Microstructure And Thermoelectric Properties Of P-type Pseudo-ternary Solid Solution Sn-doped Composites

Thermoelectric materials are functional materials that can convert thermal and electrical energy into each other.Devices made of them can improve energy utilization,but have relatively low conversion efficiency.The conversion efficiency of thermoelectric devices can be improved by optimizing the thermoelectric properties of semiconductor thermoelectric materials.In this paper,a P-type pseudo-ternary solid solution Sn doped composite thermoelectric material was 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 doping concentration and sintering temperature)on the thermoelectric properties of the material was explored by testing Seebeck coefficient,electrical conductivity,and thermal conductivity.The microstructure analysis showed that the XRD diffraction peaks do not shift before and after doping Sn.There is a single substance diffraction peak of Sn,indicating that Sn was mixed with P-type pseudo-ternary solid solution materials without any combination reaction.In the scanning electron micrograph,it can be observed that the Ptype pseudo-ternary solid solution has a lamellar structure,and metallic Sn grains are visible.The Hall effect test results show that the carriers concentration 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 than 230 ℃,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 at 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 P-type pseudoternary solid solution doped Sn composite continues to decrease,while the electrical conductivity and thermal conductivity continue to increase,mainly due to the incorporation of high carrier concentration and high conductivity and thermal conductivity of Sn;As the sintering temperature increases,the Seebeck coefficient of the P-type pseudo-ternary solid solution doped Sn composite continues to increase,mainly due to the high temperature sintering promoting the growth of the internal grains of the material,increasing the degree of crystallization,weakening the carrier scattering effect,and increasing the effective mass of the carriers.The continuous decrease in electrical conductivity is mainly caused by the increase in porosity within the material and the change in grain boundary defects caused by high-temperature sintering,resulting in an enhanced carrier scattering effect.The thermal conductivity first decreases and then increases,reaching a minimum at 230 ℃.The weakening of the phonon scattering effect leads to an increase in the lattice thermal conductivity,which determines the continued decrease in the carrier thermal conductivity.The variation of the thermoelectric merit of a material 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 materials,which can provide experimental basis and theoretical guidance for further optimizing the thermoelectric properties of thermoelectric materials.