Preparation And Thermoelectric Transport Properties Of ?-Zn₄Sb₃ Thermoelectric Materials

With the acceleration of traditional energy consumption and the aggravation of environmental pollution,the demand for clean energy makes thermoelectric materials attract more and more attention.Thermoelectric materials have unique properties,which can convert the waste heat existing in nature and human activities into high-quality electric energy through thermoelectric power generation technology based on Seebeck effect.At the same time,it has the advantages of non-pollution,large amount,renewable and so on.?-Zn₄Sb₃ compound has very low thermal conductivity and is a typical thermoelectric material with phonon glass crystal structure.Because of its low cost,environmental friendliness and non-toxicity,it is considered to be one of the most promising materials for waste heat utilization in the middle temperature zone.In this paper,thermoelectric materials of?-Zn₄Sb₃ were prepared by flux method combined with melting slow cooling technology,and the effects of different element composition,flux and element doping on the thermoelectric properties of Zn₄Sb₃ materials were investigated.The main conclusions of this paper are as follows:?-Zn₄Sb₃ thermoelectric materials were prepared by NaCl self-flux method according to the stoichiometric ratio of Zn_(4+x)Sb₃(NaCl)₇(x=0.1,0.2,0.3,0.4).The experimental results show that all the samples have hexagonal crystal structure at room temperature,and all the prepared samples contain metal Zn phase,and the space group is R(?)c.Density,TEM and SAED tests confirmed that the prepared samples had good crystallization quality.By adjusting the element composition of Zn,the carrier concentration of the material increases as a whole,the range of carrier concentration is1.86×10²⁰cm^-3-2.46×10²⁰cm^-3 and the range of mobility is 18.97cm²·V^-1·s^-1-22.34cm²·V^-1·s^-1.The electrical transport characteristics of?-Zn₄Sb₃ are effectively optimized.The ZT value of?-Zn₄Sb₃(NaCl)₇reaches the maximum value of 1.4 at 673K.This value is higher than the ZT value of?-Zn₄Sb₃prepared by traditional ball milling method(ZT is 1.21 at 673 K)and hot pressing method(ZT value is 1.09 at 673K).?-Zn₄Sb₃ thermoelectric materials were prepared by Zn-NaCl mixed flux method according to stoichiometric Zn_(4-x)Sb₃(NaCl)_7+x(x=0,0.1,0.2,0.3).The use of Zn-NaCl mixed method can effectively restrain the loss of Zn in the process of high temperature synthesis,making the actual stoichiometric ratio close to the theoretical stoichiometric ratio;FESEM diagram shows that there is no obvious macroscopic defect in the sample;TEM diagram and SAED show that the crystal quality is good;thermal analysis shows that the sample has good thermal stability.Proper Zn-NaCl flux ratio can effectively adjust the carrier concentration and mobility of the samples,so as to better optimize the electrical transport properties of the samples.The thermal conductivity of the sample decreases with the increase of Na content in the range of x is 0-0.2.At the same time,the decrease of Zn content leads to the appearance of Zn Sb secondary phase in the samples doped with x=0.3,which leads to the increase of thermal conductivity of the sample.The maximum ZT value of 1.43 is obtained at 690K.The maximum ZT value of 1.43 was obtained in the sample of x=0.2 at 690K.?-Zn_4.1Sb₃(NaCl)₇Cdx(x=0,0.05,0.1,0.15)samples with good thermoelectric properties were prepared by NaCl flux method.The TEM and SAED images of transmission electron microscope show that the crystal quality of the prepared sample is good.Hall and other test results show that with the increase of the content of Cd,the carrier concentration of the sample decreases and the mobility increases,thus the Seebeck coefficient of the sample is enhanced,and the electrical transport performance of the sample is optimized.At the same time,the effective doping of Cd atoms can reduce the thermal conductivity of the materials,thus optimizing the thermoelectric transmission properties of the samples.Finally,the maximum ZT value of the sample of x=0.1 was 1.51 at 690K,which was 8% higher than that of the undoped sample.