THE DEFECT STRUCTURE OF CONGRUENTLY MELTING LITHIUM-NIOBATE

Six samples of congruently melting lithium niobate (approximately Li0. 95Nb1.01O3) have been examined by powder x-ray diffraction for the occ urrence of niobium antisite defects (niobium on lithium sites). Contra ry to current thinking, we have found no evidence for the occurrence o f high concentrations of such defects, which also require the presence of Nb site vacancies. Rather, it was found that the number of antisit e defects is close to the minimum that is required to sustain charge n eutrality in a model of the type ([Li1-xNbx/5][Nb]O3), where the Nb si te is fully occupied.