Charge-density waves in pure and intercalated Nb3Te4

High-resolution transmission electron microscopy (HRTEM), resistivity measurements and electronic band structure calculations performed by means of the extended Huckel tight-binding method are presented for the quasi one-dimensional compounds A(x)Nb(3)Te(4) (A = In, Tl, Zn, Ag, Hg). HRTEM and electron diffraction performed on pure Nb3Te4 at room- and liquid nitrogen temperatures, reveal both the basic structure and the low-temperature charge-density waves (CDWs) modulation. Resistivity vs. temperature plots show characteristic CDW anomalies, dependent on the type and concentration of the atoms, intercalated into the large hexagonal tunnels of the host structure. It is shown that intercalation of Tl and In results in a flattening of the corresponding Fermi surfaces and that CDW formation is largely dependent on the coincidence between the Fermi level E-F and a small peak in the density of states spectrum, mainly developed from the Nb dz(2) orbitals. This peak is positioned in a minimum between the filled and empty states of the spectrum and tends to split into a doublet as a consequence of intercalation. (C) 2009 Elsevier Masson SAS. All rights reserved.