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 20Na2O–10Al2O3–70SiO2 (mol%) glass at 400°C followed by concentration equalizing treatment. The coordination number N of Cu+ in the glasses of x20Cu2O–(1−x)20Na2O–10Al2O3–70SiO2 (mol%) increased accompanying the increase of the interatomic distance rCu–O with increasing x: N=2.2, 2.8 and 3.7, and rCu–O=0.184, 0.188 and 0.191 nm for the samples of x=0.2, 0.4 and 0.63, respectively. The change in the coordination of Cu+ 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.