Of Na-doped Single-domain Ybco Superconducting Material Performance

High-temperature oxide superconductor materials have made very great progress in last 20 years, and the efforts in this direction are mainly around Y-based material. Single domain YBCO bulk superconductors are highly appreciated because of their higher Tc, Jc and levitation force. This paper mainly studied properties of Na-doped single-domain YBCO bulk superconductors, and the fabrication of Y₂Ba₄CuNbO_x powders with XRD purity.In this paper, the initial Na-doped YBCO and YbBCO powders were composited by the solidstate reaction method. YBCO bulk superconductors with different Na content were prepared by top seeded melt texturing growth technique, meanwhile, their microstructure and levitation force were analyzed systematically. Secondly, the fabrication of Y₂Ba₄CuNbO_x powders were studied preliminary, including phase composition, microstructure, carbon content, and the most appropriate synthesis temperature of the powders was established.Before preparation of the Na-doped YBCO bulk superconductor, YBa_2-xNa_xCu₃O_7-δ (x=0, 0.05, 0.1, 0.15, 0.2, 0.25, 0.3), Y₂BaCuO₅, Yb_1.8Ba_2.4Cu_3.4O_y, powders were synthesized firstly. The above-mentioned powders were sintered by solid-state reaction methods. The powders were sintered at temperature of 940℃, 920℃, 910℃for 24h and three times respectively, with an interval of ball milling after each sintering process.During the preparation of Na-doped YBCO bulk superconductors by the top seed melting texture growth method, the effect of Na-addition on the phase structure, lattice parameters of the Na-doped YBCO powder, the microstructure and levitation force of the YBCO single domain bulk superconductor were studied. In terms of YBa_2-xNa_xCu₃O_7-δ(x = 0, 0.05, 0.1, 0.15, 0.2, 0.25, 0.3) , with the increasing of Na-addition, XRD results showed that texture degree of YBCO sintered powder was improved significantly, and the diffraction angle was moved to the higher degree. SEM obseration found that the YBCO layers grew thicker, and Y211 particles grew bigger while x>0.2. In the meantime, the levitation force was measured systematically. The total area of single domain was increasing gradually with the increasing of the Na addition, the levitation force achived a largest value when x=0.2. Though the EDX analysis, indicated that the growth of single domain of YBCO bulk would be limited when the chemical composition in the liquid ahead of the YBCO crystal growth frontier was depleted in yttrium and barium.During the preparation of Y₂Ba₄CuNbO_x powders, the DTA result indicated that there are five endothermic peaks appeared near 820℃, 950℃, 970℃, 1020℃, 1100℃, each corresponding to production of new material; Y₂Ba₄CuNbO_x samples were prepared at different temperatures (1110℃～1150℃), the phase compositions and crystal structure of the samples were analyzed by X-ray diffraction (XRD). It was found that XRD purity of Y₂Ba₄CuNbO_x powder could be synthesized when the sample was sintered at 1150℃.