Defect structure analysis of lithium niobate single crystals and lithium tantalate ceramics with the next-nearest-neighbor interactions

In this work, we have proposed a theoretical description of the defect structure in LiTaO3 and LiNbO3 on the basis of vacancy models combined with a ferroelectric phase transition theory. The calculated values by our approach, which takes into account the next-nearest neighbors interactions, are closer to the experimental data and improves the theoretical approach of Safaryan. A comparative study between the calculated and measured values of the Curie temperature shows that the lithium vacancy model is the best model that has been suggested for describing the defect structure in nonstoichiometric lithium niobate single crystals and lithium tantalate ceramics.