| a great of works have been done on the fabrication and applications of the high Tc superconductors. YBCO is one of the most promising materials, which can be widely used for applications such as magnetic bearing, energy storage system, and advance motors and magnets etc.. The preparation, microstructure and levitation force of YBCO bulk superconductor have been studied in this paper.YBa2Cu3O7-x(Y123),Y2BaCuO5(Y211) and Yb1.8Ba2.4Cu3.4O7 etc. Powders were synthesized by the solid state reaction method, and all of them were prepared with two times milling and sintering process. The differential thermal analysis (DTA) and XRD analysis results indicate that the propriety reacting temperature of Y123 powder is in the range of 890～910℃, Y211 is 910～930℃, Yb1.8Ba2.4Cu3.4O7 is 920℃. The sintering time is 48h for the first time and 24h for the second time.The main work is on the effects of the top seed melt-textured growth process parameter and the addition content of Y211 phase on the quality of the YBCO sample bulks. The top seed melt-textured growth process including the heating and cooling rate, the dwelling time at high temperature, the start cooling temperature etc.. The experiments results show that single-domain YBCO bulks can be obtained with some reasonable processing parameters: the heating rate is 350℃/h, the dwelling time is 2-3h, the start cooling temperature is 1010℃, the cooling rate during the YBCO crystal growth process is less than 1℃/h. Large domain or single domain YBCO bulk can be synthesized with 30mol%-60mol% additions of Y211 particles.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 YbBCO material was just pressed on or coated on the surface of the YBCO bulks in a thin layer. The YbBCO layer is able to depress the random nucleation during the preparation of single domain YBCO superconductor bulksThe microstructure of the YBCO bulk was observed by the scanning electron microscope and optical microscope. The results show that the microstructure of YBCO bulks is of highly anisotropy. The minimum thickness of Y123 layer crystal is about 2um. There are fine 211 particles dispersion distributed in the Y123 crystals. There are cracks and gas holes in the Y123 bulks. The micro-crack is parallel to the a-b plane, and the width of the crack is in range of 0.5-2um. There are gas holes in the sample which maybe the sources of cracks creating.The effect of the approaching speed between a permanent magnet and a superconductor on the levitation force of single-domain YBCO bulk has been studied at liquid nitrogen temperature under zero field cooling condition. It is found that the maximum levitation force and the stiffness of the force-distance curve are increasing first and then decreasing with the increasing of the approaching speed and, there is a optimal speed to get the maximum levitation force.
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