Prepartion And Properties Of β-Zn₄Sb₃ Thermoelectric Materials

Development and utilization of an environmentally friendly new energy have attracted the national attention, due to the increasingly problems from the serious environmental pollution and the gradual depletion of fossil fuels. Thermoelectric materials are potential energy material,which can directly convert thermal to electricity. In fact, they are extensively used in domestic and industrial waste heat recovery, geothermal electricity and so on, due to its advantage of no fluids, no moving parts, pollution-free, reliable performance and easy assembling. β-Zn4Sb3 is one of the most promising thermoelectric materials at moderate temperature, the ZT value of which can reach 1.3 at 673 K. Meanwhile, the composition element of β-Zn4Sb3 is abundant on earth and environmentally friendly. However, the preparation process of β-Zn4Sb3 is unreliable and unstable. Therefore, how to further optimize the thermoelectric properties of β-Zn4Sb3 is also an urgent research topic.In this work, the single-phase β-Zn4Sb3 was prepared by vacuum melting combined with the plasma activated sintering(PAS) and the stability of β-Zn4Sb3 was investigated at high temperature. In order to improve the thermoelectric properties of β-Zn4Sb3, the nanoSiC particles and Bi element were introduced into the β-Zn4Sb3 to fabricate the SiC/β-Zn4Sb3 and Zn4Sb3-xBix thermoelectric materials, respectively. Then the thermoelectric properties of them were mainly studied. The main contents were as follows:The single-phase β-Zn4Sb3 has been successfully prepared at 723 K by applying a certain pressure of 80 MPa and the porosity of the single-phase β-Zn4Sb3 was about 2.9%.After heat treatment at different temperatures, the single phase β-Zn4Sb3 had a optimized thermostability at the high temperature according to the TEM analysisSiC/β-Zn4Sb3 thermoelectric composites with different contents of SiC nanoparticles were prepared by vacuum melting and quenching combined with plasma activated sintering process.The phase compositions and microstructures of the materials were characterized by X-ray diffraction and scanning electron microscope, and the resistivity, Seebeck coefficient and thermalconductivity were measured in the temperature range of 300 to 700 K. The results show that the composite was composed of SiC and β-Zn4Sb3 phases, and there was no phase transition in the PAS process. The SiC nanoparticles were randomly distributed in β-Zn4Sb3 matrix randomly. The electrical transport properties of the composites showed that the resistivity increased with the increase of SiC content, and the Seebeck coefficient increased first and then decreased. When the content of SiC was 1.0%, the thermoelectric figure of merit(ZT) reached 1.03 at 673 K, and increased by 37% compared with the single phase β-Zn4Sb3.Zn4Sb3-x Bix electrical transport properties test showed that the Seebeck coefficient of Zn4Sb3-x Bix thermoelectric materials have significantly improved whereas the resistivity is significantly higher than that of the single phase β-Zn4Sb3 and enhances with the increase of the doping concentration compared to single-phase β-Zn4Sb3. Although the resistivity has a certain increase,, the power factor of Zn4Sb3-x Bix thermoelectric material increased because of the increase of Seebeck coefficient, so as to improve the electrical properties of Zn4Sb3-x Bix thermoelectric materials. Besides, the thermal conductivity of the Zn4Sb3-xBix was lower than that of the single phase β-Zn4Sb3 combined with the higher power factor resulting in an enhancement in ZT value for the doped Zn4Sb3-x Bix thermoelectric materials at 300-710 K.As a result, the ZT value for x=0.04 reached 0.96 at 673 K, which was improved by 28% compared with that of the single phase β-Zn4Sb3 bulk material.