Structural and Electrical Properties of TlBiTe2and TlTe

Samples of TlBi${\mathrm{Te}}_2$ and TlTe were prepared and characterized by x-ray powder diffraction, differential thermal analysis, scanning-electron-microscope and electron-microprobe studies, and transport measurements. The two materials were found to be distinctly different with regard to melting point, crystal structure, temperature dependence of the resistivity and Hall coefficient, and sign of the Hall coefficient and thermoelectric power. The Hall mobilities (in ${\mathrm{cm}}^2$/V sec) are -64 and +3 at 300 K and - 128 and + 1120 at 4.2 K for TlBi${\mathrm{Te}}_2$ and TlTe, respectively. The temperature dependence of these mobilities, combined with the apparently large carrier densities, suggests that TlBi${\mathrm{Te}}_2$ is a highly degenerate $n$-type semiconductor, while TlTe is more likely to be a semimetal. Discontinuities in the resistivity and Hall-coefficient data of TlTe at 170 K suggest the occurrence of a phase change at that temperature. The two sets of results were compared with data on material which had been described by Hein and Swiggard as TlBi${\mathrm{Te}}_2$, a new nonmetallic superconductor. But the normal-state properties of a portion of this material closely resemble those of TlTe, not TlBi${\mathrm{Te}}_2$. A search for superconductivity in further samples of both compounds is needed to clarify this situation.