Effects of Zr4+ and Hf4+ substitution on the structure and dielectric response of Ba4Sm9.33Ti18O54 ceramics

Microwave dielectric ceramics with high relative permittivity ( ε r ) are commonly used for the miniaturation of microwave devices. The dielectric loss mechanism of microwave dielectric ceramics , as well as the property modification, has been a concerned topic among scholars. Herein, the lattice structure, defects, and broadband dielectric response of Zr 4+ and Hf 4+ substituted Ba 4 Sm 9.33 Ti 18 O 54 (BST) ceramics are systematically examined. The negative temperature coefficient of resonant frequency ( τ f ) of BST ceramics can be tuned to near zero via ion substitution, owing to the Sm 2 Ti 2 O 7 second phase with a large positive τ f . Optimal microwave dielectric properties of ε r  = 81.3, Q  ×  f  = 10,800 GHz, and τ f  = −4.6 ppm/°C are achieved. The lattice vibration behavior and defect concentration are analyzed by Raman spectra and thermally stimulated depolarization currents (TSDC), respectively. The increasing volume of the unit cell and TiO 6 octahedra, which is because of the large-radius substitution ions, leads to an increase in lattice vibration damping factor and the generation of more oxygen vacancies ( V O ∙ ∙ $V_{\mathrm{O}}^{\bullet \bullet }$ ). Therefore, the dielectric losses in the microwave and terahertz (THz) bands increase after substitution. Meanwhile, the low-frequency dielectric losses at high temperatures also increase due to the weak restraint of carriers by the lattice. The broadband loss mechanism of Zr 4+ and Hf 4+ substituted BST ceramics related to lattice vibration and defects might be referenced for developing low-loss dielectric ceramics.