Exploring oxygen non-stoichiometry in presumably stoichiometric double perovskites: the case study for LaCu0.5Mn0.5O3-δ

Perovskite-like oxide with the general formula LaCu0.5Mn0.5O3–δ (LCMO) was synthesized via the combustion of organo-metallic precursors. X-ray powder diffraction and high-resolution transmission electron microscopy were implemented for reliable characterization of the crystal structure of the sample obtained. Accordingly, disordered cation arrangement in B-sublattice was detected. The studied specimen was confirmed to possess non-zero oxygen vacancy concentrations at reductive annealings which were shown to modify LCMO's low-temperature magnetic properties. Density functional theory approach was also applied to assess the symmetry of the crystalline lattice and to analyze the influence of cationic order on LCMO electronic and magnetic structure. Anionic sites allocated between varying cation types were shown to possess sufficiently different vacancy formation energies and, therefore, the varied ability to release oxygen into the gas phase. The obtained results were taken into account at developing theoretical model of defect formation and equilibration in LCMO. The proposed concept was validated by a good coincidence between the experimental results on isothermal dependencies of oxygen content vs external conditions (temperature and oxygen partial pressure) and the calculations performed. Thermodynamic properties were also shown to be strongly dependent on cation ordering type. The obtained results are believed to be useful for the interpretation of dielectric and optical properties of LCMO and related oxide materials inclined to possess oxygen non stoichiometry at high temperatures.