Semi-conductors with partially and with completely filled₃<i>d</i>-lattice bands

Abstract

Attention is drawn to a class of semi-conductors or insulators with incompletely filled 3d bands. Their lack of conductivity, if the number of electrons per atom is an integer, is explained by the circumstance that a moving electron will have a large probability of being withdrawn to the initial atom, if only the potential barriers to be penetrated are sufficiently high to reduce the frequency of transition below a certain limit. This inhibiting factor disappears, if for ions of equal electronic levels the number of electrons per atom differs from an integer. In the case of NiO this condition is fulfilled if an electron is brought by thermal excitation from the lattice 3d band into the somewhat raised and less occupied levels a, a' (figure 1); these levels belong to Ni ions adjacent to a vacant Ni lattice point introduced by the deviations from stoichiometry, and two of these Ni ions are at the absolute zero Ni3+ ions. An analogous conduction mechanism holds for non-stoichiometric Cu2O, with a completely filled 3d band (figure 2).