Oxygen vacancy formation energies in Sr-doped complex perovskites: ab initio thermodynamic study

TL;DR

This study uses ab initio calculations to analyze how strontium doping affects oxygen vacancy formation energies in La1-xSrxCo0.25Fe0.75O3-delta perovskites, revealing the significant role of phonons and composition in defect energetics.

Contribution

It provides a detailed thermodynamic analysis of oxygen vacancy formation energies considering phonon contributions and Sr doping effects in complex perovskites.

Findings

Oxygen vacancy formation energies decrease with increased Sr content.

Phonon contributions become more significant at higher temperatures and Sr levels.

Experimental data analysis supports the theoretical findings.

Abstract

La1-xSrxCo0.25Fe0.75O3-delta is known as one of the best cathode materials for permeation membranes and solid oxide fuel cells. Optimization of its chemical composition is a challenging problem. One of the key properties is concentration of oxygen vacancies, controlled by their formation energies. Ab initio calculations were employed in order to study the formation of oxygen vacancies in La1-xSrxCo0.25Fe0.75O3-delta perovskites by varying the Sr content from x = 12.5% to 50%. The formation energies were obtained for different stoichiometries as functions of temperature and oxygen partial pressure. We have shown that the phonon contribution to the free formation energy becomes increasingly important in La1-xSrxCo0.25Fe0.75O3-delta not only with rising temperature but also with rising Sr content. We have shown that the formation energies are decreased significantly with increasing Sr content due to two effects: charge compensation of Sr2+ ions and phonon contribution. We have suggested a simple explanation to increasing role of phonons for the oxygen vacancies formation energies on the basis of phonon mode changes in comparison to defect-free materials. A careful analysis of the experimental results from the literature is also presented.