Electric conduction and dielectric relaxation processes in solid oxide fuel cell electrolyte La0.5Sr0.5Ga0.6Ti0.4O3−δ

Abstract

Electric conduction in the solid oxide fuel cells electrolyte, La0.5Sr0.5Ga0.6Ti0.4O3−δ, has been elucidated by dc and ac measurements as a function of temperature from 528to1103K. The sum of resistances in the bulk and boundary, Rb and Rgb, estimated in impedance analyses are nearly in agreement with dc resistance. Though Rb<Rgb at T<650K, their relative relation is reversed at T>650K. Since reciprocal resistance is proportional to conductivity, temperature dependencies of T∕Rb and T∕Rgb yield activation energies for conductions in the bulk and boundary. Two relaxation processes show up in dielectric properties, i.e., low-frequency relaxation peak due to conduction in the boundary and high-frequency peak resulting from bulk conduction. Temperature dependencies of resonance frequencies and maxima of dielectric parameters in these relaxation peaks are used to estimate migration energies of O2− ion, EM, and energies required for creation of a free oxygen vacancy assisting O2− migration, EO. The sums of EM and EO in high- and low-frequency peaks are mostly in agreement with activation energies estimated from temperature dependencies of T∕Rb and T∕Rgb.