DFT study of structural, mechanical, thermodynamic, electronic, and thermoelectric properties of new 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) were carried out using the plane‐wave pseudopotential (PP‐PW) method. The exchange‐correlation between the electrons was considered with the generalized gradient approximation of Perdew‐Burke‐Ernzerhof (PBE‐GGA). The energy band structure of the sample materials shows that it is a semiconductor with indirect energy band gaps of 0.66 eV and 0.387 eV in PdTiGe and PdTiPb, respectively, with the density of states being mainly dominated by the p states of Z and d states of Ti atom in the vicinity of the Fermi energy level. The sample compounds were found to be mechanically and dynamically stable in their non‐magnetic cubic phase. PdTiGe was found to be harder and stiffer than PdTiPb. The 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 (S) values were found to be 98.73 μV/K and 94.82 μV/K for PdTiGe and PdTiPb, respectively, whereas S values of 245.73 μV/K and 218.77 μV/K at 1200 K at n = 1021 cm−3. The lowest values of lattice thermal conductivity (KL) of 2.28 W/m‐K and .98 W/m‐K were observed for PdTiGe and PdTiPb, respectively. The optimum dimensionless figure of merits of .66 (1200 K) and .64 (1000 K) were found for p‐type PdTiGe and PdTiPb, respectively, at optimum carrier concentration.

Machine Learning-Based Predictions of Power Factor for Half-Heusler Phases

“…FFFPñ Some electronic properties of the 15 novel compounds were already discussed in the literature, e.g., the band gap of TiPdPb in terms of potential TE applications [38] and its lattice thermal conductivity (theoretical analysis) [7,8]. The DFT (GGA) study by Kalita et al [39] on TiPdPb resulted in a relatively low value of the lattice thermal conductivity (0.98 W/mK) and a figure of merit (ZT) of 0.64 at 1000 K in the p-type regime. Similar value of ZT was obtained for TiPdGe, but at high temperature [39].…”

“…The DFT (GGA) study by Kalita et al [39] on TiPdPb resulted in a relatively low value of the lattice thermal conductivity (0.98 W/mK) and a figure of merit (ZT) of 0.64 at 1000 K in the p-type regime. Similar value of ZT was obtained for TiPdGe, but at high temperature [39]. However, PF p GGA of these systems was not explicitly discussed.…”

Machine Learning-Based Predictions for Half-Heusler Phases

“…It is crucial to note that the further training of ML models is based on systems that are expected to be stable and feasible to be synthesized. Some properties of the systems presented in Table 1 were already investigated in the literature, e.g., the cubic lattice parameters (a) of 5.964 and 6.327 Å were theoretically calculated for TiPdGe and TiPdPd, respectively [36]. The reported values of the bulk modulus (B) were 132.41 and 104.14 GPa, while band gaps (E g ) were 0.66 and 0.386 eV (PBE-GGA), for the Ge-and Pb-bearing systems.…”