Transport Properties of an Intermetallic with Pseudo-hollandite Structure as a Potential Thermoelectric Material: The Example of TlxCr5Se8

The transport properties of TlxCr5Se8 pseudo-hollandite have been investigated, from 2 up to 800 K. A semiconducting behavior is observed from 200 down to 2 K, with a transition observed at T ∼ 43 K, at the antiferromagnetic transition. Above 200 K, small values of ρ are obtained, close to 10 mΩ·cm at 800 K. The Seebeck coefficient continuously increases in this range of temperature, reaching 300 μV/K at 800 K. Moreover, the thermal conductivity of this low dimensional structure is small, leading to a figure of merit ZT = S2T/(ρκ) = 0.5 at 800 K. All the electronic transport properties can be fitted by a standard Boltzmann equation, with a large scattering parameter (r = 3/2, characteristic of diffusion by ionized impurities). The combination of small thermal conductivity, large scattering parameter, and low concentration of carriers (4.5 × 1019 cm–3) is at the origin of this large ZT.