A molecular bonding theory for liquid thallium–tellurium alloys

Abstract

A molecular orbital model is proposed as the conceptual basis for the electronic structure of Tl–Te alloys. Using an expression proposed by Mott for the electrical conductivity in the strong scattering domain, existing data for the electrical conductivity σ and the thermopower S as a function of composition and temperature are compared with theory in the composition range where S is positive. This is done with the help of a theory for the equilibrium concentration of broken Te–Te bonds derived in another paper, with the dangling bonds assumed to give rise to holes. It is found that most of the observed behaviour of σ and S can be accounted for in a reasonable way. Reasons are discussed for the exceptions, which occur mainly in the behaviour of pure tellurium. We discuss the relation of our proposed model to the usual pseudo-gap model, and note a distinction between chain structures and network structures with regard to the mechanism whereby the density of states at the Fermi energy is affected by temperature.