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Three groups of Ge–Sb–Se glasses with compositions Ge x Sb10Se90–x , Ge x Sb15Se85–x , and Ge x Sb20Se80–x have been systematically studied with the aim of understanding the role of chemical composition and mean coordination number (MCN) in determining their structural and physical properties. For each group of glasses, it was found that the optical bandgap increases and the refractive index decreases with increasing Ge concentration up to a transition point which corresponds to glasses that have chemically stoichiometric compositions. Raman spectra were measured and decomposed into different structural units. While the relative number of the heteropolar bonds changes in a reasonable manner with chemical composition, the evolution of the optical bandgap and refractive index correlated closely with the number of the homopolar bonds, suggesting that the band-tails formed by homopolar bonds could reduce the optical bandgap. On the other hand, the transitions at the chemically stoichiometric compositions could be attributed to “demixing” of networks above the chemical thresholds. These transition thresholds in the three groups of glasses demonstrated that the chemical composition has significant effects on the physical properties in the Ge–Sb–Se system.

The electronic structures of half-Heusler compounds TiNiSn and TiCoSb are investigated by using the full-potential linearized augmented plane-wave method. When the spin-orbital coupling is included in the calculations, there is only a slight change in the energy band structures. The transport coefficients (Seebeck coefficient, electrical conductivity, and power factor) are then calculated within the Boltzmann theory, and further evaluated as a function of chemical potential assuming a rigid band picture. Our calculations offer a valuable insight on how to improve the thermoelectric performance of these two compounds.

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The structure of Ge x Sb 10 Se 90Àx glasses (x ¼ 7.5, 10, 15, 20, 25, 27.5, 30, and 32.5 at. %) has been investigated by x-ray photoelectron spectroscopy (XPS). Different structural units have been extracted and characterized by decomposing XPS core level spectra, the evolution of the relative concentration of each structural unit indicates that, the relative contributions of Se-trimers and Se-Se-Ge(Sb) structure decrease with increasing Ge content until they become zero at chemically stoichiometric glasses of Ge 25 Sb 10 Se 65 , and then the homopolar bonds like Ge-Ge and Sb-Sb begin to appear in the spectra. Increase of homopolar bonds will extend band-tails into the gap and narrow the optical band gap. Thus, the glass with a stoichiometric composition generally has fewer defective bonds and larger optical bandgap. V

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The crystallization kinetics of Ge–Sb–Se chalcogenide glasses prepared by melt‐quenching method was investigated using differential scanning calorimetry under non‐isothermal conditions with several different heating rates. Kissinger's equation and Matusita model were employed to analyze kinetic crystallization behavior of the glasses. The crystallization parameters were calculated and the crystallization mechanism was studied. The results indicate that the crystallization activation energy increases rapidly at the glass with a mean coordination number (MCN) of 2.4, and reaches its maximum at MCN of 2.65. These two transition thresholds correspond to the structural phase transition in the glassy network. The evolution of the glass transition temperature (Tg), activation energy for crystallization (Ec), glass forming ability and thermal ability as functions of MCN and chemical composition might have substantial implication on screening the best glass for the application in photonics.

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