Non-stoichiometry of Nickel Oxide

Nickel oxide obtained by heating nickel nitrate, carbonate and hydroxide at low temperatures exhibits a non-stoichiometric structure. An excess of oxygen decreases with an increase in the heating temperature of nickel salts. Concentration of Ni3+ determined by chemical analysis increases with the excess of oxygen. Densities of nickel oxide or activation energy of electrical conductivity decrease with an increase in the excess of oxygen, whereas lattice parameter does not vary. Isothermal change in electrical conductivity of nickel oxide shows that the decrease in vacancies may be attributed to the diffusion of vacancies to the crystal surface. The concentration of vacancies calculated from the density is higher than that from the concentration of Ni3+ ion. The disagreement may be attributed to the density measurement technique.