Synergetic Enhancement of Power Factors and Suppression of Lattice Thermal Conductivities via Biaxial Strain in ScAgSe$_2$ and TmAgTe$_2$
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2025
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| _version_ | 1866915493921685504 |
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| author | Xiong, Wu Han, Zhongjuan Xia, Zhonghao Yang, Zhilong He, Jiangang |
| author_facet | Xiong, Wu Han, Zhongjuan Xia, Zhonghao Yang, Zhilong He, Jiangang |
| contents | The challenge of achieving high thermoelectric (TE) performance is mainly from the entanglement among Seebeck coefficient ($S$), electrical conductivity ($σ$), and lattice thermal conductivity ($κ_{\mathrm{L}}$). In this work, we propose a synergetic strategy of enhancing power factor (PF, $S^2σ$) and suppressing $κ_{\mathrm{L}}$ by applying a biaxial tensile strain in two silver chalcogenides ScAgSe$_2$ and TmAgTe$_2$ with TlCdS$_2$-type structure. The forbidden $p$-$d$ orbital coupling at the $Γ$ point and allowed $p$-$d$ orbital coupling at the A point and the middle of $Λ$ line leads to high electronic band dispersion along the $Γ$-A direction and a high-degeneracy valence band valley ($Λ_2$). The elongation of the Ag-Se bond under tensile strain weakens the orbital coupling between Ag-$d$ and Se/Te-$p$ orbitals and reduces the band energy at the A point, which aligns the valence band and achieving a high band degeneracy. Concurrently, the weaker Ag-Se/Ag-Te bond under a small tensile strain leads to lower phonon group velocity and strong three- and four phonon scatterings, leading to lower $κ_{\mathrm{L}}$. Our first-principles calculations combined with electron-phonon coupling analysis as well as phonon and electron Boltzmann transport equations show that applying a 3\% (2\%) tensile strain can enhance the PF along the $c$-axis of ScAgSe$_2$ (TmAgTe$_2$) by 243\% (246\%) at a carrier concentration of 3$\times$10$^{20}$ cm$^{-3}$ and reduce the $κ_{\mathrm{L}}$ by 37\% (26\%) at 300 K. Consequently, 2 $\sim$ 4 times of $ZT$ enhancement is obtained by 3\% or 1\% tensile strain in ScAgSe$_2$ (TmAgTe$_2$) at 300 K, achieving a maximum $ZT$ of 3.10 (3.62) at 800 K. Our material design strategy based on molecular orbital analysis reveals an effective route to boosting TE performance, and can be extended to other systems as well. |
| format | Preprint |
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arxiv_https___arxiv_org_abs_2509_11051 |
| institution | arXiv |
| publishDate | 2025 |
| record_format | arxiv |
| spellingShingle | Synergetic Enhancement of Power Factors and Suppression of Lattice Thermal Conductivities via Biaxial Strain in ScAgSe$_2$ and TmAgTe$_2$ Xiong, Wu Han, Zhongjuan Xia, Zhonghao Yang, Zhilong He, Jiangang Materials Science The challenge of achieving high thermoelectric (TE) performance is mainly from the entanglement among Seebeck coefficient ($S$), electrical conductivity ($σ$), and lattice thermal conductivity ($κ_{\mathrm{L}}$). In this work, we propose a synergetic strategy of enhancing power factor (PF, $S^2σ$) and suppressing $κ_{\mathrm{L}}$ by applying a biaxial tensile strain in two silver chalcogenides ScAgSe$_2$ and TmAgTe$_2$ with TlCdS$_2$-type structure. The forbidden $p$-$d$ orbital coupling at the $Γ$ point and allowed $p$-$d$ orbital coupling at the A point and the middle of $Λ$ line leads to high electronic band dispersion along the $Γ$-A direction and a high-degeneracy valence band valley ($Λ_2$). The elongation of the Ag-Se bond under tensile strain weakens the orbital coupling between Ag-$d$ and Se/Te-$p$ orbitals and reduces the band energy at the A point, which aligns the valence band and achieving a high band degeneracy. Concurrently, the weaker Ag-Se/Ag-Te bond under a small tensile strain leads to lower phonon group velocity and strong three- and four phonon scatterings, leading to lower $κ_{\mathrm{L}}$. Our first-principles calculations combined with electron-phonon coupling analysis as well as phonon and electron Boltzmann transport equations show that applying a 3\% (2\%) tensile strain can enhance the PF along the $c$-axis of ScAgSe$_2$ (TmAgTe$_2$) by 243\% (246\%) at a carrier concentration of 3$\times$10$^{20}$ cm$^{-3}$ and reduce the $κ_{\mathrm{L}}$ by 37\% (26\%) at 300 K. Consequently, 2 $\sim$ 4 times of $ZT$ enhancement is obtained by 3\% or 1\% tensile strain in ScAgSe$_2$ (TmAgTe$_2$) at 300 K, achieving a maximum $ZT$ of 3.10 (3.62) at 800 K. Our material design strategy based on molecular orbital analysis reveals an effective route to boosting TE performance, and can be extended to other systems as well. |
| title | Synergetic Enhancement of Power Factors and Suppression of Lattice Thermal Conductivities via Biaxial Strain in ScAgSe$_2$ and TmAgTe$_2$ |
| topic | Materials Science |
| url | https://arxiv.org/abs/2509.11051 |