Low-temperature sintering of high-Q MgGa2O4 ceramics via (Li0.5Bi0.5)2+ substitution and assisting sintering atmosphere

A dual-modification strategy combining (Li 0.5 Bi 0.5 ) 2+ substitution and BaCu(B 2 O 5 )/LiF atmosphere-assisted sintering was developed to reduce the sintering temperature of MgGa 2 O 4 ceramic. The strategy achieved a 360 °C reduction in sintering temperature (from 1610 to 1250 °C) while maintaining a high performance. The optimal sample (Li 0.5 Bi 0.5 ) x Mg 1- x Ga 2 O 4 ( x  = 0.02) exhibited ε r = 9.41, Q × f = 127,159 GHz, and τ f = -39.6 ppm/°C. XRD and Rietveld refinement confirmed that the spinel structure was preserved upon doping, alongside a lattice expansion. Consistent with the enhanced Q × f , a Raman spectroscopy analysis revealed a narrowing of the T 2 g mode, indicating an improved structural ordering. Furthermore, τ f was improved to −39.6 ppm/°C, directly related to the induced lattice distortion and expansion. The enhanced performance was attributed to the synergistic effects of composite ion doping and atmosphere-assisted sintering. The former modified the intrinsic structure and polarization characteristics, while the latter facilitated the densification at lower temperatures.