Enhanced Microwave Dielectric Properties in Mg 2 Al 4 Si 5 O 18 Through Cu 2+ Substitution

The Mg 2 Al 4 Si 5 O 18 ceramic is considered as a kind of important candidates for millimeter‐wave applications. In this work, Mg 2– x Cu x Al 4 Si 5 O 18 (0≤ x ≤0.16) ceramics were synthesized by solid‐state reaction, aiming to improve the microwave dielectric properties. According to the X‐ray powder diffraction (XRD) analysis, Cu 2+ ions enter into the Mg 2 Al 4 Si 5 O 18 lattice and form a solid solution. The dense microstructure was observed in the Cu‐substituted Mg 2 Al 4 Si 5 O 18 ceramics at x =0.04 sintered at 1420 °C. The dielectric constant (ϵ r ) values depend on the microstructure, secondary phase and ionic polarizability of the samples. The quality factor (Qf) values are dominated by the microstructure, secondary phase and centro‐symmetry of [Si 4 Al 2 ] hexagonal ring. The temperature coefficients of resonance frequency (τ f ) are strongly related to the Mg/Cu−O bond valance. In comparison to pure Mg 2 Al 4 Si 5 O 18 ceramics, the excellent microwave dielectric properties with ϵ r =4.56, Qf=31,100 GHz and τ f =−52 ppm/°C were obtained at x =0.04 with sintering at 1420 °C. Thus, the Mg 2– x Cu x Al 4 Si 5 O 18 (0≤ x ≤0.16) ceramics will be promising millimeter‐wave communication materials.