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 LaNbO4. The interatomic potential model successfully reproduces the observed tetragonal scheelite-type structure of LaNbO4. Formation of an oxygen vacancy, required for protonation, is accompanied by significant local relaxation leading to an [Nb 2O7]4- group. The most favorable dopant solution energies are found for Ca2+ and Sr2+ 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 LaNbO4 system.