Ab initio study of proton-exchanged LiNbO3(I): Structural, thermodynamic, dielectric, and optical properties

TL;DR

This study uses first principles calculations to analyze the structural, thermodynamic, dielectric, and optical properties of proton-exchanged lithium niobate, revealing its enhanced dielectric constant and optical contrast for waveguide applications.

Contribution

It provides a comprehensive first-principles analysis of proton-exchanged lithium niobate's properties, including phase stability and optical characteristics, which were not fully characterized before.

Findings

Dielectric constant is significantly higher than lithium niobate.

Refractive indices vary sharply between phases and differ from lithium niobate.

Identifies stable surface and phase conditions under different environments.

Abstract

Using first principles calculations, we study the ground-state structure of bulk proton-exchanged lithium niobate, which is also called hydrogen niobate and is widely used in waveguides. Thermodynamics helps to establish the most favorable nonpolar surface as well as the water-deficient and water-rich phases under different ambient conditions, which we refer to as "dehydrated" and "rehydrated" phases, respectively. We compute the low-frequency dielectric response and the optical refractive indices of hydrogen niobate in different phases. The dielectric constant is greatly enhanced compared to lithium niobate. At shorter wavelengths, the refractive indices vary between each phase and have a sharp contrast to lithium niobate. Our study characterizes the structures and thermal instabilities of this compound and reveals its excellent dielectric and optical properties, which can be important in the future application in waveguides.