Nanocomposite structure and reactivity of perovskites based on lanthanum manganites

Abstract

Data on the real/defect structure of anion-excess lanthanum manganites are analyzed. It is shown that low-temperature materials, especially those synthesized with the use of organic additives, form nanocomposite structure due to stabilization of manganese and dopant cations in highly charged states (≥4+) at anion excess. It is established that domains (layers) with perovskite structure containing point defects are separated/intergrown by extended defect regions enriched with lanthanum or promoter cations. It is noted that the composition and concentration of extended defects are controlled by the conditions of synthesis, the calcination temperature, and the nature of the promoter; these defects, which are partly retained after high-temperature treatment, can affect the functional properties of materials. Features of the cation and anion modification of lanthanum manganites and the reactivity of nanocomposite structures with respect to oxidation reactions are analyzed. It is concluded that at a high content of weakly bound oxygen and a noticeable mobility of the lattice oxygen, the activity of these materials in various oxidation reactions is determined by their defect structure and specificity of the catalytic action.