High Pressure Synthesis And Thermoelectric Properties Of Mg₂X(X=Si?Sn) Based And CoSb₃ Based Thermoelectric Materials

Thermoelectric material is a new type of energy material that realizes the direct conversion of thermal energy and electrical energy under static conditions,and has high application prospects in the fields of thermoelectric power generation,thermoelectric cooling,and catalysis.Mg₂X(X=Si?Sn)-based compounds and Co Sb₃-based compounds are important intermediate-temperature thermoelectric materials.Mg₂X(X=Si?Sn)-based thermoelectric materials have the characteristics of low density,high melting point and small expansion coefficient,and their constituent elements are abundant in the crust,non-toxic and environmentally friendly,so they have very good application prospects.Co Sb₃skutterudite thermoelectric material has always been a research hotspot because of its large cage structure.In this paper,the preparation of Mg₂X(X=Si?Sn)-based thermoelectric materials and the filling and doping of Co Sb₃-based thermoelectric materials were studied by using high temperature and high pressure with power generation plasma sintering technology.The thermoelectric properties were regulated by element doping,phase transformation control and annealing treatment,and the following research results were obtained.Mg₂Sn thermoelectric material prepared by high pressure synthesis combined with spark plasma sintering.The phase structure and thermoelectric properties of the samples were studied.We found that the Mg₂Sn prepared at high pressure produce metastable phases such as orthogonal and hexagonal.Through further low-temperature pressure-holding treatment,the transformation of the second phase and elemental to cubic phase can be promoted.High pressure combined annealing can prepare Mg₂Sn thermoelectric materials with a single inverse fluorite structure.The high pressure conditions effectively inhibit the oxidation and volatilization of Mg.The prepared pure-phase Mg₂Sn samples obtained two-step high-pressure combined annealing.The power factor of the Mg₂Sn thermoelectric material obtained at 500 K reached the maximum value of 500?Wm^-1K^-2,and the thermal conductivity achieved the minimum value of 2.54 Wm^-1K^-1 at 700 K.The sample reaches the highest ZT value of 0.1 at 675 K.Mg_2.05(Si_0.6Sn_0.4)solid solution samples prepared by high pressure combined with spark plasma sintering.The thermoelectric properties of Mg_2.05(Si_0.6Sn_0.4)samples were optimized by doping with Sb element.The optimally doped Mg_2.05(Si_0.6Sn_0.4)_0.98Sb_0.02 sample reaches the maximum power factor of 1924.30?Wm^-1K^-2 at 773 K.The solid solution of Mg₂Si and Mg₂Sn introduces point defects in the material and enhances the scattering of phonons.The Mg_2.05(Si_0.6Sn_0.40.98)Sb_0.02 sample reaches the lowest thermal conductivity of all samples at636 K 1.43 Wm^-1K^-1.Solid solution combined with Sb doping finally made the Mg_2.05(Si_0.6Sn_0.4)_0.98Sb_0.02 sample achieve a ZT maximum value of 0.94 at 715 K.Mg_2.05(Si_0.6Sn_0.4)Sb_0.02 solid solution with high pressure phase transition was prepared by high pressure combined spark plasma sintering.The phase composition,element distribution,microstructure and thermoelectric properties of the samples were also studied.The results show that increasing the pressure and increasing the phase transition have an effect on the distribution of microscopic elements in the matrix,and there are a lot of dislocation and lattice distortion in the different lattice directions of the sample,which effectively scatter phonons,and the thermoelectric properties of the sample are improved.The maximum power factor of Mg_2.05(Si_0.6Sn_0.4)_0.98Sb_0.02 sintered under 3GPa combined with spark plasma sintering at 773K was 2983.31?Wm^-1K^-2.The lowest lattice thermal conductivity is 0.42 Wm-1K-1 at 723 K.Finally,the ZT value of Mg_2.05(Si_0.6Sn_0.4)_0.98Sb_0.02 at 773 K was 1.3 through co-optimization of thermoelectric properties.Dyx Co Sb₃(x=0,0.05,0.1,0.15)samples were prepared by high pressure combined spark plasma sintering,the structure,fracture morphology and thermoelectric properties of the samples were studied.The research results show that the XRD results of all samples are basically consistent with the standard Co Sb₃ compounds.The binary Co Sb₃ prepared at high pressure is p-type semiconductor,which is changed into n-type semiconductor by Dy filling.The filling of Dy atoms can optimize the electrical properties of the samples and reduce the lattice thermal conductivity of the samples.The power factor of the optimally filled Dy_0.15Co Sb₃ sample reaches the maximum value of 1948.80?Wm^-1K^-2 at 423 K,the thermal conductivity reaches the minimum value of 2.07 Wm^-1K^-1 at 783 K,and the ZT value reaches the maximum at 623 K.The value is 0.26.