Cu²⁺-Ion-Substitution-Driven Microstructure and Microwave Dielectric Properties of Mg_1-CuAl₂O₄ Ceramics

In this work, Cu-substituted MgAl₂O₄ ceramics were prepared via solid-state reaction. The crystal structure, cation distribution, and microwave dielectric properties of Mg_1-CuAl₂O₄ ceramics were investigated. Cu²⁺ entered the MgAl₂O₄ lattice and formed a spinel structure. The substitution of Cu²⁺ ions for Mg²⁺ ions contributed to Al³⁺ ions preferential occupation of the octahedron and changed the degree of inversion. The quality factor (Qf) value, which is correlated with the degree of inversion, increased to a maximum value at x = 0.04 and then decreased. Ionic polarizability and relative density affected the dielectric constant (ε_r) value. The temperature coefficient of the resonant frequency (τ_f) value, which was dominated by the total bond energy, generally shifted to the positive direction. Satisfactory microwave dielectric properties were achieved in x = 0.04 and sintered at 1550 °C: ε_r = 8.28, Qf = 72,800 GHz, and τ_f = -59 ppm/°C. The Mg_1-CuAl₂O₄ solid solution, possessing good performance, has potential for application in the field of modern telecommunication technology.