YBCO超导叠层膜的光辅助MOCVD生长研究

发布时间：2018-05-24 20:38

本文选题：超导体 + YBCO　；参考：《吉林大学》2015年硕士论文

【摘要】：高温超导体YBCO具有高载流强度和低交流损耗等优点,能在液氮环境下工作,在微波、能源及电力等领域有着广阔的应用前景和商业价值。研究发现,YBCO超导膜的临界电流密度会随着膜厚度的增加而降低。如何解决这一问题进一步提高YBCO超导膜的临界电流密度,成为了当前的研究热点。根据磁通钉扎理论,人为的在YBCO超导膜内引入缺陷作为钉扎中心来提高其临界电流密度是可行的。它主要是通过掺杂或者引入晶格失配来影响超导膜内的缺陷状态,提高缺陷浓度。让这些缺陷作为有效的钉扎中心,可以阻止磁通因涡旋运动而产生能量耗散,从而提高超导膜的电流承载能力。本文采用光辅助MOCVD技术,就这个问题对YBCO超导叠层膜展开了研究,具体研究内容如下： (1)对Ba源对YBCO外延膜结晶质量和表面形貌进行了研究,实验发现,在制备YBCO外延膜时,Ba源挥发率对膜结晶质量和微观形貌有较大影响,“贫钡”的YBCO薄膜表面堆积大量CuO杂质颗粒,膜内出现尺寸很大的裂缝；随着Ba源温度提高,源挥发率提高,膜内Ba含量得到补充,表面杂质颗粒逐渐减少.选用适当的Ba源加热温度,保持Ba源稍微过量能够获得结晶质量较好的膜。 (2)选用了Y2O3纳米薄层结构作为生长YBCO叠层膜的过渡层,对在YBCO超导膜上生长的Y2O3纳米过渡层的微观形貌进行了研究,随着生长时间增加Y2O3纳米点由于点与点之间的合并尺寸变大密度降低。 (3)在LAO衬底上成功制备出YBCO/Y2O3/YBCO叠层薄膜,Y2O3纳米点的大小对YBCO结晶质量、表面形貌以及临界电流密度影响很大。随着Y2O3纳米点生长时间的增加,其尺寸增大而密度降低。在上层YBCO薄膜生长过程中,由于大尺寸Y2O3纳米点的存在,其晶格排列周期性被破坏,使得膜内出现孔洞,薄膜结晶质量变差。制备得到的样品多空洞,不连续。在Y2O3纳米过渡层生长时间为20s的条件下,获得了临界电流密度最好的样品,其Jc=2.4MA/cm2(77K,OT),与未生长Y203纳米点的YBCO薄膜相比,其临界电流密度提高20%。
[Abstract]:High temperature superconductor (YBCO) has the advantages of high current carrying strength and low AC loss. It can work in liquid nitrogen environment and has broad application prospect and commercial value in microwave, energy and power fields. It is found that the critical current density of YBCO superconducting films decreases with the increase of film thickness. How to solve this problem and improve the critical current density of YBCO superconducting films has become a hot research topic. According to the flux pinning theory, it is feasible to increase the critical current density by artificially introducing defects into YBCO superconducting films as pinning centers. The defect state in the superconducting film is affected by doping or introducing lattice mismatch, and the defect concentration is increased. By using these defects as effective pinning centers, the energy dissipation of the magnetic flux due to vortex motion can be prevented and the current carrying capacity of the superconducting film can be improved. In this paper, the photo-assisted MOCVD technique is used to study the YBCO superconducting laminated films. The main contents of the study are as follows: The crystal quality and surface morphology of YBCO epitaxial films by Ba source were studied. It was found that the volatilization rate of Ba source had a great influence on the crystalline quality and micromorphology of YBCO epitaxial films. A large number of CuO impurity particles were deposited on the surface of "barium poor" YBCO film, and large cracks appeared in the film, and with the increase of Ba source temperature, the volatile rate of the source increased, the Ba content in the film was replenished, and the surface impurity particles gradually decreased. The films with good crystallization quality can be obtained by using proper heating temperature of Ba source and keeping Ba source slightly excessive. (2) Y2O3 nano-thin layer structure was selected as the transition layer for the growth of YBCO laminated film. The microstructure of the Y2O3 nano-transition layer grown on the YBCO superconducting film was studied. With the increase of growth time, the density of Y2O3 nanowires decreases due to the increase of the combined size between the dots. (3) the size of Y _ 2O _ 3 nanowires of YBCO/Y2O3/YBCO laminated films on LAO substrates has a great influence on the quality, surface morphology and critical current density of YBCO. With the increase of the growth time of Y2O3 nanowires, the size increases and the density decreases. During the growth of YBCO thin films in the upper layer, due to the existence of large size Y2O3 nanowires, the lattice arrangement is destroyed periodically, which leads to the formation of pores in the films and the deterioration of the crystalline quality of the films. The prepared samples are void and discontinuous. When the growth time of Y2O3 nanocrystalline transition layer was 20 s, the sample with the best critical current density was obtained. The critical current density of the sample was increased by 20 times compared with that of the YBCO film without Y203 nanoparticles.
【学位授予单位】：吉林大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：TM26

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