Preparation, Characterization And Thermoelectric Properties Of β-Zn₄Sb₃ Based Nanocomposite Materials

β-Zn₄Sb₃ is one of the promising thermoelectric materials in the moderate temperature range. Doping appears difficult to change the carrier transport properties due to the fact thatβ-Zn₄Sb₃ is already heavly doped compound. Therefore, the research of optimization thermoelectric properties ofβ-Zn₄Sb₃ compound is one of the urgent issues. In this thesis, Single-phaseβ-Zn₄Sb₃ compound powders were produced by melting in an evacuated quartz ampoule followed by slowly cooling. SiO₂/β-Zn₄Sb₃, Cu/β-Zn4Sb₃ and Cu (SiO₂)/β-Zn₄Sb₃ nanocomposite powders and nanocomposite materials were prepared by chemical coating and Spark Plasma Sintering (SPS). The effects of the coating layer thicknesses of nano-sized SiO₂ and Cu particles on thermoelectric properties and mechanical strength of threenanocomposite materials had been emphatically investigated.SiO₂/β-Zn4Sb₃ nanocomposite particles and nanocomposite materials were fabricated via chemical coating method and SPS process. The electrical conductivity and thermal conductivity of SiO₂/β-Zn₄Sb₃ nanocomposite materials were lower than the pureβ-Zn₄Sb₃ material, but the Seebeck coefficient were higher. Electrical conductivity and thermal conductivity decreased as the thicknesses of SiO₂ coating layers increased; the increment of the Seebeck coefficient in high-temperature areas was significantly higher than that in low-temperature areas. The thermal conductivity of the sample that the thicknesses of nano SiO₂ coating layers was 12nm was the lowest than the other samples and only 0.56 W·m^-1·K^-1 at 460 K . As a result, the ZT_max of the material was 0.87 at 700 K. Under the same temperature, the increment of ZT value of the material reached 30 % compared to the pureβ-Zn₄Sb₃ material, but the ZT was lower than the pureβ-Zn₄Sb₃ material in low-temperature areas.Cu/β-ZNn₄Sb₃ nanocomposite particles and nanocomposite materials were fabricated via the acqueous solution reduction method and SPS process. The coating layers of nano Cu significantly changed the conductive mechanism of Cu/β-Zn₄Sb₃ nanocomposite materials that revealed the intrinsic semiconductor conductive properties. The Seebeck coefficient first increased then decreased as increasing the temperature, the thermal conductivities were higher than the pureβ-Zn₄Sb₃ material and increased with the increase of the thicknesses of nanoCu coating layers.The Cu (SiO₂)/β-Zn₄Sb₃ nanocomposite particles and nanocomposite materials were fabricated via chemical coating method and SPS process. The electrical conductivity of Cu (SiO₂)/β-Zn₄Sb₃ nanocomposite materials first decreased then increased as well as the Seebeck coefficient increased with increasing the temperature, when the thicknesses of nano SiO₂ and Cu coating layers were less than 6nm. The nanocomposite materials shew heavly doped semiconductor behavior. However, it demonstrated the intrinsic semiconductor conductive properties when the thicknesses of nano SiO₂ and Cu coating layers were greater than 6nm, since the electrical conductivity increased and the Seebeck coefficient first increased then decreased with increasing the temperature. The nanocomposite materials with 3 run thicknesses of nano SiO₂ and Cu coating layers obtained the lowest thermal conductivity and result in the ZT_max of 0.88 at 700 K. Under the same temperature, the increment of the ZT value of the material reached 31% compared to pureβ-Zn₄Sb₃ material.The compressed strength of (SiO₂)/β-Zn₄Sb₃, Cu/β-Zn₄Sb₃ and Cu(SiO₂)/β-Zn₄Sb₃ nanocomposite materials were higher than the pureβ-Zn₄Sb₃ material, and the largest increment to 193 % compared to the pureβ-Zn₄Sb₃ material.