Synthesis, powder X‐ray diffraction, and ab initio study of TlInSe${}_2$: Analysis of Its thermoelectric properties

In this paper, the authors report first‐principles calculations of the Seebeck coefficient in TlInSe${}_2$. Experimental measurements demonstrate that TlInSe${}_2$ is characterized by giant values of the Seebeck coefficient at the temperature region of 320–430 K. To get insight on significant enhancement of Seebeck coefficient under temperature changing the density functional theory (DFT) and the Boltzmann transport equation are applied to calculate the semiclassical transport coefficients for TlInSe${}_2$ and its constructed models. The molecular dynamic simulations of 2 × 2 × 2 and 1 × 1 × 8 superlattices of TlInSe${}_2$, the TlInSe${}_2$_118a, TlInSe${}_2$_118b, TlInSe${}_2$_222a, TlInSe${}_2$_222b structures are performed to study their behavior in both "bulk" and "chain – like" modes. It is found that the distortions of InSe${}_4$ tetrahedra and displacements of Tl atom lead to formation of Tl–Se covalent bonds. The "bulk" TlInSe${}_2$_222b compound possesses the maximum value of Seebeck coefficient and (ZT)${}_{max}$ in comparison with another studied compounds. The hybridization of Se and Tl orbitals near the top of valence band and hybridization of the Se, Tl, and In orbitals in conduction band may lead to increasing of Seebeck coefficient in TlInSe${}_2$ at 425 K. (© 2019 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)