First principles calculations to investigate Li-based quaternary Heusler compounds LiHfCoX (X = Ge, Sn) for thermoelectric applications

Abstract

In the last few decades, the varieties of semiconductors have been explored for electronic and thermoelectric applications. As per such motivations, in present research work, the investigation of two quaternary Heuslers (QHs) i.e. LiHfCoGe and LiHfCoSn (having semiconducting nature) have been carried out for structural, electronic, vibrational, elastic, mechanical, thermodynamical and thermoelectric properties within the computational approach of Density Functional Theory (DFT) and Boltzmann transport equations. Both the alloys are enriched with p-type semiconducting nature along with the dynamical stability that crystallizes in FCC cubic structure of F-43m space group. The high Seebeck coefficient values are like of excellent fundamental thermoelectric character. The high melting points expose their scope in the high-temperature regions. Even the figure of merit (ZT) is of average range but better than many of the compounds of the same kind for the constant relaxation time approximations however all the thermoelectric properties are also measured and presented at the calculated relaxation time by deformation potential theory. The effect of spin orbit coupling is also studied on the thermoelectric properties. The practical utilization of the materials can be evaluated from the elastic and mechanical properties that are favorable to manufacturing efficient and reliable Thermoelectric Modules in high-temperature range. A sufficient discussion of thermodynamic properties is carried out to give an image of the internal lattice thermal vibrations. It is worth mentioning that the present research work has the standards to be discussed in experimental research areas of energy conversion techniques.

First-principles investigation of the electronics, optical, mechanical, thermodynamics and thermoelectric properties of Na based Quaternary Heusler alloys (QHAs) NaHfXGe (X = Co, Rh, Ir)

“…Figure 2, shows that the systems under our investigation crystallizes in T-3 configuration which is analogous and closely related to Li-based QHA studied by Kaur et al [23]. In this theoretical study they have reported the T-3 configuration is the most stable atomic arrangement for LiHfCoGe and LiHfCoSn with corresponding optimized lattice constants 6.059 Å and 6.290 Å.…”

“…In our case, the corresponding number of valence electrons contributed from the individual Na, Hf, Co, Rh, Ir, and Ge-atoms are 1, 4, 9, 9, 9, and 4 respectively, leading to M t = 0 for NaHfXGe compounds. Similar to those reported for the Li-based QHA [23]. The semi-conducting nature of QHAs are proven by performing the spin-polarized calculation based on the GGA formalism where the total magnetic moment is founf tpo be 0 µ B .…”

“…Insight into the general distribution of states at different energy levels and the charge transfer upon formation of bonds are gained through the analysis of DOS and Bader charge calculation. From the calculated DOS plotted in figure 4, it is comprehensible that in the case of X = Co and Rh, the main contributing states near the Fermi level (E F ) are from a strong hybridization between Hf-d, Co-d, and Ge-p states which is analogous to LiHfCoGe/Sn [23]. Moreover, when X = Ir, the DOS plot reveals that the metallic electronic properties are mostly dominated by the Hf-d states.…”

“…To the best of our knowledge, only a few theoretical works conducted on QHAs for their TE performance investigation have shown ZT approaching the benchmark value. From the earlier theoretical investigation led by Haleoot and Hamad [15] it was found that the QHA CoFeYGe (Y = Ti, Cr) possessed a maximum ZT of 0.64 and 0.57 at 850 K, respectively, and also from the work of Kara et al [20] on CrVNbZn it was encountered that highest value of ZT≃0.8 between 360-750 K. Recently, a work led by Kaur et al [23] had shown that for Li based QHA compounds LiHfCoX (X = Ge, Sn) the maximum ZT reported were 0.61 and 0.59 at 1600 K, respectively.…”

Theoretical insights into the structural, optoelectronic, thermoelectric, and thermodynamic behavior of novel quaternary LiZrCoX (X = Ge, Sn) compounds based on first-principles study

“…Several theoretical as well as experimental studies have been conducted recently to gain insight into the electronic behavior as well as the thermoelectric behavior of these systems. [10][11][12][13][14] First-principles calculations were utilised by Haleoot et al (2020) to analyse the exceptional thermoelectric and thermodynamic properties of the Quaternary Heusler (QH) compounds CoFeYGe (Y = Ti, Cr). 15 Density functional theory (DFT) has been used to examine another novel quaternary Heusler compound, CrVNbZn, which has the space group 216 (of cubic geometry) and shows maximum ZT = 0.79 in the wide temperature range of 260 K to 480 K as well as excellent electronic and magnetic properties.…”