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Chalcogenide glass-formers are being used in a remarkable range of various optoelectronic, photonics, photoconducting, sensing and memory device applications. The knowledge of viscosity is essential for the processing of any glass-forming material, in particular for the fabrication of precise optical elements, which is the main application field of chalcogenide glasses. This work presents an extensive collection of all available viscosity data for chalcogenides, including the measurement methods. The Mauro–Yue–Ellison–Gupta–Allan (MYEGA), Arrhenius and VFT equations are used to fit the temperature dependences of viscosity. The viscosity glass transition temperatures, fragilities and apparent activation energies are calculated from these fits. Consequently, these parameters are discussed with regard to the compositional evolution of the respective chalcogenide systems. [ABSTRACT FROM AUTHOR]

The constant heating rate crystallization of As 2Se 3 undercooled melt was measured by the differential scanning calorimetry. The nonlinear regression analysis of conversion temperature dependence was performed in frame of the classical nucleation theory supposing the normal 3D growth. The parameters of temperature dependence of nucleation rate and growth rate were determined by three step process. First the simple parabolic model was used to estimate the maximum and width of nucleation/growth rate temperature dependence. Then the obtained parabolic curves were fitted by the theoretical ones. In the third step, the obtained parameters were used as zero estimates for nonlinear regression analysis of experimental data. The results obtained by using conversion degree α were compared with the results obtained by using the −ln(1 −  α) transformed function. Although both treatments give comparable results the use of −ln(1 −  α) input data is preferred due to better numerical stability of nonlinear regression treatment. [ABSTRACT FROM AUTHOR]

Abstract: Viscosity of (GeS2) x (Sb2S3)1−x melts (x =0.1–0.9) has been measured by penetration method and parallel-plate method as a function of temperature. The temperature dependence of viscosity can be expressed by a simple equation of Arrhenius type. The kinetic fragility obtained from these plots varies linearly with composition. The Sb2S3 component probably affects the network structure and, consequently, the kinetic fragility of a supercooled melt increases. As expected, the heat capacity change at the glass transition, ΔC p, exhibits similar (though non-linear) compositional dependence. [Copyright &y& Elsevier]

Abstract: The evolution of As2Se3 glass volume below the glass transition temperature was measured by dilatometry under isothermal and non-isothermal conditions. The experimental data can be described by Tool–Narayanaswamy–Moynihan model for a single set of kinetic parameters: Δh*/R =38.3kK, ln(A/s)=−79.21, x =0.57, β =0.71. The value of Δh*/R is close to the apparent activation energy of viscous flow that was found to be E η /R =38±1kK. It is shown that the same set of kinetic parameters can be used for a description of previously reported enthalpy relaxation data. This suggests that the volume and enthalpy relaxation kinetics is comparable at least within the limit of experimental errors. [Copyright &y& Elsevier]

Abstract: The viscosity of Cu x (As2Se3)100−x melts (x =1, 5, 10 and 20) has been measured by the penetration method (8<log(η/Pas)<13). The temperature dependence of the viscosity can be expressed by a simple equation of Arrhenius type. The kinetic fragility obtained from these plots exhibits similar compositional dependence as the heat capacity change in the glass transition range. This behavior is consistent with the assumption that increasing Cu content causes topological changes in the structure of As2Se3 supercooled melts. [Copyright &y& Elsevier]

Abstract: The crystal growth kinetics of GeS2 in Ge0.38S0.62 glass has been studied by Differential Scanning Calorimetry (DSC) and microsopy. The linear crystal growth kinetics of both high temperature α-GeS2 and low temperature β-GeS2 polymorphs has been observed over a relatively broad range of temperatures, i.e. 420< T <494°C that correspond to viscosity of supercooled melt: 3×109 > η >8×105 Pas. It seems that 2D nucleated growth is the most probable mechanism of crystallization for high temperature α-GeS2 under these conditions. However, there are significant deviations for this model for the crystallization of low-temperature β-GeS2. 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 kJmol−1 is comparable with the activation energy of viscous flow in supercooled Ge0.38S0.62 melt (E η =478 kJmol−1). A more complex eutectic crystallization involving both GeS2 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. [Copyright &y& Elsevier]

The crystal growth kinetics and morphology in germanium disulfide bulk glass and glass surface is described. The structural relaxation taking place below the glass transition is slow and the corresponding volumetric change is negligible. Therefore, it does not affect substantially the crystal growth process. The crystal growth rate of low temperature β-GeS 2 and high temperature α-GeS 2 polymorphs in the bulk glass is comparable, being slightly decoupled from the shear viscosity below the glass transition. The crystal growth rate of β-GeS 2 in an amorphous thin film of the same composition is several orders of magnitude faster than that at the surface of bulk glass. This fast surface crystal growth is strongly decoupled from viscosity. Such behavior resembles the glass-to-crystal fast growth mode observed by several authors in some organic molecular glasses. Taking into account previously reported viscosity and heat capacity data, the crystal growth kinetics of both polymorphs can be quantitatively described by the 2D surface growth model for low and high supercooling. The nonisothermal differential scanning calorimetry experiments are analyzed, providing evidence of a complex nature of the overall crystallization process with apparent activation energy comparable to that obtained from isothermal microscopy measurement of crystal growth in the same temperature range.