摘要
In this report,we present a systematic study on the preparation of Co:ZnO ceramics via a standard solid-state route from different Co precursors(Co_(3)O_(4),CoO,and metallic Co)and atmospheres(O_(2)and Ar).Particular emphasis is given to defect chemistry engineering and the sintering growth kinetics.First-principles calculations based on density functional theory are employed to determine the formation en-ergy of the main point defects in ZnO and Co:ZnO systems.Based on the theoretical results,a set of chemical reactions is proposed.Detailed microstructural characterization is also performed to determine the degree of Co incorporation into the ZnO lattice.The samples prepared in Ar atmosphere and metal-lic Co present the highest Co solubility limit(lower apparent Co incorporation activation energy)due to the incongruent ZnO decomposition.Determination of the parameters of the sintering growth kinetics reveals that Co_(3)O_(4)is the best sintering additive to achieve larger grain sizes,and possible higher densi-ties,in both sintering atmospheres,while metallic Co is the best to achieve the smallest grain size with higher Co concentration and homogeneous spatial distribution for a subsequent reduction of dimension-ality.The results show that the sintering in O_(2)effectively promotes zinc vacancies in the ZnO structure,while the sintering in Ar promotes zinc interstitial defects.Our findings contribute to understanding the preparation of Co-doped ZnO ceramics and the sintering growth kinetics,which may improve the state of the art in processing the material at both bulk and nanometric scales.
基金
This work was financially supported by agencies CAPES and FAPEMIG.The authors also acknowledge Prof.Dr.A.C.Doriguetto,coordinator of the Laboratório de Cristalografia of the Universidade Federal de Alfenas where the XRD measurements were performed,and Dr.M.I.B.Bernardi of Instituto de Física de São Carlos of the Universidade de São Paulo for the photoreflectance measurements.
