Tunable dielectric behaviour and energy band gap range of ZnAl2O4 ceramics mediated by Mg substitution

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. (C) 2017 Elsevier B.V. All rights reserved.