Correlation among Oxygen Vacancies, Protonic Defects, and the Acceptor Dopant in Sc-Doped BaZrO₃ Studied by ⁴⁵Sc Nuclear Magnetic Resonance

The distribution of protons and oxygen vacancies at room temperature at different proton concentrations in 10 mol % Sc-doped BaZrO₃ was investigated to clarify the influence of proton concentration and oxygen vacancies in the trapping of protons caused by the acceptor dopant. To enhance proton conductivity for practical use, it is essential to understand this phenomenon known to limit the long-range transport of protons. In this study, ⁴⁵Sc nuclear magnetic resonance (NMR) spectroscopy combined with thermogravimetric analysis (TGA) and ¹H NMR is used to elucidate the protonic defects and oxygen vacancies formed around Sc and Zr. The results reveal that the high protonic defect concentration around Sc with a 9-10 mol % proton concentration is a clear indication for proton trapping and that the high protonic defect concentration around Zr at an intermediate proton concentration of 4 mol % suggests that the protons are residing in the nontrapping sites. The oxygen vacancies that tend to be located around Sc apparently prevent the formation of protonic defects due to the repulsive interaction between the protonic defect and the association of Sc and an oxygen vacancy, both of which have a positive net charge. This study suggests that the formation of oxygen vacancies around the acceptor may inhibit proton trapping and therefore have a positive effect on the long-range transport of protons.