CATION IMPURITY DIFFUSION IN COO AND NIO

Impurity diffusion of **5**9Fe, **5**4Mn, **4**6Sc, **8**8Y, **9**5Zr and **9**5Nb in both CoO and NiO and of **2**2Na in CoO has been measured as a function of temperature (1000-1600 C) in air by the tracer-sectioning technique. It has been shown that the larger ions diffuse more rapidly and have a smaller activation energy than do smaller ions for transition-metal impurity ions having the same valence. The absolute values of the divalent-impurity diffusion coefficients in CoO and NiO are comparable to the self-diffusion coefficients of Co and Ni, respectively. The diffusion coefficients of the trivalent impurity ions are smaller than those of the divalent impurity ions in these oxides. The activation energies for impurity diffusion in CoO and NiO are discussed in terms of the ionic size and the charge state of the diffusing ions.