A chemical approach to superconductivity

Abstract

Correlations of the important parameters of the BCS theory of superconductivity are developed with respect to the number of d‐shell electrons per atom of the transition elements predicted by the Engel‐Brewer theory of alloys. The importance of ``bonding'' on the d level as a generalized electron‐electron interaction is demonstrated; and the total attractive potential V of the BCS equation for the critical temperature T_c is shown to arise from both the phonon‐induced potential, V_ph, and a large attractive potential V_b, due to bonding and having a maximum at the half‐filled d shell. The present theory is consistent with the recent data of amorphous superconductors if their electron density of states at the Fermi level, N_o, is a constant or a shallow function of the electron‐per‐atom ratio. The anomalous isotope effect of some elements is also discussed, as well as the fundamental instability of high‐T_c superconductors and the incompatibility of ferromagnetism and superconductivity.