Exploring the best scenario for understanding the high temperature thermoelectric behaviour of Fe₂VAl

Abstract

Heusler-type Fe2VAl compound is a promising thermoelectric candidate with non-magnetic ground state. The present work investigates the Seebeck coefficient (S) of Fe2VAl in the temperature region 300 to 620 K with the help of experimental and theoretical tools. The experimental value of S is observed ∼ -130 µV/K at 300 K. Afterthat, the magnitude of S decreases gradually as the temperature increases. At T = 620 K, the value of S is found to be ∼ -26 µV/K. In order to understand the behaviour of the experimentally observed S value, the band-structure and density of states calculations are performed by using LDA, PBE, PBEsol, mBJ and SCAN within density functional theory. All the above mentioned exchange-correlation (XC) functionals (except mBJ) predict the semi-metal like behaviour of the compound, whereas the mBJ gives the indirect band gap of ∼ 0.22 eV having the well agreement with experimentally observed value. The temperature dependence of S for Fe2VAl is also calculated with the help of all the five mentioned functionals individually. The best XC functional is investigated for searching the new thermoelectric materials by taking Fe2VAl as a case example through this study. The best matching between experimental and calculated values of S as a function of temperature is observed by setting the mBJ band gap with the band-structure of PBEsol or SCAN. Therefore, the present study suggests that the bandstructure of PBEsol or SCAN with mBJ band gap can be used for searching the new thermoelectric materials.

Unexpected band gap increase in the Fe2VAl Heusler compound

“…These results at low temperature are consistent with DFT calculations (within the LDA or GGA) whose calculated band structures also show a pseudo-gap with the same magnitude. Nevertheless in these calculations an indirect bandgap Eg  -0.1eV (Eg is defined as the energy difference between the bottom of the conduction band and the top of the valence band) is predicted between the high symmetry points  and X in the first Brillouin zone [6][7][8][9][10][11]. According to Do et al [7], the residual density of states (DOS) at the Fermi level is due to the presence of d-states of vanadium constituting the bottom of the conduction band while the valence band maximum is due to d-states of iron.…”

Experimental and computational approaches to study the high temperature thermoelectric properties of novel topological semimetal CoSi

“…Realization of high ZT is really a difficult job. Because S, σ and κ e are deeply interrelated to each other through charge carrier 1,14 . Enhancement of σ without affecting κ e or minimizing κ e without disturbing σ is a terrible job as they involve linear relationship via Wiedeman-Franz law: κ e = LσT , L is Lorenz number.…”

Understanding the Seebeck coefficient of LaNiO3 compound in the temperature range 300-620 K

“…For efficient TE material it is required to maximize it's electrical power factor (S 2 σ), PF as well as to minimize the κ. But, it is difficult to optimize the electrical PF and κ at the same time because there exists a strong correlation among S, σ and κ 6,7 . Many experimental and computational approaches are used to overcome this difficulty.…”