Manifestation of thermodynamic glass transition by structure and picosecond dynamics in alkali tellurite glasses

Abstract

The Raman spectra of the 0.1Cs2O–0.9TeO2 melt were measured and analyzed over a broad temperature range including the glassy, supercooled and molten state in an effort to follow the varying structural and dynamical aspects caused by temperature and alkali modifier. The network structure of the glass/melt is formed by mixing TeO4 trigonal bipyramid and TeO3 trigonal pyramid units. Changing alkali content and/or temperature results to conversion of the TeO4 units to TeO3 units with a varying number of non-bridging oxygen atoms. The low-frequency Raman spectra reveal a well-resolved Boson peak whose frequency also depends on temperature. The variation of the maximum of the Boson peak has been determined and discussed in the framework of current phenomenological models. The short-time dynamics of the system experiences drastic changes when approaching the glass-to-liquid transition. The temperature dependent plot of the correlation times extrapolates to a crossover value, which we assign as spectral evidence of the system's known thermodynamic glass transition temperature. Similar behavior exhibit several spectral features, such as the maximum of the Boson peak, the exponent of the susceptibility and the intensity ratio related to the structural transformation from TeO4 tbp to TeO3 tp species occurring in the medium range order structure.