High thermoelectric figure of merit and thermopower of HfTe₅ at room temperature

We predict a high thermoelectric efficiency of HfTe₅, based on the first-principles calculations of the electronic structure and thermal conductivity, and the transport coefficients obtained by using the semi-classical Boltzmann transport theory in a wide temperature and carrier concentration range. The lattice thermal conductivity is calculated based on the Slack model and the result is in good agreement with the experimental value. The results of all the thermoelectric transport coefficients demonstrate anisotropic characteristics with the obvious small values along with the b direction. The figure of merit ZT computed with a temperature-dependent relaxation time can reach 2.68 along with the c direction of the n-type HfTe₅ at 300 K and an optimal carrier concentration of 5.80 × 10¹⁹ cm⁻³. The Seebeck thermopower coefficients are between 100 and 300 μV K⁻¹ at the optimal carrier concentration, but can reach nearly 1000 μV K⁻¹ at low concentration. Therefore, HfTe₅ could achieve high thermoelectric performance at room temperature by controlling the transport direction and carrier concentration. (paper)