Effect of doping of divalent and trivalent metal ions on the structural and electrical properties of magnesium aluminate

Abstract

Nanosized magnesium aluminate materials doped by divalent cations (Ca 2+, Ba 2+, Sr 2+) and trivalent cations (Cr 3+, Mn 3+, Fe 3+) having nominal compositions Mg 1− x M x Al 2O 4 and MgAl 2− x M x O 4 ( x = 0.02–0.1), respectively, were synthesized by the sol–gel method. The samples were characterized by X-ray diffraction (XRD) and dc electrical resistivity measurements. The XRD data showed that all the samples were spinel single phase cubic closed packed crystalline materials having crystallite sizes between 6 and 35 nm. The lattice constant and X-ray density were found to be affected by the ionic radii of doped metal cations investigated here. Both the bulk density ( d b) and X-ray density ( d x) of doped materials increased whereas the porosity percentage ( P) decreased with the increase in the contents of the substituents. The dc-electrical resistivity of all the samples was measured in temperature range 160–400 °C by a two-point probe method and was found to decrease with temperature as expected for semiconductors. It was observed that alkaline earth metal dopants increased the resistivity of MgAl 2O 4 more than that by transition metal dopants. Arhenius activation energy of hopping of electron for all the samples was also calculated.