STABILITY OF NB-BASED, HIGH-TC A15 COMPOUNDS

We present a unified interpretation of the relationships between superconducting critical temperature and A15 phase stability for the series Nb3X, where X = Sn, Al, Ga, Ge, or Si. This interpretation is based on the experimentally supported premise that the highest Tcfor each member of this series is obtained in the ordered 3:1 stoichiometric A15 phase, and also that Tcincreases along the series as the X-atom size decreases. The instability problem arises from the fact that as the X-atom size decreases, the ordered stoichiometric A15 Nb3X phase becomes less stable and therefore increasingly difficult to prepare. © 1978 Plenum Publishing Corporation.