<正> A-15相是一类特殊的A_3B型化合物,其中A元素必须是ⅣA,ⅤA,ⅥA族过渡元素。电子密度e/a和组元A,B的半径比r_A/r_B是决定A-15相性质的两个重要因素。Matthias首先注意到e/a对A-15相超导临界温度T_c的影响。当e/a=4.7和6.5时,T_c分布的包络线上出现两个峰。但也有不少A-15相虽然具有最适宜的e/a值,T_c仍很低,甚至根本没有超导性。Hartsough总结了影响A-15相形成的因素,认为r_A/r_B=
The binary A-15 phases formation and their T_c variation have been studied by means of the bond-parametric diagram. It was ascertained that the A-15 phases locate in a definite region on the plot of electron density e/a vs radii ratio of components r_A/r_B. The A-15 phase cannot form any longer for the ratio r_A/r_B over a certain critical value which varies with e/a periodically. On the plot, the T_c distribution of A-15 Phases is shown with regularity. The A-15 phases with T_c higher than 1, 4.2, 10, 15 or 20 K are concentrated in the regions of corresponding isotherms. The ratio r_A/r_B, and e/a as well, may be important parameters in determining T_c. As compared with Matthias' rule, a better result in determining the location of A-15 phases of high T_c has been obtained by the consideration of both factors.
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