Structural dependence of the microwave dielectric properties of Cr3+-substituted ZnGa2O4 spinel ceramics: crystal distortion and vibration mode studies

摘要

Zn[CrxGa(1-x)](2)O-4 (abbreviated Cr-ZGO) ceramics with x = 0-0.15 were synthesized by the conventional solid state method. The correlation between the microwave dielectric properties and the changes in the crystal structure and cation distribution of Cr-ZGO as a function of Cr3+ substitution for Ga3+ has been systematically investigated. The addition of Cr3+ promotes the densification of the ceramics and results in a normal spinel structure with Cr3+ occupying an octahedral site. With an increase in the Cr3+ content from 0 to 15 mol%, the epsilon(r) of the ceramics increases, while the tau(f) remains almost unchanged and the Q x f values ramp up to a maximum at 1 mol% Cr3+ addition and then ramp down continuously. 1Cr-ZGO exhibits the best microwave dielectric properties, with epsilon(r), Q x f, tan delta and tau(f) being 9.88 (@9.9 GHz), 111 470 GHz, 8.87, and -74 ppm degrees C-1, respectively. The Q x f value was increased by almost 40% compared with the pure ZGO ceramics (similar to 80 000 GHz). The enhancement of epsilon(r) and Q x f values of Cr-ZGO can be attributed to the better bulk density, but further analysis by Rietveld refinement, Raman spectroscopy and FT-IR spectroscopy elucidated that the octahedral tilting in the spinel structure and the degree of short-range cation distribution are other governing factors. The effect of Cr3+ substitution for Ga3+ on the octahedral distortion and cation distribution in the spinel structure has been discussed in detail.