Some properties of Re₂Te₅-based materials

Re₂Te₅ is a semiconducting compound with an energy band gap of about 0.8 eV. It has a relatively complex crystal structure with 84 atoms per unit cell. Initial results obtained at the Jet Propulsion Laboratory on p-type polycrystalline samples showed that they possess large Seebeck coefficient values but also large electrical resistivity values. They also exhibit very low thermal conductivity with a room temperature value of 13 mW/cmK. Another attractive feature of Re₂Te₅ is the possibility of inserting a variety of atoms in the large voids (2.8 angstroms in diameter) of the crystal structure to form Re₆M₂Te₁₅ filled compositions. The void fillers could act as phonon scattering centers, further reducing the thermal conductivity in these materials. As part of an effort to evaluate the potential of Re₂Te₅-based material for thermoelectric applications, we are currently exploring the synthesis and properties of filled compositions as well as n-type Re₂Te₅ samples. We present and discuss in this paper initial results obtained on Fe and Ag doped Re₂Te₅ samples.