Achieving both low lattice thermal conductivity and high hardness by the design of bonding structure

Bonding engineering and high entropy effect have a profound impact on lattice vibration and structural stability, which can be used to improve the lattice thermal conductivity and mechanical properties of material. Sb_Sn, V_Sn and Se_Te were simultaneously introduced in the SnTe system via the multi-element alloying design of (SnTe)_x(Sb₂Se₃), which was produced by vacuum melting and spark plasma sintering technology. The above defects induce abundant lattice distortion and mass fluctuations, which can be stabilized in the high entropy system. Lattice distortion and mass fluctuations increase phonon scattering, resulting in reduced lattice thermal conductivity from 2.42 Wm⁻¹K⁻¹ for pure SnTe alloy to 1.15 Wm⁻¹K⁻¹ for (SnTe)₁₀(Sb₂Se₃) at 323K. The calculations of -pCOHP and charge density verify that soft bonds and oscillation space exist in the system, which reveals the origin of the decrease in thermal conductivity from the perspective of bonding and the heat consumption caused by oscillation. With Sb₂Se₃ alloying, material hardness greatly increased from 82.7 HV for pure SnTe alloy to 165.7 HV for (SnTe)₁₀(Sb₂Se₃). The enhancement of hardness can be ascribed to two factors. One is an increase in average bond strength, the other is from the skeleton structure formed by stronger bonds. The accurate design of bonding structure provides an effective way to simultaneously obtain high hardness and low lattice thermal conductivity.