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

Vitreous (v) and molten (m) GeO2 were studied by Rayleigh and Mandel’shtam–Brillouin scattering spectroscopy and high-temperature acoustics. Original measurement apparatus and procedure were used that included Bayseian deconvolution of light scattering spectra of vGeO2 and a specially designed high-temperature (up to 1500 °C) acoustic interferometer to measure temperature and frequency dependence of ultrasonic (US) velocity and attenuation in mGeO2. Landau–Placzek ratios for vGeO2 were found optically (from the light scattering spectrum) and acoustically (through the Schroeder’s formalism). Dispersion of optical and other physical parameters of vGeO2 found by many authors is explained by the existence of small amount of GeO in the samples. It means that properties of vGeO2 are under the influence of redox synthesis conditions controlling the GeO2 ↔ GeO and coordination [GeO4] ↔ [GeO6] equilibrium in vGeO2. Measurements of temperature dependencies of longitudinal ultrasonic velocities in mGeO2 and in the PbO–GeO2 glass melts as a function of PbO concentration shows existence of ‘water-like anomaly’ in mGeO2 and in liquid germanates with the rich content of GeO2 where equilibrium sound velocity increases with the temperature.