Extended Study on Crystal Growth and Viscosity in Ge–Sb–Se Bulk Glasses and Thin Films

Abstract

Crystal growth rates in GeSbSe bulk glass and thin film were measured using optical and scanning electron microscopy under isothermal conditions. The studied temperature region was 255-346 °C and 254-286 °C for bulk glass and thin film, respectively. The compact crystalline layer growing from the surface into the amorphous core was formed in bulk glasses and no bulk crystallization was observed. In the case of thin films, needle-shape crystals were formed. The crystalline layer and needle-shape crystals grew linearly with time that corresponds to a crystal growth controlled by the crystal-liquid interface kinetics. In the narrow temperature range, crystal growth rates exhibit simple exponential behavior, so the activation energies of crystal growth for the studied temperature regions were estimated (E = 294 ± 6 kJ/mol for bulk glass and E = 224 ± 12 kJ/mol for thin film). Viscosity of GeSbSe material was measured in the region of the undercooled melt and glass. The extrapolation of viscosity data into the immeasurable, but important, temperature range is discussed. The experimental growth data were combined with melting and viscosity data and the appropriate growth models were proposed to describe crystal growth in a wide temperature region. The standard crystal growth models are based on a simple proportionality of the crystal growth rate to the viscosity (u ∝ η). This simple proportionality holds for the bulk material. Nevertheless, in the thin films the decoupling of the crystal growth rate from the inverse viscosity occurs, and the standard kinetic growth models need to be corrected. Such corrections provide better description of experimental data and more realistic value of the parameter describing the mean interatomic distance in the crystal-liquid interface layer, where the crystal growth takes place.

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

“…Therefore, we decided to use the crystallization enthalpy instead of the melting one. The same assumption was also made in works dealing with the crystal growth in Ge-Sb-Se system [37,38]. The calculated dependence of UR on undercooling (T) is shown in Fig.…”

“…The procedure is based on Angell plot and an assumption that all viscosity dependencies end at 10 -5 Pa•s for the infinite temperature. As we discussed earlier [38], this is definitely a simplification of viscosity behavior of glass-forming liquids (above melting point). Nevertheless, according to our opinion and experiences, this is the reasonable way to extrapolate viscosity data if melt viscosities are unknown.…”

“…If the melt viscosities are not available, there is another way how to obtain at least a good estimation of viscosity data. We described this procedure in our previous work [38]. The procedure is based on Angell plot and an assumption that all viscosity dependencies end at 10 -5 Pa•s for the infinite temperature.…”

“…Where G is difference in Gibbs free energy between undercooled melt and crystalline phase. In our previous works [11,37,38], we showed that the simple Turnbull's approximation (G = Hm•T/T) [47] can replace the temperature dependence of G with knowledge of enthalpy of melting (Hm) and temperature of melting (Tm). The melting process in the studied system is shown in the results part (Fig.…”

Effects of pressurization and surface tension on drawing Ge-Sb-Se chalcogenide glass suspended-core fiber

“…2(b)) using a specifically designed die. It was pointed out in earlier works that the Ge-Sb-Se chalcogenide glass is difficult to draw and easily crystallizes [26][27][28]. However, we found that the IG5 glass has a relatively large drawing temperature window, and can be easily drawn from 325°C to 385°C without obvious crystallization [29].…”