Structural changes in the discommensurate distortion waves of NbTe4on cooling

Nb${\mathrm{Te}}_4$ is a quasi-one-dimensional metallic compound. The crystal structure is tetragonal and is modulated by an incommensurate distortion wave at room temperature. We show that on the cooling of the crystal into the temperature range 100-50 K, two distinct sets of sharp spots can occur along the streaks that arise in the diffraction patterns. There are indications that the two types can occur in different parts of the same crystal. The interpretation of the observations in terms of discommensuration arrays is discussed.