Single-crystal x-ray diffraction employing synchrotron radiation is used to determine the low-temperature structure (at 16 K) of the charge-density-wave compound ${\mathrm{NiTa}}_2$${\mathrm{Se}}_7$. The incommensurate modulation is found to be essentially different from that in ${\mathrm{NbSe}}_3$, despite structural similarities between their basic structures. The morphology of ${\mathrm{NiTa}}_2$${\mathrm{Se}}_7$ crystals is discussed, and an alternative interpretation is given for scanning tunneling microscopy observations. Implications are considered for the microscopic origin of this CDW instability.

• Received 6 April 1995

DOI:https://doi.org/10.1103/PhysRevB.52.3892