High Oxygen Ion Conduction in Sintered Oxides of the Bi2 O 3 ‐ Dy2 O 3 System

The phase diagram of the Bi 2 O 3 ‐ Dy 2 O 3 system was investigated. A monophasic fcc structure was stabilized for samples containing 28.5 – 50.0 mole percent ( m / o ) Dy 2 O 3 . Above and below this concentration range polyphasic regions appear. The fcc phase showed high oxygen ion conduction. The ionic transference number is equal to one for specimens containing 28.5 – 40.0 m / o Dy 2 O 3 , whereas an electronic component is introduced at low temperatures for specimens containing 50.0 m / o Dy 2 O 3 . The conductivity of ( Bi 2 O 3 ) 0.715 ( Dy 2 O 3 ) 0.285 is 0.71 Ω −1 m −1 and 14.4 Ω −1 m −1 at 773 and 973 K, respectively. Relations were found between the ionic radius, the conductivity, and the minimum concentration of lanthanide necessary to stabilize the fcc phase. It is concluded that the highest ionic conductivity will be found in the system Bi 2 O 3 ‐ Er 2 O 3 or Bi 2 O 3 ‐ Tm 2 O 3 . From a study of relations between the activation energy, log σ 0 and the composition it is concluded that two conductivity mechanisms play a role.