X-ray investigation of the magnetoelastic instability ofα′−NaV2O5

We present an x-ray diffuse scattering study of the pretransitional structural fluctuations of the magnetoelastic transition in ${\alpha }^{\prime }-{\mathrm{NaV}}_2{\mathrm{O}}_5.$ This transition is characterized by the appearance below $T_{\mathrm{sp}}\sim 35\mathrm{K}$ of satellite reflections at the reduced wave vector $(\frac{1}{2},\frac{1}{2},\frac{1}{4}).\mathrm{}$ A large regime of structural fluctuations is measured up to 90 K. These fluctuations are three-dimensional between $T_{\mathrm{sp}}$ and $\sim 50\mathrm{K}$ and quasi-one-dimensional above $\sim 60\mathrm{K}.$ At 40 K the anisotropy ratio $({\xi }_b:{\xi }_a:{\xi }_c)$ is found to be (3.8:1.8:1), which reveals the importance of transverse interactions in the stabilization of the low-temperature phase. We discuss our results within the framework of recent theories dealing with the simultaneous occurrence of a charge ordering, a spin gap, and a lattice distortion in this intriguing compound.