Microstructure And Thermoelectric Properties Of N-type Gd-doped Pseudo-ternary Semiconductor Refrigeration Materials

The semiconductor refrigeration material is a functional material that can realize thermoelectric conversion.N-type semiconductor refrigeration material is favored because of its excellent performance at room temperature.Studies have shown that point defects have a greater effect on the carriers' concentration of semiconductor refrigeration materials.Therefore,the defects using the doping method can change the energy band structure of the materials,thereby improving the thermoelectric performance of the materials.The local magnetic moment of the rare earth element can improve the Seebeck coefficient of the materials,and the special f-layer electrons can form a hybrid effect with the d electrons of other elements to further optimize the thermoelectric performance of the materials.In addition,the mechanical alloying method can produce fine particles with uniform composition,so that the material has good thermoelectric properties.In this paper,N-type Gd-doped pseudo-ternary semiconductor refrigeration materials are prepared by mechanical alloying sintering hot pressing method.The microstructure is analyzed using X-ray diffractometer and scanning electron microscope.The carriers' concentration of materials is studied of by Hall Effect.By analyzing the electrical conductivity,thermoelectric potential and thermal conductivity of the test materials,the influence of the preparation process parameters on the thermoelectric properties of the N-type Gd-doped pseudo-ternary semiconductor cooling materials is analyzed,and the thermoelectric performance optimization mechanism of the pseudo-ternary semiconductor cooling materials is revealed.Microstructure analysis shows that sintering releases the internal stress of the materials,and at the same time,sintering will promote the growth of grains and cause the grains to grow up.As the hot pressing temperature increases,the XRD pattern results show that the diffraction peak increases and the half-height width decreases.SEM image results show that the crystal grains grow and the pores between the crystal grains decrease and the porosity decreases,so the increasing of the hot pressing temperature promotes the growth of the crystal grains.Hall Effect analysis shows that when the hot pressing temperature is constant,the carriers' concentration decrease first and then become constant with the hot pressing temperature.At the same time,when the Gd-doping concentration is constant,the carriers' concentration gradually increases with the increase of hot pressing temperature.When the hot pressing temperature is constant,the carriers' mobility increases first and then tends to saturation as the Gd-doping concentration increases.When the Gd-doping concentration is constant,it gradually increases with the increase of hot pressing temperature.Based on the test results of thermoelectric parameters,it can be seen that under certain conditions of other preparation process parameters,the Seebeck coefficient increases with the increase of Gd-doping concentration,and decreases slightly with the increase of hot pressing temperature.The conductivity decreases first and then increases with the increase of Gd-doping concentration.The thermal conductivity decreases first and then increases with the increase of Gd-doping concentration,and gradually increases with the increase of hot pressing temperature.The ZT value increases with the increase of Gd-doping concentration.When the Gd-doping concentration is 2.0 wt%,the hot pressing temperature is 100°C,and the room temperature is 300 K,the ZT value of the N-type Gd-doping pseudo-ternary semiconductor refrigeration material is 0.85.Both hot pressing temperature and Gd-doping change the internal structure of the materials,and affect the thermoelectric properties of the materials.