Synthesis of High Crystalline Al‐Doped ZnO Nanopowders from Al2O3 and ZnO by Radio‐Frequency Thermal Plasma

Abstract

High crystalline Al‐doped ZnO (AZO) nanopowders were prepared by in‐flight treatment of ZnO and Al2O3 in Radio‐Frequency (RF) thermal plasma. Micron‐sized (~1 μm) ZnO and Al2O3 powders were mixed at Al/Zn ratios of 3.3 and 6.7 at.% and then injected into the RF thermal plasma torch along the centerline at a feeding rate of 6.6 g/min. The RF thermal plasma torch system was operated at the plate power level of ~140 kVA to evaporate the mixture oxides and the resultant vapor species were condensed into solid particles by the high flow rate of quenching gas (~7000 slpm). The FE‐SEM images of the as‐treated powders showed that the multipod shaped and the whisker type nanoparticles were mainly synthesized. In addition, these nanocrystalline structures were confirmed as the single phase AZO nanopowders with the hexagonal wurtzite ZnO structure by the XRD patterns and FE‐TEM results with the SAED image. However, the composition changes of 0.3 and 1.0 at.% were checked for the as‐synthesized AZO nanopowders at Al/Zn ratios of 3.3 and 6.7 at.%, respectively, by the XRF data, which can require the adjustment of Al/Zn in the mixture precursors for the applications of high Al doping concentrations.