Title: Antiphase boundary defects in Strontium-doped Lanthanum Scandate

Abstract

LaScO3-based oxides are promising oxide materials for solid oxide electrochemical devices, such as protonic ceramic fuel cells, electrolysis cells, and gas sensors. The substitution of La3+ lanthanum with strontium Sr2+ should lead to a decrease in the oxygen content in the oxide lattice in order to satisfy the electroneutrality condition. The 45Sc NMR method was used to study the local structure of La1–xSrxScO3–δ oxides (x = 0, 0.04, 0.09). Only one line was found on the 45Sc NMR spectra, which corresponded to the 6-coordinate scandium in strontium-doped lanthanum scandates, and the contribution of the quadrupole broadened part of the spectrum decreased with an increase in the level of doping with strontium, indicating an increase in the local symmetry of the Sc3+ ion. EBSD and TEM study shows the existence of a structural inhomogeneity in a polycrystalline sample of strontium-doped lanthanum scandate was found in comparison with the undoped oxide. Defects, represented as straight or arbitrarily curved lines that did not extend beyond the grain boundaries, were identified as π-type antiphase boundaries. The atomic structure of possible antiphase boundaries in lanthanum-strontium scandate perovskite, a promising proton conductor, was modelled by means of DFT method. Two structural types of interfaces were modelled: edge- and face-shared. Energetic stability of all interfaces was calculated along with the oxygen vacancy formation and migration energies. Mechanisms of oxygen migration in both types of interfaces were modelled. It was shown that both types of interfaces are structurally stable and permit oxygen ionic migration. Oxygen vacancy formation in face-shared interface is by 0.2 eV lower than that in the bulk. Oxygen migration, however, most likely, will be blocked by some high-energy barriers over the O−O bonds with shared faces.