Random aliovalent cations induce synergistic bonding for high thermoelectric performance in NaSn 2 SbSe 4

Le résumé fourni par la source

The dimensionless figure of merit ZT is the key metric for quantifying thermoelectric performance; however, its optimization is inherently limited by the intrinsic coupling between electrical and thermal transport properties. Herein, we perform first-principles calculations using the temperature-dependent effective potential method to investigate cation alloying in SnSe, where Sn2+ ions were randomly substituted by aliovalent cations - specifically Na+ and Sb3+ - a strategy that induces chemical bond synergy in NaSn2SbSe4, effectively decoupling electronic and phonon transport behaviors. Random cation occupation induces a mixed covalent-ionic bonding character, generating local bond-strength fluctuations that act as phonon-scattering centers. Furthermore, localized Sb-Se and Sn-Se antibonding states below the Fermi level correlate with the softening of low-frequency optical phonon branches. Combined with pronounced lattice anharmonicity, this phonon softening significantly enhances four-phonon scattering rates and suppresses the lattice thermal conductivity. Concurrently, aliovalent cation incorporation promotes electron delocalization between Sn-5p and Se-4p orbitals and strengthens covalent bonding character. This modified orbital hybridization alters band dispersion, reducing the hole effective mass while preserving high electrical conductivity in NaSn2SbSe4. The optimal balance between low lattice thermal conductivity and high power factor yields superior thermoelectric performance for NaSn2SbSe4 relative to SnSe across the entire temperature range, with a peak ZT of 0.88 at 800 K. This study establishes chemical bonding engineering as a promising strategy for enhancing thermoelectric performance and provides guidance for exploring high-performance high-entropy thermoelectric materials.

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