CRYSTALLIZATION STUDIES OF 30LI2O-70TEO2 GLASS

The thermal stability of the 30Li2O:70TeO2 glass. identified as the eutectic composition from Li2O:TeO2 binary phase diagram, has been determined by measurement of differential scanning calorimetry, X-ray diffraction (XRD) and ac electrical conductivity. The crystallization seems to be a three-step process for powdered glass and a two-step process for bulk glass. The non-isothermal kinetics of first-stage crystallization have been analyzed in terms of the modified Ozawa and the modified Kissinger methods and the crystallization products identified by XRD. Surface nucleation appears to be the dominant mechanism for crystallization with an activation energy barrier of 429 +/- 10 kJ/mol, a value higher than for silicate glasses indicating the lower stability of the tellurite glasses. Three products of crystallization - an intermediate unidentified phase, a metastable monoclinic phase and a stable, final orthorhombic phase - are revealed in XRD. The crystallized (orthorhombic) phase has a lower ionic conductivity and higher activation energy for conduction compared to the glass.