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

Area of Science:

• Materials Science
• Solid State Physics
• Crystallography

Background:

• Intrinsic defects in lithium niobate (LN) are known to dominate its physical properties.
• In niobium-rich conditions, a niobium anti-site with four lithium vacancies is the most stable defect structure.

Purpose of the Study:

• To explore the specific configurations of lithium vacancies in lithium niobate using density functional theory (DFT).
• To understand the relationship between defect clusters and crystal polarization in pure and doped LN.

Main Methods:

• Density Functional Theory (DFT) calculations were employed to investigate defect structures.
• Analysis of defect configurations in pure and doped (Mg2+, Sc3+, Zr4+) lithium niobate.

Main Results:

• The most stable structure involves two lithium vacancies as nearest neighbors and two as second nearest neighbors to the Nb anti-site.
• Defect dipole moments were found to have no direct contribution to crystal polarization.
• Spontaneous polarization is primarily attributed to lattice distortion.

Conclusions:

• A specific arrangement of lithium vacancies around niobium anti-sites dictates the most stable defect structure in LN.
• Lattice distortion, rather than defect dipole moments, is the key mechanism driving spontaneous polarization in lithium niobate.
• This study offers a refined understanding of defect cluster behavior and its influence on the ferroelectric properties of LN.