Dielectric relaxation and microwave dielectric properties of Bi2O3-ZnO-Ta2O5 ceramics

The permittivity of two primary phases within the Bi2O3-ZnO-Ta2O5 system was measured from 100 Hz to approximately 8.7 GHz. A cubic pyrochlore (Bi3/2Zn1/2)(Zn1/2Ta3/2)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(Zn1/3Ta2/3)(2)O-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 degreesC, was 78 ppm/degreesC 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 a phase, which is modeled as a basic Debye-type relaxation.