Dielectric relaxation and microwave dielectric properties of Bi_2O_3-ZnO-Ta_2O_5 ceramics

摘要

The permittivity of two primary phases within the Bi_2O_3-ZnO-Ta_2O_5 system was measured from 100 Hz to approximately 8.7 GHz. A cubic pyrochlore (Bi_(3/2)Zn_(1/2))(Zn_(1/2)Ta_(3/2))O_7 phase (alpha phase) exhibited a dielectric constant of 71 at low frequency which decreased to 64 at approximately 10 GHz. A lower symmetry zirconolite Bi_2(Zn_(1/3)Ta_(2/3))_2O_7 phase (beta phase) was also measured and had a frequency independent dielectric constant of 60. The temperature dependence of the capacitance (tau_C), measured from -55 to 120 deg C, was 78 ppm/deg C for the beta phase and nonlinear for the alpha phase having no unique slope. The primary difference in dielectric properties between these two phases was a low-temperature relaxation of the alpha phase, which is modeled as a basic Debye-type relaxation.