Strongly improved current-carrying capacity induced by nanoscale lattice strains in YBa2Cu3O7−δ–Ba0.7Sr0.3TiO3 composite films derived from chemical solution deposition

Abstract

It is commonly expected that YBa₂Cu₃O_7−δ (YBCO) coated conductors can exhibit strong vortex pinning force when they are used at high temperature (77 K) and different magnetic field orientations which are angled to the YBCO c-axis. In this paper, we showed a simple approach, making a YBCO film to epitaxially grow on the Ba_0.7Sr_0.3TiO₃ (BST) microarray buffered LaAlO₃ (LAO) substrate, to introduce nanoscale crystalline defects into the YBCO matrix. High concentration nanodefects including dislocations, intergrowths, stacking faults and plane buckling have been observed by high-resolution transmission electron microscopy (HRTEM). It was demonstrated through magnetization vs. magnetic field strength measurement that these nanodefects could provide quasi-isotropic vortex pinning characteristic of the so-called nanostructured YBCO films, containing large numbers of defects, which would promote power applications of coated conductors. It is believed that non-superconductivity regions (the dimension is close to the order of ξ, the coherence length of YBCO) caused by nanodefects are considered as effective pinning centers to inhibit flux creep. Therefore, large pinning energy can be easily obtained for YBCO films if considerable nanodefects are introduced into the epitaxial YBCO matrix no matter which method is employed to produce the nanostructured YBCO film. We illustrated the essential reason for the strong enhancement of the critical current density of the YBCO film under both self- and applied magnetic fields, that is, lattice strains (elongated and shortened Cu–O bonds) caused by crystalline nanodefects lead to the distinctly improved current-carrying capacity of the YBCO film.