Effect of Defects on Spontaneous Polarization in Pure and Doped LiNbO3: First-Principles Calculations

Abstract

Numerous studies have indicated that intrinsic defects in lithium niobate (LN) dominate its physical properties. In an Nb-rich environment, the structure that consists of a niobium anti-site with four lithium vacancies is considered the most stable structure. Based on the density functional theory (DFT), the specific configuration of the four lithium vacancies of LN were explored. The results indicated the most stable structure consisted of two lithium vacancies as the first neighbors and the other two as the second nearest neighbors of Nb anti-site in pure LN, and a similar stable structure was found in the doped LN. We found that the defects dipole moment has no direct contribution to the crystal polarization. Spontaneous polarization is more likely due to the lattice distortion of the crystal. This was verified in the defects structure of Mg2+, Sc3+, and Zr4+ doped LN. The conclusion provides a new understanding about the relationship between defect clusters and crystal polarization.

Growing, Structure and Optical Properties of LiNbO3:B Crystals, a Material for Laser Radiation Transformation

“…This optical behavior of LiNbO 3 :B crystals is similar to the behavior of strongly doped LiNbO 3 :Zn and LiNbO 3 :Mg crystals. Photorefractive effect is suppressed in LiNbO 3 :Zn and LiNbO 3 :Mg crystals doped with near- or after-threshold concentrations [ 24 , 25 , 26 , 27 , 28 , 29 ]. Only round scattering of laser beam on static structure defects is observed in both LiNbO 3 :B and LiNbO 3 :Zn, LiNbO 3 :Mg crystals.…”

Interaction between Mo and intrinsic or extrinsic defects of Mo doped LiNbO3 from first-principles calculations

“…We have plotted the thermodynamically stable region of the LN in the former work to define the chemical potential of its components. 31 Table 1 lists the chemical potentials of Li, Nb, O, and Mo under Li-rich and Li-deficient conditions. As the as-grown crystals and films are Li-deficient composition, the chemical potentials of Nb and Li are employed according to the Li-deficient condition.…”

“…We have plotted the thermodynamically stable region of the LN in the former work to define the chemical potential of its components [37]. Table 1 lists the chemical potentials of Li, Nb, O, and Mo under Li-rich and Li-deficient conditions.…”

Lithium Niobate Single Crystals and Powders Reviewed—Part II

“…Debate still prevails on Nb ions occupying interstitial structural sites [8,41,42]. Other alternatives of intrinsic defect clusters have been proposed, perhaps more intricated [43][44][45][46]; most have been proposed to describe the effect of the localized polarization caused by the defect clusters on the overall crystal polarization of the observed features of domain stabilization and reversal [6]. Given the bilateral acceptance in what respects the defect scenario of undoped or pure LN, it is reasonable to adopt the Li vacancy model and its associated defect cluster (left side of Figure 3) as a feasible physical instance describing both the type of intrinsic defects and their ordering in off-stoichiometric LN, respectively.…”