Crystal structure and microwave dielectric properties of (Mg0.2Ni0.2Zn0.2Co0.2Mn0.2)2SiO4 - A novel high-entropy ceramic

Novel (Mg0.2Ni0.2Zn0.2Co0.2Mn0.2)2SiO4 (A5SO) high-entropy microwave dielectric ceramics with olivine structure were prepared in the sintering temperature range of 1100 °C–1300 °C via the solid-phase reaction route. The crystal structure was confirmed by XRD, Raman, and Rietveld refinement. Optimal microwave dielectric properties (εr = 8.02, tanδ = 0.00051 at 14.5 GHz, and τf = −38.2 ppm/°C) were obtained at the sintering temperature of 1250 °C, where a relative density of 95.1% was detected. The complex chemical bonding theory manifests that the εr value of A5SO is mainly affected by the ionicity of A-O (A = Mg, Ni, Zn, Co, Mn) bond, while the dielectric loss is affected by both A-O and Si–O lattice energy. The τf value is mainly influenced by the [A(2)O6] oxygen octahedral distortion (1.8 × 10−3). The experimental results of this study provide both theoretical and practical guidance for high-entropy microwave dielectric ceramic applications.