Kailash Chandra Bhamu

Explainable machine learning and first-principles calculations identify stable fluoride and oxyfluoride thermoelectrics with ultralow lattice thermal conductivity and predicted ZT values up to 5.38 at 950 K.

We investigated the structural, mechanical, and thermoelectric properties of lead‐free vacancy‐ordered double halide perovskites Cs ₂ TeX ₆ (X = Cl, Br, I) using first‐principles calculations combined with semiclassical Boltzmann transport theory. The electronic structure was calculated using the PBE functional including spin–orbit coupling (SOC), and the bandgaps were corrected using the HSE06 hybrid functional through a scissor operator approach. The calculated bandgaps are 3.27, 2.50, and 1.55 eV for Cs ₂ TeCl ₆ , Cs ₂ TeBr ₆ , and Cs ₂ TeI ₆ , respectively. The electronic band structure of Cs ₂ TeI ₆ exhibits a coexistence of light and heavy bands near the band edges, which favors a balance between a high Seebeck coefficient and enhanced electrical conductivity. As a result, Cs ₂ TeI ₆ shows superior thermoelectric performance with a maximum figure of merit ZT 1.97 at 800 K for an electron concentration of 3.35 10 . The high ZT primarily originates from its low lattice thermal conductivity ( 0.41 W at 300 K), arising from weak Te‐I bonding, localized TeX ₆ octahedra, and enhanced phonon scattering associated with transverse acoustic and optical phonon modes. These findings highlight Cs ₂ TeI ₆ as a promising candidate for thermoelectric energy conversion.

The structural flexibility and unique bonding of antiperovskites Mg ₃ AsX ₃ (X = Cl, Br) make them promising for thermoelectric (TE) applications. First‐principles density functional theory using the generalized gradient approximation‐Perdew–Burke–Ernzerhof functional was employed to investigate their structural, electronic, and TE properties. Thermal, dynamical, and mechanical stability were confirmed through ab initio molecular dynamics simulations at 500 K, phonon dispersion, and elastic constant analyses. PBE + SOC calculations show that Mg ₃ AsBr ₃ and Mg ₃ AsCl ₃ are indirect bandgap semiconductors with gaps of 1.23 eV and 2.07 eV, respectively. Sharp peaks near the Γ point, arising from orbital degeneracy at the band edges, increase carrier effective mass and enhance the Seebeck coefficient, reaching 727 μV/K for Mg ₃ AsCl ₃ . Covalent bonding, supported by electron localization function analysis and negative Cauchy pressure, influences lattice dynamics and suppresses thermal conductivity. High electron mobility leads to electrical conductivities of S/m (Mg ₃ AsBr ₃ ) and S/m (Mg ₃ AsCl ₃ ). Notably, Mg ₃ AsBr ₃ exhibits a promising TE figure of merit of ∼0.846 for p ‐type carriers, approaching benchmark values.

We investigate the structural, mechanical, and thermoelectric properties of lead-free double halide perovskites Cs2TeX6 (X = Cl, Br, I) using first-principles calculations and semiclassical Boltzmann transport theory. The HSE06 band gap is incorporated using the scissor correction method along with PBE calculated electronic band structures including spin orbit coupling to accurately predict transport properties. The band gap values are 3.27, 2.50, and 1.55 eV for Cs2TeX6 (X = Cl, Br, I), respectively. The coexistence of heavy and light bands in the Cs2TeI6 band structure helps mitigate the trade-off between the Seebeck coefficient and electrical conductivity. Among these systems, Cs2TeI6 exhibits superior performance with a ZT of 1.97 at 800 K and an electronic concentration of 3.35 x 1019 cm-3. Such a high ZT at relatively low carrier concentration arises from high electrical conductivity combined with low lattice thermal conductivity. The lattice thermal conductivity of Cs2TeI6 is found to be 0.41 W m-1 K-1 at room temperature. This low lattice thermal conductivity is attributed to weak Te-I bonding and non-uniform out-of-phase displacement of Cs atoms. The presence of local TeX6 units together with weak bonds strongly resists heat conduction, leading to significant suppression of lattice thermal conductivity. In particular, transverse acoustic phonons and optical phonons play a key role in limiting lattice thermal conductivity. These results identify Cs2TeI6 as a promising candidate for high performance thermoelectric applications.

We investigate the structural, mechanical, and thermoelectric properties of lead-free double halide perovskites Cs2TeX6 (X = Cl, Br, I) using first-principles calculations and semiclassical Boltzmann transport theory. The HSE06 band gap is incorporated using the scissor correction method along with PBE calculated electronic band structures including spin orbit coupling to accurately predict transport properties. The band gap values are 3.27, 2.50, and 1.55 eV for Cs2TeX6 (X = Cl, Br, I), respectively. The coexistence of heavy and light bands in the Cs2TeI6 band structure helps mitigate the trade-off between the Seebeck coefficient and electrical conductivity. Among these systems, Cs2TeI6 exhibits superior performance with a ZT of 1.97 at 800 K and an electronic concentration of 3.35 x 10^19 cm^-3. Such a high ZT at relatively low carrier concentration arises from high electrical conductivity combined with low lattice thermal conductivity. The lattice thermal conductivity of Cs2TeI6 is found to be 0.41 W m^-1 K^-1 at room temperature. This low lattice thermal conductivity is attributed to weak Te-I bonding and non-uniform out-of-phase displacement of Cs atoms. The presence of local TeX6 units together with weak bonds strongly resists heat conduction, leading to significant suppression of lattice thermal conductivity. In particular, transverse acoustic phonons and optical phonons play a key role in limiting lattice thermal conductivity. These results identify Cs2TeI6 as a promising candidate for high performance thermoelectric applications.