CXLIII. On conduction in impurity bands

Summary The idea of conduction by electrons in the energy bands of an impurity system is examined. For a lattice of hydrogen-like impurities the edges of the 1s, 2s, and 2p bands are calculated. Effective masses for electrons in these bands are introduced. With their help measurements of the conductivity and the Hall constant are interpreted. Depending on the density of the impurities and on the temperature, conduction takes place predominantly either in the band of the medium, or in excited impurity states, or in the Is impurity band. In this last case the activation energy vanishes. This interpretation implies a description of the electronic state of the impurities with band wave functions and indicates the validity of such a description up to rather large values of the lattice constant. This can, however, be reconciled with the insulating properties of the oxides of transition metals.