Thermal characteristics of pure and substituted gel grown Gd-molybdate crystals

Abstract

Polycrystalline spherulitic crystals of pure Gd-heptamolybdate and single and twinned crystals of substituted Gd-Ba-molybdate were grown by using gel encapsulation technique. The thermal behaviour of these crystals was studied using the thermoanalytical techniques, which included TG, DTA and DSC. Thermal analysis suggests decomposition of the materials in one or more than one stages. Results obtained on application of TG based models viz. Horowitz-Metzger, Coats-Redfern and Piloyan-Novikova, are reported. According to the results of the kinetics of thermal decomposition, the random nucleation model is shown to be the one that is relevant to the decomposition of single rare earth (Gd) containing material and contracting sphere to the decomposition of the substituted (Gd-Ba) one. The kinetic parameters viz. the order of reaction, frequency factor and energy of activation using above-mentioned models, are computed and shown to bear reasonably good agreement.