SURFACE AND BULK PHASES IN SUBSTITUTED COBALT OXIDE SPINELS

Samples of cobalt oxide spinel doped with a range of cations (Li, Ni, Zn, Cu, Al, Ga, Mn, Ti, Sn, Ge) have been prepared and examined by X-r ay diffraction and X-ray photoelectron spectroscopy. Surface enrichmen t in the dopant species is frequently observed. Determination of the r atio of the two cobalt oxidation states in the surface layers is found to be useful in distinguishing between solid solution behaviour and t he nucleation of surface phases. This ratio may also be helpful in cha racterising the preferred occupancy of octahedral and tetrahedral site s in the near surface regions.