Defects, Dopants, and Protons in LaNbO₄

Simulation methods have been used to investigate the energetics of defect formation, dopant solution, water incorporation, and defect clustering in the high-temperature proton conductor LaNbO 4 . The interatomic potential model successfully reproduces the observed tetragonal scheelite-type structure of LaNbO 4 . Formation of an oxygen vacancy, required for protonation, is accompanied by significant local relaxation leading to an [Nb 2 O 7 ] 4− group. The most favorable dopant solution energies are found for Ca 2+ and Sr 2+ on the La site. Dopant-vacancy association is predicted to occur for a wide range of divalent dopants on the La site and tetravalent dopants on the Nb site. Dopant-proton association is also predicted to occur for the range of dopants studied. The lowest M / − OH • binding energy is found for Ca, which is commonly used in compositions displaying the highest proton conductivities so far reported in the LaNbO 4 system.