INVESTIGATION OF CORRELATED DEFECTS IN NONSTOICHIOMETRIC LITHIUM-NIOBATE BY HIGH-RESOLUTION ELECTRON-MICROSCOPY

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