B-Site cation diffusivity of Mn and Cr in perovskite-type LaMnO(3) with cation-deficit nonstoichiometry.

ABSTRACT

The Mn tracer diffusivity and Cr impurity diffusivity in LaMnO(3+delta) were studied for the regime of cation-deficient nonstoichiometry with radio-isotope techniques. The effective Mn diffusion coefficient in polycrystalline LaMnO(3+delta) was successfully measured in the temperature range 1423 < or =T/K < or = 1523 and oxygen partial pressure range 0.008 < or =P(O2)/bar < or = 1. The estimated bulk diffusion coefficient of Mn in LaMnO(3+delta) 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+delta). 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.