Thermal behavior of Ge20SeyTe80−y infrared glasses (for y up to 8 at.%)

The Te-rich Ge20SeyTe80−y infrared chalcogenide glasses (for y up to 8 at.%) were studied by means of DSC, XRD, Raman spectroscopy and infrared microscopy. Thorough non-isothermal thermo-kinetic characterization of the glass transition, crystallization and melting phenomena was performed in dependence on the particle size. The Tool-Narayanaswamy-Moynihan model was successfully used to describe the structural relaxation processes; the compositional evolution of the relaxation parameters was then explained in terms of the structural changes and movements of the characteristic structural units detected by Raman spectroscopy. The nucleation-growth Johnson-Mehl-Avrami model and empirical Autocatalytic model were used to describe the complex kinetics of the DSC crystallization data. Based on the XRD and microscopic analyses the following crystallization mechanisms were revealed: initial nucleation-growth precipitation of hexagonal Te (surface-located) followed by a bulk-located autocatalytic growth of rhombohedral GeTe; in case of higher Se contents an additional formation of the Ge-Te-Se crystalline phase occurred at high temperatures. Higher glass-stability determined for increasing Se content can be associated with the partial inhibition of the crystallization processes, the initial Te precipitation remains, however, further unaffected once Se content reaches ∼4 at.%.