Tunable microware dielectric properties of high-entropy (Mg1/2Zn1/2)0.4+xLi0.4(Co1/2Ni1/2)0.4-xAl2O4 ceramics with low loss

In present study, high-entropy (Mg_1/2Zn_1/2)_0.4+xLi_0.4(Co_1/2Ni_1/2)_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 (ε_r) of 7.92, a high-quality factor of 135,525 GHz, and a temperature coefficient of resonance frequency (τ_f) of −49 × 10⁻⁶ °C⁻¹. The ε_r 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 τ_f 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.