Effect Of Different Preparation Conditions On Physical Properties Of La_1-xSb_xMnO₃Ceramics

Perovskite manganites have been a subject of vivid interest in recent yearsbecause of the observation of colossal magnetoresistance (CMR) in the materials. Onone hand, these materials have great potential value of applications; on the other hand,the CMR materials are typical of strongly correlated systems, with a wealth ofphysical content. This thesis focuses on the physical properties of La-Sb-Mn-Oceramics synthesized by the solid state reaction including the effect of sinteringtemperature and doping concentration on their physical properties. The main contentsinclude the following aspects:1. An introduction of the history and research status about CMR materials waspresented. First, the crystal structure, electronic structure, electrical transport behaviorand magnetic properties of these materials were introduced. Then the mechanism ofCMR effects which included double exchange interaction, super exchange interactionand phase separation were summed up. Finally, the study object and content weregiven on the basis of existing theories.2. Polycrystalline samples La0.62Sb0.38MnO3were prepared by the conventionalsolid-state reaction method. Structural, magnetic and electrical transport propertieshave been researched. X-ray diffraction analysis confirms the hexagonal crystalsymmetry. The scanning electron microscopy (SEM) results for La0.62Sb0.38MnO3ceramics show that the quality of the sample is excellent. Magnetizationmeasurements indicate La0.62Sb0.38MnO3experienced from paramagnetic toferromagnetic state transition with decreasing temperature at about225K. Resistivitydependences on temperature exhibit metal-insulator transition (MIT). The curves ofhigh-temperature region were fitted by small polaron hopping model. The resultsshow that with magnetic field increasing, the small polaron activation energy Eαdecreases. The curves of low-temperature region were fitted by a phenomenologicalequation. It was found that with the magnetic field increasing, fitting parametersbecomes small which indicating that the magnetic field caused the scattering reducedand resistivity decreased.3. Polycrystalline sample La0.93Sb0.07MnO3sintered at different temperatureswere studied. It is observed the properties of La0.93Sb0.07MnO3compounds strongly depend on sintering temperatures (TS). With TSincreasing, the degree of latticedistortion has been weakened and the grain size has become larger. Furthermore, theresistivity was reduced, the Curie temperature and metal-insulator transitiontemperature was enhanced; the saturation magnetization has decreased with TSincreasing. The structure distortion and grain boundary plays a key role in thephysical properties.4. The infrared absorption spectra of the La1-xSbxMnO3（x=0.15，0.20）withdifferent doping concentrations was fitted by Gauss function. The results show thatthe phase separation phenomena exist in the sample. It is observed that with dopingconcentration increasing, the magnetization increased.