Extended aging of Ge–Se glasses below the glass transition temperature

Abstract

Germanium selenide glasses of compositions spanning the whole glass-formation range are aged at room temperature for up to twenty years. A prominent enthalpy relaxation process is observed in all glasses and its structural origin is analyzed by Raman spectroscopy. The structural relaxation is manifested in the Raman spectra as a decrease in the ratio of edge to corner-sharing GeSe 4/2 tetrahedral units. This structural evolution can be explained in terms of configurational entropy and density changes. Changes in Raman features and enthalpy follow an identical stretched exponential relaxation function characteristic of ageing in glasses. The compositional dependence of enthalpy relaxation after twenty years is in agreement with kinetic considerations based on the glass transition temperature of each glass. The relaxation behavior and heat-capacity curves are consistent with standard glass relaxation models for all compositions. These results indicate that the non-reversing enthalpy obtained by modulated differential scanning calorimetry (MDSC) which suggests the existence of non-aging glasses is not a reliable measure of the ability of a glass to relax. Instead, it is suggested that an interpretation of MDSC data in terms of complex heat capacity provides a more complete and reliable assessment of the relaxation properties of glasses. I.

Fragile‐to‐Strong Transition in Phase‐Change Material Ge3Sb6Te5

“…The higher the fragility, the more structural relaxation the system will experience while in the glassy state (RESET state). [ 59 ] This is detrimental as pronounced relaxation processes lead to pronounced aging effects like density increase and resistivity drift. [ 14 ] Small temperature changes also lead to a large change in relaxation time in fragile systems, thereby leading to the potential instability of the glassy memory cell upon temperature variations.…”

Aging-Induced Structural Evolution of a GeSe2 Glass Network: The Role of Homopolar Bonds

“…On the other hand, spectroscopic studies on As 30 Se 70 glass have indicated that prolonged (20 years) aging at ambient temperature results in a net conversion of two As–Se–Se–As linkages into one As–Se–As and another As–Se–Se–Se–As linkage . In the case of the Ge–Se system, previous Raman spectroscopic studies have shown that the most prominent aging-induced T f -dependent structural change in glasses with excess Se (70–90% Se) involves the conversion of the edge-shared GeSe 4 tetrahedra into corner-shared tetrahedra. , The timescale of this conversion process was shown to be consistent with that of enthalpy relaxation and to be an important source of S conf in supercooled Ge 20 Se 80 liquid near the glass transition range. Similarly, T f -dependent tetrahedral speciation was reported in a recent Raman spectroscopic study to be responsible for the structural relaxation of Si 25 Se 75 glass during aging at 40 K below T g .…”

Structure–property relationships in critically connected (GeTe4)100−x(As2Se3)x glasses

“…34,35 In region II, new bands at 140, 169 and 195 cm −1 are observed, mainly characteristic of AsTe (3/2) , Se–Te and GeSe tetrahedral structures. 16,36,37 At higher concentrations of As 2 Se 3 , Raman bands at 167, 194 and 229 cm −1 are observed and are characteristic of As–Se based vibrational units. 38 These observations indicate the influence of As 2 Se 3 on modulating the structural network of (GeTe 4 ) 100− x (As 2 Se 3 ) x glasses.…”

“…discussed that the compositions outside and inside the IP window show significant relaxation with time. 16…”

“…King et al discussed that the compositions outside and inside the IP window show significant relaxation with time. 16 Understanding the variation of viscosity of glass forming liquids as a function of temperature is an important aspect to understand glass formation. Based on the variation of viscosity with reduced temperature (T g /T ), glass forming liquids are classified into fragile and strong liquids.…”