CHARGE-DENSITY WAVES IN SOME NB AND TA CHALCOGENIDES

A brief description of the competing mechanisms important for the stability of composition- and temperature-dependent modulation phases of Nb1-xTaxTe4 is given, with some emphasis on the microstructural changes at the two high temperature phase transitions in TaTe4. The charge density wave sliding in NbSe3 is explained on the basis of a structural model which takes into account the easy switching between the two modulation wavevectors along the same trigonal prismatic columns. The dependence of the interpolytypic transitions and various charge density wave transition temperatures on the amount of intercalated Ag in 1T-TaS2 is discussed.