Experimental Studies Of Mg₂Si-based Thermoelectric Materials Through High Pressure Preparation Method And Their Properties

Based on Seebeck effect and Peltier effect,the thermoelectric conversion technology has attributed to energy conversion between heat and electricity for recycle.Among thermoelectric materials,the Mg₂Si compound has significant advantages such as non-toxicity and sustainability.High-temperature High-pressure?HTHP?is rarely studied in thermoelectric materials compared with other traditional methods,so it will be more significant to obtain Mg₂Si-based thermoelectric materials through HTHP.In this work,the synthesis process of Sb-doped Mg₂Si materials is optimized under conditions of high temperature and high pressure,and the thermoelectric and mechanical properties are investigated.The main results are as follows:?1?Sb-doped Mg₂Si materials can be synthesized by HTHP method under conditions of 2.5 GPa and 1073 K by using hexagonal big chamber compressor.The impurity phases and surface cracks get less after heat and pressure preservations during the cooling and decompression processes.?2?The thermoelectric properties of Sb-doped Mg₂Si materials prepared by HTHP method are investigated.The grain sizes are about 4-30?m,and the lattice parameters increase with the increasing Sb content,which suggests Sb atoms are introduced into the Mg₂Si lattice.Sb doping can attribute to a higher electrical conductivity compared with pure Mg₂Si,and the electrical conductivity homogeneously increases with the increasing Sb content.Sb doping leads to decrease of lattice thermal conductivity,mainly due to the point defect scattering which is caused by the mass and strain field fluctuations.The maximum thermoelectric figure of merit?ZT?of the Mg₂Si_0.99Sb_0.01 reaches 0.55 at 773 K.?3?The mechanical properties of Sb-doped Mg₂Si materials prepared by HTHP method at moderate temperature are investigated.At 300 K,373 K,473 K and 573 K,results show that the bending strengths are 81.1 MPa,70.7 MPa,69.6 MPa and 59.8MPa,the elastic moduli are 52.5 GPa,47.4 GPa,38.9 GPa and 34.1 GPa,the compress strengths are 513.1 MPa,416.7 MPa,370.6 MPa and 318.2 MPa.These characters all decrease as the temperature increases.At 300 K,the Vickers hardness is5.40 GPa,and the fracture toughness is 0.56 MPa m^1/2.