First-principles study on the formation energies of intrinsic defects in LiNbO3 Original Research Article

First-principles plane-wave ultrasoft pseudopotential method within local density approach (LDA) has been used to study three possible vacancy-defect models for non-stoichiometric lithium niobate (LiNbO3): (1) the oxygen-vacancy model View the MathML sourceVO2++2VLi-, (2) the niobium-vacancy model View the MathML source5NbLi4++4VNb5-, and (3) the lithium-vacancy model View the MathML source4VLi-+NbLi4+. The corresponding formation energies are obtained via energy minimization of a supercell. In Nb-rich environment, the calculated defect formation energies, both under oxidation and reduction conditions, show little effect on the intrinsic defect structures. We find that the lithium vacancy model View the MathML source4VLi-+NbLi4+ has the most stable configuration in the non-stoichiometric lithium niobate crystals. Our calculations also show that the formation of any type of neutral defects and Frenkel pairs in a Nb-rich environment is difficult.