Superconducting Material Prepared SmBCO Block Top-seeded Infiltration

The higher critical temperature, larger levitation force and the stronger trapped magnetic field of REBCO bulk superconductors make it possible of a widely applications in many fields. YBCO bulk superconductors are one of the most important materials and widely investigated, so the preparation technology and physical properties are relatively well known. But there is seldom work done on SmBCO bulk superconductors, although its critical temperature Tc and critical current density Jc are relatively higher than that of YBCO bulk, especially it can keep a relatively higher Jc under higher magnetic field. Therefore SmBCO bulk superconductors are of more powerful potential for applications.In this paper, the top seed infiltration and growth method (TSIG) are adopted to fabricate SmBCO bulk superconductors. Firstly, the precursor powder we need in the fabricating bulk superconductors and the fabrication process of single domain SmBCO bulks were studied; Secondly, according to the problems that macroscopic crack can occur in the single domain SmBCO bulk superconductors during the TSIG process, we have done some research work to solve the problem; Finally, we have fabricated some single domain SmBCO bulk superconductors with different Sm2O3and BaCuO2proportion in the solid phase, then the surface morphology and levitation force of the fabricated samples have also been studied.For the preparation of initial powder, solid state reaction was used for the synthesis of BaCuO2precursor powders by sintering at910℃with three times sintering and four times ball milling process, XRD pure BaCuO2precursor powders can be obtained by this method. In heat treatment process, the technical parameters (slow-cooling temperature window) for the crystal growth of single domain SmBCO bulk superconductors were determined by quenching technology under different supercooling temperatures. The results indicated that, when the sample was kept at1055℃, there isn’t any SmBCO crystal nucleation around the seed and any signs of growth of SmBCO crystal in the rest parts; when the temperature was decreased to and kept at1050℃, SmBCO crystal was able to epitaxialiy nucleated and grew from the NdBCO seed crystal, which shows that the nucleation and growth of SmBCO crystal begins at this temperature; when the sample was kept at1040℃, some random nucleation of SmBCO crystal arose at the edge of the sample and growth of the single domain SmBCO grain were interrupted. There would be more and more random nucleations, if the temperature decreased further more. Based on the above results, the slow-cooling temperature window of SmBCO bulk is defined in the range of1050℃and1040℃.In order to prevent the occurring of macroscopic crack in the samples during fabrication of the SmBCO bulk superconductors, a new method has been developed to overcome this problem in the traditional TSIG by adding a thin layer of BaCuO2pellet between solid phase and liquid phase. This is because that the BaCuO2chip inserted between solid phase and liquid phase blocks, can act as a lubricant layer at evaluated temperature in the crystal growth temperature window of SmBCO bulks, and result in a reduction of the interaction force between the liquid and solid phases in the traditional TSIG process.Based on the above method, SmBCO bulk superconductors were fabricated by different ratio of Sm2O3and BaCuO2in solid phase source. Single domain SmBCO bulks can be fabricated with different ratio of Sm2O3:BaCuO2=1:x,1<x<2, the best one of the sample is obtained with x=1.2. The levitation force of the SmBCO bulks is increasing first and decreasing then with the increasing of BaCuO2additions. When the ratio of Sm2O3and BaCuO2is1:1.2, levitation force reaches the largest value(19N). For the ratio of Sm2O3and BaCuO2is1:1, which is equal to using Sm211as solid phase source in the traditional method, when BaCuO2phase increased, which is equal to adding a certain amount of BaCuO2phase in Sm211. For the ratio of1:1, the density of Sm211in the sample is higher and the superconducting phase is less, so the levitation force is smaller; when the ratio of BaCuO2is larger than1.2, because BaCuO2phase increases in the sample, the density of Sm211decreases, which lead to a reduction of flux pinning force in the sample, and result in a lower levitation force. When the ratio of Sm2O3and BaCuO2is1:1.2, superconducting phase and Sm211phase in the sample reach an appropriate proportion, so the performance of the sample is the best.