NaV2O5 as a Quarter-Filled Ladder Compound

TLDR: In this article, a new x-ray diffraction study of the one-dimensional spin-Peierls compound with one type of V site was performed, showing that it has a centrosymmetric crystal structure with one V site.

Abstract: A new x-ray diffraction study of the one-dimensional spin-Peierls compound ${\ensuremath{\alpha}}^{\ensuremath{'}}\ensuremath{-}\mathrm{Na}{\mathrm{V}}_{2}{\mathrm{O}}_{5}$ reveals a centrosymmetric $(\mathrm{Pmmn})$ crystal structure with one type of V site, contrary to the previously postulated noncentrosymmetric ${P2}_{1}\mathrm{mn}$ structure with two types of V sites ( ${V}^{+4}$ and ${\mathrm{V}}^{+5}$). Density-functional calculations indicate that $\mathrm{Na}{\mathrm{V}}_{2}{\mathrm{O}}_{5}$ is a quarter-filled ladder compound with the spins carried by V-O-V molecular orbitals on the rungs of the ladder. Estimates of the charge-transfer gap and the exchange coupling agree well with experiment and explain the insulating behavior of $\mathrm{Na}{\mathrm{V}}_{2}{\mathrm{O}}_{5}$ and its magnetic properties.