Alloy Materials With Half-Heusler Stucture And Devices:Preparation And Thermoelectric Properties At Shallow Cryogenic Temperature

In recent years,the rapid development of society leads to increasing energy consumption and environmental problems,which have become the particularly prominent issues.However,the utilization rate of energy in production and life is low,and a large amount of energy is lost in the form of waste heat or cold energy.Therefore,improving the utilization rate of energy is of great significance to alleviate the shortage of resources and environmental problems.Although the recovery and utilization technology of high temperature waste heat resources is mature,the utilization means of low temperature waste heat and cold energy resources are few.Thermoelectric devices is an energy collection device made of thermoelectric materials.It uses the directional movement of carriers inside the materials to realize the mutual conversion between heat energy or cold energy and electrical energy.The ZT value of thermoelectric materials determines the conversion performance of thermoelectric devices,so improving the ZT value of thermoelectric materials is a key factor to improve the conversion efficiency of devices.With the development of synthesis technology and the improvement of thermoelectric mechanism,thermoelectric materials have been developed by leaps and bounds.At present,the research of thermoelectric materials is mainly concentrated above room temperature,while the research of shallow cryogenic（173-300 K）thermoelectric materials is rare,which will seriously affect the recovery and utilization of cold energy.Therefore,finding new high performance shallow cryogenic temperature thermoelectric materials is one of the important means to improve the efficiency of shallow cryogenic temperature thermoelectric modules.In this paper,high performance TiNiSn-based thermoelectric materials were successfully prepared by a modified solid-state reaction method combined with additional Zr doping,and on this basis,the power factor of TiNiSn-based thermoelectric materials was increased by Sb doping at shallow cryogenic temperature.Secondly,Cu-doped MgAgSb-based alloys were successfully prepared by ordinary ball milling and solid-state reaction.The thermoelectric properties of the samples synthesized by different synthesis methods at shallow cryogenic temperature were studied.In addition,Bi-Sb based alloy was obtained by melt sealing and tube melting method,and the shallow cryogenic temperature thermoelectric module based on MgAgSb-Bi Sb based alloy was prepared for the first time.The following results have been achieved:（1）TiNiSn-based alloys doped with extra Zr were successfully prepared by modified solid-state reaction method.On the one hand,Zr doping reduces the unstable Sn elemental and improves the Seebeck coefficient optimization power factor.On the other hand,the generated large number of second phase nanoparticles and superlattice nanodomains help to inhibit the lattice thermal conductivity.Finally,the power factor of the sample is increased by 50%and the thermal conductivity is decreased by 40%,and the maximum ZT value is 0.88 at780 K.（2）The power factor of TiZr_0.015Ni Sn-based alloy at shallow cryogenic temperature was optimized by Sb doping.In the end,the power factor of TiZr_0.015Ni Sn_0.98Sb_0.02 is 1624.87 W m^-1 K^-2 at 300 K,which was two times higher than that of the un-optimized sample.（3）Cu-doped MgAgSb-based alloys were prepared by ordinary ball milling and solid-state reaction respectively and their thermoelectric properties at shallow cryogenic temperature were studied.Due to the high crystallinity of solid-state reaction,the thermal conductivity of the sample is higher,and the average ZT value is 0.24 in the shallow cryogenic temperature region of 173-300K.Because the particle size prepared by ordinary ball milling is small,it is beneficial to reduce the thermal conductivity of the material,so the average ZT value reaches 0.38.（4）The shallow cryogenic thermoelectric module was fabricated based on MgAgSb-Bi Sb-based alloy,and the structure of the module was optimized by COMSOL simulation software.Finally,when the working temperature zone is200-300 K,the maximum conversion efficiency reaches 1.76%,which proves that it has good performance at the shallow cryogenic temperature,and provides a new idea for the utilization of cold energy at the shallow cryogenic temperature.