sound velocity; full squares represent the data obtained in the present work; literature data are also reported: open diamonds from[22] and open circles from[23].…”

Brillouin spectroscopy of Nd–Ge co-doped silica fibers

“…This is considerably smaller ($40%) than previously reported for bulk GeO 2 [21,22]. The acoustic velocity becomes a strong function of frequency at temperatures (highly dispersive) above about 500°C, with increasing velocity towards hypersonic frequencies (GHz) (>3400 m/s) and considerable reduction in velocity towards ultrasonic frequencies (MHz) (<1500 m/s) [21]. Unfortunately, a reference with measured acoustic velocities of pure germania at hypersonic frequencies and temperatures similar to those used in silica fiber processing could not be found.…”

“…9) to 100% GeO 2 gives rise to a value of about 2160 m/s. This is considerably smaller ($40%) than previously reported for bulk GeO 2 [21,22]. The acoustic velocity becomes a strong function of frequency at temperatures (highly dispersive) above about 500°C, with increasing velocity towards hypersonic frequencies (GHz) (>3400 m/s) and considerable reduction in velocity towards ultrasonic frequencies (MHz) (<1500 m/s) [21].…”

“…We assumed the same material values for the glass as defined before, namely the density of pure silica is assumed to be 2200 kg/m 3 . We also assume a 'typical' density of pure germania to be 3620 kg/m 3 [21,22], as before. The only fit parameters are then M L s and M L g , from which the acoustic velocities for bulk, pure materials can be extrapolated.…”