Thermoelectric properties of Pb0.833Na0.017(Zn0.85Al0.15)0.15Te-Te composite

Abstract

Nanoparticles of Zn0.85Al0.15Te and Pb0.98Na0.02Te were used as the starting materials to prepare p-type Pb0.833Na0.017(Zn0.85Al0.15)0.15Te-Te composite. The resulting powder was densified, sintered at 380 °C for 24 h in an evacuated and encapsulated ampoule and its thermoelectric transport property was characterized between 300 K and 600 K. At 300 K, the electrical resistivity of Pb0.833Na0.017(Zn0.85Al0.15)0.15Te-Te composite is 4.2 mΩ-cm; exhibits nonmetal-like behavior from 300 K to 375 K and degenerate behavior beyond 375 K. The temperature dependence of the electrical conductivity shows deviation from the normal power law (1/Tδ, δ ≈ 1.84–2.27 for lead chalcogenides), suggesting a sharp drop in mobility in 425 K–600 K which is ascribed to defects, grain boundaries, and potential energy fluctuation due to atomic disorders. The maximum thermopower of Pb0.833Na0.017(Zn0.85Al0.15)0.15Te-Te is 400 μVK-1 at 600 K. Assuming acoustic phonon scattering is the dominant mechanism, we calculate the reduced Fermi energy and Lorenz numbers and compare them with other materials. As-calculated Lorenz numbers is used to estimate the lattice thermal conductivity, which is 11% lower than the total thermal conductivity at 300 K. The lattice thermal conductivity varies as κL ~ T-0.46 proving the presence of grain boundary scattering, dislocations, and alloy scattering. The maximum power factor (P.F.) of 17.7 μWcm-1K-2 is observed at 400 K. Finally, the Pb0.833Na0.017(Zn0.85Al0.15)0.15Te-Te composite exhibits a dimensionless figure-of-merit (zT) of 1.08 at 600 K, demonstrating the material from the current study can compete with many high performing PbTe-based materials.