The influence of dopents (Li₂O, Na₂O, Al₂O₃ and In₂O₃) on the sintering of ZnO and NiO has been studied in the temperature range 750° to 1200°C in air. The dopents, Li₂O and Na₂O, were found to promote the sintering of ZnO and the other dopents, Al₂O₃ and In₂O₃ to inhibit. The result is explained by the diffusional transfer of interstitial zinc ions.
While for the sintering of NiO, the Li₂O and Na₂O were found to promote the sintering, the Al₂O₃ and In₂O₃ to inhibit. This result shows evidently that material transport in NiO does not depend on the concentration of nickel ion vacancies, but on the concentration of electron holes, trivalent nickel ions Ni³⁺, which have smaller ionic radii than bivalent nickel ions.