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 AnBn−1O3n type hexagonal perovskite in BaO–ZrO2–Nb2O5 system) using a solid-phase reaction method, which shows good microwave dielectric properties of εr ∼ 33.5, Q × f ∼ 56 500 GHz and τf ∼ −17 ppm °C−1 (Ba7Zr2Nb4O21) and εr ∼ 32, Q × f ∼ 63 000 GHz and τf ∼ −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 εr 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 εr 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 τf 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.