CdI2 structure type as potential thermoelectric materials: Synthesis and high temperature thermoelectric properties of the solid solution TiSxSe2−x

Polycrystalline samples of the solid solution TiSxSe2−x with x varying from 0 to 2 were prepared using direct high temperature reaction of stoichiometric amounts of the elements. Rietveld refinements of powder X-ray diffraction data are consistent with the existence of a full solid solution. High temperature Seebeck coefficient, electrical resistivity and thermal diffusivity measurements were performed on pellets densified by spark plasma sintering. These measurements reveal that along the solid solution the transport properties vary from the rather metallic and p-type character of TiSe2 to the semiconducting and n-type of TiS2. This change of conduction regime is responsible for the peculiar evolutions of transport properties of TiS0.5Se1.5 with increasing temperature that vary somewhat differently than that of the other members of the solid solution. As expected, the disorder generated by the mixed occupancy of the S and Se on the anionic site is responsible for the diminution of the lattice thermal conductivity. A maximum zT above 0.4 at 400 °C is reached for TiS1.5Se0.5.

► CdI2 layered structure as potential thermoelectric material.
► The full solid solution goes from p-type TiSe2 to n-type TiS2.
► Chalcogenides anionic disorder reduces the thermal conductivity.