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 degrees 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, epsilon', similar to 60-80 and low dielectric losses, tan delta, similar to 0.01-0.20 at 1 MHz and ambient temperature, similar to 28 degrees C. The recorded low activation energies, 0.32-0.40 eV suggesting these electroceramics were of semiconductor-type at elevated temperatures. (C) 2016 Elsevier B.V. All rights reserved.