Long-term degradation of Ta2O5-doped Bi2O3 systems

Bismuth oxide in δ-phase is a well-known high oxygen ion conductor and can be used as an electrolyte for intermediate temperature solid oxide fuel cells (IT-SOFCs). 5–10 mol% Ta2O5 are doped into Bi2O3 to stabilize δ-phase by solid state reaction process. One Bi2O3 sample (7.5TSB) was stabilized by 7.5 mol% Ta2O5 and exhibited single phase δ-Bi2O3-like (type I) phase. Thermo-mechanical analyzer (TMA), X-ray diffractometry (XRD), AC impedance and high-resolution transmission electron microscopy (HRTEM) were used to characterize the properties. The results showed that holding at 800–850 °C for 1 h was the appropriate sintering conditions to get dense samples. Obvious conductivity degradation phenomenon was obtained by 1000 h long-term treatment at 650 °C due to the formation of α-Bi2O3 phase and Bi3TaO7, and 〈1 1 1〉 vacancy ordering in Bi3TaO7 structure.