Enhanced ionic conduction in dispersed solid electrolyte systems (DSES) and/or multiphase systems: AglAl 2O 3, AglSiO 2, AglFly ash, and AglAgBr
Alternating current electrical conductivity (σ) data are presented for AgIAl 2O 3, AgISiO 2, AgI-fly ash, and AgIAgBr as functions of composition, temperature, and frequency. Unlike the predictions of the classical theories of Rayleigh and Maxwell, conductivity enhancements by as much as two to three orders of magnitude have been obtained at 25°C without appreciable change in the electronic conductivities. The σ enhancement strongly depends on the particle size and the concentration of the dispersoids, as well as on the process variables, e.g., the heat treatment of the dispersoids, premelting of the electrolytes, etc., and also on cold and hot pressing. The Al 2O 3 is found somewhat unique in the sense that it leads to a maximum enhancement (by ∼ 10 3 times) when used as received and when the electrolyte in the mixture is premelted, while SiO 2 and fly ash (without premelting the electrolyte) lead to an enhancement by a factor of ∼50 and show no significant effect of premelting. SEM studies, coupled with the frequency-dependent σ data, suggest that the enhancement is due to bulk rather than grain-boundary or surface conduction. The enhanced σ is usually accompanied by a decrease in activation energy, suggesting that the dispersoids generate excess of lattice defects and thereby increase the conductivity, which is consistent with a recent theoretical model, as well as with the latest thermoelectric power measurements.