Structural and physical properties of Ag-As-Te glasses

Differential scanning calorimetric (DSC), de electrical conductivity, X-ray diffraction and EXAFS measurements for (Ag2Te)(x)(AsTe)(1-x) glasses with x = 0 to 0.3 have been carried out to investigate physical properties and the co-ordination environment of constituting atoms in ternary Ag-As-Te glasses. Results of the DSC measurement suggest that the glass structure is more thermally unstable with increasing Ag content. The incorporation of Ag2Te into AsTe glass is responsible for a pronounced increase in the electrical conductivity and corresponding decrease in the electrical activation energy. Least-squares fit analyses for the observed X-ray structure functions have been carried out under the assumption that the first co-ordination shell is composed of As-Te, Ag-Te and As-As correlations. The results indicate that the interatomic distances of three atomic correlations are all composition-independent. The co-ordination number of As atoms is determined to be about three and remains practically unchanged. Ag atoms are roughly fourfold coordinated with Te atoms, as suggested by the formal valence shell (FVS) model proposed for the chalcogenide glasses. The co-ordination number of Te atoms increases from 1.93 to 3.60 with increasing Ag content. The thermal stability and electrical properties of the present glasses may be associated with the local structure and bonding nature of Ag-Te bonds. (C) 2001 Elsevier Science B.V. All rights reserved.