Correlation between Structural and Physical Properties in Ge–Sb–Se Glasses

Abstract

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.

Distribution and Substitution Mechanism of Ge in a Ge-(Fe)-Bearing Sphalerite

“…XANES/EXAFS (Extended X-ray Absorption Fine Structure) were measured on the reference materials, which included GeO2 (99.999%, Strem Chemicals; tetragonal modification with quartz-like structure [20]); germanite Cu13Fe2Ge2S16 (South Australian Museum (SAM) G4777, Tsumeb Mine, Namibia; Ge, Cu, Fe); partially oxidized powdered Ge metal (British Drug House (BDH)) Chemicals; 99.99% Ge); stannite (Cu2FeSnS4, SAM G19206 Yaogangxian Mine, Hunan, China; Cu, Fe); and chalcopyrite CuFeS2 (SAM G22621, Moonta Mines, South Australia; Cu, Fe). In addition, argyrodite Ag8GeS6 (Museum Victoria (M), Melbourne, Australia, sample number M3071; [21]); renierite Cu11ZnGeFe4S16 (M47647); synthetic GeS2 glass (synthesized by heating high-purity (5N) Ge and S that had been vacuum sealed in quartz ampules to 900 °C, rocked for 10 h and then quenched in air [22][23][24]); synthetic GeSe2 glass (synthesized via the melt-quenching method [25,26]); and synthetic GeS (orthorhombic; Strem Chemicals, 99.999%) were measured in transmission mode on pellets either at the X-ray Absorption Spectroscopy (XAS) beamline of the Australian Synchrotron or at BM18, the Core EXAFS beamline at the Diamond Light Source. Beamline energies were calibrated using Fe and Cu foils as well as Ge-metal; in addition, the same GeO2(s) pellet was measured at all three beamlines to provide a direct comparison across the datasets.…”

Evidence of homopolar bonds in chemically stoichiometric GexAsySe1−x−y glasses

“…In particular, it is normally expected that the number of the homopolar bonds should be minimum in chemically stoichiometric glasses. [12][13][14][15] However, in ternary glasses like GeAsSe, one can prepare many chemically stoichiometric glasses with different chemical compositions. The question, therefore, is whether the composition has any effect on the formation of homopolar bonds.…”

Ab Initio Comparison of Bonding Environments and Threshold Behavior in GexAs10Se90–x and GexSb10Se90–x Glass Models

“…9, 10 We observe that the refractive index minima for the models occur approximately at the maximal population of length-one segments.…”

“…The constant population The Journal of Physical Chemistry A Article of Se−As and Se−Sb bonds across a wide range of Ge concentrations has also been experimentally detected 10 along with the decreasing Se−Se bonding, which was seen in previous modeling work 16 and in Raman studies. 10 According to constraint-counting models for Se-even stoichiometry, enough Se bonds exist to saturate all the Ge and As/Sb atoms, which should theoretically result in no homonuclear bonding. These models show (along with previous models of GeAsSe glasses 16,17 ) that homonuclear bonding is found even in Serich systems.…”