Crystal Growth Kinetics in GeS₂ Glass and Viscosity of Supercooled Liquid

Abstract

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-GeS2 and high temperature α-GeS2 polymorphs in the bulk glass is comparable, being slightly decoupled from the shear viscosity below the glass transition. The crystal growth rate of β-GeS2 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.

Direct comparison of surface crystal growth kinetics in chalcogenide glass measured by microscopy and DSC

“…For many chalcogenide systems, the crystal growth rate u measured by microscopy can be described in a narrow temperature range using an Arrhenius‐type equation: 30–32 $$$$\begin{equation}u{\rm{(}}T{\rm{)}} = {A_{\rm{G}}} \cdot {{\rm{e}}^{ - \;\frac{{{E_{\rm{G}}}}}{{RT}}}}\end{equation}$$$$where A G is the preexponential factor and E G is the activation energy of the crystal growth.…”

“…For many chalcogenide systems, the crystal growth rate u measured by microscopy can be described in a narrow temperature range using an Arrhenius-type equation: [30][31][32] where A G is the preexponential factor and E G is the activation energy of the crystal growth. Assuming a spherical grain of glass with radius r, the volume of the grain V is given by 𝑉 = (4∕3)𝜋𝑟 3 .…”

“…Significant crystallization studies were reported for phase change materials of chalcogenides 28,29 . Some authors also focused their attention on the combined study of the kinetics of crystal growth of chalcogenide glasses by microscopy and DSC 30–33 . The crystal growth rate in thin chalcogenide films was calculated using a correlation between DSC data (described by the JMAK model) and microscopy data 29,34,35 .…”

“…28,29 Some authors also focused their attention on the combined study of the kinetics of crystal growth of chalcogenide glasses by microscopy and DSC. [30][31][32][33] The crystal growth rate in thin chalcogenide films was calculated using a correlation between DSC data (described by the JMAK model) and microscopy data. 29,34,35 However, to our knowledge, there are not as many articles that provide a model for the direct calculation of crystal growth data from DSC measurements.…”

Determination of the activation energy under isothermal conditions: revisited

“…The isothermal kinetic analysis continues to be amply employed nowadays to study a wide range of processes. Thus, it is the most feasible option for reactions studied under realistic conditions of operation [19,20], long-term curing [21,22], oxidation and reduction processes [23,24], hydration and dehydration processes [25][26][27], reactions followed through X-ray diffraction [28] or those studies intended to discriminate the kinetic model under isothermal conditions [29][30][31][32].…”