Thermoelectric power studies on MgO-stabilized β″-alumina

Abstract.

A study of the temperature dependence of thermopower is known to yield auxiliary information about the electronic conductivity of a mixed conductor. In light of the above, thermoelectric power (TEP) measurements were made on MgO-stabilized β″-alumina over the temperature range from 773 to 1223 K under conditions of different sodium activities in the ambient in order to substantiate the existing information on the electronic conductivity of sodium beta alumina (SBA). A mixture of Na _x Si _m O_{2 m + x /2} and SiO₂ in an environment of fixed $P_{{\rm O}_{\rm 2} }$ served as electrodes reversible to Na⁺. The heat of transport obtained using the thermopower data at higher temperatures (973–1223 K) was in fair agreement with the activation energy of electrical conduction determined by other studies like impedance measurements and molecular dynamics simulation. It could be inferred from these results that there is negligible electronic conductivity in SBA under the conditions of measurement. The average TEP for SBA was determined to be 700–800 µV/K and the partial molar entropy of Na⁺ in SBA was found to be ~98 J mol^–1 K^–1.