V-V dimerization effects on bulk-sensitive hard x-ray photoemission spectra for Magneacuteli phase vanadium oxides

Highly bulk-sensitive hard x-ray photoemission has been performed for the Magneacuteli phase V(5)O(9) and V(6)O(11), which are composed of V(2)O(3) and VO(2) from chemical point of view. The valence-band spectra near the Fermi level are rather similar between V(5)O(9) and V(6)O(11) in both metallic and insulating phases. Although the core-level spectra in the metallic phase are similar between V(5)O(9) and V(6)O(11), the core-level spectra in the insulating phase are noticeably different. Our results are understood by considering the contribution of the V-V dimerization effects, which are strong in V(6)O(11) and negligible in V(5)O(9). Comparison of the core-level spectra of V(5)O(9) and V(6)O(11) with those of VO(2) has revealed that the mechanism of the metal-insulator transitions for the former two compounds is different from that for VO(2).