Microwave Synthesis And Thermoelectric Properties Of Half-heusler Mnisn (M=Ti,Zr,HF) Bulks

Thermoelectric materials can realize the conversion between electrical energy and heat energy,which can be used for generation of waste heat and replace the traditional cooling mode.For the current environment and energy crisis,thermoelectric materials provide a solution for waste heat reuse.Half-Heusler with a narrow band gap is a new promising thermoelectric materials for application in middle and high temperature.The traditional methods of preparing Half-Heusler bulk materials include mechanical alloy method,suspension melting method and solid phase synthesis method.The traditional preparation methods have the disadvantages of long preparation cycle and high cost.In this paper,the microwave process mainly relies on the coupling between the material and the microwave radiation to prepare the Half-Heusler bulk materials through rapid heating.And the preparation cycle and cost are greatly reduced by microwave process.Based on the above measurement and investigations,the main results are summarized as follows:The effect of different content Hf doping on the thermoelectric properties of TiNiSn was studied.The results show that the precursor is prepared by microwave process at 4 min30 s,and the Half-Heusler block is prepared after 20 min sintering at 20 MPa pressure.The use of microwave heating can make the sample produce nano-precipitates and nano-pores,can enhance the phonon scattering,and thus lattice thermal conductivity reduction;Hf doping caused lattice distortion,increased point defects,limiting the size of grain,About 10?m,is conducive to reducing the lattice thermal conductivity.Although the doping of Hf increases the resistivity of TiNiSn material,the Seebeck coefficient is improved to a large extent,and the power factor is improved.The power factor of Ti0.9Hf0.1NiSn is 3475?Wm^-1K-2 at 627 K,which is 20 40% higher than that of the similar doping in the literature.Ti0.9Hf0.1NiSn thermal conductivity in the test range of 4.4 5.5W * m^-1K^-1.Much smaller than the thermal conductivity of undoped and similarly doped samples.The ZT value of the material is improved.Wherein the ZT value of the Ti0.9Hf0.1NiSn sample is 0.42 at 673 K.Compared to the doped TiNiSn block,increased by 20 30%.In order to improve the ZT value of the TiNiSn block,the TiNiSn compound is used as the doping object,and the Zr between the Ti and the Hf is introduced.Study on Thermoelectric Properties of TiNiSn by Zr Doping.Zr-doped Half-Heusler blocks were prepared using the same process as Hf doping.The results show that the microwave heating can also make the sample produce nano-precipitates and nano-pores,lattice thermal conductivity decreased.After Zr is doped with Zr,Zr is replaced by Ti,and the crystal structure of the sample is distorted.The Seebeck coefficient is slightly increased and the power factor is improved.The power factor of Ti_0.7Zr_0.3NiSn sample reaches 2415?Wm^-1K-2 at 627 K,which is 10 20% higher than that of undoped.The introduction of Zr dopants leads to an increase in point defects,which makes the lattice thermal conductivity of the samples significantly reduced.The thermal conductivity of Ti_0.7Zr_0.3NiSn is only 1.51 2.17 W * m^-1K^-1 in the test range,which is 40 60% lower than that in the literature.Thereby increasing the ZT value of the material.Wherein the Ti_0.7Zr_0.3NiSn sample has a Zt value of 0.59 at 627 K.Relative to the non-doping of the work increased by 60 80%.The preparation process was simplified and the preparation cycle was shortened through the microwave technology,which presents a new approach to prepare low cost and commercially valuable thermoelectric materials and promote the practical application of thermoelectric materials in daily life.