Mg dopants in lithium niobate ( LiNbO 3 , LN): Defect models and impact on domain inversion

The optical and ferroelectric properties of lithium niobate ( {LiNbO}₃ , LN), including the orientation of the ferroelectric domains, i.e., the poling behavior, are decisively influenced by dopants. In this study, we apply density functional theory (DFT) to understand the microscopic origin of the beneficial (and impairing) effects of different Mg-doping concentrations, including nominally undoped stoichiometric and congruent compositions, particularly on the ferroelectric domain inversion. {Mg}_Li⁺ tends to be the dominant defect for lower doping concentrations, and a combination of {Mg}_Li⁺ and {Mg}_Nb³⁻ for intermediate doping concentrations. Single {Mg}_Li defects are found to be a possible seed point for domain inversion, while the combination of {Mg}_Li and {Mg}_Nb defects is suggested to inhibit poling. In this case, the reaction pathways for the inversion are not symmetric and are characterized by different activation energies for each direction, which could promote the crystal to more easily revert to its original polarization.