Effect of addition of Ag on the microstructures and electrical properties of sol-gel derived SnO2 glass composites

The effect of addition of Ag on the microstructure and electrical propertie s of sol-gel derived SnO2-glass composites was examined. Comparisons of the microstructures and electrical properties were carried out between glass c omposites prepared by a sol-gel method and a conventional one using glass f rit. The glass composite gels and the SnO2-glass powder mixtures containing AgNO3 were calcined at 500 degrees C in order to decompose AgNO3 into Ag a nd then fired at 900 degrees C. In the sol-gel derived glass composites, th e grain growth of Ag was suppressed and Ag particles connected mutually at the boundaries of aggregated gel particles to form three-dimensional networ ks. Thus, the glass composite derived by the sol-gel method showed a high e lectrical conductivity and a positive temperature coefficient of resistance (TCR). The highly electrical conductive paths of Ag in the glass composite were effectively formed when powder compacts were formed at a higher press ure. On the other hand, in the glass composites prepared using SnO2-glass p owder mixtures, coarse-grained Ag particles were isolated in closed pores r egardless of the forming pressure, and therefore did not contribute to elec trical conduction in the glass composite.