Impurity diffusion of 141Pr in LaMnO3, LaCoO3 and LaFeO3 materials

The impurity diffusion of Pr3+ in dense polycrystalline LaMnO3, LaCoO3 and LaFeO3 was studied at 1373-1673 K in air in order to investigate cation diffusion in these materials. Cation distribution profiles were measured by secondary-ion mass spectrometry and it was found that penetration profiles of Pr3+ had two distinct regions with different slopes. The first, shallow region was used to evaluate the bulk diffusion coefficients. The activation energies for bulk diffusion of Pr3+ in LaMnO3, LaCoO3 and LaFeO3 were 126 +/- 6, 334 +/- 68 and 258 +/- 75 kJ mol(-1), respectively, which are significantly lower than previously predicted by atomistic simulations. The bulk diffusion of Pr3+ in LaMnO3 was enhanced compared to LaCoO3 and LaFeO3 due to higher concentrations of intrinsic point defects in LaMnO3, especially La site vacancies. Grain-boundary diffusion coefficients of Pr3+ in LaCoO3 and LaFeO3 materials were evaluated according to the Whipple-Le Claire equation. Activation energies for grain-boundary diffusion of Pr3+ in LaCoO3 and LaFeO3 materials were 264 +/- 41 kJ mol(-1) and 290 +/- 36 kJ mol(-1) respectively. Finally, a correlation between activation energies for cation diffusion in bulk and along grain boundaries in pure and substituted LaBO3 materials (B = Cr, Fe, Co) is discussed.