A—15型化合物的超导性经验规律

本文给出一张既能考虑A-15结构型变,又能描述A-15型化合物T_c(超导临界温度)变化规律的图。从而预言:所述A-15系列中大概不会存在T_c很高(>25K)的化合物;铌系列中Nb₃Ge的T_c可能是最高的;钒系列中T_c可望还能提高(>17.1K),V₃Ge可望提高到12K以上。检查Nb₃Si,得不到Geller那样的乐观估计,并认为:以新工艺得到的A-15相Nb₃Si,是以牺牲正当化学配比或改变正常原子体积为代价而获得的非理想结构。从T_c与半径比关系及理想A-15结构对半径比的要求来看,笔者认为文献上关于Nb₃Si在有较高T_c(>23K)的种种预言,都是缺乏充分依据而不足置信的。 关键词：

AN EMPIRICAL RULE FOR SUPERCONDUCTING A-15 TYPE COMPOUNDS

A diagram which not only considers the transition of the structural type hut also describes the rule of change of T_c in the A-15 compounds is given in this paper. From this diagram it can be seen that compounds with very high T_c(>25K) are not likely to exist in the A-15 series considered. In the Nb series, Nb₃Ge probably has the highest T_c; in V series, the T_c can still be expected to be raised (>17.1K), the T_c of V₃Ge is likely to be raised to above 12 K. Examining the case of Nb₃Si, one can not get the optimistic estimation as that of Geller. It is considered that Nb₃Si of A-15 type obtained by present new technology is a non-ideal structure formed at the expense of the normal stoichiometric ratio or by a change of the ordinary atomic volume. On the basis of the relationship between T_c and radii ratio and on consideration of the radii ratio required by the ideal A-15 structure, the point of view presented in this paper does not agree with the various predictions that the Nb₃Si might have a high T_c(>23 K).