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

Herein, Zn 1- x Ca x ZrTa 2 O 8 (0 ≤  x  ≤ 0.1) ceramics with wolframite structure were prepared via the solid-state reaction method. Zn 0.94 Ca 0.06 ZrTa 2 O 8 exhibited the best dielectric properties with ε r = 23.14, Q × f = 140,915 GHz (@7.79 GHz), and τ f = −26.42 ppm/°C. ε r increases gradually with the Ca 2+ content. The change in ε r is related to the Ca 2+ ion polarizability and the redshift of Raman vibrational modes. Appropriate Ca 2+ 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 Ca 2+ leads to an increase in the electron cloud density of the [Zn/Ca/ZrO 6 ] octahedra, resulting in lower dielectric losses. Suitable Ca 2+ substitution resulted in higher bond energy and smaller [Zn/Ca/ZrO 6 ] octahedral distortion, implying that τ f is closer to 0 ppm/°C.