First evidence for charge ordering in NaV2O5 from Raman spectroscopy

Abstract We argue on the basis of symmetry selection rules and Raman scattering spectra that NaV 2 O 5 undergoes a charge ordering phase transition at T c =34 K. Such a transition is characterized by the redistribution of the charges at the phase transition and corresponds to the change of the vanadium ions, from uniform V 4.5+ to two different V 4+ and V 5+ states. In the low temperature phase the V 4+ ions are forming a “zig-zag” ladder structure along the b -axis, consistent with the symmetry of the P2/b space group.