Preparation And Properties Of Mg₃Sb_2-xBi_x?0?x?1.2? Thermoelectric Materials By Solid State Reaction Combined With Spark Plasms Sintering

Thermoelectricity technology is an effective green energy conversion method,which can realize the mutual transformation between thermal energy and electric energy.With the advantages of small size,no noise,maintenance-free,and high security,it has broad application prospects in the energyharvestfield.Mg₃Sb₂,apromisingmaterialsappliedin medium-temperature?450-800 K?,is characterized with aboundatn reserves,low cost,non-toxic and benign to environment,etc.In this thesis,the orientation of Mg₃Sb₂ prepared by solid-state reaction followed by spark plasma sintering was studied,and its thermoelectric performance including thermal conductivity and carrier concentration has effectively been improved by adjusting the concentration of Bi.The results are listed as following:In this paper,Mg₃Sb₂ based thermoelectric materials were prepared by solid state reaction?SSR+SSR?and spark plasma sintering technology,and the anisotropy of the materials was analyzed systematically.The material exhibits isotropy in the direction perpendicular to and parallel to the sintering pressure by analyzing the microstructure and thermoelectric properties of the samples.In addition,the orientation of Mg₃Sb₂ prepared by one-step solid state reaction and ball milling?SSR+BM?combined with spark plasma sintering was studied.The results revealed that the Mg₃Sb₂ compound still showed the isotropic characteristics,which means the preparation methods does not change the orientation.The properties and phase composition of Mg₃Sb₂ synthesized by SSR+BM and SSR+SSR respectively were compared.It is indicated that,there is no second pahse were detected in the product prepared by SSR+SSR due to its lower reaction temperature,while secondary phase Sb was detected in the product by SSR+BM.The effect of Bi solid solution on thermoelectric properties was studied.With the increase content of Bi?x=0¹.2?,the carrier concentration enhanced greatly as well as the conductivity.The Seebeck coefficient decreased because it is inversely proportional to carrier concentration.The thermal conductivity of the solid solution with Bi was also greatly reduced from 1.7Wm^-1K^-11 to0.8Wm^-1K^-11 at room temperature due to the lattice distortion and the scattering of phonons by the introduction of Bi.The thermoelectric properties of the sample were improved obviously and the maximum value of ZT reached 0.96 in Mg_3.06Sb_1.2Bi_0.8.8 at 700 K.