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<p>We performed a thorough first-principles study of Mg<sub>2</sub>TeS and Mg<sub>2</sub>TeSe, including structural, electronic, optical, and transport features. Structurally, both compounds have a trigonal R3m structure with different polyhedral designs. Mg<sub>2</sub>TeSe shows a larger equilibrium volume, and thermodynamic parameter (E<sub>coh</sub> ≈ − 3.65&#xa0;eV/atom for Mg<sub>2</sub>TeS and − 3.79&#xa0;eV/atom for Mg<sub>2</sub>TeSe; ΔHf ≈ − 2.17 and − 2.53&#xa0;eV/atom) indicate both are energetically valuable, with Mg<sub>2</sub>TeSe relatively more stable. Electronically, these materials are found as direct band gap semiconductors. The WC-GGA underestimated band gaps with values of (≈ 1.49&#xa0;eV and 1.83&#xa0;eV), which were then corrected by SOC + TB-mBJ with values of (≈ 2.64&#xa0;eV and 2.71&#xa0;eV) for Mg<sub>2</sub>TeS and Mg<sub>2</sub>TeSe, respectively. Projected density of states indicates valence bands are dominated by Te states and conduction bands by Mg states, and replacing S with Se narrows the band gap while shifting density of states toward the Fermi level. Optically, notable interband responses occur with ε<sub>1</sub>(ω) and refractive index maxima between 5.0 and 5.5&#xa0;eV, ε<sub>2</sub>(ω) peaks ≈ 5.5–5.8&#xa0;eV, static refractive index ≈ 2.1, absorption peaking at ≈ 4.0&#xa0;eV (Mg<sub>2</sub>TeS) and ≈ 3.5&#xa0;eV (Mg<sub>2</sub>TeSe), low static reflectivity (~ 0.12), and plasmonic loss peaks near 17.0 and 16.0&#xa0;eV. The transport results demonstrate modest Seebeck at low T, electrical conductivity σ/τ ≈ 2.27 × 10<sup>19</sup> and 2.24 × 10<sup>19</sup> (Ω·m·s)<sup>−1</sup> at 300&#xa0;K, lower lattice thermal conductivity and a greater power factor for Mg₂TeSe, and ZT increasing with temperature to maxima ≈ 0.32 (Mg<sub>2</sub>TeS) and 0.24 (Mg<sub>2</sub>TeSe) at 1200&#xa0;K, illustrating Mg<sub>2</sub>TeSe’s promise for thermoelectric applications.</p>

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Exploring multifunctional properties of ternary chalcogenides for advanced energy applications

  • 期刊论文

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  • 发表日期：

    2025年11月24日

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  • Muhammad Salman Khan,
  • Mohannad Al-Hmoud,
  • Sarah Nabirye,
  • Siti Maisarah Aziz

摘要

We performed a thorough first-principles study of Mg2TeS and Mg2TeSe, including structural, electronic, optical, and transport features. Structurally, both compounds have a trigonal R3m structure with different polyhedral designs. Mg2TeSe shows a larger equilibrium volume, and thermodynamic parameter (Ecoh ≈ − 3.65 eV/atom for Mg2TeS and − 3.79 eV/atom for Mg2TeSe; ΔHf ≈ − 2.17 and − 2.53 eV/atom) indicate both are energetically valuable, with Mg2TeSe relatively more stable. Electronically, these materials are found as direct band gap semiconductors. The WC-GGA underestimated band gaps with values of (≈ 1.49 eV and 1.83 eV), which were then corrected by SOC + TB-mBJ with values of (≈ 2.64 eV and 2.71 eV) for Mg2TeS and Mg2TeSe, respectively. Projected density of states indicates valence bands are dominated by Te states and conduction bands by Mg states, and replacing S with Se narrows the band gap while shifting density of states toward the Fermi level. Optically, notable interband responses occur with ε1(ω) and refractive index maxima between 5.0 and 5.5 eV, ε2(ω) peaks ≈ 5.5–5.8 eV, static refractive index ≈ 2.1, absorption peaking at ≈ 4.0 eV (Mg2TeS) and ≈ 3.5 eV (Mg2TeSe), low static reflectivity (~ 0.12), and plasmonic loss peaks near 17.0 and 16.0 eV. The transport results demonstrate modest Seebeck at low T, electrical conductivity σ/τ ≈ 2.27 × 1019 and 2.24 × 1019 (Ω·m·s)−1 at 300 K, lower lattice thermal conductivity and a greater power factor for Mg₂TeSe, and ZT increasing with temperature to maxima ≈ 0.32 (Mg2TeS) and 0.24 (Mg2TeSe) at 1200 K, illustrating Mg2TeSe’s promise for thermoelectric applications.