Synergistic Regulation Of Thermoelectric Properties In SnTe Via Band Engineering And Endotaxial Nanostructures

The toxicity of lead in the traditional thermoelectric material lead telluride PbTe poses a great threat to the environment and limits the further application of lead-based thermoelectric materials.As a lead-free analog of PbTe,SnTe has become an environmentally friendly alternative to PbTe for power generation applications.However,the thermoelectric performance of pure SnTe is not ideal.Although SnTe systems have been improved through the abovementioned strategies,most high-ZT SnTe thermoelectrics are obtained by either alloying with toxic elements(such as Cd and Hg)or adopting high-content doping(such as Ge,Mn,and Cd).Generally,low levels of precious metal doping can effectively reduce the cost of thermoelectric devices.Moreover,the endotaxial nanostructures are very effective in scattering phonons and reducing thermal conductivity.In this context,this article takes SnTe thermoelectric materials as the research object,and through a facile and controllable one-step method combined with spark plasma sintering,in the first step,low-content non-toxic elements Ge and Sb co-doping are used to introduce energy band convergence in the SnTe system,greatly improved the Seebeck coefficients and power factors of materials;In the second step,we found that the lattice thermal conductivity of the material still has room for improvement,and a phase separation strategy is proposed to introduce the endotaxial Cu₂Te nanostructures into the SnTe co-doping system,and finally the high-thermoelectric-performance,low-cost and environmentally friendly polycrystalline SnTe thermoelectric material are successfully prepared.The contents of this dissertation are concluded as follows:1.Through a facile and controllable one-step method combined with spark plasma sintering,low-content non-toxic elements Ge and Sb are doped in SnTe.It is found that in Ge and Sb co-doping system,Sb³⁺ion is substituted for Sn²⁺to introduce a large amount of excess electrons and the intrinsic high tin hole concentration is compensated,so that the energy band convergence is introduced and the band structure is improved and modified,leading to the enhancement of Seebeck coefficients and the power factors;The dual-atom point-defect scattering,which enhances the phonon scattering and Ge off-centering,which causes more local interactions with acoustic phonons,lead thermal conductivity of the material to reduce.As a result,the lattice thermal conductivity of Sn_0.92Ge_0.04Sb_0.04Te sample was reduced to 1.01 W m^-1 K^-1 at 873 K.Because of the two favorable factors in the performance of electric and thermal transfer,the highest ZT value of 0.84 at 873 K is obtaines in Sn_0.92Ge_0.04Sb_0.04Te sample,and increased by more than 150%compared with the ZT of the pure SnTe(0.33).The findings show that SnTe systems can achieve high thermoelectric performance while maintaining low cost and environmental friendliness and thus provide a new perspective for being able to carry out practical applications.2.Through a facile and controllable one-step method combined with spark plasma sintering,a phase separation strategy is used to introduce the endotaxial Cu₂Te nanostructures into the SnTe co-doping system by a facile and controllable one-step method combined with spark plasma sintering.It was found that the endotaxial Cu₂Te nanostructures were successfully introduced into the Ge and Sb co-doped SnTe.Endotaxial Cu₂Te nanostructures are more effective in scattering phonons and reducing thermal conductivity than previously reported interstitials defects.For Sn_0.92Ge_0.04Sb_0.04Te-5%Cu₂Te,the lattice thermal conductivity was significantly reduced to 0.27 W m^-1K^-1 at 873 K and an ultralow lattice thermal conductivity was obtained.Therefore,an outstanding thermoelectric ZT of 1.5 was achieved at 873 K.Compared with pure SnTe,the high ZT of Sn_0.92Ge_0.04Sb_0.04Te-5%Cu₂Te was increased by more than 350%and possesses high repeatability and stability.This study is the first to achieve a high ZT in SnTe without high-content doping and environmentally harmful elements.The high performance improves the prospects of realizing very efficient thermoelectric devices with SnTe as a p-type leg.