  In this report we present a systematic study on the preparation of Co:ZnO
ceramics via standard solid-state route from different Co precursors (Co3O4,
CoO and metallic Co) and atmospheres (O2 and Ar). Particular emphasis was done
on the defect chemistry engineering and on the sintering growth kinetics.
First-principles calculations based on density functional theory were employed
to determine the formation energy of the main point defects in ZnO and Co:ZnO
systems. Based on the theoretical results a set of chemical reactions was
proposed. A detailed microstructural characterization was performed in order to
determine the degree of Co incorporation into the ZnO lattice. The samples
prepared in Ar atmosphere and from metallic Co presents the highest Co
solubility limit (lower apparent Co incorporation activation energy) due to the
incongruent ZnO decomposition. The determination of the parameters of the
sintering growth kinetics reveals that Co3O4 is the best sintering additive in
order to achieve higher densities in both sintering atmospheres. The results
give evidences that the sintering in O2 is effective in promoting zinc
vacancies in the ZnO structure, while the sintering in Ar promotes zinc
interstitial defects. Our findings give valuable contribution to the
understanding of the preparation of Co-doped ZnO ceramics and the sintering
growth kinetics, what would allow to improve the state of the art on the
processing of the material at both bulk and nanometric scales.

Materials Science