A series of polycrystalline samples of the type La1-xAxMnO3+δ, quenched in air at 800C, was analyzed in order to determine the defectiveness and its evolution as a function of the atomic fraction of Na or K. It was found that, from the crystallochemical point of view, both series were very similar. They represented solid solutions of rhombohedral symmetry and of perovskite structural type, both extending slightly over xA~0.25. The variation of the average valence of Mn ions in the series confirmed the initial structure deficiency (2Δ) of the binary matrix to be of cationic type: i.e. La(1-Δ)Mn(1-Δ)O3+Δ, partly compensated by excess O (Δ) with the latter presumably located in vacant positions of the metal sub-lattices. Within the domain of homogeneity, the solid solutions exhibited some anomalies at xNa~0.138 and at xK~0.147; both connected with a substantial change in the defectiveness, and clearly seen in xA variations of the (La = Mn)-site deficiency (Δ). The sample densities indicated that the excess O, present in the matrix, quickly disappeared as a function of La substitution (at xNa~0.04 and at xK~0.05). However, the cationic deficiency persisted in the series up to the concentrations of the above anomalies; whereupon it vanished. Upon further increasing the Na or K content, the crystal structure (being free of any defects) began to exhibit an increasing level of O deficiency: Δ oxyg=(3+2x-VMn)/2.

Nature of Structure Defects in Rhombohedral Series of La1-xAxMnO3+δ (A = Na, K). R.Horyń, E.Bukowska, A.Sikora: Journal of Alloys and Compounds, 2002, 346[1-2], 107-15