X-ray Absorption Spectroscopic Study on La_(0.6)Sr_(0.4)CoO_(3-δ) Cathode Materials Related with Oxygen Vacancy Formation

摘要

The electronic structural changes of La_(0.6)Sr_(0.4)CoO_(3-δ) cathodes with oxygen vacancy formation by reducing oxygen partial pressures, p(O2)'s were investigated in detail using X-ray absorption spectroscopy to understand metallic-like electronic conduction mechanism. The oxygen nonstoichiometry of La_(0.6)Sr_(0.4)CoO_(3-δ) was controlled by annealing the samples under various p(O2)'s and quenched to room temperature. Co K-edge X-ray absorption near edge structure (XANES) spectra revealed that the Co average valence decreased with decreasing p(O2), which was also confirmed by iodometric titration. The Co L-edge XANES spectra were hardly changed with changing p(O2)'s. Meanwhile, the peak area of the OK-edge XANES spectra strongly depended on p(O2). This result revealed the strong hybridization between the O 2p and Co 3d states. It was concluded the introduction of oxygen vacancies narrowed the hybridized orbital of O 2p and Co 3d states, resulted in a decrease in the mobility as well as the concentration of electron holes with decreasing p(O2).