Processing and Sintering of Zn0.92Sn0.04Bi0.02Co0.02OβNanopowders

This study aims at investigating the processing and sinterability of Zn0.92Sn0.04Bi0.02Co0.02Oβ nanosized powders synthesized by chemical precipitation method. Addition of tin has been reported to influence the non-linear properties in ZnO-based systems. The precipitates were calcined at 800̊C, as determined by Thermogravimetric analysis (TGA) and Fourier Transform Infrared Spectroscopy (FTIR), to remove organic residues. X-ray diffraction (XRD) revealed zincite as a main phase with small traces of Bi2O3. The averaged crystallite sizes were anisotropic (60.4 nm along [100], 27.9 nm along [002] and 46 nm along [101]). These sizes, along with elongated shape, were confirmed by Transmission electron microscopy (TEM). Sintering with a relative density of 95% was readily obtained at 1000̊C. However, comparing with the undoped sample (Zn0.96Bi0.02Co0.02Oβ), the densification rate of the currently investigated samples was slower at temperatures below 1000̊C. This lower sintering rate could possibly be related to the increase in crystallinity of Bi2O3 and formation of another secondary phase (spinel Zn2SnO4) as seen by XRD. The phasic nature in these samples was highly dynamic; the spinel phase disappeared at the sintering temperatures of 1200̊C and higher. Reduction in the averaged grain size was observed, and elemental analysis confirmed the composition of the phases previously found by XRD. The grain boundary liquid phase contained both Zn and Bi, indicating the plausible solubility between these two species. The smaller averaged grain size, in addition to the superior properties of SnO2, resulted in a higher breakdown voltage (1730 V/cm comparing to 310 V/cm for the undoped sample).