Investigation of Oxide Ion Conductivity in Mo2Ta2O11

Interest in oxide-ion conducting materials has grown recently due to their application as electrolytes in solid-oxide fuel cells (SOFCs). In order to make SOFCs more economical, it 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 Mo2Ta2O11.
Preliminary impedance spectroscopy characterization shows that Mo2Ta2O11 exhibits sizeable oxide ion conductivity with a total conductivity in dry air of 1 x 10-4 S cm-1 at 600 °C. This demonstrates that Mo2Ta2O11 has potential as an electrolyte for ceramic fuel cells if the conductivity can be improved further by chemical doping. Negative thermal expansion (NTE) is also observed in Mo2Ta2O11 over a wide temperature range but to date no neutron diffraction experiment has been performed.
In order to understand the mechanisms of oxide ion conductivity and NTE in Mo2Ta2O11, 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.