Local structural arrangements around oxygen and hydrogen-related defects in proton conducting LaP ₃O ₉ investigated by first principles calculations

Local structural arrangements and stabilities of oxygen and hydrogen-related defects in proton-conducting LaP ₃O ₉ were studied using first principles calculations. When an oxygen was removed from LaP ₃O ₉, the crystal lattice was significantly distorted. Resulting structural arrangements considerably depended on the oxygen deficient site, and phosphate ions tended to condense by sharing a corner oxygen of PO ₄ tetrahedra. On the other hand, when a proton was introduced, the proton was located at the interstitial sites positioned approximately 1 away from the nearest oxygen forming an O-H bond. The LaP ₃O ₉ lattice was only slightly distorted even after introduction of an interstitial proton. Based on the calculation results, the stabilities of the defects under moisturized conditions was discussed.