Stabilized δ-Bi2O3 phase in the system Bi2O3–Er2O3–WO3 and its oxide-ion conduction

In the ternary system Bi2O3–Er2O3–WO3, the truly stabilized δ-Bi2O3 type fcc phase has been prepared in a limited solid-solution region. This δ-phase shows good oxide-ion conduction, e.g., (Bi2O3)0.735(Er2O3)0.21(WO3)0.055 at 550 °C, σ = 0.05 S cm− 1 with the activation energy = 0.9 eV and the oxide-ion transport number = 0.94. In contrast to “the stabilized δ-phase” reported to date in the binary system Bi2O3–Ln2O3, where Ln is a lanthanoid element including Y, the present δ-phase indicates very little time-dependent degradation of electrical conductivity because of the realization of stabilization, e.g., (Bi2O3)0.705(Er2O3)0.245(WO3)0.05 at 600 °C showing no degradation up to 1100 h. The present δ-phase is thermally stable up to about 1000 °C, since the melting onset temperature is about 1015 °C with negligibly small weight loss < 1%.