Two dimensional ordering and fluctuations in α‱-NaV₂O₅

X-ray diffraction measurements of Bragg and diffuse scattering associated with charge ordering in the inorganic compound α‱-NaV₂O₅ show a continuous phase transition at a temperature of about 33.1 K. Many of this material’s properties suggest a spin-Peierls transition, as established in CuGeO₃ and MEM(TCNQ)₂. We compare the order parameter as well as fluctuations in the order parameter in these materials, and conclude that α‱-NaV₂O₅ is dissimilar, and that the transition is two dimensional in nature, due to charge ordering associated with the fractional average valence at the vanadium site within the orthorhombic a-b plane.