Cation distributions and microwave dielectric properties of Cu-substituted ZnGa₂O₄ spinel ceramics

Spinel Zn_1-xCu_xGa₂O₄ (x = 0–0.05) ceramics were prepared by the conventional solid-state method. Only a single phase was indexed in all samples. The relative density increased with Cu-substitution. Refined crystal structure parameters suggested that Cu²⁺ preferentially occupies the octahedron site and formed inverse spinel structure. The relative intensity of A*_1g mode in Raman spectra confirmed that the inversion degree climbed with the growing content of Cu. The differences of ion dielectric polarizability resulted in the shift of absorption bands in Fourier transform infrared (FT-IR) spectroscopy. Ion dielectric polarizability and cell volumes differences affected permittivity (ε_r) and increased ε_r slightly during Cu-substitution. The temperature coefficient of resonant frequency (τ_f) kept steady, however, the quality factor (Q × f) value of Zn_1-xCu_xGa₂O₄ ceramics increased by 50% due to the Cu-substitution (from 85,824 GHz to 131,445 GHz). Zn_0.99Cu_0.01Ga₂O₄ ceramic s sintered at 1400 °C for 2 h exhibited good microwave dielectric properties, with ε_r = 9.88, Q × f = 131,445 GHz, tan δ = 6.85 × 10⁻⁵,and τ_f = −60 ppm/°C.