Electrical Conductivity of Single Crystalline Nickel Oxide

Abstract

The electrical conductivity of single crystalline NiO was found to be proportional to the 1/4 power of the oxygen pressure for oxygen partial pressures between 10⁰and 10⁻⁴atm over the temperature range of 900 to 1200 °C. These results are in agreement with singly ionized cation vacancies as the predominant nonstoichiometric defect. The sum of the enthalpies of formation of nonstoichiometric disorder and activated enthalpy of movement of an electron hole was found to remain constant when thermodynamic equilibrium was maintained. The activated enthalpy of movement of an electron hole, however, was found to obey the “Meyer‐Neldel” relationship, that is, it increased as the concentration of electron holes decreased. An argument has been offered for the explanation of the “Meyer‐Neldel” rule. This explanation involves consideration of another equilibrium between free electron holes and those trapped at imperfections (such as dislocations) which are not usually considered in the usual theory of point defects in nonstoichiometric compounds.