Electrical Properties of Non‐Stoichiometric Nickel Oxide

The temperature dependence of the electrical conductivity and of the Seebeck coefficient of NiO samples with various Ni3+ concentrations is determined. These samples are obtained from a nickel salt, using various decomposition temperatures. The temperature dependence of the hole concentration, pα, is calculated from the Seebeck coefficient. Since pα is constant up to about 500 °K, the exponential temperature variation of the conductivity must be attributed to the temperature dependence of the mobility. It seems, therefore, that at least up to the Néel temperature non‐stoichiometric NiO exhibits a similar conduction mechanism to Li‐doped NiO, with holes hopping between Ni2+‐ions. The discrepancies between the values of the hole concentration determined from the Seebeck coefficient and those given by the chemical analysis are discussed in terms of a simplified model, taking into account the non‐uniform distribution of the excess‐oxygen atoms throughout the volume of the NiO grains. The results confirm that for NiO samples of high excess oxygen content the electrical conduction is mainly due to grain boundaries.