High-entropy ceramics, Microwave dielectric properties, High-entropy composition design, High Q×f value, Crystal structure, Materials of engineering and construction. Mechanics of materials, TA401-492

In present study, high-entropy (Mg1/2Zn1/2)0.4+xLi0.4(Co1/2Ni1/2)0.4–xAl2O4 (x = 0.00–0.40) ceramics were fabricated via the solid-state reaction approach. The high-entropy ceramics exhibited a spinel structure with short-range local disorder and long-range structural order. The reduction of Co2+ and Ni2+ content suppress the damping behavior of atomic vibrations, promoting the structural ordering and contributing to higher quality factor (Q×f). The x = 0.35 sample with sintering at 1550 °C exhibited great microwave dielectric properties: a low dielectric constant (εr) of 7.92, a high-quality factor of 135,525 GHz, and a temperature coefficient of resonance frequency (τf) of −49 × 10−6 °C−1. The εr value was jointly dominated by both polarizability and relative density. The Q×f value was primarily connected to relative density, atomic vibrations, and the degree of covalency. The τf value was highly associated with the bond strength. These findings demonstrate the effectiveness of adopting high-entropy composition design for significantly improving microwave dielectric properties.