Conductivity of Boules of Single Crystal Sodium Beta-alumina

The ionic and electrochemical polarization characteristics of two boules of single crystal sodium beta-alumina (Na20.8Al203), 2 cm in diameter, were investigated over the range of 250 to 30* C using 2and 4-probe ac and dc techniques with reversible and ion-blocking electrodes. Textural (or internal) polarization at 270 C was present only in boule 1 which cleaved easily. Interfacial polarization, using solid sodium electrodes, was present at 270 C in the 2-probe conductivities L for both boules. Cleaning with liquid sodium at.3000 C reduced its magnitude, but some interfacial polarization was still present in the 2-probe conductivities for boule 2 below about 1400 C. Above 140* C, with liquid sodium electrodes, the 2-probe conductivities, essentially polarization-free, were given by KT = 3300 exp(-3650/RT). The conductivity of boule 2 at 1800 C remained essentially constant with increasing current density up to about 140 ma/cm CONDUCTIVITY OF BOULES OF SINGLE CRYSTAL SODIUM BETA-ALUMINA by William L. Fielder, Harold E. Kautz, J. Stuart Fordyce, and Joseph Singer Lewis Research Center