Charge-density wave modulations in the transition metal chalcogenides

Abstract

The transition metal chalcogenides, due to the typically large covalency of the metal-chalcogenide bonds, often adopt low-dimensional structures and exhibit charge-density wave (CDW) modulations. Incommensurate (IC) or commensurate (C) modulations structures are observed as well as a rich variety of phase transitions driven by the temperature dependence of the CDW amplitude and phase. Defects of the CDW modulation, including antiphase boundaries (APB) and discommensurations (DC), are of determinate importance for the mediation of these phase transitions. The microstructural phenomena occurring in the quasi-one-dimensional chalcogenides will be surveyed with emphasis on two representative systems: the Nb1-xTaxTe4 solid solution and the MxNb3Te4 (M = In or TI) intercalation compound.The NbxTa1-xTe4 compounds are based on a tetragonal subcell with axes (a x a x c) and consist of an extended chain of metal atoms centered within an antiprismatic cage of Te atoms.