Non-isothermal analysis of the crystallization of the amorphous germanium dioxide

The amorphous germanium dioxide devitrification has been investigated, with particular regard to the kinetic aspects and to the crystallization mechanism. The amorphous material transforms into the hexagonal dioxide modification, which is metastable at the considered temperatures. This fact is in accordance with the presence of tetrahedrally coordinated Ge in both the glass and the devitri fied material. The crystallization kinetics has been investigated by means of the DTA technique; a rigorous method of analysis has allowed the determination of the activation energy E_act, the Arrhenius preexponential factor A and the morphological index n characteristic of the devitrification reaction. We have so obtained the following values: E = 233 kJmol^?1, A = 6.57 · 10⁷s^?1 and n = 2.44. These results are not in total accordance with previous studies carried on with similar non-isothermal techniques. Our interpretation is supported also by the morphological study of the GeO₂ crystal growth carried out by scanning electron microscopy.