Gd ₂ Ba ₄ NbCuO _Y Doping Improvement And Preparation Methods Affect The TSIG Law YBCO Superconductor Material Properties

The high temperature superconductors (HTS) are of highly attractive to the scientists world wide due to the novel physical properties and potentials for applications since the discovery of it in1986. In order to obtain high quality YBCO bulk superconductors, much more attentions are focused on the modification of the fabrication process, introducing effective flux pinning centers, and how to fabricate larger-sized YBCO bulk superconductors in this field. Top seed infiltration growth process (TSIG) is one of the most effective method of fabricating large and high-quality YBCO bulk superconductors, since the TSIG method can suppress segregation and emission of the liquid source, maintain the initial shape of the samples during TSIG process.A series of single domain YBCO bulk superconductors doped Gd2Ba4CuNbOy (GdNb2411) have been fabricated by TSIG process in this paper. Using the modified new TSIG method we have fabricated two groups of single domain YBCO bulk superconductors. The first group samples are fabricated with new solid phase (Y2O3+xBaCuO2) and liquid phase (YBa2Cu3O7-δ+3BaCuO2+2CuO); the second group are fabricated with new solid phase (Y2O3+xBaCuO2) and liquid phase (Y2O3+6CuO+10BaCuO2). The effects of the different x on the growth morphology, magnetic levitation force and the microstructure of the single domain YBCO bulk superconductors have been investigated.After studying the doped GdNb2411single domain YBCO bulk superconductors, we found that when GdNb2411addition x<6%, obviously the samples can grow into single domain and the domain areas can grow up to the whole samples. when GdNb2411addition x>6%, the single domain areas gradually decrease and accompanied with random nucleations, meanwhile, there are many steps around the seed in a square shape.②Along with increasing the GdNb2411addition the samples’ levitation force firstly ascend and then decrease, When the ratio of the GdNb2411x=4%, the max levitation force37.7N has been obtained, and the force density (the maxforce/area) is12.ON/cm2.③Microstructure of the samples shows when GdNb2411addition x<4%, the density of the Y211prticles is higher and the density of the GdNb2411prticles is less; when the addition x=4%, there is a reasonable quantity of Y211and GdNb2411in the samples. when GdNb2411addition x>4%, density of the Y211particles decreases and the density of GdNb2411increases with the increasing of the addition of the GdNb2411particles. While the addition of GdNb2411particles is in a higher level, the GdNb2411in the samples are very easy to gathering into cluster, and result in a bad microstructure for the YBCO bulk superconductors. So reseanable GdNb2411addition is helpful for us to fabricate high quality samples.Single domain YBCO bulk superconductors of20mm in diameter have fabricated with new solid phase (Y2O3+xBaCuO2) and liquid phase (YBa2Cu3O7-δ+3BaCuO2+2CuO); new solid phase (Y2O3+xBaCuO2) and liquid phase (Y2O3+6CuO+10BaCuO2). It is found that when the ratio x<1, it is difficult to grow up to single domain for the sample. When the ratio x≥1, the samples can grow up to single domain samples, but the single domain areas gradually decrease when the ratio x>2.The largest forces are49.2N、46.9N when the ratio x=1.2, and the force densities are16N/cm2、15.2N/cm2respectively. So the optimal BaCuO2additon is x=1.2.When the ratio x<1.2, the levitation force continuously increases with the increase of the the ratio, because the samples grow up to single domain and proper small Y211particles are in the samples.When the1.2<x<2, the decrease of the Y211should account for the reduction of the levitation force.When the x>2, the single domain areas and the decrease of the Y211particles are correspond to the reduction of the levitation force.Compared with the conventional TSIG process, there are many advantages in the new TSIG process:①Using the new solid phase, only the BaCuO2powder must be prepared, so the working efficiency of fabricating YBCO bulk superconductors can be considerably improved.②The Y211particles in the samples fabricated by the new TSIG process are much smaller.③The ratio of Y211particles dispersed in the YBCO bulk superconductors can be easily controlled during the new TSIG method.Base on the modified new TSIG process, the single domain YBCO bulk superconductors of30mm and40mm in diameter have been fabricated with new solid phase (Y2O3+xBaCuO2) and liqid phase (Y2O3+6CuO+10BaCuO2). The maximum levitation force of the sample of30mm in diameter is83.82N and the force density is11.86N/cm2. The modified new TSIG process is able to fabricate larger-sized YBCO bulk superconductors, which also can improve the working efficiency and decrease the cost of fabricating the YBCO bulks.