Cation Self-Diffusion and Nonstoichiometry of Lanthanum Manganite Studied by Diffusion Couple Measurements

Reaction kinetics between dense, polycrystalline pellets of La 2 O 3 and Mn 3 O 4 was investigated at temperatures of 1370−1673 K and oxygen partial pressures of 40 Pa to 50 kPa. The formation of a single product phase, nonstoichiometric La 1 - x Mn 1 - y O 3 ± δ, was confirmed by X-ray diffraction and electron microprobe analysis. The solid solubility limits of La 1- x Mn 1- y O 3 ± δ determined by wave dispersive spectroscopy were in good agreement with previous reports, and equilibrium was achieved at the phase boundaries in the diffusion couples. Vacancies at the La and O sub-lattices are proposed to be the dominating point defects in the product layer. The growth of the product phase followed the parabolic rate law. The location of Pt markers demonstrated that diffusion of Mn cations in La 1- x Mn 1- y O 3 ± δ dominated over diffusion of La 3+ . The diffusion coefficient of Mn 3+ was determined from the parabolic rate constant, and an activation energy of 280 ± 40 kJ mol -1 was found. The results are discussed in relation to cation diffusion in other LaBO 3 ± δ oxides (B = Cr 3+, Mn 3+, and Fe 3+ ).