FAST/SPS sintering of nanocrystalline zinc oxide—Part II: Abnormal grain growth, texture and grain anisotropy

This second part describes the retention of nanocrystallinity during sintering of ZnO by means of Field-assisted Sintering Technique/Spark-Plasma-Sintering (FAST/SPS), whereas the first part [doi: 10.1016/j.jeurceramsoc.2015.12.009] concentrated on hydroxide-ion-enhanced densification and defect stoichiometry. Interface design by surface bound water on zinc oxide offers a novel method to control in a new way diffusion in nanocrystalline polycrystals. Therefore, zinc oxide powder was humidified or dried and afterwards heated quickly (100 K/min) by FAST/SPS. Interestingly, the densification is strongly promoted in presence of water reducing the sintering temperature to 400 °C. Thus, grain growth is decreased by one order of magnitude while achieving full densification. The crystalline texture developed irrespective of temperature or presence of water. Moreover, the formation of hydroxide complexion at grain boundaries is discussed as it might modify grain boundary mobility and lead to pronounced grain anisotropy perpendicular to the uniaxial applied load.