Phase evolution and microware dielectric properties of high-entropy spinel-type (Mg0.2Co0.2Ni0.2Li0.4Zn0.2)Al2O4 ceramics

In this study, high-entropy spinel-type (Mg0.2Co0.2Ni0.2Li0.4Zn0.2)Al2O4 ceramics were synthesized by solid-state reaction method. The raw materials gradually formed spinel aluminates from 700 to 1400 °C and finally formed high-entropy (Mg0.2Co0.2Ni0.2Li0.4Zn0.2)Al2O4 ceramics after calcination at 1400 °C for 4 h. The high-configuration entropy and low average atomic-size difference were beneficial to form single-phase high-entropy ceramics. Partial lattice distortion occurred within the high-entropy (Mg0.2Co0.2Ni0.2Li0.4Zn0.2)Al2O4 ceramics structure, and its grain size gradually increased with increasing sintering temperature. The high-entropy (Mg0.2Co0.2Ni0.2Li0.4Zn0.2)Al2O4 ceramics exhibited good microwave dielectric properties when sintered at 1550 °C for 4 h: dielectric constant (εr) = 7.4, quality factor (Qf) = 58,200 GHz, and temperature coefficient of resonance frequency (τf) = –64 ppm/°C. The εr values were mainly affected by the dielectric polarizability. The Qf values were highly related to the relative density and covalency of A-site bond, whereas the τf values closely depended on the bond strength of A-site.