Crystal Growth Kinetics in Se-Te Bulk Glasses

The isothermal crystal growth in Se100-xTex bulk glasses (x = 10, 20, and 30) was studied directly using infrared microscopy. The crystals grew spherulitically and linearly in the course of time, which is typical for crystal growth controlled by liquid-crystal interface kinetics. An operative growth model was found using a combination of growth and viscosity data, and using two different approaches for calculations of the Gibbs free energy change between the undercooled melt and crystalline phase. The study shows that the exact knowledge of the Gibbs free energy change calculated from both, heat capacities, and the simple approximation proposed by Turnbull, can provide comparable results regarding determination of an operative crystal growth model. A detailed discussion about the relationship between the kinetic coefficient of crystal growth rate and viscosity (u(kin) proportional to eta(-xi)) is presented. Moreover, the activation energies of crystal growth were found to be higher than the activation energies of the overall crystallization process obtained by differential scanning calorimetry. The relation between these two quantities is considered under the experimental conditions.