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

Abstract

The structural evolution of GeSe2 glass during aging is studied using Raman spectroscopy and density relaxation measurements. The Raman spectra indicate volume- and entropy-driven changes in the relative concentrations of the corner-sharing (CS) and edge-sharing (ES) GeSe4 tetrahedra and in the degree of chemical order of the tetrahedral network during aging at 65 °C below the nominal glass transition temperature. The attendant structural changes involve a progressive increase in the CS:ES ratio and in the chemical order that can be expressed in the form of a reaction Ge–Ge + Se–Se → 2 Ge–Se, which shifts to the right, with lowering of fictive temperature. The isothermal relaxation of both the structure and density during aging displays rather similar stretched exponential kinetics with a stretching exponent β ∼0.54 and an average relaxation time of ∼13.5 h. In situ high-temperature Raman spectroscopic measurements indicate that structural relaxation does not affect the anharmonicity of the vibrational potential wells in the energy landscape of GeSe2 glass.

Sources of Configurational Entropy versus Compositional Trends in Fragility of Inorganic Glass‐Forming Liquids

“…Two such temperature-dependent "reactions" that have been studied in the literature in detail in the Ge x Se 1Àx system using Raman spectroscopy are 1) the conversion of GeSe 4 tetrahedra between edge-shared and corner-shared geometry and 2) the conversion between homopolar and heteropolar bonds, e.g., Ge-Ge þ Se-Se ↔ 2 (Ge-Se). [12,13] The latter reaction may, in fact, become a dominant source of temperature-dependent configurational entropy in chalcogen-deficient GFLs with an excess of Ge or As, which is consistent with the experimental observation that the m of Ge/As-Se networks increases with increasing connectivity in Se-deficient compositions (Figure 1). [14] In fact, the m of As x Se 100Àx GFLs starts to increase even for compositions with x ≥ 35 as As-As homopolar bonds begin to appear in slightly Se-excess compositions.…”

The effect of the structure on the physical properties in GexAs10Se90-x glasses

“…For chalcogenide glasses As x Se 1-x , the vibration peaks of AsSe 3/2 pyramidal units appear at 230 cm -1 and 268 cm -1 [29][30][31]. The vibration peak at around 247 cm -1 is ascribed to the homopolar bond As-As of the As 4 Se 4 structural unit [32]. However, due to the vibration modes of the ternary Ge-As-Se glass are overlapping each other, and the Ge, As and Se atom are very close to each other in the periodic table of elements (atomic radius and mass are similar), therefore, it is difficult to distinguish each structural unit one by one in the Raman spectra.…”

Structural relaxation dynamics of a silicate glass probed by refractive index and ionic conductivity

“…Furthermore, knowledge about this dependence is key to optimizing the processing conditions of glasses to obtain the desired properties. 9 Relaxation-also known as aging-experiments may be followed through measurement over time of certain properties, for example, viscosity, 10 refractive index, 11 density, 12 ionic conductivity, 13 enthalpy, 14 or thermal expansion coefficient, 15 among others. These experiments are quite challenging when performed well below the glass transition region because of the long times involved, which can exceed the typical laboratory time scales.…”

“…Thus, all glass properties depend on its thermobaric history. Furthermore, knowledge about this dependence is key to optimizing the processing conditions of glasses to obtain the desired properties 9 …”