B-Site cation diffusivity of Mn and Cr in perovskite-type LaMnO3 with cation-deficit nonstoichiometry

Abstract

The Mn tracer diffusivity and Cr impurity diffusivity in LaMnO_3+δ were studied for the regime of cation-deficient nonstoichiometry with radio-isotope techniques. The effective Mn diffusion coefficient in polycrystalline LaMnO_3+δ was successfully measured in the temperature range 1423 ≤T/K ≤ 1523 and oxygen partial pressure range 0.008 ≤P_O2/bar ≤ 1. The estimated bulk diffusion coefficient of Mn in LaMnO_3+δ is quite high compared with the other perovskite oxides reported in literature, which is regarded to reflect the high cation vacancy concentration of LaMnO_3+δ. The Mn diffusivity shows a weak temperature dependence with an apparent activation energy of 0.6 eV and a strong P_O2 dependence. Both dependencies may indicate a Mn diffusion mechanism by means of B-site vacancies which is, however, facilitated by the presence of A-site vacancies; that is, the Mn diffusivity depends on the vacancy concentrations not only at the B-sites but also at the A-sites. The Cr impurity diffusivity is significantly smaller than the Mn tracer diffusivity.