A comprehensive study on the processing of Co:ZnO ceramics: defect chemistry engineering and grain growth kinetics

TL;DR

This study systematically investigates Co:ZnO ceramics, focusing on defect chemistry and grain growth kinetics, using experiments and first-principles calculations to optimize processing conditions and understand defect formation.

Contribution

It provides new insights into defect chemistry engineering and sintering kinetics in Co:ZnO ceramics, highlighting the effects of different precursors and atmospheres.

Findings

Co solubility is highest with metallic Co in Ar atmosphere.

Sintering in O2 promotes zinc vacancies, while Ar promotes zinc interstitials.

Co3O4 is the most effective sintering additive for higher density.

Abstract

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.