Linking Viscosity and Diffusion with Interface-Controlled Crystal Growth in Ge ₂₅ S ₇₅ Bulk Glass

Crystal growth kinetics in bulk Ge25S75 glass were investigated using infrared microscopy in the temperature range of 640–780 K, enabling direct observation of β-GeS2 crystal growth. The temperature dependence of viscosity was determined by thermomechanical analysis and described using the Mauro-Yue-Ellison-Gupta-Allan model. Crystal growth rates exhibit linear time dependence, indicating interface-controlled kinetics. Analysis using a normal growth model reveals moderate decoupling between viscosity and diffusion, with a decoupling parameter of ξ = 0.68 ± 0.02. Effective self-diffusion coefficients were derived from the kinetic data and compared with values obtained from the Stokes–Einstein-Eyring relation. The results show that crystal growth is governed primarily by diffusion processes and follows a power-law relationship between growth rate and diffusion coefficient, similar to that observed in molecular glass formers. These findings provide insight into the relationship between transport properties and crystal growth mechanisms in chalcogenide glasses.