The effect of nickel doping on the structural, defect structural, optical and magnetic properties of zinc oxide nanoparticles

Positron annihilation lifetime (PAL) spectroscopy has been applied in the present work to study the defect structure changes of the Zn 1-x Ni x O (0% ≤ x ≤ 10%). This system has been synthesized in nanosize by coprecipitation method. Nanostructure features of the prepared samples have been investigated by X-Ray diffraction (XRD) and TEM. The XRD data has revealed that the prepared samples are crystalline and belong to space group P6 3 mc. The deduced estimated average crystallite size is varying from 20 nm to 96 nm in agreement with TEM measurements The variation of lattice parameters and internal strain that have been deduced from XRD data, have shown that the solubility limit of NiO in ZnO does not exceed 5% and are correlated with PAL parameters. At 7% and 10% concentrations the XRD spectra has revealed the presence of secondary peaks due to creation of a new NiO phase, which indicates that Ni is no more incorporated in the ZnO structure. This has been also confirmed by the variation of the energy gap E g deduced from the UV absorbance spectra and the variation of FTIR absorption bands. The (M-H) curves have shown that the saturation magnetization M s suggest the presence of ferromagnetism which decreases with increasing Ni content up to 5%. This is associated with an increase in the formation of vacancy clusters and positron trapping rate in the interface region. In addition, the vacancy defects play an important role in mediating the ferromagnetism behavior in agreement with the polaron model.