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Studies on the Control of the Critical Current Density of High-Quality Bi-System Superconductor Thin Films And Its Application

高质量双系超导薄膜临界电流密度控制及其应用研究

基本信息

批准号：
09650355
负责人：
INOUE Masumi
金额：
$ 2.05万
依托单位：
Nagoya University
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (C)
财政年份：
1997
资助国家：
日本
起止时间：
1997 至 1998
项目状态：
已结题

来源：
https://kaken.nii.ac.jp/grant/KAKENHI-PROJECT-09650355/
关键词：
oxide superconductor BSCCO thin film critical current density annealing surface resistance intrinsic junction

项目摘要

The critical current density J_C required for Bi_2Sr_2Ca_<n-1>Cu_n0_x(BSCCO) superconductors depends on the application. Therefore, the control of J_C over a wide range is necessary for the practical application of this material. In this research, the control of J_C of BSCCO high-quality films by annealing and the relationship between J_C, and other material properties were investigated using the 2212 phase (n=2).1. Control of the Critical Current Density by Annealing :Since J_C does not reflect the intrinsic material properties when the film is composed of small grains, annealing in oxygen at high temperatures was tried and grains as large as the mesa size could be obtained. By controlling the oxygen content in BSCCO by annealing in nitrogen at low temperatures, J_C along the c-axis direction decreased over the range of 10^4-10^1A/cm^2 with increasing annealing time. The critical temperature increased steeply and then decreased slowly as a function of the annealing time. It was suggested that these phenomena reflect the change in the carrier density.2. Relationship between the Critical Current Density and Other Properties :Relationship between J_C along the ab-direction and the surface resistance was mainly investigated. The dependence of the surface resistance on the product of the grain size and J_C, which is reported for Y-system superconductors, was not confirmed, while its dependence on J_C, was suggested.3. Application Possibility of the Control Method of the Critical Current Density :As an application of the control method of J_C, intrinsic junctions were fabricated and the correlation between J_C and the device properties was investigated. Their current-voltage (I-V) characteristics were classified into two types : one was the flux-flow type and the other was the multiple-branching type typical for intrinsic junctions showing voltage jumps and hystereses. The I-V curve with multiple branches was observed for samples with J_C of 10^3A/cm^2 or less.

Bi_2Sr_2Ca_<n-1>Cu_n0_x(BSCCO) 超导体所需的临界电流密度 J_C 取决于应用。因此，在较宽的范围内控制J_C对于该材料的实际应用是必要的。本研究利用2212相(n=2)研究了通过退火对BSCCO高质量薄膜J_C的控制以及J_C与其他材料性能之间的关系。1．通过退火控制临界电流密度：由于当薄膜由小晶粒组成时，J_C不能反映材料的固有特性，因此尝试在高温下在氧气中退火，可以获得与台面尺寸一样大的晶粒。通过低温氮气退火控制BSCCO中的氧含量，随着退火时间的增加，沿c轴方向的J_C在10^4-10^1A/cm^2范围内下降。临界温度作为退火时间的函数急剧增加然后缓慢降低。认为这些现象反映了载流子密度的变化。 2．临界电流密度与其他性能的关系：主要研究ab方向的J_C与表面电阻的关系。 Y系超导体表面电阻对晶粒尺寸和J_C乘积的依赖性尚未得到证实，但提出了其对J_C的依赖性。 3．临界电流密度控制方法的应用可能性：作为J_C控制方法的应用，制造了本征结并研究了J_C与器件性能之间的相关性。它们的电流-电压（I-V）特性分为两种类型：一种是磁通流型，另一种是多分支型，典型的本征结表现出电压跳跃和迟滞。对于 J_C 为 10^3A/cm^2 或更小的样品，观察到具有多个分支的 I-V 曲线。