Unveiling the varistor and dielectric properties of a new binary ceramic compound based on hematite and non-stoichiometric manganese ferrite

In this study, a binary ceramic compound based on hematite and non-stoichiometric manganese ferrite was prepared through microwave-assisted hydrothermal method. Samples were synthesized at 100°C and 130°C with soaking times of 5 and 15 min, followed by drying, calcination, pelletizing, and sintering at 1100 °C. Final samples were labeled MnFe100_5, MnFe130_5, MnFe100_15, and MnFe130_15 based on synthesis parameters. Quantitative phase analysis confirmed the formation of α-Fe2O3 and Mn0.43Fe2.57O4 phases. Scanning electron microscopy (SEM) images revealed a mixed microstructure formed by equiaxial and elongated grains. Direct current (DC) electrical measurements demonstrated significant improvements in breakdown electric field strength and non-linearity for the samples synthesized for 15 min. The sample MnFe100_15 exhibited exceptionally low-voltage varistor characteristics, including a nonlinear coefficient of 25, a current leakage of 0.38 mA/cm², and a breakdown voltage of 21 V/cm. Impedance spectroscopy revealed larger semicircles and higher bulk and grain boundary resistances for the 15-minute sintered samples regardless of temperature. The α-Fe2O3 phase contributed to high breakdown voltage and stability, while the Mn0.43Fe2.57O4 phase enhanced the non-linear behavior and varistor performance by optimizing grain boundary properties and minimizing leakage currents. MnFe100_5 exhibited a high dielectric constant (1.48 ×10 ³), low loss (0.86), but weak non-ohmic behavior, thus indicating synthesis conditions can tailor materials for dielectric or non-ohmic applications.