Electrical conductivity of Ag+/Na+ ion-exchanged titanosilicate glasses

The Ag2O–TiO2–SiO2 glasses were prepared by Ag+/Na+ ion-exchange method from Na2O–TiO2–SiO2 glasses at 380–450 °C below their glass transition temperatures (Tg), and their electrical conductivities were investigated as functions of TiO2 content and the ion-exchange ratio (Ag/(Ag+Na)). In a series of glasses 20R2O·xTiO2·(80−x)SiO2 with x=10, 20, 30 and 40 in mol%, the electrical conductivities at 200 °C of the fully ion-exchanged glasses of R=Ag were in the order of 10−5 or 10−4 S cm−1 and were 1 or 2 orders of magnitude higher than those of the initial glasses of R=Na. The glass of x=30 exhibited the highest increase of conductivity from 3.8×10−7 to 1.3×10−4 S cm−1 at 200 °C by Ag+/Na+ ion exchange among them. When the ion-exchange ratio was changed in 20R2O·30TiO2·50SiO2 system, the electrical conductivity at 200 °C exhibited a minimum value of 7.6×10−8 S cm−1 around Ag/(Ag+Na)=0.3 and increased steeply in the region of Ag/(Ag+Na)=0.5–1.0. When the ion-exchange temperature was changed from 450 to 400 °C, the conductivity of the ion-exchanged glass of x=30 decreased. The infrared spectroscopy measurement revealed that the ion-exchange temperature of 450 °C induced a structural change in the glass of x=30. The Tg of the fully ion-exchanged glass of x=30 was 498 °C. It was suggested that the incorporated silver ions changed the average coordination number of titanium ions to form higher ion-conducting pathway and resulted in high conductivity in the titanosilicate glasses.