Sc modification induced short-range cation ordering and high microwave dielectric performance in ZnGa₂O₄ spinel ceramics

Sc³⁺ (0,0.1,0.3,0.5,0.7 mol%) modified ZnGa₂O₄ (abbreviated Sc-ZGO) ceramics were synthesized by solid-state method. The relationship between microwave dielectric performance and bonds vibration has been systematically investigated. With Sc³⁺ modification, the ε_r of Sc-ZGO keeps steady (~10). While τ_f values (increasing from −71 ppm/°C to −39 ppm/°C) show linear correlation with Sc³⁺ concentration. And Q×f values climb up to a maximum value and then ramp down. The Q×f value of Sc-ZGO increased by almost 45% compared with normal spinel ZnGa₂O₄ ceramics. The enhancement of τ_f and Q×f on Sc modified ZnGa₂O₄ can be attributed to higher densification, however, further analysis elucidated that short-range cation ordering degree is another governing factor. The influence of Sc³⁺ modification on ZnGa₂O₄ bonds vibration has been discussed in detail. 5Sc-ZGO sintered at 1350 °C for 2 h exhibits the best microwave dielectric properties: ε_r = 9.9, Q×f = 124,147 GHz, tanδ = 7.98 × 10⁻⁵, and τ_f = −56 ppm/°C (@9.9 GHz).