Electron microscopy study of transition-metal tetrachalcogenide (MSe₄)_nI (M=Nb, Ta)

Abstract

The new tetrachalcogenide compounds have a one-dimensional structure and two of these show transport properties which are characteristic of this type of conductor. The authors electron microscopy study permits them to show clearly and characterise the charge density waves which appear at 263 and 285K in (TaSe4)2I and (NbSe4)103/I respectively. Moreover, they describe the behaviour of (TaSe4)3I and (NbSe4)3I when the temperature changes. These compounds undergo a space group change around 200 and 280K respectively. The results are connected to those obtained in other works by the study of transport phenomena or by band scheme calculations.