Synthesis And Properties Of Perovskite-Type Nanocrystalline LaMnO₃ And LaFeO₃

There has been a long interesting in perovskite-structured compounds (of general formula ABO3), because of their good colossal magnetoresistance, catalytic performance and gas-sensing properties. The function of ABO3-type with perovskite structure can be controlled by changing A and B atoms or choosing suitable chemical doping. ABO3-type materials were found to have low price, a good selectivity and an excellent stability as catalysts and acuators. Due to its potential use in catalytic and gas-sensing application, the perovskite-type oxide attracts much attention and becomes one of the most popular topics in the field of materials. Among these materials, LaMnO3 and LaFeO3 were paid much attention. The properties of perovskite-type oxides are strongly related with the materials'inherent physical and chemical properties, also with the composition, morphology and structure of the materials. In this article, LaMnO3 and LaFeO3 with different composition, morphology and structure had been synthesized by hydrothermal, carbon template and sol-gel route. alkaline-earth metal had been used as additive to improve LaFeO3 sensor's gas sensing property. The following is the details:1. LaMnO3 nanorods were synthesized by hydrothermal route, a suitable ratio of La(NO3)3, Mn(NO3)2, PEG and ammonia water were dissolved absolutely into water solution. The reactants were transformed into a 100 ml teflon-sealed autoclave and heated at 150℃for some hours. The LaMnO3 finally had been gotten by dried and calcined. The composition, morphology and structure of the materials were characterized. It was found that the suitable reaction time is between 24h-28h, when we add a little PEG, regular nanorods can be received.2. LaMnO3 hollow nanospheres were synthesized by carbon template route. The carbon template had been synthesized by hydrothermal route. LaMnO3 hollow nanospheres could be prepared by adsorbing La3+, Mn2+ on the surface of the carbon sphere templates, and then removing the templates. The composition, morphology and structure of the materials were characterized. The catalytic performance of these hollow nanospheres with different calcined temperature had also been investigated. It was found that different calcination temperature result to different catalyst activity. When the sample was calcined at 600℃,it becomes hollow nanospher with an average diameter of 30nm and has the best catalyst activity for CO and carbon-hydrogen compound.3. La(1-x)MgxFeO3 was synthesized by sol-gel route. a suitable ratio of Fe(NO3)3,La(NO3)3, Mg(NO3)2 and citric acid were dissolved absolutely into water solution. The reactants were heating in water bath for some hours, then the sample was transformed into a 100 ml teflon-sealed autoclave and heated at 130℃for some hours. The La(1-x)MgxFeO3 finally had been gotten by dried and calcined. The composition, morphology and structure of the materials were characterized. The doped material with different ratio had been fabricated to gas sensor and the gas sensing property of the products was investigated. It was found that when the Mg2+ was doped at x= 0.1, it has the best gas sensing property for ethanol and NO.