Microstructure And Thermoelectric Properties Of N-type Pseudo Ternary Semiconductor Doped Sn Composite Materials

The semiconductor thermoelectric materials can achieve direct conversion of thermal and electrical energy,and improving conversion efficiency is the most important step in the development of thermoelectric materials.N-type pseudo ternary semiconductor materials are currently the best thermoelectric materials at room temperature.In this paper,N-type pseudo ternary semiconductor Sn doped composite thermoelectric materials were prepared by hot pressing sintering method.The microstructure was analyzed using X-ray diffraction,scanning electron microscopy,and Hall effect analyzer.The mechanism of the influence of preparation process parameters(Sn doped concentration and sintering temperature)on the thermoelectric properties of the materials was explored by testing Seebeck coefficient,electrical conductivity,and thermal conductivity.The microstructure analysis shows that there is no shift in the X-ray diffraction peak before and after doping Sn,and there is a single substance diffraction peak of Sn,indicating that Sn is mixed with N-type pseudo-ternary semiconductor materials without any combination reaction.In the scanning electron micrograph,it can be observed that the N-type pseudo-ternary semiconductor has a lamellar structure and there are metallic Sn grains.The Hall effect test results show that the carriers’ concentration gradually increases with the increase of Sn doping concentration,which is mainly caused by the high carriers’ concentration of Sn.After sintering at different temperatures,the X-ray diffraction peak changes significantly.When the sintering temperature is lower than230 ℃,the X-ray diffraction peak narrows and increases with the increase of the sintering temperature,indicating that higher sintering temperature will promote grain growth and improve the crystallization degree of the materials.When the sintering temperature is higher than the melting point of Sn 230 ℃,the X-ray diffraction peak shape becomes low,indicating that excessive sintering temperature and the melting of Sn will damage the crystallinity of the materials.The thermoelectric performance test results show that the Seebeck coefficient of the N-type pseudo-ternary semiconductor Sn doped composite continues to decrease with the increase of Sn doping concentration,while the electrical conductivity and thermal conductivity continue to increase,mainly due to the incorporation of high carriers’ concentration and high conductivity and thermal conductivity Sn.As the sintering temperature increases,the Seebeck coefficient of the N-type pseudo-ternary semiconductor Sn doped composite continues to decrease,while the electrical conductivity and thermal conductivity first increase and then decrease,reaching the highest at 230 ℃.The continuous decrease of Seebeck coefficient with the increase of sintering temperature is mainly caused by the decrease of scattering factor due to the improvement of crystallinity.The variation rules of electrical conductivity and thermal conductivity are highly consistent with the experimental results of X-ray diffraction.The variation of the thermoelectric merit of the materials depends entirely on the Seebeck coefficient,electrical conductivity,and thermal conductivity.The relevant research results in this paper reveal the internal physical mechanism of the influence of preparation process parameters on thermoelectric parameters of the materials,which can provide experimental basis and theoretical guidance for further optimizing the thermoelectric properties of thermoelectric materials.