Preparation And Acetone Sensitive Properties Of LaFeO₃-based Thin Films By Polymerizable Complex Method

Perovskite structure LaFeO₃ thin films were prepared by polymerizable complexmethod, of which the synthetical processes and sensitive properties to acetone gashave been discussed. Relation of the composition, synthetical process, structure andsensitive property to acetone gas of LaFeO₃ thin films was investigated in this paper.With citric acid used as complex agent and ethylene glycol as crossing agent, theprecursor solution was prepared by dissolving La(NO₃)₃, FeCl₃ and other inorganicsalts into water, of which the concentration was 0.3mol/L. LaFeO₃ thin films withperovskite structure nano-crystalline grains were fabricated after the dip-coating,drying, pre-heating and sintering. FT-IR, TG-DTA, XRD, SEM and AFM were usedto analyze the precursor and the thin films. Sintering temperature, roughness of theAl2O3 substrates and concentration of the precursor were discussed as the key factorsto the thin films morphology. The kinetic model of the growth of LaFeO₃ thin filmthrough polymerizable complex method was proposed as the following steps, (1)solution film to gel film, (2) gel film decomposed into La-Fe-O amorphous film, (3)crystallization of the La-Fe-O amorphous film, (4) grain growth in the polycrystallinefilm.The LaFeO₃ thin films exposed to 80ppm acetone gas show that sensitivity are315, and response time are within 15s at the testing temperature of 350°C. Itsconductive and sensitive mechanism was proposed, with the types and concentrationof defects and conductive carrier discussed. The sintering temperature, structure of thethin films and testing temperature are the main factors to the sensitive properties ofLaFeO₃ thin films to acetone gas. With the Cu²⁺ doped and substituted for Fe3+, thestable temperature range of the thin films enlarged, and the recovery speed andstability enhanced. The sensitivity of the LaFe_0.95Cu_0.05O₃ thin films has a simplelinear relation to the concentration of acetone gases higher than 5ppm. With the Mo6+doped and substituted for Fe³⁺, the response property to acetone gas of theLaFe_0.95Mo_0.05O₃ thin film is different to LaFeO₃ and LaFe_0.95Cu_0.05O₃ thin filmabsolutely, which was explained by discussing the types of the defects and theirinteraction.