X-ray study of vanadium-doped blue bronze

We present an x-ray diffraction study of the charge-density wave (CDW) in a blue-bronze single crystal doped with vanadium atoms. We show that the 2$k_f$ ($k_f$ is the Fermi wave vector) component of the distortion wave vector, which is about 0.75 at low temperatures in the standard blue bronze ${\mathrm{K}}_{0.3}$ ${\mathrm{MoO}}_3$, is strongly shifted to a smaller value of about 0.685 in the doped compound ${\mathrm{K}}_{0.3}$ ${\mathrm{V}}_{\mathrm{x}}$ ${\mathrm{Mo}}_{1\mathrm{-}\mathrm{x}}$ ${\mathrm{O}}_3$, which roughly corresponds to the calculated value 0.690 using a structural determination of the stoichiometry x≊0.024±0.002 and assuming two quasi-one-dimensional bands filled by the total number of electrons provided by the alkali metal. Moreover, we show that while in the pure sample, the width of the satellite profile is limited by the instrumental resolution, it is much larger in the doped crystal, indicating that the long-range order associated with the CDW formation is somewhat hampered by the incorporated impurities. The Peierls phase transition evolves into a smeared transition to a disordered state characterized by a short-range CDW order that remains temperature independent below 100 K.