Synthesis and structure analysis of aluminum doped zinc oxide powders

Hexagonal Al-doped zinc oxide (ZnO) powders with a nominal composition of Zn(1-x)Al(x)O (0 <= x <= 0.028) were synthesized by the co-precipitation method. The contents of the Al element in the samples were measured by the inductively coupled plasma-optical emission spectroscopy (ICP-OES) technique. The structures of the Zn(1-x)Al(x)O (0 <= x <= 0.028) compounds calcined at 1000 and 1200 degrees C have been determined using the Rietveld full-profile analysis method. Rietveld refinements of the diffraction data indicated that the addition of Al initially has a considerably positive effect on the decreasing of the lattice parameters a and c of Zn(1-x)Al(x)O, but the effect becomes very slight and even negative with the further increase of the Al content. The solid solubility limit of Al in ZnO (mole fraction y) is 2.21%, resulting in Zn(0.978)Al(0.22)O. It seems that when the Al content is excessive, Al prefers to form a ZnAl(2)O(4) compound with ZnO, but not to incorporate into the ZnO lattice to occupy the Zn(2+) cites. Two phases, [ZnO] (or Al-doped ZnO) and [ZnAl(2)O(4)], are obviously segregated in Zn(1-x)Al(x)O while the value of x is larger than 0.024. The UV-Vis absorption spectra show that the Al-doped ZnO exhibits a red-shift in the absorption edge without reduced transmission compared with pure ZnO, which also confirms that Al ions enter the ZnO lattice and form a Zn(1-x)Al(x)O solid solution.