Subsolidus phase equilibria and electrical properties of pyrochlores in the Bi2O3-CuO-Ta2O5 ternary system

Subsolidus phase relations had been determined for the Bi2O3-CuO-Ta2O5 (BCT) system over the temperature range 700-950 °C in air. Two structurally distinct ternary phases of different symmetries, a cubic pyrochlore and a monoclinic zirconolite were observed. Phase-pure pyrochlores existed in a unique boomerang-shaped area, which could be described using the general formula, Bi2.48+yCu1.92−xTa3.6+x−yO14.64+3x/2−y: 0.00(1) ≤ x ≤ 0.80(1) and 0.00 (1) ≤ y ≤ 0.60(1), respectively. BCT subsolidus pyrochlores exhibited low electrical conductivities, 10−7-10−6 S cm−1, moderate dielectric constants, ε′, ∼60-80 and low dielectric losses, tan δ, ∼0.01-0.20 at 1 MHz and ambient temperature, ∼28 °C. The recorded low activation energies, 0.32-0.40 eV suggesting these electroceramics were of semiconductor-type at elevated temperatures.