Abstract
In this work, we report a systematic variation in the band gap of stoichiometric Zn1−xMgxAl2O4 ceramics with varying contents of Mg (x), x = 0.0, 0.2, 0.4, 0.6, 0.8 and 1.0, synthesized by the microwave-assisted sol–gel combustion technique. X-ray diffraction confirmed the cubic spinel structure of all the prepared samples. Real and imaginary dielectric constants were in full agreement with the general trend of the spinel series, showing a decrease with increasing frequencies, in accordance with non-Debye characteristics. For this purpose, a modified form of the Debye relation was used to explain the problem. Gradual substitution of Mg at Zn site affected the modulus characteristics and resulted in an increase in the resistance of the samples. The Cole–Cole plots were explained in the light of grain size distribution and dielectric polarisation. UV–Visible (UV–Vis) diffuse reflectance spectroscopy determined a wide range of band gap energies, ranging from 4.46 to 5.71 eV, obtained without any significant change in lattice parameters. The present work provides a detailed overview of Mg–Zn-based aluminates featuring stepped or graded energy band gaps that can be used for optoelectronic devices.
•Synthesis of Mg-substituted ZnAl2O4 at low temperature using low cast fuel agents.•Variation in dielectric parameters explained by a modified Debye relation.•Wide variation in energy band gaps without significant change in lattice constants.•Frequency response of dielectric constant confers the suitability for use as MCIs.•Mg–Zn-based aluminates featuring graded Eg values viable for optoelectronic devices.