Investigation of the microstructure, cation distribution and optical properties of nanoscale NixMg1-xAl2O4 spinel pigments

Abstract Nanoscale Ni x Mg 1-x Al 2 O 4 spinel pigments were synthesized by a citric acid precursor combined with the gel-casting method. The microstructure, cation distribution and optical properties as a function of calcining temperature and nickel content were investigated by the X-ray diffraction (XRD) Rietveld refinement, transmission/field emission scanning electron microscopy (TEM/FESEM), X-ray photoelectron spectroscopy (XPS), colour measurement and UV–vis–NIR spectrophotometry. Upon increasing the calcining temperature, both Ni 2+ and Mg 2+ hindered the migration of Al 3+ to octahedral sites. When the Ni content increased, the cation site percentage of Ni 2+ in the tetrahedral and octahedral sites varied slightly while that of Al 3+ and Mg 2+ change substantially. The cation exchange resulted in an increase in the inversion parameters and a decrease in the lattice parameters with increasing temperature or Ni content. Furthermore, Rietveld refinement also showed a shrinkage of the tetrahedra and an expansion of the distorted octahedra in the spinel structure. Short-range information based on optical spectra suggests that variation in the splitting energy of tetrahedra and octahedra caused the change in the spectral absorption. This study may deepen the understanding of the structural-optical property relationship of Ni x Mg 1-x Al 2 O 4 spinel, which is vital to the further colour modification of ceramics and glazes.