DFT study of Structural, Mechanical, Thermodynamical, Electronic and
Thermoelectric properties of PdTiZ (Z = Ge and Pb) half Heusler
compounds
Abstract
A first principle investigation of structural, mechanical,
thermodynamical, electronic and thermoelectric properties of PdTiZ (Z =
Ge and Pb) was carried out using plane wave pseudopotential (PP-PW)
method. The exchange-correlation was considered with the generalized
gradient approximation of Perdew-Burke-Ernzerhof (PBE-GGA). The energy
band structure of the sample material exhibited semiconducting energy
band structure with indirect energy band gaps of 0.66 eV and 0.387 eV in
PdTiGe and PdTiPb respectively with density of states being mainly
dominated by the p state of Z and d states of Ti atom around the
vicinity of the Fermi energy level. The sample compounds were found to
be mechanically stable in their non-magnetic cubic phase. PdTiGe was
found to be harder and stiffer than PdTiPb. The positive phonon modes of
the compounds predicted their dynamical stabilities. Thermodynamic study
revealed that pressure has a negative effect on heat capacity whereas
Debye temperature increases with enhanced pressure in both the sample
compounds. The thermoelectric properties of the sample compounds
predicted that p-type nature of the sample compounds possess better
thermoelectric performance. The room temperature Seebeck coefficient
values are found to be 98.73 µV/K and 94.82 µV/K for PdTiGe and PdTiPb,
respectively, whereas they reflected the S values of 245.73 µV/K and
218.77 µV/K at 1200 K at n = 1021 cm-3. The lowest value of lattice
thermal conductivity (K_L) of 2.28 W/m-K and 0.98 W/m-K was observed
for PdTiGe and PdTiPb respectively. The optimum dimensionless figure of
merit of 0.66 (1200 K) and 0.64 (1000 K) were found for p-type PdTiGe
and PdTiPb, respectively at optimum carrier concentration.