Origin Of The Contrasting Effects Of Oxygen Reduction On The Transport Properties Of La1-Delta Mno3+Delta And La1-Xmxmno3+Delta (M : Ca,Sr) Thin Films

The effects of oxygen reduction treatments on the transport properties of La1-DeltaMnO3+delta and La1-xMxMnO3+delta thin films (M: Sr,Ca) have been investigated to understand the origin of the contrasting behaviors observed for the vacancy and Ca, Sr doped lanthanum manganites. It is found that the vacancy doped (La deficient) films with different doping levels (La deficient levels) showed a continuous change in the transport properties with increasing reduction of oxygen. The films reduced under P-O2 of 1 Pa at 1173 K showed almost insulating behavior independent of the doping level, whereas the Sr doped films showed well-known Sr doping level dependent properties. The continuous change in the transport properties for the vacancy doped (La deficient) thin films suggests that the Mn4+ concentration of the films decreases continuously with the reduction of oxygen. This behavior is in contrast with that found in the Sr doped films in which the Mn4+ concentration approaches the value characteristics of the Sr doping level under the same reduction conditions. The origin of the contrasting effects of oxygen reduction is interpreted on the basis of the proposed defect model that vacancies generated by the La deficiency Delta are partially replaced with Mn ions to give both La and Mn site vacancies, which decrease continuously with decreasing excess oxygen delta. (C) 2002 American Institute of Physics.