Recommended strategies for quantifying oxygen vacancies with X-ray photoelectron spectroscopy

Oxygen vacancies play a crucial role in shaping the properties of metal oxides for diverse applications such as catalysis, ferroelectricity, magnetism, and superconductivity. Although X-ray photoelectron spectroscopy (XPS) is a robust tool, accurate quantification of oxygen vacancies remains a challenge. A common mistake in XPS analysis is associating the 531-532 eV feature in O 1 s spectra with oxygen vacancies. This is incorrect because a vacant oxygen site does not emit photoelectrons and therefore does not generate a direct XPS spectral feature. To address this issue, we propose three alternative approaches for oxygen vacancy analysis with XPS through indirect features: (1) quantifying cation valence state variations, (2) assessing oxygen nonstoichiometry via normalized oxygen spectral intensity, and (3) evaluating Fermi energy changes from electrostatic shifts in the binding energy. This work will enable precise XPS analysis of oxygen vacancies, promoting future studies in understanding and manipulating oxygen vacancies for advanced material development.