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

Spinel Zn1-xCuxGa2O4 (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 (epsilon(r)) and increased epsilon(r) slightly during Cu-substitution. The temperature coefficient of resonant frequency (tau(f)) kept steady, however, the quality factor (Q x f) value of Zn1-xCuxGa2O4 ceramics increased by 50% due to the Cu-substitution (from 85,824 GHz to 131,445 GHz). Zn0.99Cu0.01Ga2O4 ceramic s sintered at 1400 degrees C for 2 h exhibited good microwave dielectric properties, with epsilon(r) = 9.88, Q x f = 131,445 GHz, tan delta = 6.85 x 10(-5),and tau(f) = -60 ppm/degrees C.