Oxygen vacancies in bulk and at neutral domain walls in hexagonal YMnO$_3$

TL;DR

This study uses density functional theory to analyze oxygen vacancy behavior in bulk and at neutral domain walls in hexagonal YMnO$_3$, revealing stability patterns, migration barriers, and effects on polarization and lattice parameters.

Contribution

It provides new insights into the stability, migration, and distribution of oxygen vacancies in YMnO$_3$, especially their interactions with ferroelectric domain walls.

Findings

Oxygen vacancies are more stable in Mn-O layers than Y-O layers.

Migration barriers for planar oxygen vacancies are high.

Vacancy concentration reduces polarization and expands lattice parameters.

Abstract

We use density functional calculations to investigate the accommodation and migration of oxygen vacancies in bulk hexagonal YMnO$_3$, and to study interactions between neutral ferroelectric domain walls and oxygen vacancies. Our calculations show that oxygen vacancies in bulk YMnO$_3$ are more stable in the Mn-O layers than in the Y-O layers. Migration barriers of the planar oxygen vacancies are high compared to oxygen vacancies in perovskites, and to previously reported values for oxygen interstitials in h-YMnO$_3$. The calculated polarization decreases linearly with vacancy concentration, while the out-of-plane lattice parameter expands in agreement with previous experiments. In contrast with ferroelectric perovskites, oxygen vacancies are found to be more stable in bulk than at domain walls. The tendency of oxygen vacancies to segregate away from neutral domain walls is explained by unfavorable Y-O bond lengths caused by the local strain field at the domain walls.