Element Doping On The Performance Of Single-domain Ybco Superconductor

High Tc YBa₂Cu₃O_7-x material is one of the most useful high temprature supercomductors which is widely used for applications such as magnetic bearing, energy storage system, advanced motors and magnets etc., a lot of works have been done in researching this field. It is know that single domain YBCO bulk can be fabricated using melt-texture-growth method, however it is quite difficult to prepare single domain YBCO bulk with large size especially in a isoathermal condation. In this paper, the solid state reaction method was used for the synthesis of YBa₂Cu₃O_7-x(Y123), Y₂BaCuO₅(Y211), and Yb_1.8Ba_2.4Cu_3.4Ox (Y1.8) powders. The single domain bulks were fabricated by top-seed-melt-textures-growth method (TSMTG). The effect of second phase Yb1.8 addition was adopted to prevent the egression of the liquid phases and depress the random nucleation which makes YBCO bulks fabrication possible in a furnace with uniformly distributed temprature. Yb_1.8Ba_2.4Cu_3.4Ox with lower melting point than YBa₂Cu₃O_7-x, can prevent the egression of the liquid phases remarkablely and depress the random nucleation at the bottom and the side surface of the bulk, thus it is helpful for the growth of the single domaim bulk. the effect of CeO₂ doping on the property of YBCO bulk was reseached in this paper. The trapped field and levitation force was increased with the doping of CeO₂.The YBa₂Cu₃O_7-x (Y123), Y₂BaCuO₅(Y211), and Yb_1.8Ba_2.4Cu_3.4Ox (Ybl.8) powders were synthesized synthesized by the solid state reaction method, and all of them were prepared by milling and sintering process alternatively several times. The The XRD results indicate that the Y123 phases can be obtained while the sintering temprature is in the range of 900-950℃, but the EDX results indicate that when the sintering temperature sintered between 900-910℃the carbon content is higher than that of the sintering tenperature in the range of 920-950℃. So range of 920-950℃was chosen for the preparation of Y123 powder. The sintering time is 24h three times. It is also found that single phase Y211 powder can be fabricated between 910-930℃, and Ybl.8 powder can be synthesized at 920℃.In order to depress the random nucleation during the preparation of single domain YBCO superconductor bulks, YbBCO material with lower melting temperature (compared with YBCO) is used to realize this goal. The Ybl.8 material was enwraped on the surface of the YBCO bulks in a thin layer. The Yb1 .8 layer is able to depress the random nucleation during the growth preparation of single domain YBCO superconductor bulks. SEM and EDX analysis show that Yb1.8 enwraping can prtevent the egression of the liquid phases and depress the random nucleation effectively.The single domain YBCO bulk superconductors with dimeter of 30mm have been fabricated using this method in a furnace with isothermal temperature condition.It is found that the doping of CeO₂ can dramatically affect the macrostructure, microstructure of the bulk, the trapped field density and the levitation force. The Y211 particles are bigger and inhomogeneously distributed in the bulk without any doping of CeO₂, while the Y211 particles in the CeO₂ doping samples are much smaller than that in the undoping samples, with the average size 0.05μm. Thus flux pinning force is improved by the adtion of CeO₂. The result shows that the maximum trapped field density and levitation force are obtained in the samples with CeO₂ adation of 0.5wt%. it is difficult to prepare single domainYBCO bulks wile the addition of CeO₂ over 2wt%.