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<p>Using first-principles density functional theory (DFT), we investigate the structural, electronic, mechanical, and thermoelectric properties of monolayer HfX<sub>2</sub> (X = S, Se) in both the T and H polymorphs. Formation-energy calculations confirm that the T phase is energetically favorable, with values of –5.57 eV (HfS<sub>2</sub>) and –4.83 eV (HfSe<sub>2</sub>), compared with –4.91 eV and –4.30 eV for the H phase. Electronic structures obtained using the Tran–Blaha modified Becke–Johnson (TB-mBJ) potential reveal indirect band gaps of 1.93 eV and 1.68 eV for T- and H-HfS<sub>2</sub>, respectively, and 1.12 eV and 1.10 eV for T- and H-HfSe<sub>2</sub>. All systems satisfy the two-dimensional Born mechanical stability criteria and display nearly isotropic elastic behavior. Thermoelectric analysis shows pronounced phase and carrier-type dependencies: the T phase exhibits excellent n-type transport, achieving thermoelectric figure of merit values up to ~ 7 for HfS<sub>2</sub>and ~ 4.5 for HfSe<sub>2</sub> at 900 K, while the H phase is more favorable for p-type transport, reaching thermoelectric figure of merit values as high as ~ 3.5. These results demonstrate that HfX<sub>2</sub> monolayers are mechanically robust, electronically tunable, and highly efficient for thermoelectric energy conversion, underscoring their potential for phase-engineered applications in advanced nanoelectronic and high-temperature thermoelectric devices.</p>

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Structural stability and thermoelectric properties of two-dimensional HfX2 monolayers

  • 期刊论文

  • 发表日期：

    2026年2月2日

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  • Khatir Ouail,
  • Samia Ferahtia,
  • Salima Saib,
  • Nadir Bouarissa

摘要

Using first-principles density functional theory (DFT), we investigate the structural, electronic, mechanical, and thermoelectric properties of monolayer HfX2 (X = S, Se) in both the T and H polymorphs. Formation-energy calculations confirm that the T phase is energetically favorable, with values of –5.57 eV (HfS2) and –4.83 eV (HfSe2), compared with –4.91 eV and –4.30 eV for the H phase. Electronic structures obtained using the Tran–Blaha modified Becke–Johnson (TB-mBJ) potential reveal indirect band gaps of 1.93 eV and 1.68 eV for T- and H-HfS2, respectively, and 1.12 eV and 1.10 eV for T- and H-HfSe2. All systems satisfy the two-dimensional Born mechanical stability criteria and display nearly isotropic elastic behavior. Thermoelectric analysis shows pronounced phase and carrier-type dependencies: the T phase exhibits excellent n-type transport, achieving thermoelectric figure of merit values up to ~ 7 for HfS2and ~ 4.5 for HfSe2 at 900 K, while the H phase is more favorable for p-type transport, reaching thermoelectric figure of merit values as high as ~ 3.5. These results demonstrate that HfX2 monolayers are mechanically robust, electronically tunable, and highly efficient for thermoelectric energy conversion, underscoring their potential for phase-engineered applications in advanced nanoelectronic and high-temperature thermoelectric devices.