| Popis: |
The sigma and alpha-manganese structures formed by binary alloys between the group (V, Nb, Ta, Cr, Mo, W) and the group (Mn, Fe, Co, Ni, Ru, Rh, Pd, Re, Os, Ir, Pt) were investigated for superconductivity down to 1°K. Nineteen new superconductors were found in these two systems with the majority occurring in the sigma phase. A plot of superconducting transition temperature of the sigma phases against the average number of valence electrons per atom exhibited a maximum at approximately 612 electrons per atom. This maximum is similar to those found for other structures by Matthias, however it is displaced somewhat from the vicinity of 5 or 7 electrons per atom which Matthias indicated to be characteristic of other systems. The sigma phase data therefore suggests to us that in compound formation between pairs of transition elements, the d-band shape is preserved to some extent and is filled at an intermediate level by the available electrons. |
