Conductivity relaxation experiments on Ni1-delta O

The chemical diffusion coefficient (D) over tilde of polycrystalline nickel oxide was studied as a function of oxygen activity (10(-5) atm < p(O2) < 1 atm) and temperature (700 degreesC < T < 1200 degreesC) employing electron ic conductivity relaxation experiments in the van der Pauw configuration. W ith this technique the sample is equilibrated under a given oxygen pressure . The oxygen content of the atmosphere surrounding the sample tablet is the n changed stepwise and re-equilibration of the sample is followed by monito ring the conductivity relaxation. The chemical diffusion coefficient is obt ained from the time-dependent variation of the electronic conductivity. The temperature dependence of (D) over tilde between 700 and 1200 degreesC can be described by (D) over tilde (cm(2) s(-1)) = 2.40 x 10(-3) exp(-0.70+/-0 .05 eV/kT). The chemical diffusion coefficient is found to be almost indepe ndent of the oxygen partial pressure and thus of oxide composition. The ele ctronic conductivity at 1000 degreesC shows a 1/6 dependence on the oxygen partial pressure, indicating the presence of doubly ionized nickel vacancie s and electron holes as predominant defects. The (D) over tilde values are compared with literature results on single crystals. (C) 2000 Elsevier Scie nce B.V. All rights reserved.