Chemical alloying induced collapse of reversibility windows in ternary As-S-I glasses*

Thermally reversing windows represent glass compositions across which glass transitions are thermally reversing in character. These windows have been observed in several chalcogenide glasses, and are identified$^{1}$ with self-organized phases of glassy networks. Upon alloying halogen (iodine) in base chalcogenide glasses (Ge-Se, Ge-S), the reversibility windows collapse$^{2}$ about the mean-field rigidity transition. We attempt to understand this behavior better. We have now synthesized ternary glass compositions of the type, (AsI$_{3})_{x}$(As$_{0.30}$S$_{0.70})_{1-x}$ and (AsI$_{3})_{y}$ (As$_{2}$S$_{3})_{1-y}$ over wide composition ranges of x and y, and have examined them systematically in Raman scattering and MDSC experiments. Along with earlier results$^{3}$ on binary As$_{z}$S$_{1-z}$ glasses, the present results permit mapping the reversibility window over the glass forming range of the present As-S-I ternary. The results show the window region to be of nearly triangular shape, with a base extending in the 0.20 $<$ z $<$ 0.27 range and a vertex located near y = 0.28. A possible interpretation of the results will be presented. * Supported by NSF grant DMR-04 -56472 1. P.Boolchand et al.Phil. Mag \underline {85},3823 (2005). 2. Y. Wang et al. Phys. Rev. Lett. \underline {87}, 18, 5503 (2001) 3. D.G. Georgiev, Ph.D. Thesis , Univ. of Cincinnati (2003) unpublished