The phase stability and electrical conductivity of Bi2O3 ceramics stabilized by Co-dopants

Abstract

In this study, Gd2O3, Nb2O5, Sc2O3, ZrO2, and BaO are chosen as co-dopants with Y2O3 to stabilize δ phase Bi2O3 ceramics. Under a fixed dopant concentration, the effects of the co-dopants on the phase stability and electrical properties of Bi0.76Y0.24−xMxO1.5+δ (M=Gd, Nb, Sc, Zr, and Ba) are investigated. Based on the study results, all co-doped specimens exhibit a sintering temperature lower than that of the Bi0.76Y0.24O1.5 ceramic. The Bi0.76Y0.24−xGdxO1.5, Bi0.76Y0.24−xNbxO1.5+δ, and Bi0.76Y0.24−xScxO1.5 ceramics retain a cubic fluorite structure of δ-Bi2O3 phase while Bi0.76Y0.24−xBaxO1.5−δ displays a mixture of cubic and rhombohedral phases. Despite the fact that the ionic radius of Sc3+ and Zr4+ ions are smaller than that of Y3+ ion, the lattice constant of the Bi0.76Y0.24O1.5 ceramic rises with the Gd2O3, Sc2O3, or ZrO2 replacement but drops with the Nb2O5 substitution. Of the compositions studied, the Bi0.76Y0.20Zr0.04O1.5+δ ceramic emerges with the best electrical conductivities of 0.27 and 0.55Scm−1 at 600 and 700 °C, much higher than those of the Y2O3-doped and ZrO2-doped Bi2O3 ceramics. It is observed that, with the same total dopant concentration, the co-dopant stabilized Bi2O3 ceramics outperforms their single-dopant stabilized counterparts in terms of conductivity, probably due to the larger lattice constants.