Kinetics of crystal growth of germanium disulfide in Ge0.38S0.62 chalcogenide glass

Abstract The crystal growth kinetics of GeS 2 in Ge 0.38 S 0.62 glass has been studied by Differential Scanning Calorimetry (DSC) and microsopy. The linear crystal growth kinetics of both high temperature α-GeS 2 and low temperature β-GeS 2 polymorphs has been observed over a relatively broad range of temperatures, i.e. 420 T 9 > η > 8 × 10 5 Pa s. It seems that 2D nucleated growth is the most probable mechanism of crystallization for high temperature α-GeS 2 under these conditions. However, there are significant deviations for this model for the crystallization of low-temperature β-GeS 2 . This might indicate some changes in crystal-melt interfacial energy or break down of Stokes–Einstein relation in that particular case. At temperatures below 500 °C the temperature range of directly observed crystal growth overlaps with isothermal DSC measurements. In this case overall crystallization kinetics can be described by the Johnson–Mehl–Avrami (JMA) nucleation-growth model for kinetic exponent n ≅ 4. The value of activation energy of nucleation estimated from these experiments E N = 434 kJ mol −1 is comparable with the activation energy of viscous flow in supercooled Ge 0.38 S 0.62 melt ( E η = 478 kJ mol −1 ). A more complex eutectic crystallization involving both GeS 2 and GeS phases has been observed at higher temperatures. This process is probably associated with secondary nucleation and cannot be described by a simple JMA model.