Tsmtg Preparation Gdbco Bulk And Its Performance

The top seeded melt texture growth (TSMTG) process is one of the most effective methods for fabricating large YBCO bulk superconductors. The single-domain YBCO samples can be prepared by TSMTG in a large size YBCO. The GdBa2Cu3O7-δbulk superconductors have significant potential for practical applications, such as superconducting motors, maglev, magnetic bearings, permanent magnets, flywheel energy storage systems etc, since they have high critical temperature(Tc), high critical current density(Jc) and high trapped magnetic fields.In this paper, the precusor powder was prepared by the solid- state reaction method. Single domain GdBCO bulk superconductors with different BaCuO2 additions were prepared by top-seeded melt texture growth technique, meanwhile, their microstructure and levitation force were analyzed systematically. Secondly, TSMTG (Gd,Y)BCO bulk superconductors have been fabricated by mixing Y2O3 and GdBa2Cu3O7-δ(Gd123) in different mass ratio, meanwhile, their microstructure and levitation force were analyzed systematically. In addition, the influence of the processing parameters on the properties and growth morphology of (Gd,Y)BCO bulk superconductors have also been studied.During the preparation of the GdBCO bulk superconductor, GdBa2Cu3O7-δ(Gd123),Gd2BaCuO5(Gd211) and BaCuO2(Gd011) powders were synthesized by sintering and grinding process alternatively for several times, their sintering temperature is 940℃,920℃,910℃respectively.The effect of BaCuO2 addition on the growth morphology, microstructure and levitation force of single domain GdBCO bulk superconductor have been investigated. The results indicate that single domain GdBCO bulk samples can be fabricated with the precursors of Gd123:Gd211:Gd011 =1:0.4:x(x=0, 0.1, 0.2,0.3,0.4,0.5). The microstructure of the samples showes that the average Gd211 particles size was gradually decreased with increasing BaCuO2 addition. The decrease could be explained by a reaction between Gd211 and liquid phase due to excess BaCuO2 content which can consume Gd211. Additionally, the distribution of Gd211 particles in the quasi-single domain GdBCO bulk superconductor were investigated, scan electron microscope (SEM) analysis results show that the Gd211 particles are not uniformly distributed in the Gd123 matrix. The magnetic levitation force measurement results show that the levitation force of the samples is much different with different additions of BaCuO2. It is found that the optimal initial molar ratio is Gd123:Gd211: Gd011=1:0.4:0.2. The effect of Y2O3 addition on the growth morphology, microstructure and levitation force of single domain GdBCO bulk superconductor by the top-seeded melt texture growth process(TSMTG) has been studied. The results show that when Y2O3 addition is in a little ration, single domain (Gd,Y)BCO bulk can be obtained; when the mass ratio is larger than 100:4, the single domain area decreases monotonically with increasing Y2O3; when the mass ratio is higher than 100:15, there is nearly no distinct superconducting phases in the sample. The chemical component analysis of the crystal growth front indicates that the reason for the stopping growth of (Gd,Y)BCO crystal is because of the distinct deviation of the Gd3+,Y3+,Ba2+ and Cu2+ from the standard chemical ratio for (Gd,Y)BCO crystal growth. In those samples prepared with Y2O3 additions, the density of RE211 particles were monotonically increased with increasing Y2O3, meanwhile, RE123 content were gradually decreased. The magnetic levitation force is much different for the samples with different Y2O3 additions. It is found that the optimal mass ratio is 100:4 for preparation of (Gd,Y)BCO bulk superconductors. Besides, the influence of the heat processing parameters on the properties and growth morphology of (Gd,Y)BCO bulk superconductors have been studied. Too high or too low of the maximum melting tempreture(Tmax) is going to depress the crystal growth, the optimal Tmax is about 1070℃. The growth tempreture window is directly related to sample quality, the optimal growth tempreture window has been determined by some experiments.