NaV_2O_5 as a quarter-filled ladder compound

TL;DR

This study revises the crystal structure of NaV_2O_5 to a centrosymmetric form and identifies it as a quarter-filled ladder compound with specific electronic and magnetic properties.

Contribution

It provides a new crystal structure determination and electronic model for NaV_2O_5, clarifying its nature as a quarter-filled ladder compound.

Findings

Revised crystal structure to centrosymmetric Pmmn

Identified V-O-V molecular orbitals as the spin carriers

Theoretical estimates match experimental charge gap and magnetic behavior

Abstract

A new X-ray diffraction study of the one-dimensional spin-Peierls compound \alpha-NaV_2O_5 reveals a centrosymmetric (Pmmn) crystal structure with one type of V site, contrary to the previously postulated non-centrosymmetric P2_1mn structure with two types of V sites (V^{+4} and V^{+5}). Density functional calculations indicate that NaV_2O_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 NaV_2O_5 and its magnetic properties.