Flux Pinning Characteristics of Artificial Pinning Centers With Different Dimension

Abstract

The crystal defects of the nano-scale, which are called artificial pinning centers (APCs), were successfully introduced into high-temperature superconductors (HTS) by nanotechnology, in order to strongly pin the quantized vortices. Critical current densities of the HTS films were dramatically improved by APCs whose dimensions were controlled. By this method, the in-field (77 K) of the high-quality, epitaxial films was improved by one order of magnitude or more compared with the values of the past. A current outline of the research is described in this paper.

Microstructures of REBa2Cu3Oy films containing artificial pinning centers of various dimensions

“…In the case of two-dimensional APCs, the pinning forces were the strongest among APCs of all dimensional, as found by the simulation of the quantum magnetic flux movement inside superconducting films with various APCs, using a time-dependent Landau equation [13]. On the contrary, because a grain boundary that represents the two-dimensional APCs generally works to block a current across a grain boundary, the two-dimensional APCs, such as planelike defects are very difficult to fabricate as effective pinning centers in superconducting films.…”

Artificial pinning center technology to enhance vortex pinning in YBCO coated conductors

“…Another possibility is to consider the relation between the APCs and the superconducting matrix: (i) increasing the number of the structural defects that are naturally present in a superconducting film, such as dislocations [37], stacking faults [38] or grain boundaries [39], (ii) damaging the matrix by heavy ion irradiation, producing columnar defects [22], (iii) subtracting matter in a chemical or physical route, producing nanopores or nanovoids [40], or (iv) adding second phases to the superconducting matrix. The technique of adding the second phase is a large category of APCs and many papers have been recently published on this topic [3,13]. A consequent classification of the APCs is the composition of the second phases: metals (Au [41], Ag [42], and so on), phases belonging to the YBCO phase diagram (Y 2 O 3 [15], Y-211 [43] and so on), perovskites (BaIrO 3 [44], BaHfO 3 [45], BZO [14], BSO [16]) and so on.…”

“…However, the small angle grain boundary can be considered as a dislocation array, and there is a possibility of working as strong pinning centers, as suggested by Pan et al [8] when the misorientation angle is small. Matsumoto et al [13] have reported the use of grain boundaries as effective pinning centers in GdBCO films. By varying the oxygen partial pressure during deposition, the size of the grains continuously changed from 196 to 92 nm, as shown in figure 7(b).…”

“…Figure 1 shows the progress of J c of YBCO films and coated conductors from the recent advances in the biaxial texturing technique and from APC technology. It has already been confirmed experimentally that the in-field J c of YBCO at 77 K greatly exceeds that of commercial Nb-Ti wire at 4.2 K. The introduction of APCs with controlled dimensionality is indispensable to achieve a high J c [13]. The great improvements of J c in YBCO films were obtained by onedimensional APCs (1D-APCs), such as dislocations, BaZrO 3 (BZO) nanorods [14], and by three-dimensional APCs (3D-APCs), such as Y 2 O 3 nanoparticles [15].…”

Current Distribution in Y-Ba-Cu-O Superconducting Microbridges Containing Π-Shaped Channel for Easy Vortex Motion

“…The biasing current density predetermines the strength of F L . The force F p depends on the homogeneity of the superconducting thin film's composition [2], structure [3], and geometry (e.g., thickness and/or width) [4]. Thus, F p can be modified * corresponding author; e-mail: arturas.jukna@vgtu.lt using various methods: an introduction of columnar defects into the superconducting film [3], local variations in film's thickness or in chemical composition [2,4], introduction of periodic magnetic barriers [5], etc.…”