Research Of High Pressure Synthesizing Process And Thermal/Electrical/Mechanical Properties Of Mg₂Si Based Thermoelectric Materials

Based on Seebeck and Peltier effect,thermoelectric technology can directly realizes the converting between heat and electricity,which is strategic for recovering waste heat and saving energy.As one of middle temperature thermoelectric materials,Mg₂Si based materials?low cost,non-toxic and abundant elements?have been studied widely.Compress science,as being the requirements and challenges of science in the21^st century,may introduce unique structure and unusual properties.Up to now,however,there is no reports related to the magnesium silicide prepared by the high pressure high temperature?HPHT?method and their thermal/electrical/mechanical properties.In this paper,we focused on the HPHT processing of preparing magnesium silicide and their thermoelectric and mechanical properties.The following conclusions are established:?1?The nearly single phase magnesium silicide are obtained under the conditions of 923 K and 2 GPa by using the hexagonal big chamber compressor.The effects of excess Mg in Mg_2+?Si??=0,0.03,0.08?are evaluated.Accounting for the negligible loss of Mg,excess magnesium is not necessary in the process of the HPHT,which contrasts sharply with the traditional solid state reactions with excess magnesium due to its evaporation.This is one predominant character of HPHT in preparing the samples with accurate composition.?2?The Sb doped Mg₂Si are obtained by HPHT method and their thermoelectric properties are investigated.The lattice parameter increases with the increasing Sb contents.The distributions of Sb element are not uniform through micro morphology analysis.Compared with pure Mg₂Si,the electrical conductivity of Sb doped Mg₂Si raised about 2³ orders of magnitude.The absolute value of Seebeck coefficient increases with temperature.The lattice thermal conductivity of Mg₂Si_0.995Sb_0.005decreased about 25%in comparing with Mg₂Si at room temperature.The highest figure of merit?ZT?of Mg₂Si_0.995Sb_0.005.005 reaches⁰.2 at 800 K.?3?The mechanical properties of Mg₂Si_0.995Sb_0.005.005 prepared by HPHT method are investigated.The compress strength is 299.5 MPa and hardness is 4.13 GPa.However,the flexural strength,elastic modulus and fracture toughness are relatively poor(34.9MPa,58.7 MPa and 0.15 MPa m^1/2,respectively).Further optimizations of thermoelectric and mechanical properties?made by HPHT?are necessary so as to put the Mg₂Si into application.