SEGREGATION IN MGO-DOPED CONGRUENT LINBO3

A series of MgO-doped LiNbO3 crystals were grown from MgO-doped congru ent LiNbO3 melts. The compositional relationship between the melts and crystals grown from these melts was studied. It was found that as the MgO content increases, the Li2O and Nb2O5 contents as well as the Li/ Nb molar ratio in crystals decrease. In general, MgO-doping tends to d ecrease the effective distribution coefficient of Li2O and increase th at of Nb2O5. It can be concluded that from a congruent LiNbO3 melt dop ed with 4-6 mol% MgO, as usually adopted, crystals with a high composi tional homogeneity cannot be obtained. Problems associated with binary and ternary congruent compositions and the defect structure in MgO-do ped LiNbO3 are also discussed.