23Na NMR study of local symmetry and electronic structure of the quasi-one-dimensional conductor β-Na0.33V2O5

23Na NMR measurements have been made on a single crystal to study the local symmetry and the electronic state in the quasi-one-dimensional conductor β-Na0.33V2O5. We observed the characteristic 23Na NMR spectra in the metallic and insulating phases. The characteristic spectra are well explained by the lattice symmetry proposed by the X-ray diffraction and the neutron scattering studies. From the analysis of the 23Na Knight shift, we find that the metal-insulator (MI) transition is accompanied not by the charge ordering (CO) of V4+ and V5+ but by the charge disproportionation (CD). A model of the electronic structure is proposed in the insulating phase