Structural properties of the glass system As-Se-S studied by x-ray absorption spectroscopy

The structural properties of As-Se-S glass system were investigated by x-ra y absorption spectroscopy (XANES and EXAFS) using synchrotron radiation. A preliminary characterization by x-ray powder diffraction, differential scan ning calorimetric and thermogravimetric measurements was also carried out. The changes in glass transition temperature (T-g) and glass decomposition t emperature (T-d) associated with glass compositions indicate that sulfur co ntributes to the instability of the ternary As-Se-S glass system. The XANES and EXAFS results suggest that arsenic is in trivalent state with approxim ately threefold coordination and selenium is in approximately twofold coord ination in all the glass compositions under study. The homopolar bonding (A s-As and Se-Se) has a significant contribution in AsSe1.42 glass matrix unl ike in AsS1.56 glass where homopolar bonding (As-As) is negligible. However , the homopolar bonding (As-As) is increasingly eliminated with increasing replacement of selenium by sulfur in ternary glasses. In addition, the cont ribution of sulfur to the coordination of arsenic is more dominant than sel enium even when glass matrices contain a larger quantity of selenium. Thus the present XANES and EXAFS results demonstrate that the As-Se-S glass syst em is well represented by the chemically ordered network model. (C) 2000 Am erican Institute of Physics. [S0021-8979(00)09513-X].