Investigation of Dual Ionic Conductivity in Ba6Nb2.1Na2V1.9O17

Interest in oxide-ion and proton-conducting materials has grown recently due to their application as electrolytes in solid-oxide fuel cells (SOFCs). In order to make SOFCs more economical is highly desirable to move towards lower working temperatures. To reach this goal new electrolyte materials are needed with high oxide ion conductivity at 400 – 600 °C. We have investigated the crystal structure and electrical properties of Ba6Nb2.1Na2V1.9O17.
Preliminary impedance spectroscopy characterization shows that Ba6Nb2.1Na2V1.9O17 exhibits both oxide ion and proton conductivity with a total conductivity in wet air of 5 x 10-4 S cm-1 at 650 degrees C. This demonstrates that these materials have potential as electrolytes for ceramic fuels if the conductivity can be improved by chemical doping.
In order to understand the mechanisms of oxide ion and proton conductivity in Ba6Nb2.1Na2V1.9O17, we aim to perform a variable temperature neutron diffraction experiment on Polaris. Neutrons will be essential for the identification and accurate determination of the position of the oxygen atoms and to check if there are any oxygen interstitials present. This experiment will also enable us to observe any structural rearrangement of the oxygen sub-lattice upon heating and/or change in crystal symmetry and develop structure property relationships.