Electrical Conductivity and Superconductivity in the γ Phase of the Tl–Te System

Two methods for the preparation of single crystals of the γ phase of the Tl–Te system, Tl5Te3, are described. An analysis of electrical resistivity data on both single-crystal and polycrystalline material over the temperature range 4.2° to 500°K and thermal conductivity data on polycrystalline material over the temperature range 77° to 360°K indicates metallic behavior. Typical electrical characteristics at 300°K are: resistivity 2.5×10−4Ω·cm, carrier concentration 1.5×1022/cm3, and mobility 2.0cm2/V·sec. A transition to the superconducting state was observed at 2.19°K; this transition was studied as a function of magnetic field strength. The existence of superconductivity in the γ phase is generally compatible with predictions for the occurrence of superconductivity in degenerate semiconductors and semimetals with positive Hall coefficients.