Composite strategy toward thermally stable ZnNb2O6-based microwave ceramics with near-zero τf

The large negative temperature coefficient of resonant frequency ( τ f ) remains a critical bottleneck restricting the high-temperature application of ZnNb 2 O 6 microwave ceramics. In this work, a titanium-tungsten (TiW) complex cation co-doping strategy was employed to modulate the crystal structure and improve the intrinsic microwave properties of ZnNb 2 O 6 . The optimized ZnNb 1.98 (TiW) 0.02 O 6 ceramic exhibited excellent microwave performance, with a dielectric constant ( ε r ) of 24.0, a high Q×f value of 120,000 GHz, and a τ f of −100.0 ppm/°C at a sintering temperature of 1100 °C. To further address the thermal instability issues, a composite ceramic system combining (1-x) ZnNb 1.98 (TiW) 0.02 O 6 with xNi 0.5 Ti 0.5 NbO 4 was developed, which effectively compensated for the large negative τ f and strikes a balance between thermal stability and dielectric performance. When x = 0.6, the composite ceramic exhibited a higher ε r of 31.7, a Q×f value of 29,800 GHz, and τ f of 0 ppm/°C. These results demonstrate that the composite strategy enables simultaneous optimization of temperature stability and dielectric properties. This approach offers a promising route for thermally resistant microwave ceramics in extreme-environment applications.