纳米铁电相增强YBCO薄膜磁通钉扎性能的研究

YBCO Coated Conductors will become the second high-temperature superconductor tapes instead of the Bi2223 tapes due to their excellent superconducting properties. However, the critical current density decreases rapidly as the applied magnetic field increases, which has been the main obstacle for coated conductors to be applied in the heavy current field. Our previous results showed that the flux pinning of YBCO films can be markedly enhanced through introducing Y2O3 nanoparticles into YBCO matrix, thus resulting in the improved critical current density of YBCO films at applied magnetic field. Based on this result, if one can introduce some nanophases with special physical properties into YBCO matrix to form YBCO functional nanocomposite film, the superconducting properties of YBCO films could be improved and endowed with some novel physical properties. In this project, the functional nanocomposite films such as superconductor/single ferroelectric phase and superconductor/(ferroelectric-ferromagnetic mixture phases) will be prepared by using chemical solution doping method, and the influence mechanism of these functional nanophases on the flux pinning of YBCO films is discussed. It could be expected that the flux pinning of YBCO films is further enhanced by an additional pinning contribution, thus bringing high current carrying capacity to the coated conductors at a wide range of magnetic field and temperature even all the magnetic field orientations. The results of this study are very significant for us to explore high property coated conductor and understand the high temperature superconductor mechanism.

YBCO涂层导体凭借其优异的超导性能将成为替代铋系带材的第二代高温超导带材。然而，YBCO薄膜的临界电流密度随外磁场的增大而迅速减小的问题却成为涂层导体在强电领域应用的主要障碍。我们的前期研究发现，通过化学掺杂的方法引入Y2O3纳米颗粒可显著增强YBCO薄膜的磁通钉扎性能，有效提高磁场下薄膜的临界电流密度。在此基础上，若能在薄膜中引入具有特殊物理性质的纳米相，那么在增强YBCO薄膜本身超导性能的同时也可能赋予其一些新的物理特性。该项目拟通过化学溶液掺杂的方法制备超导/单一铁电相和超导/(铁电-铁磁混合相)纳米复合薄膜，研究铁电、铁磁等功能性纳米相对超导薄膜磁通钉扎性能的影响机制，以期获得额外的磁通钉扎贡献，进一步增强YBCO薄膜的磁通钉扎性能，使涂层导体在尽可能宽的磁场角度、大小及温度范围内获得更高的载流能力。该研究无论对高性能涂层导体的开发应用还是对高温超导机制的深入理解均具有重要意义。

本项目采用新型感光溶胶-凝胶光刻法成功制备了Y2O3、YSZ、PZT、BST、LSMO以及PZT-LaCoO3等金属氧化物的微细图形或微阵列，随后利用改进的无氟溶胶-凝胶法在有上述微细图形或微阵列缓冲（或修饰）的LAO单晶衬底上制备了YBCO/Y2O3、YBCO/YSZ、YBCO/PZT、YBCO/BST、YBCO/LSMO以及YBCO/（PZT-LaCoO3）等纳米复合薄膜，并借助高分辨TEM获得了清晰的内部微结构照片。研究发现，在有微细图形修饰的LAO衬底上也能生长出c轴外延取向的YBCO薄膜，说明适当的图形修饰不会影响YBCO薄膜在LAO衬底上的外延生长特性；YBCO/PZT和YBCO/BST复合薄膜内部均出现了不同程度的晶体缺陷（如：晶面弯曲、堆垛层错、晶格畸变及纳米孪晶等），尤其是YBCO/BST复合薄膜的内部缺陷密度更大且主要表现为堆垛层错和晶格畸变，这些缺陷的存在迫使YBCO内部Cu-O键被压缩或拉长，极大地提高了YBCO薄膜在自场和磁场下的临界电流密度，这不仅对解释高温超导机理具有重要价值，而且对于高性能YBCO涂层导体的应用具有重要意义。此外，YBCO/LSMO和YBCO/（PZT-LaCoO3）复合薄膜尽管在自场下的载流性能有所下降，但在磁场下却表现出了较纯YBCO薄膜更为优异的超导性能，说明磁性的LSMO或LaCoO3为YBCO薄膜提供了额外的磁通钉扎贡献，这为研究超导与磁性物质之间的耦合效应提供了实验证据。. 该项目还研究发现在YBCO与CeO2的界面处形成的BaCeO3 纳米颗粒和一些晶体缺陷，有效提升了YBCO薄膜在2-3T磁场下的临界电流密度。YBCO与Y2O3之间的晶格失配产生压应力，导致Cu-O面间距适当增大，从而提高了YBCO薄膜的Tc值。在LAO纳米颗粒上生长的YBCO薄膜内部的一些纳米级的堆垛层错缺陷，也可有效提高YBCO薄膜在磁场下的Jc。这些结果进一步证实了晶格缺陷引起的Cu-O键键长的变化是导致YBCO薄膜超导性能改变的本质原因。. 项目执行期间培养了3名硕士研究生；申请了4项专利，其中1项已批准，另有3项在审查；发表了6篇学术论文，5篇被SCI收录，1篇被作为英国皇家化学学会Journal of Materials Chemistry C期刊2016年第7期的封底文章出版。