The XRD patterns of the as-cold-sin

The XRD patterns of the as-cold-sintered ZnO ceramics and those after subsequent post-heat-treatment under various atmospheres at 300-800℃ are shown in Fig. 1. All diffraction peaks of the as-prepared samples can be well indexed by the standard XRD patterns (PDF #36-1451), indicating pure hexagonal wurtzite structure. However, the diffraction peak intensity is slightly weaker for the as-cold-sintered and 300℃ post-heat-treated samples, when compared with those post-heat-treated at higher temperatures over 400℃. After that, nearly no change in diffraction peaks is observed by further increasing the post-heat-treating temperature. The slightly weaker diffraction peak intensity may result from the insufficiency in crystallinity for the as-cold-sintered samples and those post-heat-treated at low temperature. It should be point out that even though the intensity of diffraction peaks is slightly lower for the as-cold-sintered and 300℃ post-heat-treated samples, it is still very strong and there is no background related to amorphous phase observed, which indicates both of them possess very high crystallinity. As post-heat-treating temperature increases, the crystallinity improves, leading to stronger peak intensity. It should be noted that the crystal structure and crystallinity of the as-cold-sintered ZnO ceramics after post-heat-treatment are independent of the atmosphere used, as the heat-treated samples in air and argon at 500℃ show similar XRD pattern (Fig.1).