Bimodal T_gs and Macroscopic Phase Separation in Ag-Ge-S bulk glasses^*
Abstract
Ternary glasses of the composition (GeS_3)_1-xAgx in the 0 < x < 0.35 range are synthesized and examined in T-modulated DSC and Raman scattering. Bimodal endotherms are observed, one at a fixed temperature Ta = 320^oC and the other one in the 345^oC < Tb < 370^o C range that progressively upshifts as x increases to 0.30. We identify Ta with Tg of an Ag_2S glass phase that segregates from the base glass phase (with Tg = T_b). The base glass Tg upshifts in T with increasing x because Ag reacts with S to form the Ag-rich glass phase leaving a base glass that is S-deficient. Justification of Tg of the Ag_2S glass phase, modeled after the superionic α -Ag_2S and a count of Lagrangian constraints, was discussed earlier^1 within the context of work on corresponding selenides. Raman scattering results show that with increasing x, an increasing fraction of the Ag additive also enters the base glass as Ag^+ with S^- anions serving to form thiogermanate species with one, two and three non-bridging S^- species. The thermal results thus complement the optical ones to provide a global view of structure. 1. P. Boolchand and W.J. Bresser, Nature 410, 1070 (2001). * Supported by NSF grant DMR-01-01808
- Publication:
-
APS March Meeting Abstracts
- Pub Date:
- March 2004
- Bibcode:
- 2004APS..MARN15013B