Developing low-loss and temperature-stable Ban(Zr,Nb)n−1O3n (n = 7, 8) microwave dielectric ceramics by investigating the relationship between the structure and properties

Abstract

In this work, we prepare novel Ba₇Zr₂Nb₄O₂₁ and Ba₈Zr₃Nb₄O₂₄ ceramics with a smaller tolerance factor (for the A_nB_n−1O_3n type hexagonal perovskite in BaO–ZrO₂–Nb₂O₅ system) using a solid-phase reaction method, which shows good microwave dielectric properties of ε_r ∼ 33.5, Q × f ∼ 56 500 GHz and τ_f ∼ −17 ppm °C⁻¹ (Ba₇Zr₂Nb₄O₂₁) and ε_r ∼ 32, Q × f ∼ 63 000 GHz and τ_f ∼ −27 ppm °C⁻¹ (Ba₈Zr₃Nb₄O₂₄). Rietveld refinement of XRD and TEM shows that Ba₇Zr₂Nb₄O₂₁ and Ba₈Zr₃Nb₄O₂₄ with the BaO₃ layer stacking sequence of (cccccchh) and (ccch)₂ are eight-layer shifted and twinned hexagonal perovskite, respectively. As the sintering temperature increases, the ε_r and Q × f values of Ba₇Zr₂Nb₄O₂₁ and Ba₈Zr₃Nb₄O₂₄ exhibit a strong correlation with relative density. The relationship between the structure and properties is discussed in BaO–Zr/Sn/TiO₂–Nb₂O₅ systems. The porosity excluded ε_r is mainly influenced by ion polarization, while the cell volume is also an essential factor affecting the permittivity. The variation of Q × f is related to the packing fraction in BaO–Zr/SnO₂–Nb₂O₅ systems. The variation of τ_f is mainly regulated by the tolerance factor. This study shows that there is an opportunity to improve the microwave dielectric properties by adjusting the size of the B-site cation.