PHASE DIAGRAM AND DIELECTRIC PROPERTIES OF MATERIALS IN Bi2O3-ZnO-Ta2O5 SYSTEM

Abstract

The subsolidus phase diagram of the system Bi₂O₃-ZnO-Ta₂O₅ in the region of the cubic pyrochlore phase has been determined at 1050 °C. This phase forms a solid solution area that includes the ideal composition P, Bi₃Zn₂Ta₃O_14. Possible solid solution mechanisms for the cubic pyrochlore phase are proposed. Density measurements of Zn deficient solid solutions were carried out in order to determine the possible solid solution formation mechanisms. The general formula of the solid solutions is proposed to be Bi_3+yZn_2-xTa_3-yO_14-x-y, based on the mechanisms of Zn/oxide ion vacancies and variable Bi/Ta ratio. Solid solution series at x = 0 and y = 0 were investigated using impedance spectroscopy for their dielectric properties. These materials appeared to be dielectric. Bi₃Zn₂Ta₃O₁₄ has ε’ of 42 at 30 °C and 1 MHz; ε’ for the solid solutions ranges from 39 to 65. A high degree of dispersion on the permittivity at low frequencies (<1 kHz) and temperatures above 600 °C is apparent.