高价离子掺杂对Bi系成相和结构的影响(Ⅱ)

EFFECTS OF HIGH VALENCE CATIONS DOPED ON THE PHASE FORMATION AND THE CRYSTAL STRUCTURE IN THE Bi SYSTEM (Ⅱ)

Sunshine等在BiSrCaCuO体系掺入Pb^(2+)取代部分Bi,经较长时间灼烧后.获得T_(c(0))?110 K以2223相为主的样品,Hongbao等又报导了用Sb部分取代Bi(Pb)SrCaCuO体系中的Bi的研究结果.我们曾用Sb^(5+)、Sn^(4+)、W^(6+)、Mo^(6+)等高价离子部分取代Bi,研究这些离子对BiSrCaCuO体系成相的影响,发现掺高价离子后2223相易于生成并易于得到T_(c(0))?111K的超导体.本文则进一步探讨高价离子掺入的影响及其加速2223相生成的原因。

In our previous work we have found that the 2223 phase is formed more rapidly and the structural stability can be enhanced by doping high valence cation(Sn^(4+)、Sb^(5+)、V^(5+)、W^(6+)、Mo^(6+) etc .) in the Bi(Pb)SrCaCuO system. In this paper the effects of highvalence cations doped on the phase formation and the crystal structure are discussedfurther. The Aurivillus building and rocksalt building unit coexist in the Bi double lay-ers. The structural variety strongly affects the structural stability. Owing to Pb^(2+)addition the probability of Aurivillus building is increased,the stability of 2223 phasecan be promoted. However, the structure is still not stable, since the addition ofPb^(2+) has decreased the valence state of Bi site and the oxygen positions are not fullyoccupied. By doping high valence cation, especially, when the valence of Pb_x^(2+)+M_y^(n+)equals to +3 the structure of the 2223 phase can be stabilized. This result has beenobserved with examining elemental content of 2223 phase. The melting point of the grain boundaries are much lower after doping high valence cations,therefore the ion diffusion is more rapid and acceleration of the 2223 phase formation is observed.