Improvement of τ_f in HfTiO₄ microwave dielectric ceramics with Zr‐ and Sn‐substitution

Abstract (Hf 1‐x Zr x )TiO 4 and (Hf 1‐x Sn x )TiO 4 ceramics were prepared through a standard solid‐state reaction route, and the microwave dielectric characteristics were determined together with the microstructures. The single‐phase solid solution in space group Pbcn was obtained in (Hf 1‐x Zr x )TiO 4 , while the two‐phase structure with (HfTiO 4 (s.s.) major phase in space group Pbcn and Sn 0.3 Ti 0.7 O 2 secondary phase in space group P 4 2 / mnm ) was determined in (Hf 1‐x Sn x )TiO 4 . The temperature coefficient of resonant frequency τ f could be significantly improved to near‐zero in both systems, and the best combination of microwave dielectric characteristic was achieved at x = 0.5 in (Hf 1‐x Zr x )TiO 4 : ε r = 39.0, Qf = 43,150 GHz at 5.3 GHz and τ f = 3 ppm/°C, and at x = 0.225 in (Hf 1‐x Sn x )TiO 4 : ε r = 37.2, Qf = 52,600 GHz at 5.5 GHz and τ f = ‐6 ppm/°C. In the solid solutions, the obvious improvement of τ f could be deeply linked with the degree of covalency and the restoring forces of structure. While, the intermediate near‐zero τ f is achieved by mixing the phases with opposite τ f in multiphase materials. The present work provided an effective way to modify the temperature coefficient of resonant frequency in microwave dielectric ceramics.