Synthesis And Thermoelectric Property Of Mg₂Si-Based Thermoelectric Material

Thermoelectric materials are used for converting heat energy to electric energy directly as functional materials with Seebeck effect and Peltier effect, they are essential materials in new energy field, and have immense prospects with many applications in thermoelectric power generation and refrigeration. The thermoelectric materials of Mg₂Si-based possess a potentially high dimensionless figure of merit ZT in intermediate temperature regime of operation. It is very difficult to synthesize Mg₂Si alloy as magnesium possess high activity. It becomes the researching key of how to synthesize Mg₂Si-based thermoelectric materials with high performance. In this paper, Mg₂Si-based alloy are synthesize by mechanical alloying (MA) and suspension induction melting respectively. Following , the bulk alloy are synthesized by Spark Plasma Sintering (SPS) technology. The microstructure and thermoelectric properties were systematically investigated by X-ray diffraction, scanning electron microscopy, transmitting electron microscopy, electric constants instrument and laser thermal conductivity instrument etc.First, this paper systematically studies the effect of different Sn doping amount(x=0, 0.4, 0.5, 0.6) on alloy microstructure and thermoelectric property based on Mg₂Si_1-xSn_x alloy synthesized via Mechanical Alloy (MA) and spark plasma sintering technology. Results show that partly-activated Si exists after 5-hour milling and when Sn doping amount (x) equals 0. And with the increasing amount of Sn, complete alloy will be achieved. For alloy powder with different amount of Sn, Mg₂Si_1-xSn_x alloy can be synthesized under the same SPS sintering conditions that SPS pressure equals 30 MPa, sintering temperature is 700 degree and sintering time span is 10 to 25 minutes. In addition, compound decomposition happens in Mg₂Si_1-xSn_x alloy with mixed Sn when sintering temperature is 750 degree while when the temperature equales 200 degree, highest power of the sample (Sn doping amount x=0.4) arrives at 6.25×10^-4WK^-2m^-1 . In addition, this paper also studies the fabrication process of Mg₂Si_1-xSn_x alloy (x=0, 0.4, 0.5, 0.6) and its thermoelectric properties, applying suspension induction melting combined with SPS. The raw materials are pieces of Mg, Si and Sn, of which all purity is above 99.0wt%. Firstly, with the protection of Ar air, all raw materials are melted into ingot, then ball-milled into powder and finally formed Mg₂Si_1-xSn_x alloy by SPS. Results show that increase of Sn is conducive to formation of Mg₂Si_1-xSn_x solid solution and Mg₂Si_1-xSn_x alloy possessing 98% relative density is synthesized via SPS at 700℃sintering temperature after 0.5 hour milling of Mg₂Si_1-xSn_x alloy powder. Test of thermoelectric properties demonstrate that resistivity of all samples is negatively related to temperature, showing transmission characteristics of semi-conductor. What is more, increase of Sn is positively related to the absolute value of Seebeck index for Mg₂Si_1-xSn_x alloy, showing no obvious difference in thermal conductivity. Within the span of testing temperature, Mg₂Si_0.4Sn_0.6 alloy possesses the highest ZT value (0.25) at 400℃.