Effects Of Sb And Al On Microstructure And Properties Of Ni-Co-Mn-Sn Thermoelectric Alloys

Among many existing thermoelectric materials,half-Heusler alloys have received extensive attention due to its many unique advantages.However,a major factor restricting the development of these alloys is the high intrinsic thermal conductivity.This article looks at Ni-Mn-Sn-based alloy,firstly explores the effect of different preparation processes on the microstructure of Ni-Mn-Sn alloy,and then systematically analyzes the effect of solid solution of Sn-site Sb and Al elements on the structure and thermoelectric properties of Ni-Co-Mn-Sn-based alloy.The experimental results are as follows:（1）The research results show that second smelting can obtained Ni-Mn-Sn bulk alloys which have more finer grains,more ordered structure and more uniform composition.The grain size of the NiMnSn alloy obtained by smelting is in the micron level,and after high-energy ball milling,the size of powder particles is about one hundred nanometers.Compared with the samples of hot pressing,SPS sintering can obtain more finer grains,and meanwhile have more higher sintering efficiency.（2）The alloys of Ni_0.8Co_0.2MnSn_1-xSb_x（x=0,0.2,0.4,0.6,0.8,1.0）and Ni_0.8Co_0.2MnSn_1-x-x Al_x（x=0.2,0.4,0.6,0.8,1.0）are prepared by smelting,ball milling and then SPS sintering.The particle size of the ingot alloy after ball milling can reach tens of nanometers,and the grain size after SPS sintering is approximately several hundred nanometers.Although the grain size have grown during sintering process,however compared with smelting ingots,it is significantly reduced and can contribute to reduce the thermal conductivity.（3）Based on the Ni-Co-Mn-Sn alloy,the substitution of Sb atoms can be used.The study results find that with the increase of Sb doping content,thermal conductivity and the absolute value of Seebeck coefficient are reduced,and electrical conductivity is significantly improved.The ZT value of alloyed samples have been improved to a certain extent in comparison with unalloyed samples,where the x=0.2 sample has the best thermoelectric performance,and the maximum ZT value of 0.0315 is obtained at 700 K.（4）Based on the Ni-Co-Mn-Sn alloy,the substitution of Al atoms can be used.It was found that thermal conductivity and electrical conductivity are decreased,the absolute value of Seebeck coefficient increased when Al concentrations increases.The power factor of samples are optimized,and the performance are enhanced.The x=0.4 sample at 800 K obtains a maximum ZT value of 0.0303.