Subhalides of tellurium: Electrical conductivity in relation to crystal structure

Subhalides of Te are compounds of the type Te_yX with y ?1 and X = Cl, Br, I. Within this group of compounds the structural building unit of elemental tellurium - the Te-screw with 3₁ or 3₂ symmetry - is continuously modified and yields a series of crystal structures from one-dimensional Te-Te arrangements to a zero-dimensional type. We show qualitatively how the electrical conductivity of these compounds is correlated to the various crystal structures. Gap energies are determined from the temperature dependence of the electrical conductivity.