Nanorods and nanoparticles are commonly introduced to REBCO coated conductors as artificial pinning centers to improve the critical current density in high magnetic fields and to reduce the anisotropy with respect to the magnetic field angle. In this article the pinning properties are theoretically analyzed based on the classic condensation energy pinning interaction mechanism (δTc pinning) of these pinning centers and the results are compared with experimental results. The agreements show that the critical current density can be designed by controlling the microstructure of pinning centers and factors such as the size, number density and morphology. It is also pointed out that the upper critical field is enhanced via the electron scattering of the interface between the pinning center and the superconducting matrix. Hence, the upper critical field can also be controlled to enhance the irreversibility field by controlling the interface area in a unit volume of the superconductor. It is expected that the high field performance can be optimized by controlling the pinning strength and the upper critical field in the future.
There are high expectations for REBa2Cu3Oy (REBCO: RE=Rare Earth) coated conductors for superconducting power applications as a substitute for intermetallic superconducting wire. Especially, GdBa2Cu3Oy coated conductors have attracted attention owing to their high superconducting properties. In this study, in order to investigate the superconducting properties and microstructures in GdBa2Cu3Oy thin films with straight BaHfO3 (BHO) nanorods introduced, we fabricated BHO doped GdBa2Cu3Oy thin films. The BHO doped GdBa2Cu3Oy thin films were fabricated on a IBAD-MgO substrate using the pulsed laser deposition method. From transmission electron microscopic images, the BHO nanorods grew continuously and straight from the substrate to the surface of the films in 1.5 vol.% BHO doped GdBa2Cu3Oy film. The mean diameter was approximately 4.4 nm. The critical temperature and Jc in the self field of the films linearly decreased with increasing BHO content. The magnetic field dependence of Jc of all the BHO doped films showed wide plateau regions in which there was little decrease of the Jc. The results showed that the Jc in the magnetic field were dramatically improved compared with those of pure GdBa2Cu3Oy thin films. These films showed high pinning force density; in particular, 2.2 vol.% doped films showed 26.8 GN/m-3 at 77 K, B = 6 T.