| Summary: | New, nontoxic and earth-abundant materials for heat-energy interconversion are urgently required to mitigate the over-reliance on finite fossil fuels supply. Herein, using ab initio quantum mechanical calculations and Boltzmann theory, optimization of thermoelectric performances instable, mechanically robustCm-SnSSe and P3m1-SnSeS phases was performed. These phases exhibit an intrinsically low thermal conductivity of ~1.00 W m−1 K−1 at room temperature. Beyond 400 K, both phases display satisfactory thermoelectric performances, namely figure of merit ZT > 0.7 and power factor PF > 3.0 mW K−2 m−1. Better performances were obtained through holes doping at 1020 cm−3 concentration, where their ZT values reach 0.9 at 500 K and fluctuate minimally over broad temperature plateau, retaining the high PF over 3.0 mWK−2 m−1. Evolution into layered structure is also possible, with the calculated p-type doping of P3m1-SnSSe monolayer displaying decent ZT ~ 0.7 and very high PF > 6.0 mWK−2 m−1 beyond 300 K. In bulk form, the study specimens display superior machinability and mechanical properties, as evidenced by the approximately 8-fold increase in their Vickers hardness when compared to PbTe and Bi2Te3 materials, while maintaining their plasticity characteristic. The computed E2D of 55.50 N m−1 is relatively low, which means Sn-S-Se alloy remains ductile when progressing to 2D state. Biaxial strain-induced results show enhanced anharmonicity phonon scattering and thermopower increment, enabling maximum ZT ~ 1.0 and PF > 7.0 mW m−1 K−2 to be achieved in the appealing industrial waste heat akin 373 ≤ T ≤ 773 K range under 10% tensile strain. © 2020 John Wiley & Sons Ltd
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