Effect Of Rare Earth Doping On The Structure And Electromagnetic Properties Of Perovskite Manganese Oxides

The perovskite manganese oxide La_1-xCa_xMnO₃has been widely concerned by scholars because of its unique electromagnetic properties.In this paper,the structure and electromagnetic properties of La_1-xCa_xMnO₃have been systematically studied,and the influence of Dy doping on the La_1-xCa_xMnO₃(LCMO)system has been discussed.The main conclusions were drawn as follows:Firstly,using La₂O₃?MnO₂and Ca CO₃as the raw materials,La_1-xCa_xMnO₃(x=0.1,0.2,0.3,0.4,0.5,0.7,0.9)were prepared by a solid-state reaction method.The crystal structure of La_1-xCa_xMnO₃was analyzed by X-ray diffraction.The morphology features of La_1-xCa_xMnO₃were obtained by scanning electron microscopy.The Electron Spin Resonance(ESR)spectrogram of La_1-xCa_xMnO₃were measured at different temperatures.The free radical concentration of La_1-xCa_xMnO₃at different doping concentrations were obtained.The experimental results show that with the increase of Ca doping concentration,the cell volume of La_1-xCa_xMnO₃gradually decreases,closer adhesion and less pores between particles are observed.At20?,with the increase of Ca doping concentration,the magnetoresistance of La_1-xCa_xMnO₃increasing first,reaching the maximum around x=0.3,and then decreasing gradually.At the same doping concentration,the ESR spectrum intensity of La_1-xCa_xMnO₃decreases gradually with the increasing temperature,so as the concentration of free radicals in La_1-xCa_xMnO₃.With the increase of Ca doping concentration,the ESR spectrum intensity of La_1-xCa_xMnO₃first increased and then gradually decreased at the same temperature.The free radical concentration in La_1-xCa_xMnO₃follows the same trend,increasing first,reaching the maximum around x=0.3,and then decreasing gradually.For the temperature higher than 20?,the variation of the free radical concentration of La_1-xCa_xMnO₃to temperature is similar to that of magneto-resistance of La_1-xCa_xMnO₃.Secondly,using La₂O₃?Dy₂O₃?MnO₂and Ca CO₃as the raw materials,(La_1-xDy_x)_0.7Ca_0.3MnO₃(x=0.1,0.2,0.3,0.4,0.5,0.7)were prepared by a solid-state reaction method.The morphology features and crystal structure of(La_1-xDy_x)_0.7Ca_0.3MnO₃were analyzed.The Electron Spin Resonance spectrogram of(La_1-xDy_x)_0.7Ca_0.3MnO₃were measured at different temperatures.The free radical concentration of(La_1-xDy_x)_0.7Ca_0.3MnO₃at different doping concentrations were obtained.The experimental results show that with the increase of Dy doping concentration,the cell volume of(La_1-xDy_x)_0.7Ca_0.3MnO₃gradually decreases,closer adhesion and less pores between particles are observed.At 20?,with the increase of Dy doping concentration,the magnetoresistance of(La_1-xDy_x)_0.7Ca_0.3MnO₃gradually increases.At the same doping concentration,the ESR spectrum intensity of(La_1-xDy_x)_0.7Ca_0.3MnO₃decreases gradually with the increasing temperature,so as the concentration of free radicals in(La_1-xDy_x)_0.7Ca_0.3MnO₃.With the increase of Dy doping concentration,the ESR spectrum intensity of(La_1-xDy_x)_0.7Ca_0.3MnO₃first decreased and then gradually increased at the same temperature.The free radical concentration in(La_1-xDy_x)_0.7Ca_0.3MnO₃follows the same trend,decreasing first,reaching the minimum around x=0.4,and then increasing gradually.Under the same measurement condition,the magnetoresistance of(La_1-xDy_x)_0.7Ca_0.3MnO₃is much larger than that of La_0.7Ca_0.3MnO₃,indicating that the doping of Dy will significantly increase the magnetoresistance of perovskite manganese oxide.With the increase of Dy doping concentration,the magnetoresistance of(La_1-xDy_x)_0.7Ca_0.3MnO₃increases.With the increase of temperature,the free radical concentrations of(La_1-xDy_x)_0.7Ca_0.3MnO₃and La_0.7Ca_0.3MnO₃decrease continuously.Rare earth element doping can obviously change the electromagnetic properties of perovskite manganese oxides,which has important research significance in improving the properties of materials and reducing the use conditions.