Abstract

Sintered bodies of BaM2O4 (M: La, Nd, Sm, Gd, Ho or Y) with CaFe2O4-related structure were synthesized by sintering BaCO3-M2O3 mixtures. The temperature dependence of oxygen ionic conductivity and the relationship between the ionic radius of M3+ ions in B sites and the crystal structure of BaM2O4 were investigated. The ionic conductivity type in BaM2O4 was divided into two groups; (a) BaLa2O4, BaNd2O4 and BaSm2O4 with order-disorder transition and (b) BaGd2O4, BaHo2O4 and BaY2O4 without the transition. There were vacant spaces in the crystal structure of BaNd2O4 and BaSm2O4 with order-disorder transition due to the distortion in the a-axis direction of an oxygen octahedron. By assuming that the vacant space is an oxygen vacancy, the ionic conductivity in BaLa2O4, BaNd2O4 and BaSm2O4 has been explained with a model of the order-disorder transition for oxygen vacancies without significant shifting of cations in the crystal lattice.

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