Electronic structure and crystallography of MoTe2and WTe2

Abstract

Calculations of electronic structure have been undertaken using ab initio tight-binding (TB) method comparing the group VIb ditellurides WTe₂ and MoTe₂ in their various guises. The group VIb ditellurides show deviation from a simple band model which predicts semiconducting behaviour due to a trigonal prismatic crystal-field splitting of a filled nonbonding d_z2 orbital. For WTe₂ and beta -MoTe₂ the metal atom is displaced from the centre of an octahedron of Te atoms, and metal-metal chains with bond lengths only slightly longer than the elemental metals run along the layers. The reduced Madelung term for this configuration compensates for loss of the lone d_z2-based band and thus results in semi-metallic crystals. Mo but not W occurs with a trigonal prismatic coordination ( beta -MoTe₂). beta -MoTe₂ differs from WTe₂ only slightly-in the stacking of layers; a low-temperature polymorph is believed to stack identically to WTe₂.