In Nb${\mathrm{Se}}_3$ one-dimensional diffuse scattering was observed above 140 K and the satellite spots at a lower temperature. They correspond to the Kohn anomaly and the superlattice coupled with charge-density wave, respectively. The superlattice was found to be incommensurate, with the period $a^{\prime }=a$, $b^{\prime }\simeq 4.1b$, and $c^{\prime }=c$.

• Received 12 August 1977

DOI:https://doi.org/10.1103/PhysRevLett.39.1675