Ni-Co Complex Ionic Synergistically Modifying Octahedron Lattice of Cordierite Ceramics for the Application of 5G Microwave-Millimeter-wave Antennas.

In this work, phase-pure Mg 1.8 (Ni 1- x Co x ) 0.2 Al 4 Si 5 O 18 (0 ≤ x ≤ 1) ceramics were synthesized by a high-temperature solid-state method. On the basis of Rietveld refinement data of X-ray powder diffraction and Phillips-Vechten-Levine theory, the atomic ionicity, lattice energy, and bond energy of the compound were calculated to explore their influence on the microwave dielectric properties of ceramics. The Mg 1.8 Ni 0.1 Co 0.1 Al 4 Si 5 O 18 ( x = 0.5) ceramic exhibited the best microwave dielectric properties: ε r = 4.44, Qf = 73 539 GHz@13 GHz, and τ f = -23.9 ppm/°C. (Ni 1- x Co x ) 2+ complex ionic doping, compared with only Ni 2+ or Co 2+ , is beneficial for improving the symmetry of [Si 4 Al 2 O 18 ] hexagonal rings and reducing distortion. Subsequently, 8 wt % TiO 2 was added to Mg 1.8 Ni 0.1 Co 0.1 Al 4 Si 5 O 18 , resulting in a near-zero τ f and high Qf values for the composite ceramic, with ε r = 5.22, Qf = 58 449 GHz@13 GHz, and τ f = -2.06 ppm/°C. Finally, a 5G millimeter-wave antenna with a central operating frequency of 25.52 GHz was designed and fabricated using the Mg 1.8 Ni 0.1 Co 0.1 Al 4 Si 5 O 18 -8 wt % TiO 2 ceramics. Operating in the 24.7-26.0 GHz range, it demonstrated favorable radiation characteristics with a simulated efficiency of 85.2% and a gain of 4.58 dBi. The antenna's performance confirms the high potential of the cordierite composite for application in 5G communication systems.