Low frequency dielectric characteristics of ionic conducting glasses

Abstract

In the study of the dielectric properties of ionic conducting glasses the mechanisms of electrode polarization and dielectric relaxation phenomenahave been disputed for a long time. In general, these phenomenawere explained commonlyby the motion of charge carriers in the glass.

Numerous suggested theories for the dielectric relaxation mechanisms were evaluated with respect to experimental observation. Of all the proposed explanations, the random zig-zag paths model appears to give the best quantitative agreement-with the experimental data

Electrical measurements were made with an ac capacitance bridge, and de transient charge-discharge measurements were performed to support the results of the ac measurements. Experimental results thus obtainedwere discussed in terms of existing theories. A satisfactory explanation for the electrode polarization was obtained with the space charge mechanism. Utilizing this space charge mechanism, an investigation of the glass surface structure was possible. In particular, 25 mol % Na₂0-Si0₂ glass and soda-lime glass were studied in more detail and infrared measurements to determine the water content of the surface of these glasses were made to support the analyses. In addition, preliminary experiments on electronic conducting glass were conducted to see if the ionic and electronic conducting glasses behave similarly.

On the other hand, the dielectric relaxation is closely related to the short range motion of the mobile ions. Thus it must be related with bulk properties of glasses such as glass structure and phase separation. From the frequency and temperature dependences of the dielectric relaxation characteristic, information on bulk properties ofglasses is obtained. The electrode polarization is sensitive to surface condition while the dielectric relaxation is not.

Since electrode polarization is observed at lower frequencies than dielectric relaxation, the former might be concerned with the long range motion of charge carriers and the later their short range motion. Thus the electrode polarization is expected to be a function of parameters such as sample thickness, temperature, frequency, and surface environments (blocking or non-blocking electrode conditions, electrode materials, ion exchanged surface structure, etc.).