Low temperature X-ray study of β-AxV2O5 Original Research Article

The vanadium oxide bronzes β(β′)-AxV2O5 of A=Na (x=0.33), A=Sr (x=0.33) and A=Cu (x=0.65) having one-dimensional chain and ladder along the b-axis were studied by X-ray diffraction measurements. We observed the satellite reflections of q=1/2b∗ due to A-site cation ordering below 260 K for A=Na and room temperature for A=Sr. And then, we observed the satellite reflections of q=1/6b∗ below the metal–insulator transitions of 135 K for A=Na and 165 K for A=Sr. Moreover, we found the reflection accompanying the symmetry breaking below 255 K for A=Cu, corresponding to the slight anomaly in the resistivity of the metallic behavior. The superstructure analyses indicate the characteristic movement of vanadium atoms in the ladder, suggesting the charge disproportionation below 135 K for A=Na and 255 K for A=Cu.