HIGH PERFORMANCE n-TYPE PbTe-BASED COMPOUNDS FOR THERMOELECTRIC APPLICATIONS

Thermoelectricity links thermal and electrical phenomena and energy conversion from one to the other. The thermoelectric (TE) figure of merit (ZT) is derived from three main transport properties of the material: Seebeck coefficient (α), electrical resistivity (ρ) and thermal conductivity (κ) (ZT= α²Tρ^-1κ^-1).

The main goal of the current research is to develop and examine IV-VI semiconducting compounds known as highly efficient for TE applications within the temperature range of 300-500⁰C. Sodium (Na) and chlorine (Cl) influence on the TE properties of PbTe-based samples were studied. Both experimental research and theoretical calculations based on the Density Functional Theory (DFT) were approached.

Using the theoretical modeling it was shown that while PbTe was doped by Na or Cl p-type and n-type conductivities were observed, respectively, while upon doping of a PbTe matrix by a NaCl molecule, n-type conductivity was observed. While analyzing the obtained theoretical results, it has been noticed that dissociation occurs and the Cl donation of n-type carriers overcomes the Na donation of holes leading to the n-type conductivity as was experimentally observed.

In addition, a considerable improvement of over 30% ZT enhancement was observed upon NaCl doping compared to each of the Na and Cl solely doped compositions, with a maximal ZT_max of ~1.27 at 375⁰C for the 0.3at% NaCl doped composition. These values were achieved mainly due to reduction of the lattice thermal conductivity (k_L).