Formation of high oxide ion conductive phases in the sintered oxides of the system Bi 2O 3 Ln2O 3 ( Ln = LaYb)

The electrical conduction in various phases of the system Bi ₂O ₃ Ln₂O ₃ ( Ln = La, Nd, Sm, Dy, Er, or Yb) was investigated by measuring ac conductivity and the emf of the oxygen gas concentration cell. High-oxide-ion conduction was observed in the rhombohedral and face-centered cubic (fcc) phase in these systems. The fcc phase could be stabilized over a wide range of temperature by adding a certain amount of Ln₂O ₃. In these cases, the larger the atomic number of Ln, the lower the content of Ln₂O ₃ required to form the fcc solid solution, except in the case of Yb ₂O ₃. The oxide ion conductivity of this phase decreased with increasing content of Ln₂O ₃. Maximum conductivity was obtained at the lower limit of the fcc solid solution formation range in each system, which was more than one order of magnitude higher than those of conventional stabilized zirconias. Lattice parameters of the fcc phase were calculated from the X-ray diffraction patterns. The relationship between the oxide ion conductivity and the lattice parameter was also discussed.