Order-disorder transition in the new ionic conductor Cs2MoO4

Hydrogen technologies such as ceramic fuel cells can use hydrogen as a fuel to produce electrical energy with zero greenhouse emissions. To enable the widespread deployment of hydrogen-based technologies, fundamental research is urgently needed to develop new conductors with superior ionic conductivity. We have discovered significant ionic (oxide ion-proton) conductivity in Cs2MoO4, which shows an order-disorder phase transition to a highly conducting disordered phase at 568 °C. The ionic conductivity of the high temperature phase is higher than the conductivity of commercially available electrolyte materials, making Cs2MoO4 suitable for practical applications at reduced temperature. In order to fully characterise the structural transition and the high temperature phase of Cs2MoO4, we propose to perform high-resolution neutron powder diffraction measurements on HRPD as function of temperature. The experimental findings will shed light on the link between crystal structure and the mechanism of ionic conduction in Cs2MoO4, so to inform further materials design in this newly discovered class of ionic conductors.