Influence of Al Doping on the Structural, Optical, and Electrical Characteristics of ZnMn2O4

Doped zinc manganite samples were synthesized using the sol-gel method, incorporating varying amounts of aluminum (ZnMn2-xAlxO4, x = 0, 0.03, 0.05, 0.07, 0.1). High quality X-ray diffraction data enabled detection and accurate quantification of the predominant phase ZnMn2O4 (ZMO) and minor phase ZnO. The structure and microstructure of developed phases were investigated applying the Rietveld refinement method. The nanoscale nature of the samples was examined by High-resolution transmission electron microscopy (HRTEM); the incorporation of Al into the ZMO matrix and the oxidation states of various cations were studied through X-ray photoelectron spectroscopy (XPS). The introduction of Al has resulted in a modification of the light-absorption characteristics of the ZMO sample. Specifically, the direct optical band gap energy of ZMO decreased from 2.45 to 2.25 eV with an increase in the amount of Al doping to 0.1. Moreover, an investigation was conducted into the impact of Al doping amount, frequency, and temperature on the dielectric constant, dielectric tangent loss, ac conductivity, complex impedance, and complex electric modulus. It was observed that all samples, except for the sample with x = 0.05, exhibited ferroelectric features. The activation energies for the samples with x = 0, 0.03, 0.05, 0.07, and 0.1 were determined to be 0.274, 0.456, 0.099, 0.103, and 0.152 eV, respectively. The conduction mechanism type in the different samples was identified. The obtained changes of dielectric properties indicated the capability of improving the ZMO characteristics for various applications via controlling the doping content of Al.