Thermodynamic stability of oxygen point defects in cubic Zirconia

TL;DR

This study uses ab-initio calculations to analyze the structural, electronic, and thermodynamic stability of oxygen point defects in cubic zirconia, revealing multiple configurations and charge states with implications for material properties.

Contribution

It introduces a comprehensive analysis of oxygen defect configurations and their stability in cubic zirconia, including a method to determine chemical potential under various conditions.

Findings

Oxygen interstitials have five configurations, with <110> dumbbell being most stable for neutral and singly charged states.

Doubly charged oxygen interstitial prefers the octahedral site energetically.

Both oxygen vacancy and interstitial are negative-U defects, unstable at any Fermi level.

Abstract

Zirconia (ZrO2) is an important material with technological applications which are affected by point defect physics. Ab-initio calculations are performed to understand the structural and electronic properties of oxygen vacancies and interstitials in different charge states in cubic zirconia. We find oxygen interstitials in cubic ZrO2 can have five different configurations - <110> dumbbell, <100> dumbbell, <100> crowd-ion, octahedral, and <111> distorted dumbbell. For a neutral and singly charged oxygen interstitial, the lowest energy configuration is the <110> dumbbell, while for a doubly charged oxygen interstitial the octahedral site is energetically the most favorable. Both the oxygen interstitial and the oxygen vacancy are negative-U, so that the singly charged defects are unstable at any Fermi level. The thermodynamic stability of these defects are studied in terms of Fermi level, oxygen partial pressure and temperature. A method to determine the chemical potential of the system as a function of temperature and pressure is proposed.