Zigzag Charge Ordering in <i>α^′</i>-NaV_{<b> 2</b>}O_{<b> 5</b>}

Abstract

23Na NMR spectrum measurements in alpha'-NaV2O5 with a single- crystalline\nsample are reported. In the charge-ordered phase, the number of inequivalent Na\nsites observed is more than that expected from the low-temperature structures\nof space group Fmm2 reported so far. This disagreement indicates that the real\nstructure including both atomic displacement and charge disproportionation is\nof lower symmetry. It is suggested that zigzag ordering is the most probable.\nThe temperature variation of the NMR spectra near the transition temperature is\nincompatible with that of second-order transitions. It is thus concluded that\nthe charge ordering transition is first-order.\n