COMMENTS ON THE DEFECT CHEMISTRY OF MAGNESIUM-DOPED LITHIUM-NIOBATE (LINBO3)

Congruently grown LiNbO3 is known to be highly defective due to its si gnificant Li2O deficiency. At present two stoichiometry-related defect -chemical models are discussed which can be distinguished with respect to the occurrence of Li or Nb vacancies, The Nb-vacancy model takes a dvantage of ilmenite-structured LiNbO3 and predicts a niobium antisite concentration being at least five times as large as in the Li-vacancy model, In the present contribution it is argued that the magnesium-do ping mechanisms are essentially independent of these particular differ ences. It is argued that extended stoichiometry-related defect cluster s represent a key for a proper understanding of the defect chemistry o f impurity cations, The discussion is mainly based on our recent shell -model simulations of perfect and defective LiNbO3. (C) 1996 Academic Press, Inc.