According to a systematic investigation of Altman et al. for lanthanide sesquioxides (Ln 2 O 3 ) , the twin-peak shape of the O K-edge spectra is a common feature observed in most rare-earth sesquioxides in a stable phase at ambient pressure through high energy resolution X-ray absorption spectroscopy (XAS) measurements. They concluded that the twin-peak shape is attributed to the π-and σ-type bonding between O 2p and Ln 5d orbitals, respectively. They also observed a small peak between A and B peaks that was assigned to the hybridization between O 2p and Ln 6p orbitals. (We should note that peaks A and B in our study correspond to peaks A and C in their paper, respectively.) Among the above, in the spectra of hexagonal Nd 2 O 3 and cubic Gd 2 O 3 , peak A is embedded in the shoulder of peak B. Furthermore, the peak positions were extracted via a decomposition process. For cubic Gd 2 O 3 , this seems to be consistent with those of other previous studies . Meanwhile, in the recent work with EELS by Shu et al., two peaks corresponding to peaks A and B have been clearly identified . This disagreement suggests the importance of theoretical confirmation. A twin-peak shape similar to those of Ln 2 O 3 has also been observed for cubic Y 2 O 3 .