Research On The Preparation And Properties Of N-type Mg₃Sb₂ Based Thermoelectric Materials

Thermoelectric materials,a new type of green,eco-friendly materials,can enable direct conversion between thermal and electrical energy.Mg3Sb2-based thermoelectric materials,which are characterized by phonon-liquid and electron-crystal,and have merits of low-cost and richness in composition,could be promising in thermoelectric applications.In this thesis,we conduct research from three perspectives in order to find the techniques that can augment the thermoelectric performance of Mg3Sb2-based thermoelectric materials.First,we prepare pure-phase n-type Mg3Sb2-based thermoelectric materials by combining high-energy ball mill(HEBM)with spark plasma sintering(SPS)techniques,optimize the options of sintering temperature,and investigate the effects of sintering temperature on thermoelectric performance.We find that at low sintering temperature,Mg3Sb2 cannot be sufficiently sintered,leading to unevenness and low relative density.In contrast,high sintering temperature is able to adjusting scattering mechanisms of Mg3Sb2 thermoelectric materials and optimizing their electrical transport performance,thereby enhance their thermoelectric performance.Our experiment results indicate that at sintering temperature of 1073 K,Mg3Sb2-based thermoelectric materials exhibit best thermoelectric performance.Second,we fabricate highly porous Mg3Sb2 samples with low relative density by modifying spark plasma sintering modes,and further explore the impact of this porous structure on thermoelectric performance of Mg3Sb2.We discover that the introduction of porous structure into Mg3Sb2-based thermoelectric materials can strengthen phonon scattering and reduce lattice thermal conductivity of Mg3Sb2 significantly.Therefore,such introduction is conducive to heightening their thermoelectric performance and can improve thermoelectric performance of Mg3Sb2-based thermoelectric materials in the lower range of temperatures.In our experiments,we obtain the optimal zT of 0.8 at temperature of 323 K for Mg3Sb2 samples with relative density of 85%.In the last,we prepare Ni-doped Mg3Sb2-based thermoelectric materials and examine the doping effects of element Nickel.We observe that when doping concentration is relatively low,the element of Nickel is able to modulate the scattering mechanism and carrier concentration of Mg3Sb2,a characteristic regulating their thermoelectric performance;when doping concentration is relatively high,Ni atoms seems to be over-doped,giving rise to significant decrease in carrier concentration of Mg3Sb2 and degrading their thermoelectric performance.Our experimental results reveal that for the doped Mg3Sb2 sample with chemical composition of Mg3.225Ni0.075Bi0.5Sb1.49Te0.01,the optimal zT reaches 0.79 at the temperature of 323 K.