A combined neutron and x-ray diffraction study of short- and intermediate-range structural characteristics of Ge–As sulfide glasses

Abstract

A combination of neutron and x-ray diffraction has been employed to study the compositional dependence of the atomic structures of GexAsxS100−2x glasses with S concentration varying between 33.3 and 70.0 at.%. The nearest-neighbor coordination numbers of Ge and As atoms are always found to be 4 and 3, respectively, irrespective of the glass composition. Ge and As atoms have primarily heteropolar bonding to S atoms in stoichiometric and S-excess glasses with x≤18.2. Low and intermediate levels of deficiency of S (20≤x≤25) are accommodated via the formation of homopolar As–As bonds while Ge atoms remain primarily bonded to four S atoms, resulting in As-rich regions in the glass structure. Ge starts to participate in metal–metal bonding only in the highly S-deficient glasses with 27.5≤x≤33.3. The intermediate-range order and its topological influence on atomic packing in these three compositional regions, in the order of increasing deficiency in S, are controlled by (a) a mixed GeS2 and As2S3 network, (b) the coexistence of a GeS2 network and As clusters, and (c) large Ge–As metal-rich regions. This evolution of the intermediate-range structure with composition is consistent with the corresponding variation of the position, intensity and width of the first sharp diffraction peak in the structure factor.

Physical properties of GexAs2xTe100−3x glasses and Raman spectroscopic analysis of their short-range structure

“…This structural scenario is in excellent agreement with the results of a previous Ge and As K-edge EXAFS spectroscopic study of short-range order in ternary Ge 0.1 As x Te 0.9 − x glasses with x = 0.15, 0.20, 0.46 and 0.54 that indicated the presence of Ge/As-Ge/As bonds even in Te-excess glasses [14]. It should also be noted here that glass compositions along similar tie lines in Ge-As-S and Ge-As-Se ternary systems do not show any evidence of such gross violation of shortrange chemical order [11,12,19,21,22]. Violation of chemical order in Ge-As-Te glasses may be related to the significantly higher metallicity of Te compared to S or Se.…”

“…Recently there has been a renewed surge of interest in telluride glasses as amorphous Ge-Sb-Te thin film materials exhibit interesting phase change phenomena induced by optical or electrical switching that can be exploited in rewritable optical data storage and in non-volatile electronic memory applications [5][6][7][8][9]. Consequently, the structure-property relationships in ternary chalcogenide glasses have received a great deal of research attention in recent years [10][11][12][13][14][15][16][17][18][19][20][21][22]. The results of these studies have shown that in ternary Ge-As-S/Se glasses the nearest-neighbor coordination numbers of Ge and As atoms are always 4 and 3, respectively, regardless of glass composition.…”

Temperature-dependent structural heterogeneity in calcium silicate liquids

“…2,3 This is despite the analysis of quenched glass structures that indicate atomic to nanometer scale structural heterogeneity must occur in the liquid state. [4][5][6][7] Silica is classified as a strong liquid with an Arrhenius viscosity-temperature relation and only subtle differences occur between the liquid and glass structures. 8,9 In contrast CaO-SiO 2 liquids can be considered fragile based on viscosity measurements 10,11 and consequently larger structural rearrangements are likely to be necessary to form a glass.…”

Communication: X-ray scattering from ionic liquids with pyrrolidinium cations

“…8,9,13 The FSDPs have been observed in the structure function S(q) obtained from x-ray and neutron scattering in glasses, melts and liquids with intermediate range order. 5,6,[23][24][25][26] The FSDP is frequently observed for molten metal halides, 5 mixtures of tetrahedral glass-formers 25 and binary selenides. 26 For these systems, the FSDPs are typically observed for magnitudes of the scattering vector in the range from 0.9 ≤ q ≤ 1.5 Å −1 .…”