Influences of Na doping on the superconducting properties of Bi-2212 High temperature superconductors

Abstract:

Polycrystalline bulks Bi_2.1Sr_1.96Ca_1-xNa_xCu_2.0O_8+d (Bi-2212) with Na doping content of x=0, 0.02, 0.05 and 0.10 were fabricated by spark plasma sintering (SPS) process. The Bi-2212 precursor powders were synthesized by modified co-precipitation process, and NaOH powders were added into as dopants before calcination. The influences of Na^₊ ions doping on the lattice parameters, phase composition, microstructures as well as related superconducting properties were systematically investigated. The introduction of Na in Bi-2212 system could cause an obvious decrease of phase transition temperatures. Thus during the SPS process, although the sintering temperature has been greatly decreased accordingly, Na doped Bi-2212 bulks still tended to decomposed into Bi₂Sr₂CuO₆ (Bi-2201) phase, which led to the decrease of both superconducting phase content and texture degrees, and thus caused negative effects on superconducting properties. On the other hand, Na doping introduced more point defects into Bi-2212 matrix, which acted as flux pinning centers during current transport process, and contributed to the increase of current capacity under high field. Therefore, Na doping with optimized sintering parameters should be considered as a promising method for the enhancement of high field current capacity in Bi-2212 system.