Crystal structure and charge order below the metal-insulator transition in the vanadium bronze β-SrV₆O₁₅

Single crystal X-ray diffraction measurements were performed on one-dimensional mixed valence vanadium bronze $\beta$-SrV$_6$O$_{15}$ in which a metal-insulator transition exists at 170 K. Above 170 K the P2$_1$/a structure with zigzag order of Sr in the tunnels of vanadium is confirmed. In the structure below 170 K, the P2$_1$/a space group is retained with a b-axis threefold increase and a charge order appears. A Bond Valence Sum analysis shows that the charge order may consist in clusters of V$^{4+}$ regularly spaced along 1D direction.