ИСТИНА

We studied the flux-pinning characteristics of GdBa2Cu3O7-x (GdBCO) coated conductors (CC) doped with BaSnO3 (BSO) artificial pinning centers. The samples were fabricated by SuperOx LLC and SuperOx-Japan LLC in collaboration by using pulsed laser deposition method. The amount of BSO dopant was varied from 0 to 7 % (mass.) together with the deposition parameters such as substrate temperature and repetition rate to obtain the better in-field transport properties of the coated conductor. To observe them we have measured critical current over the field (up to 8 T) curves and got from them the pinning force dependence at 77 K. Angular dependences of critical current under 1 and 3 T field (also in 77 K) were used to explore the anisotropy. We observed the decrease of the H||ab peak and the rise of the peak in the H||c area of the angular dependence for doped samples obtained under appropriate conditions. But for other doped samples dopping caused only decrease of critical current for all of the angles. The anisotropy of the doped tapes was reduced. Thus for pure GdBCO the ratio between critical current in parallel and perpendicular field orientations in 1 T was 2.39, that changed for dopes samples to 1.24-1.45 values. Some samples showed the significant H||c peak with the 1.15-1.17 anisotropy ratio. The form of the critical current angular dependences showed the existence of BSO nanoparticles, existing in most of the samples and BSO nanorods in some of them. Further investigating these samples the magnetization loops and flux relaxation curves were measured at lower temperatures: 4.2, 20, 30, 50, 65 and 77 K. These experiments got the good estimate of transport currents and the effect of BSO doping in these temperatures. Also the relaxation measurements got us the pinning energy value in field perpendicular to the CC surface. All of the samples were also studied by means of X-rays diffraction (for phase composition and texture analysis), SEM, EDX and ICP mass-spectroscopy (for element analysis). Presence of BSO nanoparticles was proved. Their size was about 6 nm along ab-plane and about 9 nm along c-axis. All the particles had the same orientation of crystallographic directions. Best samples were analyzed by HR TEM. This work presents a comprehensive study of the introduction of BSO into GdBCO coated conductors, its behavior in high fields and low temperatures.