Structure evolution and microwave dielectric characteristics of Hf₁−xSnxO₂ ceramics

High Q (Hf 1− x Sn x )O 2 ceramics were prepared via a standard solid‐state reaction route, and the microwave dielectric characteristics were investigated systematically together with the structure evolution. With increasing x , the structure changed from HfO 2 (monoclinic in space group P 2 1 / c , x = 0 and 0.03) to Hf 0.77 Sn 0.23 O 2 (orthorhombic in space group Pbcn , x = 0.23), while the two‐phase structure: HfO 2 major phase and Hf 0.77 Sn 0.23 O 2 secondary phase, was determined for x = 0.05–0.21, and Hf 0.77 Sn 0.23 O 2 major phase combined with SnO 2 tetragonal secondary phase in space group P 4 2 /mnm was confirmed for x = 0.30–0.40. The Qf value was significantly increased from 24,500 to 167,650 GHz by Sn‐substitution, and the best combination of microwave dielectric characteristics was obtained in Hf 0.77 Sn 0.23 O 2 ceramics: ε r = 17.2, Qf = 167 650 GHz at 9.6 GHz and 230 710 GHz at 26.1 GHz, and τ f = −52.6 ppm/°C. The dielectric loss was deeply linked with the structure stability and lattice‐distortion. Also, the phase composition, the bond strength, as well as the degree of covalency, had a tight connection with dielectric loss. The present ceramics were expected to be the promising candidates as low‐ε r microwave dielectric ceramics.