Temperature dependence under pressure of the kinetics of crystallization of bulk amorphous selenium

Abstract

The pressure (0·28–0·69 GPa)–temperature (382–409 K) dependence of the kinetics of the crystallization of amorphous Se to the trigonal phase has been investigated. The crystallized fraction-time data under different isobaric-isothermal conditions have been obtained, by monitoring the time dependence of the volume change, using the piston-displacement technique. The temperature dependence of the spherulitic growth rate g at different pressures has also been measured by optical microscopy. The isothermal rate of crystallization is found to increase with increase in temperature and to decrease with increase in pressure. The temperature dependences of the incubation period, the time t_0·5 for 50% crystallized fraction and g at each pressure have been used to determine the activation energy barriers for nucleation, for overall crystallization and for the growth processes. Ali these energies correspond to the activation energy ΔG*_d for the diffusion process involved in the nucleation of spherulites. ΔG*_d is found to increase from 39·5 ± 5 kcal mol⁻¹ at 0·28 GPa to 51·2 ± 4 kcal mol⁻¹ at 0–69 GPa. t _0·5 and g at different pressures and temperatures are found to lie on master curves with the reduced temperature as a variable.