Divalent beta″-aluminas: High conductivity solid electrolytes for divalent cations

The Na+ content of beta″-alumina can be replaced by a variety of divalent cations in simple ion exchange reactions. The resulting divalent beta″-aluminas are the first family of high conductivity solid electrolytes for divalent cations. Divalent beta″-aluminas which have been prepared so far include conductors of Ca2+, Sr2+, Ba2+, Zn2+, Cd2+, Pb2+, Hg2+, and Mn2+. Most have conductivities of about 10-6 (Ω cm)-1 at 40°C and 10-1 (Ω cm)-1 at 300–400°C. However, the conductivity of Pb2+ beta″ alumina is 4.6x10-3 (Ω cm)-1 at 40°C, nearly equal to that of Na+ beta″-alumina. Preliminary structures studies indicate that order-disorder reactions among the divalent cations and vacancies in the conduction region of beta″-alumina critically influence conductivity in the structure.