锶掺杂钴酸镧薄膜的微观结构及其物理性能研究

发布时间：2018-06-01 14:39

本文选题：钙钛矿薄膜 + 微观结构　；参考：《青岛大学》2017年硕士论文

【摘要】：钴酸镧具有稳定的晶体结构、独特的电磁特性以及较高的电催化活性,在信息存储、环境保护和工业催化等领域有广泛的应用前景。在钴酸镧薄膜中掺杂锶或引入氧空位,能显著改变其物理性能。本论文利用高分辨透射电子显微学系统地研究了锶掺杂和氧空位对La_(1-x)Sr_xCoO_3(LSCO)薄膜微观结构的影响,并关联了其电、磁性能。本硕士论文共分为四章。第一章主要对钙钛矿氧化物的晶体结构、前期理论模型以及研究现状进行综述。介绍了钙钛矿氧化物的微观结构及其物理特性,分析了近期LSCO体系的研究现状,指明了未来的研究方向,阐明了选题的目的及意义。第二章利用高分辨透射电子显微镜系统地研究了退火及未退火La_(0.33)Sr_(0.67)CoO_3薄膜的微观结构,并关联了其电磁性能。研究发现,未退火薄膜中只有A位存在由阳离子有序导致的调制结构;真空退火薄膜的A位和B位分别存在由阳离子有序和氧空位有序导致的调制结构。氧空位有序导致薄膜由退火前的铁磁性金属导体转变为退火后的无磁性半导体。第三章通过调控薄膜沉积过程中的氧压制备了不同氧含量的La_(0.67)Sr_(0.33)CoO_(3-δ)薄膜。利用x射线衍射仪和高分辨透射电子显微镜系统研究了薄膜的结构及微观结构,并关联了其磁学性能。研究发现,氧空位的引入导致薄膜面外晶格拉长。结合磁性能测试和第一性原理计算,证实氧空位是通过改变薄膜中钴离子的价态而影响钴离子间的交换耦合进而抑制薄膜的铁磁性,其工作机制与锶掺杂类似。第四章研究了锶掺杂和氧空位对LSCO薄膜电输运性能的影响。研究发现,当锶掺杂量从0增加到0.3时,薄膜的电输运机制从变程跃迁变为双交换作用,同时薄膜由半导体变为金属性导体。高分辨透射电子显微学观察研究发现,只有当锶掺杂量为0.3时,LSCO薄膜中双交换作用最强,导电性最佳。
[Abstract]:Lanthanum cobalt has stable crystal structure, unique electromagnetic properties and high electrocatalytic activity. It has a wide application prospect in the fields of information storage, environmental protection and industrial catalysis. Doping strontium or introducing oxygen vacancy into lanthanum cobalt thin film can significantly change its physical properties. In this paper, the effects of strontium doping and oxygen vacancy on the microstructure of LaStuff thin films have been systematically studied by means of high resolution transmission electron microscopy (HRTEM), and their electrical and magnetic properties have been correlated. This thesis is divided into four chapters. In the first chapter, the crystal structure of perovskite oxide, the previous theoretical model and the research status are reviewed. The microstructure and physical properties of perovskite oxides are introduced, the recent research status of LSCO system is analyzed, the future research direction is pointed out, and the purpose and significance of selecting the topic are expounded. In chapter 2, the microstructures of annealed and unannealed La_(0.33)Sr_(0.67)CoO_3 films are systematically studied by means of high resolution transmission electron microscopy (HRTEM), and their electromagnetic properties are correlated. It is found that only A site has modulation structure caused by cationic order in unannealed films, and A site and B site in vacuum annealed films have modulation structures caused by cationic order and oxygen vacancy order, respectively. The order of oxygen vacancies leads to the transformation of the thin films from ferromagnetic metal conductors before annealing to nonmagnetic semiconductors after annealing. In chapter 3, different oxygen contents are prepared by controlling the oxygen in the deposition process of the thin films. The structure and microstructure of the films were studied by means of X-ray diffractometer and high resolution transmission electron microscope, and their magnetic properties were correlated. It is found that the introduction of oxygen vacancies leads to the elongating of the off-plane lattice of the thin films. Combined with magnetic properties test and first-principle calculation, it is proved that oxygen vacancy affects the exchange coupling between cobalt ions by changing the valence state of cobalt ions in the films, and thus inhibits the ferromagnetism of the films, and its working mechanism is similar to that of strontium doping. In chapter 4, the effects of strontium doping and oxygen vacancy on the electrical transport properties of LSCO thin films are investigated. It is found that when the doping amount of strontium is increased from 0 to 0.3, the electric transport mechanism of the film changes from variable range transition to double exchange interaction, and the film changes from semiconductor to gold attribute conductor. The results of high resolution transmission electron microscopy (TEM) show that the double exchange effect is the strongest and the conductivity is the best when the doping amount of strontium is 0.3.
【学位授予单位】：青岛大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：O484

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