Chemical state of oxygen in Ag+/Na+ ion-exchanged sodium silicate glass

The chemical state of oxygen in Ag+/Na+ ion-exchanged sodium silicate glass was investigated using X-ray photoelectron spectroscopy and Si-29 nuclear magnetic resonance spectroscopy. Ion-exchange treatment was performed on 34Na(2)O-66SiO(2) glass at temperatures well below T-g of the mother glass, giving glass samples with various Ag+/Na+ ratios. The glass transition temperature decreased about 150 K with increase in Ag+ concentration, accompanied by the simultaneous decrease of the thermal expansion coefficient by about 50%. Large changes in O1s XPS spectra were observed; the bridging and non-bridging oxygen peaks shifted toward larger binding energies, and the ratio of non-bridging oxygen (NBO) to bridging oxygen decreased with increasing Ag+ concentration. This trend revealed that the increased covalency of Ag+-O-nb bonds decreased T-g and the thermal expansion coefficients. Si-29-NMR results showed that Q(3) units decreased while Q(2) units increased without accompanying Q(4) units. These results suggested that two coordinated Ag+ ions with non-bridging and bridging oxygen would be formed in the sample glasses. (C) 1997 Elsevier Science B.V.