EXAFS study on the local environment of Cu+ ions in glasses of the Cu2O-Na2O-Al2O3-SiO2 system prepared by Cu+/Na+ ion exchange

The local environment around Cu+ in Cu+/Na+ ion-exchanged sodium aluminosilicate glasses was investigated as a function of the ratio x (x = Cu+/[Cu+ + Na+]) by extended X-ray absorption fine structure spectroscopy (EXAFS). Glass specimens with various ratios were prepared by ion exchange in 20Na(2)O-10Al(2)O(3)-70SiO(2) (mol%) glass at 400 degreesC followed by concentration equalizing treatment. The coordination number N of Cu+ in the grasses of x20Cu(2)O-(1-x)20Na(2)O-10Al(2)O(3)-70SiO(2) (mol%) increased accompanying the increase of the interatomic distance r(Cu-o) with increasing x : N = 2.2, 2.8 and 3,7, and r(Cu-o) = 0.184, 0.188 and 0.191 nm for the samples oft = 0.2, 0.4 and 0.63, respectively. The change in the coordination of Cui was discussed in relation to the structural evolution caused by ion exchange. These changes seem to induce a change in the environment around Cu+ from twofold to fourfold coordination structure. The fourfold site for Cu+ offered a favorable situation for ionic conduction, because these highly ion-exchanged glass samples showed high electrical conductivity. (C) 2000 Elsevier Science B.V. All rights reserved.