Fabrication and characterization of polycrystalline bulk ZnO with large grain size of ∼100 µm by the spark plasma sintering

Abstract We investigated to fabricate polycrystalline ZnO bulk crystal with large grain size up to 100 µm by the spark plasma sintering (SPS) in the atmosphere of low‐vacuum of ∼1 Pa air or in atmospheric pressure air. 1 µm average‐size ZnO powder of 99.999% purity was used as the raw material for sintering. The shape of samples was disk‐like of which diameter and thickness were 20 mm and 0.5–1.0 mm, respectively. We studied how the sintering conditions, in particular the sintering temperature and the applied pressure, affect the properties of sintered ZnO crystals. No additive to enhance the sintering process was used in this work. It was found that the SPS was very effective to enhance the sintering itself resulting in the grain size ranging from a few µm to ∼100 µm. Further the electrical properties of the sintered ZnO crystals were found to be very sensitive to the sintering conditions, i.e., their resistivity varied in the range from 0.02 Ω cm to ∼1000 kΩ cm depending on the grain size. The resistivity saturated in the order of 0.01 Ω cm when the grain size was above about 20 µm. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)