The effect of partial crystallinity on Se70Te30 crystallization kinetics

The effect of partial crystallinity on Se70Te30 crystallization kinetics was investigated in dependence on experimental conditions of the measurement (applied heating rate and particle size of the powdered material). The whole range from completely glassy to almost fully crystalline Se–Te material was examined in this regard; the reproducible initial degree of crystallinity was achieved by preceding non-isothermal heating to a certain selected temperature. With the increasing degree of initial crystallinity, the defects-based crystallization mechanisms begin to dominate over the classical-nucleation-theory-based nucleation–growth crystallization mechanism, with the apparent activation energy and Johnson–Mehl–Avrami kinetic exponent limiting the values characteristic for the crystallization of fine powders (~140 kJ mol−1 and 1.4, respectively). The kinetic analysis based on the advanced interpretation of the characteristic kinetic functions provided detailed description of the changes associated with the complex crystallization process consisting of the competing surface- and volume-located growth mechanisms occurring in the grains of finite size.