The metal-semiconductor transition in thallium-rich liquid Tl-Te alloys

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Abstract
Evidence that liquid T1xTe1-x alloys in the composition range ⅔ > × > 1 are pseudobinary mixtures Tl+Tl2Te prompts the examination of the implications of this molecular structure for the change in the electronic structure as the composition is changed continuously from a typical metal T1 to a typical liquid semiconductor T12Te. By ignoring the mixing of states, a first approximation is derived from a superposition of tight-binding bands due to the two constituents T1 and T12Te. The relative energies of the bands due to the two constituents are strongly affected by charge transfer between them. When the semiconductor constituent has a small band gap and a large high-frequency dielectric constant as in T12Te, the conduction-band edge of the semiconductor drops below the Fermi energy when the metal concentration is still large. This is in contrast to the case of a metal dissolved in a wide band gap semiconductor such as argon, where the conduction band of the metal simply narrows and becomes an impurity band within the argon band gap, as suggested by the pseudogap model. The effects of mixing of states between bands are considered qualitatively. Experimental data for T1-Te alloys are discussed which indicate that the transition between the two kinds of conduction band (T1 and T12Te) occurs at ≅0.8.