Correlation between the structure and glass transition temperature of potassium, magnesium and barium tellurite glasses

Abstract

The Mössbauer spectrum of tellurite glasses, containing 5 mol% Fe₂O₃ as a probe, consists of a paramagnetic quadrupole doublet with an isomer shift of 0.39 ± 0.01 mmsec⁻¹. This indicates that Fe³⁺ ions are present at substitutional sites of Te⁴⁺ ions constituting distorted TeO₄ trigonal bipyramids, each of which has one oxygen vacancy at an equatorial site. On increasing the K₂O content from O to 35 mol%, the quadrupole splitting (Λ) for potassium tellurite glasses decreases continuously from 0.76 to 0.44 mm sec⁻¹. On the other hand, Λ for magnesium and barium tellurite glasses increases with increasing MgO and BaO content, respectively. When the alkali or alkaline earth oxide contents are the same as each other, Λ increases in proportion to the ionic potential (Z/r) of the alkali or alkaline earth metal ion. These results suggest that the glass matrices of alkaliv and alkaline earth tellurite glasses are continuously changed into a chain and a three-dimensional network structure, respectively. Differential thermal analysis studies reveal that there exists a linear relationship between the glass transition temperatureT _g and the quadrupole splitting, indicating thatT _g is primarily determined by the magnitude of the distortion of TeO₄ trigonal bipyramids. This relationship is also applicable to several oxide glasses.