Polarizing oxygen vacancies in insulating metal oxides under high electric field

TL;DR

This paper presents a thermodynamic model to analyze how high electric fields influence the formation of neutral oxygen vacancies in insulating metal oxides, revealing polarization effects and defect energetics.

Contribution

It introduces a novel thermodynamic formulation combined with DFT and Berry phase calculations to quantify defect formation energetics under high electric fields in insulators.

Findings

Polarization lowers the electric Gibbs energy of vacancy formation.

Electrons trapped in vacancies are easily polarized, reducing defect formation energy.

Defect-induced phonon softening influences defect stability.

Abstract

We demonstrate a thermodynamic formulation to quantify defect formation energetics in an insulator under high electric field. As a model system, we analyzed neutral oxygen vacancies (color centers) in alkaline-earth-metal binary oxides using density functional theory, Berry phase calculations, and maximally localized Wannier functions. Work of polarization lowers the field dependent electric Gibbs energy of formation of this defect. This is attributed mainly to the ease of polarizing the two electrons trapped in the vacant site, and secondarily to the defect induced reduction in bond stiffness and softening of phonon modes. The formulation and analysis have implications for understanding the behavior of insulating oxides in electronic, magnetic, catalytic, and electrocaloric devices under high electric field.