Conductivity dispersion in single-crystal β-alumina electrolyte

Abstract

WE report data which demonstrate the existence of a conductivity dispersion in single-crystal β-alumina and, we believe, for the first time, a distribution of conductivity relaxation times in any single-crystal ionic conductor. A cylindrical boule of high quality Na β-alumina grown at Union Carbide was supplied to us by Roditi International Corporation. Figure 1 shows the frequency-dependent conductivity of this crystal in the range 10²–10⁷ Hz, measured at various subambient temperatures (for details of the apparatus see refs 1 and 2). At normal temperatures, electrode effects produce an apparent dispersion in conductivity. At these lower temperatures, however, the dispersion seems to be an intrinsic property of the bulk material since it starts at frequencies which are related to the level of the d.c. conductivity (f = σ/2πε)^1,3 as indicated by arrows in (Fig. 1). This behaviour closely resembles the dielectric behaviour which has been studied in silicate and other glasses^3,4. The dispersions in conductivity cannot be accounted for in terms of the conventional (Debye) theories of dielectric loss; indeed, the departures from Debye behaviour are probably more marked in single-crystal β-alumina than in many vitreous electrolytes.