Relationship between microwave dielectric properties and structure of Ca2+-substituted ZnZrTa2O8 ceramics

Abstract

Herein, Zn1-xCaxZrTa2O8 (0 ≤ x ≤ 0.1) ceramics with wolframite structure were prepared via the solid-state reaction method. Zn0.94Ca0.06ZrTa2O8 exhibited the best dielectric properties with εr = 23.14, Q × f = 140,915 GHz (@7.79 GHz), and τf = −26.42 ppm/°C. εr increases gradually with the Ca2+ content. The change in εr is related to the Ca2+ ion polarizability and the redshift of Raman vibrational modes. Appropriate Ca2+ substitution makes the dominant Ta-O have higher lattice energy, resulting in a lower dielectric loss. In addition, the reduction of FWHM of Raman characteristic peaks also had a positive effect on reducing the dielectric loss. First-principles calculations illustrate that the trace substitution of Ca2+ leads to an increase in the electron cloud density of the [Zn/Ca/ZrO6] octahedra, resulting in lower dielectric losses. Suitable Ca2+ substitution resulted in higher bond energy and smaller [Zn/Ca/ZrO6] octahedral distortion, implying that τf is closer to 0 ppm/°C.