Analysis of crystal growth and viscosity in Ge-Sb-Se-Te undercooled melts

A comprehensive analysis on crystal growth and viscosity is presented for the Ge2Sb2Se5-xTex (x = 0.5 and 1) undercooled melts in this article. Temperature dependence of the measured viscosities (10(7.5)-10(12.5) Pa.s) can be described by a simple exponential Arrhenius type equation in the relatively narrow temperature region in which the measurements were performed. Fragility of the measured materials are all roughly equal to 43, which means that these materials belong to the so called "intermediate" liquids (lying in the middle between strong and fragile liquids) and cannot be described by simple Arrhenius type equation if the temperature region is expanded from glass transition to melting, which is important for description of crystal growth. Therefore, MYEGA equation is used to extrapolate the viscosity data into the temperature region of studied crystal growth. Nucleation and crystal growth started on a surface of studied samples. The isothermal growth rate of the formed surface crystalline layer was measured at various temperatures. Analysis of the growth data revealed a crystal growth driven by liquid-crystal interface kinetics. Therefore, the standard crystal growth models were used for description of crystal growth rates in the studied systems.