Synthesis And Performance Optimization Of SnTe-based Thermoelectric Materials

Thermoelectric materials play an important role in the global sustainable development strategy.Thermoelectric materials can improve the energy utilization by converting waste heat energy to electrical energy directly,or even converting electrical energy to heat energy directly.PbTe-based thermoelectric materials are considered as the best thermoelectric materials in the middle temperature region.However,it will cause serious pollution to the environment because of the Pb's poisonousness.SnTe is a environment friendly material which has the same crystal structure and band structure with PbTe,so SnTe has the high probability of ZT value.Due to the intrinsic Sn vacancy,SnTe has a high p-type carrier concentration,which results in low Seebeck coefficient and high electronic thermal conductivity.What's more,SnTe has high lattice thermal conductivity.These reasons lead to its poor thermoelectric performance.In this paper,we used different synthetic methods and different doping elements to improve the electrical properties of SnTe,and we also controled the microstructure of SnTe to reduce the lattice thermal conductivity,so as to improve the thermoelectric performance of SnTe.The specific contents are as follows:?1?Through exploring the SPS sintering process,it was found that the best SPS sintering temperature of SnTe is 723 K-773 K.By combining solid-phase synthesis with SPS sintering method,we synthesized Sn_1-xAg_xTe samples.The point defect and AgTe₃precipitated phase caused by Ag doping could strengthen phonon scattering and reduce lattice thermal conductivity,which ultimately enhanced the ZT value of Sn_1-xAg_xTe samples.?2?We synthesized Sn_1-xMg_x/2Ca_x/2Te samples by integrating solid-phase synthesis with SPS sintering method.Because of the convergence of valence band by Mg/Ca doping,the Seebeck coefficient increased prominently.And the point defects,the second phase precipitation and a large number of grain boundaries could strengthen the phonon scattering and reduce the lattice thermal conductivity.Finally,Sn_0.865Mg_0.0675Ca_0.0675samples gained the maximum ZT value of 0.53 at 773 K.?3?Solid-phase synthesis and mechanical alloying are the best methods of synthesising SnTe-based thermoelectric materials.We synthesized Sn_1-xBi_x/2Sb_x/2Te samples by combining mechanical alloying with SPS sintering method.The electrical properties of samples were improved by Bi/Sb doping.The point defects and a large number of grain boundaries caused by Bi/Sb doping could strengthen the phonon scattering and reduce the lattice thermal conductivity.And the donor Bi³⁺and Sb³⁺could reduce the electron thermal conductivity.These reasons led to a substantial decline of the thermal conductivity of Sn_1-xBi_x/2Sb_x/2Te samples.In particular,Sn_0.96Bi_0.02Sb_0.02Te samples gained the high ZT value of 0.63 at 773 K,however the pure phase SnTe was only 0.18 at 723 K,which was increased by about 2.5 times.