‘Horror Vacui’ in the Oxygen Sublattice of Lithium Niobate Made Affordable by Cationic Flexibility

Abstract

The present review is intended for a broader audience interested in the resolution of the several decades-long controversy on the possible role of oxygen-vacancy defects in LiNbO3. Confronting ideas of a selected series of papers from classical experiments to brand new large-scale calculations, a unified interpretation of the defect generation and annealing mechanisms governing processes during thermo- and mechanochemical treatments and irradiations of various types is presented. The dominant role of as-grown and freshly generated Nb antisite defects as traps for small polarons and bipolarons is demonstrated, while mobile lithium vacancies, also acting as hole traps, are shown to provide flexible charge compensation needed for stability. The close relationship between LiNbO3 and the Li battery materials LiNb3O8 and Li3NbO4 is pointed out. The oxygen sublattice of the bulk plays a much more passive role, whereas oxygen loss and Li2O segregation take place in external or internal surface layers of a few nanometers.