Al-Doping Effects on Structural and Morphological Properties of ZnO Aerogels Synthesized in Supercritical Ethanol

Aerogels of pure and aluminium doped ZnO (Al-ZnO) were synthesized by sol-gel route followed by supercritical drying in ethanol. The atomic percentage of the dopant is fixed at 1, 3, 5 and 10 at.%. The elaborated aerogels were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), X-ray energy dispersive analysis (EDAX) and Fourier transform infrared spectroscopy (FTIR). The DRX results revealed good crystalline quality of the synthesized samples with hexagonal wurtzite crystallographic structure. No crystalline phase related to aluminum ions or aluminum based compounds has been detected. With increasing Al content in aerogels, the crystallinity deteriorates and the cell parameters are found to be slightly changed. SEM images showed that the presence of Al atoms in the ZnO lattice strongly alters grain morphology, especially for higher doping levels (≥ 5 at.%). The EDAX spectra showed well-defined peaks related only to Zn, O and Al and confirmed the absence of peaks related to other impurities. FTIR measurements have shown that the introduction of the A1 ions in the aerogels greatly reduces the intensity of the Zn-O bond-vibrating band and shifts it towards low wavenumbers.