Anion order and spontaneous polarization in LaTiO\textsubscript{2}N oxynitride thin films

TL;DR

This study uses density functional theory to explore how epitaxial strain influences anion order and spontaneous polarization in LaTiO2N thin films, revealing potential for improved photocatalytic efficiency by suppressing charge recombination.

Contribution

It demonstrates that epitaxial strain induces polar anion order in LaTiO2N, which can enhance photocatalytic performance by creating a built-in electric field.

Findings

Polar anion order appears under >4% compressive strain.

Strained LaTiO2N exhibits coercive fields comparable to ferroelectrics.

Strain-induced polarization could suppress charge recombination.

Abstract

The perovskite oxynitride LaTiO\textsubscript{2}N is a promising material for photocatalytic water splitting under visible light. One of the obstacles towards higher efficiencies of this and similar materials stems from charge-carrier recombination, which could be suppressed by the built-in electric field in polar materials. In this study, we investigate the spontaneous polarization in epitaxially strained LaTiO\textsubscript{2}N thin films via density functional theory calculations. The effect of epitaxial strain on the anion order, resulting out-of-plane polarization, energy barriers for polarization reversal and the corresponding coercive fields are studied. We find that for compressive strains larger than 4\% the thermodynamically stable anion order is polar along the out-of-plane direction and has a coercive field comparable to other switchable ferroelectrics. Our results show that strained LaTiO\textsubscript{2}N could indeed suppress carrier recombination and lead to enhanced photocatalytic activities.