Structure of fast-ion-conducting AgI-doped borate glasses in bulk and thin film forms

Abstract

B2O5 42 BO3 32 1BO 4 2 for n50.5. Both reactions shift to the right upon increasing the amount of AgI. This influence of the doping salt on the glass structure causes the lowering of the glass transition and fictive temperature at which the structure of the supercooled liquid is frozen into the glassy state. A parallel study of infrared transmission spectra of thin films in the diborate family showed the presence of a background interference wave that affects strongly the relative intensity of bands due to borate tetrahedra and triangular units. This finding suggests that conclusions based on direct comparison of infrared spectra of thin film and bulk samples of the same composition should be drawn with caution. The study of the far-infrared profiles of glasses in the pyroborate series suggested that the majority of silver ions exist in two distributions of coordination environments; one is formed primarily by oxygen atoms provided by the borate network and the other is made mainly by iodide ions, without excluding the presence of mixed oxyiodide sites. The spectroscopic characteristics of silver iodide sites were found to change progressively with AgI addition and to point towards sites of tetrahedral coordination such as those found in crystalline AgI. However, for diborate glasses the far-infrared results suggest the presence of oxide, iodide, and mixed O/I environments for silver ions. Therefore, this study shows that the formation and organization of separate silver iodide sites in xAgI-(12x)@Ag2O-nB2O3# glasses depends on both Ag2O and AgI content. @S0163-1829~99!02030-5#