Thermal diffusivity and electrical conductivity in fast ion conducting composites: A correlation

The thermal diffusivity and electrical conductivity have been measured for two ion conducting polyethylene oxide (PEO) based polymer-ceramic composites viz. (PEO:NH4I) + xAl2O3, (PEO:LiBF4) + xBa0.70Sr0.30TiO3 and two solid-solid composites viz. AgI + xAl2O3, AgI +xBa0.70Sr0.30TiO3. The thermal diffusivity has been measured by the novel photoacoustic technique while the electrical conductivity has been measured by impedance spectroscopy technique using complex impedance plots. The pattern of variation in the electrical conductivity (σ) vs. composition plot and that in the thermal diffusivity (αs) vs. composition plot are similar. Interestingly, the correlation between αs and σ is not only qualitative but is quantitative as well in the sense that the ratio (αs / σ) remains constant for all the samples within the same system (though their conductivities are different) similar to Wiedmann-Franz law applicable to metallic conductors.