新型纳米掺杂多层钆钡铜氧超导薄膜制备和磁通钉扎机理研究

Despite the superconducting technology successes, however, there is still much about high temperature superconductor that we can not understand. But the time has come for concerted study of the interrelationships between processing, film defects, and flux pinning, because crossing the threshold of commerical viability may depend on the kind of performace improvements that can be achieved through a better understanding of these relationships. So the nano particle doping of GdBa2Cu3O7-δ（GdBCO）superconducting films, the preparatrion of Ba1-xSrxZrO3 doped GdBCO /SrTiO3 and Sr2Nb2O7 doped GdBCO /Sr2Nb2O7 multilayer, and the preparation of Ba1-xSrxZrO3 doped GdBCO/YBCO and Sr2Nb2O7 doped GdBCO /YBCO multilayer are studied in this project. Through controlling growth of nano particles and multilayer, the relationship between the characteristic of new nano particels, such as category, size and density, and the performance of superconducting films is explicited, the mechanisms of flux pinning of nano particles, multilayer and combine of two types of artificial pinning are revealed, the relation between the defects in the superconducting films and flux pinning is indicated. A theoretical basis for the flux pinning theory is proved and a preparation technique of doped GdBCO superconducting thin films is developed, which have high critical current density and critical current in the magnetic field deposited by pulsed laser deposition.

尽管超导技术成功了，但关于超导仍有许多不明白。是时候协同研究工艺、薄膜缺陷和磁通钉扎之间的相互关系。因为超导带材商业化的实现依靠其性能的提高，可以通过更好地理解这些关系来提高性能。为此，本项目将研究GdBa2Cu3O7-δ（GdBCO）超导薄膜的纳米颗粒掺杂、Ba1-xSrxZrO3掺杂的GdBCO /SrTiO3和Sr2Nb2O7掺杂的GdBCO /Sr2Nb2O7多层膜制备、以及Ba1-xSrxZrO3掺杂的GdBCO/YBCO和Sr2Nb2O7掺杂的GdBCO/ YBCO多层膜制备；通过纳米颗粒和多层膜控制生长，明确新型纳米颗粒种类、大小、密度等特征与超导性能之间的关系，揭示纳米颗粒、多层膜和共同作用下的磁通钉扎机制，阐明超导薄膜缺陷和磁通钉扎之间的关系，为磁通钉扎理论提供依据，并且研发出磁场下具有高临界电流密度和临界电流的掺杂GdBCO超导薄膜的脉冲激光沉积方法制备技术。

以(REBa2Cu3O7-x)(Re=Y, Gd, Sm等稀土元素，简称为ReBCO)为基础的第二代高温超导带材具有磁场下电流密度高、交流损耗小等优点，从而拥有广阔的应用前景。在第二代高温超导带材的研制中，如何获得具有双轴织构特性的基带是首要条件。其次，高质量的缓冲层的制备和缓冲层的生长机理的研究对获得高性能的第二代高温超导带材非常重要。再者，提高超导膜的电流载流能力，特别是高磁场下的性能，是目前二代高温超导带材应用函需解决的问题。.为此，本项目开展以下几个方面的研究：（1）采用离子束辅助沉积方法制备具有良好织构的氧化镁薄膜；（2）研究不同工艺参数对CeO2隔离层生长的影响；（3）选用GdBa2Cu3O7-x(GdBCO)作为基本材料，研究靶材密度、隔离层厚度和超导膜的厚度效应；（4）PLD制备GdBCO/SrTiO3(STO)/GdBCO多层膜；（5）PLD制备BZO和SNO掺杂GdBCO超导薄膜。.本项目取得了以下主要研究成果：（1）IBAD-MgO薄膜的取向和表面形貌对镀膜工艺参数非常敏感，其最佳厚度为10nm左右。通过优化工艺参数，制备出具有纯C轴向和非常光滑表面的IBAD-MgO薄膜，表面粗糙度小于1nm。（2）在优化条件下制备的CeO2薄膜具有纯c轴取向，面内织构仅为2.9°。（3）确定了最佳靶材密度为4.0g/cm3，隔离层的厚度为200 nm左右。通过分层制备技术，减弱了超导膜的厚度效应。（4）研制出沉积温度（400-750 ℃）、氧分压（5-200 mTorr)和厚度（20-300 nm）范围都很宽的STO夹层制备工艺，GdBCO/STO/ GdBCO多层膜具有良好的C取向和光滑表面，适合于超导厚膜制备。（5）240nm厚的GdBCO+1.5%BZO薄膜在77K、自场条件下临界电流达到60A，在4.2K，B//c和9T下临界电流达到921A。（6）制备出磁场下具有高性能的SNO掺杂GdBCO薄膜，240 nm厚GdBCO+1.5%SNO薄膜在4.2K，B//c和9T下临界电流达到705 A，Jc高达29.4 MA/cm2,是其77k、自场下Jc的20倍。.本项目阐明了夹层、BZO和SNO各自的钉扎类型以及钉扎效果，为进一步提高磁场下超导膜的载流能力提供科学依据。