STRUCTURAL STUDY OF GES2-AG2S GLASSY SYSTEM BY SILVER K-EDGE EXAFS EXPERIMENTS MADE AT ROOM AND LOW-TEMPERATURE

The silver environments in (1-y)GeS2+yAg2S (0 < y less-than-or-equal-to 0.5) ternary glasses have been characterized by Ag K-edge EXAFS experiments performed at room and low temperature. Several glassy compositions and the a low temperature crystalline forms of Ag2S and Ag8GeS6 phases were studied. The comparison between glassy and crystalline silver sites have allowed us to determine the silver surroundings in these glasses and to suggest a hypothesis of their structure. Thus, for weak Ag2S concentrations (y < 0.3) the glassy Ag sites seem to present some analogies with those of alpha-Ag2S crystal. On the other hand, when Ag2S proportion increases in the glass (y greater-than-or-equal-to 0.3), the silver sites are rather similar to those encountered in alpha-Ag8GeS6. These results would be explained by the formation, for weak silver amounts, of Ag2S clusters in the glassy matrix which is mainly constituted by the GeX4 clustering. For higher Ag2S contents, the breaking of GeX4 Connection increases, leading to a better distribution of the Ag2S glass modifier and thus to a much more homogeneous glass.