A-site nonstoichiometry and B-site doping with selected M3+ cations in La2-xCu1-y-zNiyMzO4-delta layered oxides

In this work studies on a modification of Cu-based, layered oxides with K2NiF4-type structure are presented concerning formation of cationic nonstoichiometry in the A-sublattice of the parent La2CuO4, as well as an introduction of selected M3+ cations (Sc, Ga, In) at the B-site into La1.9Cu1-xMxO4 and Ni-containing La1.9Cu0.45Ni0.45M0.1O4. It is shown that synthesis of phase-pure La2-xCuO4 can be done with values of x <= 0.1, and in the A-site nonstoichiometric materials further doping with M3+ is also achievable. Formation of solid solutions for M3+ -doped samples follows the expected trend, with the widest range observed for the smallest Sc3+ cation, z <= 0.1. Apart from a different structural behavior of the doped oxides at high temperatures, it is documented that the discussed substitution affects strongly the oxygen content (e.g. high concentration of the oxygen vacancies is present in La1.9CuO4-delta), as well as electrical conductivity. This is documented by the high-temperature X-ray diffraction, thermogravimetric, iodometic titration and electrical measurements. Since the compounds possess good transport properties, are stable at elevated temperatures, exhibit moderate thermal expansion and are Co-, Sr- and Ba-free, the proposed doping strategy seems interesting concerning development of the oxygen-transporting membranes based on Cu-containing oxides. For example, 1 mm thick La1.9Cu0.9Sc0.1O4-delta membrane was found to deliver 0.37 mL cm(-2) min(-1) oxygen flux at 950 degrees C, a very high value for the K2NiF4-type materials.