Preparation And Thermoelectric Porperites Of Magnesium Silicide-based Materials By One-step Synthesis

Thermoelectric material is a kind of energy materials which can carry outdirect conversion between heat energy and electric energy through carrierdiffusion. It’s characterized by light, small, environmentally friendly and longlife, which makes it is initially popularized in the recycle of automobile exhaustand the recovery of industrial waste heat. This material can be focused ondevelopment as green material. There are many kind of thermoelectric materials,which based magnesium silicon is got people’s attention extensively for itsabundant raw materials, non-toxic, safety and reliability.Magnesium is volatilized and oxidized easily during the preparation ofthermoelectric materials based magnesium silicon by the tradition method. Tosolve this problem, combining with an electric field to activate thepressure-assisted synthesis technology (Field-Activated and Pressure-AssistedSynthesis, FAPAS),MgH2was used instead of Mg,that could achieve one-stepsynthesis method which was used to prepare the thermoelectric materials basedmagnesium silicon with Bi-doped Mg2Si and Mg2Si1-xSnx（0.3≤x≤0.5）in thispaper. The thermoelectric properties and thermal stability were characterized. This method has many advantages such as simple process, short preparationtime, the sample with nano-sheet structure and pure density. The main resultswere as follows:MgH2, Si, Bi powder as raw material, preparing the Mg2Si bulk materialwith different proportions and Bi content by the one-step synthesis, and theresults showed that the thermal conductivity and electrical conductivity wereinfluenced because of the change of ratio MgH2/Si and Bi. When the ratio ofMgH2/Si was1.95:1and1at%-Bi doped, sample Mg2Si got the best ZT valuesat775K, and the value of ZTmaxwas0.77.MgH2, Si, Sn, Bi powder as raw material, preparing the thermoelectricmaterial based Mg2Si1-xSnxwith different content of Bi by the one-step synthesis,and the results showed that the thermoelectric material based Mg2Si1-xSnxperformed the best property when x=0.4. On this basis, improving thethermoelectric properties by doping different content of Bi, and the sampleMg2Si0.6Sn0.4Bi0.01got the maximum ZT value of1.29at770K. The samples areprepared for natural aging and annealing. All the samples after natural agingprocess in the whole temperature range for the best performance, sampleMg2Si0.6Sn0.4Bi0.02got the maximum ZT value of1.29at775K. ZT values ofannealed samples were upward trend leveled off after the700K, and the ZTvalue of all the sample is closer indicating that the thermoelectric properties tostabilize. When the temperature at775K, the Mg2Si0.6Sn0.4Bi0.01sample afterannealing got the maximum ZT value of0.9.