Effects of sintering temperature and doped Al content on the microstructure and physical performances of AZO ceramics

Abstract

In order to enhance the physical performances of aluminum-doped ZnO (AZO) ceramics, AZO powders with different doped Al concentrations were synthesized by in situ hydrothermal method, and the high density AZO ceramics were prepared by spark plasma sintering (SPS) technologies. Effects of the sintering temperature and doped Al content on the relative density, crystal structure, composition and physical properties of AZO ceramic were studied by means of X-ray diffraction (XRD), field emission scanning electron microscope (FSEM), fluorescence spectrophotometer, ultraviolet–visible spectrophotometer (UV) and four-point probes. The results show that the nanoparticle AZO powders prepared by hydrothermal method were fine with uniform particle size. The relative density of AZO ceramic increases first and then decreases with the increase of sintering temperature. Accordingly, the resistivity decreases first and then increases. Enhancing the sintering temperature can improve the peak strength of photoluminescence (PL) but has little effect on its peak position. Meanwhile, the UV absorption peak first shifts to the red, then shifts to the blue and then slightly shifts to the red, resulting in the band gap width first narrates, then widens and then narrates. It should be noted that when the sintering temperature exceeds 1400 °C, the second phase ZnAl2O4 spinel can be formed, which will reduce the bulk density of the ceramic, and then weaken the resistivity and photoelectric properties of the material. Doped Al content has obvious effect on the electrical conductivity of AZO ceramics. With the increase of doped Al content from 1 wt. % to 3 wt. %, the resistivity decreases from 1.42 Ω٠m to 0.77Ω٠m. However, Al doping content only increased the peak strength of PL spectrum but did not change its peak position. When the doped Al content is 1 wt. % and SPS sintering temperature is 1300 °C, AZO ceramics have the excellent physical properties with the relative density of 96.2% and the resistivity of 1.42 Ω٠m.