CORRELATION BETWEEN THE STRUCTURE AND GLASS-TRANSITION TEMPERATURE OF POTASSIUM, MAGNESIUM AND BARIUM TELLURITE GLASSES

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 temperature Tg and the quadrupole splitting, indicating that Tg is primarily determined by the magnitude of the distortion of TeO4 trigonal bipyramids. This relationship is also applicable to several oxide glasses. © 1990 Chapman and Hall Ltd.