The solid state interaction of the nominal Zn1-xCoxO system was investigated by means of diffusion couples and analysis of co-precipitated samples. The formation of an homogeneous Co:ZnO solid solution was found to be determined by the crystal structure from which CoII ions diffuse into the wurtzite lattice. No diffusion was observed whenever the CoO rock-salt structure was formed from the CoII precursor. On the contrary, the diffusion from the Co3O4 spinel phase was feasible but had a limited temperature range defined by the reduction at a high temperature of CoIII–CoII, since this process again led to the formation of the rock-salt structure. However, when using a highly reactive and homogeneous co-precipitated starting powder, neither the spinel phase nor the rock-salt structure was formed, and a CoII:ZnO solid solution was obtained, which remained stable up to high temperatures.

Influence of Crystal Structure on the CoII Diffusion Behaviour in the Zn1-xCoxO System. Peiteado, M., Makovec, D., Villegas, M., Caballero, A.C.: Journal of Solid State Chemistry, 2008, 181[9], 2456-61