Electrical conductivity of ion-exchanged oxide glasses

Bulk glasses in the system Na₂O-CaO-Al₂O₃-B₂O₃-SiO₂ have been subjected to a sodium ⇌ silver exchange reaction. The application of a suitable combination of electric field and temperature brings about switching to a high conducting state (HIE). The critical electric field, E_c, has a value in the range 2 to 20 V cm^-1 and E_c values decrease as a function of temperature. The resistivity in the HIE state is of the order of 10 Ωcm and the activation energy is 0.01 eV. Wagner's asymmetric polarization cell measurements show that the conductivity is ionic in nature. No switching is observed in the case of glasses subjected to a sodium ⇌ copper exchange reaction carried out on these glasses at 525 ° C for 12h. This is ascribed to the microstructure exhibited by such exchanged samples which consists of copper-rich droplet phases dispersed within a copper-deficient matrix. The rather large inter-droplet separation makes it difficult for the copper-rich phase to grow to its percolation limit.