高温超导薄膜应力分析及其对超导临界参数的影响研究

High temperature superconducting (HTS) films, whose products represented by superconducting quantum interference device (SQUID), superconducting micro-wave filter and 2G HTS films, etc., have wide application in the fields of scientific research, normal production and living, and national defense security, especially in the next generation of superconducting quantum photon device (SQPD) and superconducting quantum computers (SQC)， which are also significant scientific frontiers that studied by international communities. It should be noted in these applications, the basic elements of devices of superconducting materials always have film-substrate structures and are served in extreme working conditions, usually involved with multi fields of low temperature, high current and magnetic field, hence superconducting films are inevitably subjected thermal and electromagnetic forces. Due to the limit of these extreme conditions, the experimental study of film stresses on electromagnetic elastic deformation has not get a further progress, particularly the influences of deformations caused by these stresses on basic critical parameters, such as critical temperatures and critical current densities, have not been well revealed, which has impeded the application of large area HTS films. Based on the work of measuring of HTS film stress, this project is intend to design a new apparatus for loading on HTS films and can simultaneously measure the electromagnetic varieties at cryogenic temperatures. The objective of this project is to reveal the mechanics of how stresses influence the properties of HTS films and provide references for further utilization of HTS films.

高温超导薄膜在电子领域应用非常广泛，其产品量子干涉器(SQUID)，高温超导滤波器和二代高温超导带材在科学研究、生产生活、国防安全等具有重要的应用，特别是未来的超导光子器件和超导量子计算机技术成为各国研究的前沿领域。在这些应用中，超导体均以薄膜基底结构形式，运行在低温、高磁场与复杂电流极端环境，超导薄膜不可避免承受结构失配与电磁力的共同作用。受限于极端环境，超导薄膜的电磁应力实验研究一直没有显著进展，特别是由这些应力引起的材料变形对超导材料的基本特征参数如临界电流和临界磁场的影响物理机制一直没有揭示清楚，成为横亘在超导薄膜大面积应用的一个关键科学问题。本项目将在解决超导薄膜电磁应力分析的基础上，设计一种薄膜类结构的低温力学加载装置，实现力学加载的同时可测量其电磁学特征，以揭示超导薄膜特征参数随应力变化的物理机制，为高温超导薄膜的进一步工程应用提供参考依据。

YBCO超导薄膜及其有多层薄膜结构的二代高温超导涂层导体，在强弱电领域均具有重要的应用。针对应用过程中应力对超导薄膜电磁特性和结构的影响这一问题。在本项目的资助下开展了以下工作：1. 理论上与实验上分析了面内光栅倾角对CGS系统测量影响的规律，提出了修正方法；2. 在实验系统及方法上，设计并研制可测量临界电流密度的低温薄膜加载系统，实现了对超导硬质薄膜的高压缩应变（-0.5%）的加载。设计并研制用于测量低温物体表面温度分布的荧光可视化系统，实现了超导带全场温度可视化测量，实验验证了计算超导带等效热传导系数麦克斯韦计算模型正确性。研制基于法拉第效应的低温真空显微观测系统，实现了在极端环境下超导薄膜表面磁通显微可视化观测。设计组建超快磁通崩塌测试系统实现了ns尺度磁通崩塌的观测；3. 在实验新结果方面，探究了拉伸应变作用下超导带内部的磁通低速间歇性的穿透特征，发现了内部损伤模式为沿超导带厚度方向和宽度方向上的裂纹扩展，其中厚度方向上裂纹源于基底，部分止于超导层，超导层裂纹尖端呈现非晶化，宽度方向上95%主要表现为超导层穿晶断裂，其余为裂纹偏转和裂纹钉扎模式。利用这一特性，提出在预拉伸的钢带上焊接超导带，使其该复合结构在自由状态下超导带承受与压缩应力，这一工艺使得超导带拉伸可逆应变极限从0.39%提升至0.73%。该工艺可以为后续超导带磁体应用提供新的借鉴。