Stoichiometry-related defect structure in lithium niobate and lithium tantalate

Congruently grown LiNbO3 (LiTaO3) is known to be highly defective due to its significant Li2O deficiency. We present in this work a comparative study between normal LiNbO3 (LiTaO3) and ilmenite structural LiNbO3 (LiTaO3). Namely, the normal cation stacking sequence is replaced by ilmenite ordering ‘…Nb (Ta) Li vacancy Li Nb (Ta) vacancy Nb (Ta) Li vacancy Li Nb (Ta) vacancy…’. From Safaryan’s approach which combines a ferroelectric phase transition theory and vacancy models, we calculated the Curie temperature in ilmenite LiNbO3 (LiTaO3). We have shown that ilmenite structural LiNbO3 (LiTaO3) is in excellent agreement with the result of the experiment compared to normal LiNbO3 (LiTaO3).