【作者】 王强；

【导师】 段苹；

【作者基本信息】 北京工业大学 ， 凝聚态物理， 2014， 硕士

【摘要】 钙钛矿锰氧化物由于具有CMR效应而引起人们的广泛关注，一方面是因为，庞磁电阻有着巨大的潜在应用价值，另一方面，这类材料属于典型的强关联体系，具有丰富的物理内涵。本论文重点研究了电子掺杂锰氧化物La-Sb-MnO体系多晶样品的物理性质以及烧结温度和掺杂浓度对其物性的影响。主要研究内容包括以下几个方面：1.概述了钙钛矿CMR锰氧化物的研究历史和研究现状。首先介绍了该类材料的晶体结构、电子结构、电磁特性等。接着介绍了CMR效应的机理研究，主要包括双交换作用、超交换作用和相分离。最后，在现有理论的基础上提出了本文的研究思路。2.采用高温固相烧结法制备了La0.62Sb0.38MnO3多晶样品。样品的XRD和SEM测试结果表明样品的成相质量很好。对样品进行了磁性质的研究，发现样品在居里温度处约225K出现明显的铁磁—顺磁转变，并且存在自旋冻结现象。通过标准四探针法测试了La0.62Sb0.38MnO3多晶样品不同磁场下电阻率随温度的变化，发现样品存在金属—绝缘体转变现象，并且体现了良好的CMR效应。我们对电阻率随温度的变化曲线进行了分段拟合，高温区域采用小极化子跃迁模型拟合，发现随着磁场的增加，小极化子激活能Eα逐渐减小；在低温区域我们采用了一个唯象方程进行拟合，发现随着磁场的增强拟合参数均变小，这表明磁场增强造成了散射减弱，电阻率减小。3.研究了不同烧结温度下制备的La0.93Sb0.07MnO3多晶样品，发现样品的物理性质对烧结温度有着较强的依赖关系。随着烧结温度的增加，多晶样品的晶粒逐渐增大，畸变逐渐变弱。通过电输运性质和磁性质测试发现样品的电阻率和饱和磁化强度随着烧结温度增加均减小，金属—绝缘体转变温度和居里温度均增大。我们分析认为晶粒的结构畸变和晶界效应在物理性质中起着关键作用。4.对不同掺杂浓度下的La1-xSbxMnO3（x=0.15，0.20）红外吸收光谱进行了高斯拟合，发现该样品中存在相分离现象。测试研究了不同掺杂浓度下样品的磁性质和电输运性质。更多还原

【Abstract】 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.更多还原