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

Weiwei Wang,Hongde Liu,Yongfa Kong,Jingjun Xu,Dahuai Zheng,Mengyuan Hu,Shahzad Saeed,Lixin Zhang

doi:10.3390/ma12010100

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.

Highlights

As an important functional material, lithium niobate (LiNbO3, LN) possesses a range of excellent properties, such as acousto-optic, ferroelectric, and photorefractive properties and it has been widely used in a series of nonlinear optical devices [1,2]
In the most stable model, the polarization direction of the defect cluster dipole moment was perpendicular to the bulk polarization direction (c axis), which indicated that the defects dipole moment had no direct contribution to the crystal polarization
We found that the lithium vacancy of LN:Mg, LN:Sc, and LN:Zr lies in 2NN rather than the 1NN, and the defect possible defect cluster combinations

Summary

Introduction

As an important functional material, lithium niobate (LiNbO3 , LN) possesses a range of excellent properties, such as acousto-optic, ferroelectric, and photorefractive properties and it has been widely used in a series of nonlinear optical devices [1,2]. In these applications, defects play an important role, so the defect structure is a significant part of LN research. From literature and experimental data, the Li-vacancy model consists of niobium anti-site and Li vacancies are energetically more favorable [3,4,5]. Afterwards, Xu et al [7] pointed out the configuration that four lithium vacancies all located at the NN sites possess the lowest energy

Methods

Results

Conclusion