Compositional modulation in ZnGa2O4 via Zn2+/Ge4+ co-doping to simultaneously lower sintering temperature and improve microwave dielectric properties

Abstract

Abstract AB 2 O 4 -type spinels with low relative permittivity ( ε r ) and high quality factor ( Q × f ) are crucial to high-speed signal propagation systems. In this work, Zn 2+ /Ge 4+ co-doping to substitute Ga 3+ in ZnGa 2 O 4 was designed to lower the sintering temperature and adjust the thermal stability of resonance frequency simultaneously. Zn 1+ x Ga 2−2 x Ge x O 4 (0.1 ⩽ x ⩽ 0.5) ceramics were synthesised by the conventional solid-state method. Zn 2+ /Ge 4+ co-substitution induced minimal variation in the macroscopical spinel structure, which effectively lowered the sintering temperature from 1385 to 1250 °C. All compositions crystallized in a normal spinel structure and exhibited dense microstructures and excellent microwave dielectric properties. The compositional dependent quality factor was related to the microstructural variation, being confirmed by Raman features. A composition with x = 0.3 shows the best dielectric properties with ε r ≈ 10.09, Q × f ≈ 112,700 THz, and τ f ≈ −75.6 ppm/°C. The negative τ f value was further adjusted to be near-zero through the formation of composite ceramics with TiO 2 .