Cu 2+ -Ion-Substitution-Driven Microstructure and Microwave Dielectric Properties of Mg 1- x Cu x Al 2 O 4 Ceramics.

In this work, Cu-substituted MgAl 2 O 4 ceramics were prepared via solid-state reaction. The crystal structure, cation distribution, and microwave dielectric properties of Mg 1- x Cu x Al 2 O 4 ceramics were investigated. Cu 2+ entered the MgAl 2 O 4 lattice and formed a spinel structure. The substitution of Cu 2+ ions for Mg 2+ ions contributed to Al 3+ 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- x Cu x Al 2 O 4 solid solution, possessing good performance, has potential for application in the field of modern telecommunication technology.