Ag and I co-doping realizes high ZT of In_3.97Pb_0.03Se₃ thermoelectric materials

In this study, the Ag and I co-doping In_3.97Pb_0.03Se₃ (IPS) thermoelectric (TE) materials (IPS-(AgI)_x), which is based on In₄Se₃ TE materials, was prepared successfully by spark plasma sintering (SPS) method. And the effect of doping content on the energy band structure, microstructure and thermoelectric properties of IPS-(AgI)_x has been investigated. The results show that the Ag and I co-doping can increase the carrier concentration of IPS. The grain size of microstructure with nanopores at the grain boundaries in IPS-(AgI)_x is submicron as well as some Pb and Ag nanoparticles can be found in the matrix. After the decomposition of AgI, the Ag and I atoms enter the lattice of In₄Se₃, and the I atoms appear as donor doping, while Ag atoms also exist in the form of interstitial atoms, resulting in increasing of the carrier concentration of IPS-(AgI)_0.03 sample up to 2.44 × 10¹⁹ cm⁻³ at room temperature, which increases the conductivity dramatically without a significant decrease in the Seebeck coefficient. The thermal conductivity of IPS-(AgI)_x is below 0.60 W•m⁻¹K⁻¹ at 723 K due to the scattering effect of multi-scale defects including point defects, nanoparticles, grain boundaries and the nanopores. The maximum ZT value of IPS-(AgI)_x thermoelectric material achieves 1.65, which is the maximum for In₄Se₃ based TE material up to now.