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YBCO superconductor is the most studied high-temperature superconducting materials and superconducting materials most widely used one, has attracted worldwide attention. Among them, the use of melt-textured top seeded method (TSMTG) GdBCO single domain superconductor prepared, because it has a high critical temperature, the larger the carrying capacity unimpeded and strong ability to capture the magnetic flux, making the superconducting Maglev trains, magnetic bearings, strong magnetic field of permanent magnets, superconducting magnetic energy storage flywheels and superconducting motors has broad application prospects. To further improve the single domain GdBCO bulk superconductor performance, we adopted the method of doping in the superconducting matrix introduction of effective pinning centers, improved superconductor levitation force and the critical current density J. And other properties. In this paper, the traditional solid-phase sintering process prepared a relatively pure initial powder and the new second phase nanoparticles Gd2Ba4CuNbOy (GdNb2411) powder. Successfully prepared using TSMTG process GdNb2411 nanoparticles doped single domain GdBCO bulk superconductor, and doped with different GdNb2411 growth morphology of the sample surface, levitation force and microscopic structure of the system analysis; On this basis, Furthermore, the effects of different sizes and different locations GdNb2411 doping on the mezzanine single domain GdBCO bulk superconductor performance. In the initial powder preparation, the use of three and four milling sintering method of combining the obtained XRD purer GdBa2Cu3O7-δ (Gd123), Gd2BaCuO5 (Gd211), YBa2Cu3O7-δ (Y123) and Y2BaCuO5 (Y211) relative to the initial powder body, they correspond to sintering temperatures of 940 ℃, 930 ℃, 920 ℃ and 910 ℃. In the new second phase nanoparticles GdNb2411 powder preparation, the systematic study of its phase composition, crystal structure, morphology, particle size and carbon content, etc., and to determine its optimal sintering temperature is 1140 ℃ C . Studied GdNb2411 doping on TSMTG prepared single domain GdBCO bulk superconductor growth morphology, levitation force, microstructure and composition distribution of growth front. The molar ratio of the sample GdNb2411 accordance Gd123: Gd211: GdNb2411 = 1: (0.4-x): x ratio of preparation, from the sample surface growth morphology analysis: growth morphology of the samples is closely related with the doping level x when x ≤ 0.06mol, the smooth surface on the sample size and four distinct seasons, showed a typical single-domain morphology; when x ≥ 0.08mol, the samples of single-domain region is no longer smooth and flat surface wrinkles, and with mixed complex increases, the single domain area becomes smaller and smaller. Levitation force of the sample test results showed that: the sample with doping x levitation force increases first and then decreases when x = 0.06mol, the sample levitation force reaches a maximum of about 25N. Microstructure analysis of samples show that: with the increase in doping, GdNb2411 increasing the density of the particle, the particle diameter of between 100nm-300nm, but too large doping, GdNb2411 particles into larger aggregates particles, which may lead to changes in the sample surface topography and the main reason for its lower magnetic force. The growth front of the sample composition analysis showed that: As doping increases, the number of particles and Gd211 GdNb2411 Gd123 phase particles are introduced into the substrate outside the area of ??the sample was not grown serious deviation from the content of each element of Gd: Ba: Cu = ratio of 1:2:3, slow cooling of the molten sample resulting growth process, can not generate Gd123 superconducting phase, which may be caused to stop the growth of main samples. The effects of different size and different locations GdNb2411 mezzanine GdBCO doped superconductor single domain growth morphology, properties and microstructure of levitation force of impact. By observing the surface morphology of the samples, we found that: different size and different locations GdNb2411 mezzanine powder doped samples, can grow out of the sector with four smooth morphology typical single domain. Levitation force sample test results showed that: in doping are x = 0.06mol, used for the 360,240,120 Number of mesh and 80 mesh powders doped case, GdBCO superconductor levitation force With doping GdNb2411 powder particle size decreases and increases, when n = 360 mesh sieve mesh, the sample of levitation force, with almost 25N; when using lamellar GdNb2411 for 2-2 composite with Gd123 , the results showed that: the location of the doped layer with GdNb2411 down, the sample showing the maximum magnetic force gradually increasing trend, when laminated in h = 3/4 at the time, the magnetic force of the sample reaches a maximum of about 14N. In addition, we microstructure of the samples were observed and analyzed, the results show that: with the powder sieved samples doped GdNb2411 mesh size decreases, the sample size of nanoparticles GdNb2411 increases, resulting in the sample levitation force performance degradation; samples doped with mezzanine position GdNb2411 lower mezzanine GdNb2411 no significant change in particle size, but both appeared particle agglomeration sample levitation force depends on the size ratio of superconducting bulk upper mezzanine . Finally, the single domain GdBCO bulk superconductor microstructure of the system of observation and analysis, found that there are a lot Gd211 sample particle agglomeration and growth phenomena and bubbles, voids and macro cracks and other defects, their presence will reduce the superconductor performance, need to be further optimized.
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