Conduction Model of Oxide Ions at Grain Boundary of Solid Electrolyte

Abstract

A flux of oxide ions of solid electrolyte at a grain boundary was correlated to the difference of activity (a_r) of oxide ions within two adjacent grains with different curvature at a given electric field. The flux leads to two types of conductivity : increased conductivity (σ_i (+)) and decreased conductivity (σ_i (-)) with decreasing grain size. Both the conductivities reach a maximum or minimum value at r = r_c where a _r = 1 (for r > 0) or a_r = a₀² ( for r < 0, a ₀ is the activity for r = ∞). As a result, total conductivity σ(t) (=(σ_i (+)+σ_i (-))/2) is expressed as a curve of second degree of reciprocal grain size (1/r) and reaches a maximum value at r = r_c.