Indexed on: 25 Jul '17Published on: 25 Jul '17Published in: Journal of Physical Chemistry B
Crystal growth rates in Ge18Sb28Se54 bulk glass and thin film were measured using optical and scanning electron microscopy under isothermal conditions. The studied temperature region was 255 - 346 °C and 254 - 286 °C for bulk glass and thin film, respectively. The compact crystalline layer growing from the surface into the amorphous core was formed in bulk glasses and no bulk crystallization was observed. In the case of thin films, needle-shape crystals were formed. The crystalline layer and needle-shape crystals grew linearly with time that corresponds to crystal growth controlled by the crystal-liquid interface kinetics. In the narrow temperature range, crystal growth rates exhibit simple exponential behavior, so the activation energies of crystal growth for the studied temperature regions were estimated. The found values of activation energies of crystal growth were estimated (EG = 294 ± 6 kJ/mol for bulk glass and EG = 224 ± 12 kJ/mol for thin film). Viscosity of Ge18Sb28Se54 was measured in the region of the undercooled melt and glass. The extrapolation of viscosity data into the immeasurable but important temperature range is discussed. The experimental growth data were combined with melting and viscosity data and the appropriate growth models were proposed to describe crystal growth in a wide temperature region. The standard crystal growth models are based on simple proportionality of crystal growth rate to viscosity. This assumption was tested and a correction of the standard growth model is suggested.