A NEW PREPARATION METHOD OF LAMNO3 PEROVSKITE USING ELECTROCHEMICAL OXIDATION

LaMnO3 perovskite was prepared by heat treatment of an oxide film which was electrochemically deposited on a Pt electrode in solutions containing both La3+ and Mn2+ ions. The La Mn ratio in the deposited oxide films increased with an increase in the [La3+] [Mn2+] ratio in solution and with a positive shift of electrode potential. The maximum value in this ratio was about one, and was obtained in solution with [La3+] [Mn2+] > 500 and/or in a potential region more positive than about 1.9 V vs. Ag AgCl. It was presumed from IR, TG, XRD, and XPS measurements that the incorporation of La3+ ion into the oxide film during electrochemical deposition is based on a specific adsorption of La3+ ions onto the surface of amorphous and hydrous ε-MnO2, which has some oxygen deficiencies, and that the La3+ ion exists as a hydroxide in the oxide. A single phase of LaMnO3 perovskite was obtained by heat-treatment of the deposited oxide film with La Mn ≒ 1.0 at a temperature higher than about 750°C, which was always lower than the preparation temperature in the ceramic technique (about 1200°C). The crystallization process in the heat treatment was also discussed from TG and XRD analysis. © 1991.