Research On The Structure And Properties Of Microwave Assisted Synthesized La_1-xSr_xMnO₃

La_1-xSr_xMnO₃ materials owing to their unique structural and electronic structure characteristics are widely used in the fuel cells, catalytic reduction and microwave materials etc. It has great social benefits to search new synthesis methods with lower processing costs, better product performance and little environmental pollution.Microwave heating has some characteristics: volumetric heating, selective heating, rapid temperature rising rate, self-heating and microwave non-thermal effects, etc. Upon this, the method will be substantial reduction in cycle time, saving energy, eco-friendliness. So, researching on microwave synthesis methods will be beneficial to decrease energy exhaust and protect environmental.Pure La_0.7Sr_0.3MnO₃ powder is synthesized using domestic microwave oven by microwave solid method and microwave hydrothermal method from the reactants of La₂O₃, SrCO₃, MnO₂, and Sr(NO₃)₂, La(NO₃)₃·6H₂O, Mn(NO₃)₂ In this thesis, the powder dispersion state and micro-morphology were studied by ESEM and TEM. Crystal structure and the grain size were analyzed by XRD Rietveld structure refinement method. The magnetic properties have been studied by physical property measurement system (PPMS).Through 13min microwave radiation, the single phase of La_0.7Sr_0.3MnO₃ powder was synthesized by microwave solid method,. Comparing with conventional solid synthesis method, the powder synthesized by microwave solid-phase method has uniform size distribution, no hard agglomeration by SEM observation TEM pictures show that the powder has inhomogeneity grain size, small grains in 10nm～40nm, and there are still a certain of the more than 100nm flake grains.The powder synthesized by microwave hydrothermal method without aggregate, uniform grains distribution. The grain is rod structure and the length-diameter ratio is 10/3. The Rietveld structure refinement results show that products synthesized by microwave solid-phase method is rhombohedral structure and its space group is R-3CH(167), a=b=5.4989 (A|°), c=13.661 (A|°). Crystal cell is more large than conventional solid synthesis.The magnetism testing results showed the ferromagnetic-paramagnetic transition temperature, saturation magnetization and coercivity of the product synthesized by microwave solid method is approximately equal to conventional solid method. The product, synthesized by microwave hydrothermal method, has a low saturation magnetization and high coercivity. Its ferromagnetic-paramagnetic transition is a gradual process and the Curie temperature higher than 340K. The reason of La0.7Sr0.3MnO3 powder synthesized by microwave solid-phase method, with high saturation magnetization is its larger crystal cell. A longer interatomic distance is beneficial to magnetic dipole orientation and to atom magnetic moment arrangement.Thesis also studied on the process of microwave synthesis and the results show there are different process between conventional solid synthesis method and microwave solid-method. The specific reasons remain to further investigation.