EXAFS studies of the local thermal expansion in borate glasses

Temperature-dependent EXAFS measurements have recently been made on the silver borate glass [Ag2O . 4B(2)O(3) ], and the superionic AgI-doped glass [AgI](0.75)[3Ag(2)O . 1B(2)O(3)](0.25). The Ag-O co-ordination has been studied in the first sample, the I-Ag in the second one. In both cases a significant reduction of the first shell inter-atomic distance has been observed as temperature increases from 15 to 300 K. Here a detailed analysis of the EXAFS results for the AgI-doped glass is presented. The distributions of first shell I-Ag distances reconstructed from EXAFS for the glass and c-AgI, and their leading statistical parameters, are compared and critically discussed. The local negative expansion in the glass is partially attributed to the relaxation of the a-AgI network within the host binary matrix. (C) 2001 Elsevier Science B.V. All rights reserved.