EXAFS study on the local environment of Cu + ions in glasses of the Cu 2O–Na 2O–Al 2O 3–SiO 2 system prepared by Cu +/Na + ion exchange

Abstract

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 2O–10Al 2O 3–70SiO 2 (mol%) glass at 400°C followed by concentration equalizing treatment. The coordination number N of Cu + in the glasses of x20Cu 2O–(1− x)20Na 2O–10Al 2O 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 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.