Conductivity relaxation experiments on Ni1−δO
The chemical diffusion coefficient D of polycrystalline nickel oxide was studied as a function of oxygen activity (10 5 atm < p O2 < 1 atm) and temperature (700°C < T < 1200°C) employing electronic conductivity relaxation experiments in the van der Pauw configuration. With this technique the sample is equilibrated under a given oxygen pressure. The oxygen content of the atmosphere surrounding the sample tablet is then changed stepwise and re-equilibration of the sample is followed by monitoring the conductivity relaxation. The chemical diffusion coefficient is obtained from the time-dependent variation of the electronic conductivity. The temperature dependence of D between 700 and 1200°C can be described by D(cm 2 s -1 ) = 2.40 × 10 -3 exp(-0.70±0.05 eV/kT). The chemical diffusion coefficient is found to be almost independent of the oxygen partial pressure and thus of oxide composition. The electronic conductivity at 1000°C shows a 1/6 dependence on the oxygen partial pressure, indicating the presence of doubly ionized nickel vacancies and electron holes as predominant defects. The D values are compared with literature results on single crystals.