Crystallisation of levitated TeO2 glass

The non-isothermal crystallisation of levitated TeO 2 glass beads was studied by thermal analysis and Raman spectroscopy. It was found that metastable γ-TeO 2 , whose structure is closest to that of glass, already nucleates in the bulk at the onset of the glass transition region. On the surface, heterogeneous crystal nucleation resulted to immediate growth of the thermodynamic stable α-TeO 2 . This led to a scenario in which a crystallised layer of α-TeO 2 grew from the surface inwards and encountered growing γ-TeO 2 crystallites in the interior, which were transformed by the contact. By simulating the non-isothermal crystallisation, the share of heat that was due to this transformation could be determined and initial data on the growth and nucleation rates of the corresponding crystalline polymorphs in pure TeO 2 glasses were obtained.