QUESTIONS CONCERNING FORM TAKEN BY CHARGE-DENSITY WAVE AND ACCOMPANYING PERIODIC-STRUCTURAL DISTORTIONS IN 2H-TASE2, AND CLOSELY RELATED MATERIALS

An attempt has been made to understand the detailed form and phasing taken by the periodic-structural distortions (PSD) as developed in the various d1-d0 charge-density-wave (CDW) bearing materials. The diagrammatic mode of presentation which is used facilitates insight into the forces at work at the unit-cell level. In the fully investigated case of the 2H structure, with its trigonal prismatically coordinated sandwiches, these are able to modify substantially the simple relationship between PSD and CDW. The proposed phasing of the CDW in the case of 1T-TaS2 (1T-TaSe2) goes against recent interpretation of the available data, and a revised interpretation of that data is given. The two PSD's reported for NbTe2 have for the first time been brought satisfactorily into the present CDW scheme. 3d1 VSe2 and 3d0 TiSe2 provide interesting and illuminating contrasts in behavior compared with 5d1 1T-TaSe2. © 1978 The American Physical Society.