Thermodynamic properties of Na ions in beta- and beta'-Al 2O 3 through thermoelectric power data

Thermoelectric power determinations allow one to evaluate some thermodynamic properties of ionic mobile species of solid electrolytes, provided that suitable reversible electrodes are employed in assembling the thermocell. The experimental data reported previously (see Solid State Ionics, vol.5, p.187, 1981) for beta- and beta"-Al 2O 3 have been employed here to evaluate the partial pressure of Na(v) in equilibrium with these solid electrolytes in the T ranges 300-500K and 340-580K, respectively, and the Na entropy difference between beta- and beta"-Al 2O 3 in the T range 340-500K. The latter depends on T in such a way as to suggest that a second order transition would occur in beta"-Al 2O 3 at about 450