FAST/SPS sintering of nanocrystalline zinc oxide—Part I: Enhanced densification and formation of hydrogen-related defects in presence of adsorbed water

This part is focused on the effect of surface bound water on the densification behavior and defect stoichiometry of zinc oxide. The second part [doi: 10.1016/j.jeurceramsoc.2015.12.008] concentrates on the effect of hydroxide complexions on the microstructural development, texture formation and anisotropic grain morphology. Nanocrystalline zinc oxide powder was humidified or dried followed by quick heating (100 K/min) with field-assisted sintering technique/spark plasma sintering (FAST/SPS). Densification is strongly enhanced due to hydroxide-ion-diffusion mechanism, which shows species with lower valence and ionic radius in comparison to oxygen ions. The lowered activation energy for densification exhibits no impact of the sintering electric current on this enhanced densification behavior. The defect stoichiometry and structure of sintered zinc oxide was analyzed by several spectroscopic methods, indicating the formation of hydrogen-related defects for sintering in presence of bound water, while no hydrogen was detected for sintering of dried powder.