IMPORTANCE OF SHORT INTERLAYER TE-TE CONTACTS FOR THE STRUCTURAL DISTORTIONS AND PHYSICAL-PROPERTIES OF CDI2-TYPE LAYERED TRANSITION-METAL DITELLURIDES

We examined how the short intra- and interlayer Te···Te contacts of layered transition-metal tellurides affect their structures and physical properties by carrying out tight-binding band electronic structure calculations for the CdI2-type layered transition-metal dichalcogenides TiX2 (X =S, Se, Te) and MTe2 (M =V, Nb, Ta) on the basis of the extended Huöckel method. In the CdI2-type tellurides, the top portion of the Tep-block bands overlaps significantly with the bottom portion of the metal d-block bands, thereby causing a substantial electron transfer from the p- to the d-block bands. For this p → d electron transfer, the interlayer Te···Te contacts are found to be essential because the overlap between the Tepz-orbitals (perpendicular to the layer) associated with the interlayer Te···Te contacts is most effective in raising the top portion of the Tep-block bands. As a consequence, layered transition-metal tellurides are likely to possess a three-dimensional metallic character, and a slight change in their interlayer Te···Te contacts significantly affects their electrical and other physical properties. © 1992 Academic Press, Inc. All rights reserved.