Effect of sintering temperature on structural, microstructural, and dielectric properties of (Co0.2Fe0.2Ni0.2Al0.2Ti0.2)3O4 multi-cations high entropy oxides

The study reports the effect of sintering temperature on structural, microstructural, and dielectric properties of (Co0.2Fe0.2Ni0.2Al0.2Ti0.2)3O4 spinel high-entropy oxides (HEOs) synthesized through the solid-state mechanochemistry method. The sintering of the ceramic powders was accomplished at three different temperatures (1000 °C, 1100 °C, and 1250 °C), followed by air quenching. XRD analysis along with Le-Bail refinement confirms that 1100 °C and 1250 °C sintered oxides comprised of a single cubic spinel phase ( F d 3 ‾ m ), while 1000 °C sintered oxide contains constituent oxides and a spinel phase. The phase formation of oxides sintered at 1100 °C and 1250 °C has also been confirmed by Raman spectroscopic analysis. Microstructural analysis revealed that the aggregated particle size increases with the rise in sintering temperature. With the change in sintering temperature, the dielectric behavior of the ceramic changed extensively. The 1100 °C sintered ceramic exhibits high frequency-dependent behavior, whereas the 1250 °C sintered ceramic yields low frequency-dependent behavior. The 1250 °C sintered HEO exhibits low-loss tangent ( tan δ = 0.01) with higher dielectric permittivity ( ε ′ = 44) at high frequency (1 MHz) compared to the 1100 °C sintered ceramic and many other conventional dielectrics. Fractal concept and impedance analysis have been employed to correlate the microstructure-dielectric property relation of (Co0.2Fe0.2Ni0.2Al0.2Ti0.2)3O4 spinel HEOs. The found Hurst exponent values for both different temperature-sintered HEOs are less than 0.5, indicating the anti-persistent behavior. This signifies that the height variations at neighboring pixels are negatively correlated. The present work is of fundamental importance in employing fractal analysis for the first time on spinel HEOs and correlating their properties. It also shows that processing conditions can effectively tailor the dielectric properties of the materials.