Crystallization kinetics of Ge–Sb–Te alloys with metastable phase formation

The purpose of this work is to investigate the microstructural transformations during the isothermal amorphous-to-crystalline phase transition process in alloys with compositions around the pseudobinary GeTe–Sb2Te3 line using electrical impedance, optical transmission, and X-ray diffraction measurements. Experimental measurements indicate that the process of isothermal crystallization in GeTe, Ge2Sb2Te5, and Ge1Sb2Te4 takes place in two stages: in the first stage, nuclei of a metastable phase precede the formation of stable phases; in the second stage, the nuclei transform into their corresponding equilibrium fcc stoichiometric structures. The kinetics of this crystallization processes were analyzed through results from impedance measurements, in which Bruggerman’s effective medium approximation was employed, considering that the amorphous matrix contained inclusions of two different phases. Furthermore, a theoretical stochastic model of crystallization was developed based on a two-stage process representing the growth of an fcc stoichiometric phase from a metastable crystalline phase.