Investigation of correlated defects in non-stoichiometric lithium niobate by high resolution electron microscopy

An investigation of intrinsic defects in lithium niobate, using High Resolution Electron Microscopy (HREM) was carried out. It was found that crystals, around and at congruent composition, have a large number of clustered defects about 1 nm in diameter. Models of planar and spatially correlated defects were developed and used for the simulation of HREM images, along with other existing models of non-stoichiometric defects. It was found that neither randomly distributed antisite defects, compensated by lithium or niobium vacancies, nor clustered lithium and oxygen vacancies could produce the contrast variation observed in the images. A new model of small Nb2O5 clusters is also suggested as a possible candidate for the defects responsible for the nonstoichiometry of the crystals. (C) 1997 Elsevier Science Ltd.