Investigation of the thermoelectric properties of Zintl LiCdSb material from first principles

In this thesis, the structural, electronic, lattice dynamical, and thermoelectric properties of half-Heusler LiCdSb material in the Zintl phase have been calculated using the first principles approach. The calculations are carried out in the density functional theory framework using plane waves and pseudopotentials and generalized gradient approximation. The thermoelectric coefficients were obtained by solving the semi-classical Boltzmann transport equation. As a result of the calculations, the lattice parameters of the LiCdSb material in the Zintl phase with the PBEsol approach were found to be compatible with the existing experimental results and other calculations in the literature. In addition, the elastic stability criteria and phonon dispersion curves of the structure show that the lattice is dynamically stable. It was found that the band gap value decreased significantly by taking into account the spin-orbit interaction in Zintl LiCdSb material and it was concluded that this interaction is important for electronic and thermoelectric properties. Within the rigid-band approximation, thermoelectric properties are calculated under the assumption of constant relaxation time. As a result of the calculations, we predict ZT=1.90 for p-type doping at a carrier concentration of 5x10^19 cm^-3 at 1000 K and ZT=1.97 for n-type doping at a carrier concentration of 2,5x10^19 cm^-3 at 1000 K for LiCdSb material in Zintl phase. This study shows that in half-Heusler materials, which are known for their high power factor, the Zintl phase LiCdSb material with lower thermal conductivity can exhibit a promising thermoelectric performance.