Low lattice thermal conductivity induced by antibonding sp-hybridization in Sb2Sn2Te6 monolayer with high thermoelectric performance: A First-principles calculation

Abstract

Utilizing first-principles calculations and Boltzmann transport theory, the crystal structure, thermal and electronic transport, and thermoelectric (TE) properties of the Sb₂Sn₂Te₆ monolayer are evaluated in the current work. The Sb₂Sn₂Te₆ monolayer is an indirect band gap semiconductor with a band gap of 0.81 eV using the Heyd-Scuseria-Ernzerhof (HSE06) functional in combination with the spin-orbital coupling (SOC) effect. The antibonding states formed by the hybridization of Sb s orbital with Te p orbital near the Fermi level weaken the bonding strength of the Sb-Te bond, leading to significant anharmonicity and low group velocity. Thus, a low lattice thermal conductivity of 2.77 W/m K is achieved for the Sb₂Sn₂Te₆ monolayer at 300 K. The band convergence and multivalley characteristics in the electronic band structure give birth to the enhancements of Seebeck coefficients and carrier mobilities, resulting in a substantial power factor of 76.69 μW/mK² at 300 K under the carrier concentration of 3.20×10²⁰ cm⁻³. An optimal figure of merit (ZT) of 2.37 at 900 K for the Sb₂Sn₂Te₆ monolayer is obtained under the carrier concentration of 2.42×10²⁰ cm⁻³. The present work not only provides fundamental insights into the correlation between the antibonding state, chemical bond and lattice thermal conductivity in Sb₂Sn₂Te₆ monolayer, but also elaborates on the promising prospect of the Sb₂Sn₂Te₆ monolayer in the TE application with high conversion efficiency.