Na掺杂对Bi-2212高温超导体性能影响研究

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

摘要:

本文采用放电等离子烧结(SPS)工艺制备了Na掺杂的Bi_2.1Sr_1.96Ca_1-xNa_xCu_2.0O_8+d超导材料。Bi-2212前驱体粉末采用改进的共沉淀工艺制备,并在烧结前将前驱体粉末与NaOH混合。本文系统研究了Na离子掺杂对Bi-2212体系晶格结构、相组成、微结构和相关超导性能的影响。Na离子掺杂导致Bi-2212体系相转变温度的显著降低。因此在SPS过程中,烧结温度相应发生了变化。但Na掺杂仍然导致大量Bi₂Sr₂CuO₆ (Bi-2201)相生成,进而导致了超导相含量的降低和织构度的破坏,所以给体系的超导电性带来了负面的影响。另一方面,Na掺杂相Bi-2212中掺入了大量的点缺陷,这些点缺陷可以作为有效钉扎中心。因此,通过优化Na掺杂Bi-2212的烧结工艺,有可能在高场条件下获得体系性能的改善。

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.