Neutron-scattering investigation of the charge-density wave inTl0.3MoO3

Elastic-neutron-scattering experiments, performed on a single crystal of ${\mathrm{Tl}}_{0.3}$ ${\mathrm{MoO}}_3$, show the formation of a periodic distortion below the metal-semiconductor transition at about 170 K. Similar to the isostructural blue bronzes ${\mathrm{K}}_{0.3}$ ${\mathrm{MoO}}_3$ and ${\mathrm{Rb}}_{0.3}$ ${\mathrm{MoO}}_3$, this periodic distortion is characterized by a temperature-dependent wave vector q=(0,${\mathit{q}}_{\mathit{b}}$(T),0.5) referring to the high-temperature space group C2/m. The incommensurate component ${\mathit{q}}_{\mathit{b}}$(T) decreases continuously from 0.267 at the transition temperature to 0.253 at about 100 K, below which it remains constant down to 10 K. Unlike the K and Rb analogs for which there is still some debate on whether there is a commensurate-incommensurate transition at 100 K, the Tl blue bronze is clearly incommensurate down to low temperatures. While the magnetic susceptibility shows a substantial anomaly around 50 K, detailed neutron-scattering studies in this temperature region reveal no significant effect on the charge-density wave.