Investigation of YBa2Cu3O x , Bi(Pb)-HTSC and Nd(123)-Particles in a Running Magnetic Field Near the Superconducting Transition Temperature

A novel system of electromagnetic separation (EMS) employing an alternating magnetic field (RMF) of suspended HTSC-particles in liquid nitrogen is described (Broide in Supercond. Cryoelectron. Summer:33, 1998]; Broide in Superconductor Week 12, No. 21, 1998]; Broide in US Patent 5,919,737, 1999]; Broide et al. in International Conference, Barcelona, Spain, 1999]). The EMS method is realized at temperatures close to those of the HTSC transition by extracting particles of YBaCuO, BiSrCaCuO, BiPbSrCaCuO, and NdBaCuO with optimal physical properties from the powders, concentrating particles with a greater critical current at one side. This process has shown great promise in its ability to produce high quality superconducting materials, being also an effective method of testing and analyzing powders to determine if synthesis adjustments are necessary in order to achieve optimal materials properties. In addition, a correlation between the speed of YBa₂Cu₃O _x particles and the percentage of oxygen (O _x ) was discovered. Since the temperature of the superconducting (SC) transition (T _c ) practically has a linear dependence on the oxygen percentage, the knowledge of the speed of the HTSC-particles during the separation, one may immediately give (within 10 s) the percentage of the oxygen in the chemical structure of the new HTSC materials. The EMS method enables statistical improvement in the uniformity of HTSC powders by decreasing the quantity of defective zones in the separated powders, the number of nonvalid admixtures, and thus, an increase in T _c and I _c (critical current). At the same time, ΔT _c the width of the SC-transition is decreased. Three YBa₂Cu₃O _x thick films have been produced by the paint method on MgO substrates from the source material, the separated high-quality concentrate, and the low-quality remnant (tail). The films exhibit different structural and electrical properties, in particular, different I _c , and ΔT _c . For the film that was made from the high-quality concentrate, ΔT _c is decreased from 5–7 K to 1–2 K. I _c is increased by a factor of 2–5 from the I _c of the source material (before EMS) and T _c is changed from 89 K to 93 K. Thick films, which had been produced from low-quality remnant (tail) do not have SC transition down to 77 K.