Microstructure And Thermoelectric Properties Of Mg₂Sn Based Thin Films Deposited By Magnetron Sputtering

Thermoelectric materials,as a kind of functional materials which can realize the direct conversion between heat energy and electric energy,are widely used in waste heat utilization and electronic refrigeration.Mg₂X（X=Sn,Si,Ge）based materials are favored by thermoelectric materials researchers because of their excellent thermoelectric properties,abundant raw materials,low cost,non-toxic and harmless,and light weight.Mg₂Sn material has a relatively low band gap and is an ideal thermoelectric material at low temperature（<500K）.Therefore,the research of Mg₂Sn-based thermoelectric materials has both theoretical significance and practical value.In this paper,Mg₂Sn-based films and Mg₂Sn/Mg nano-multilayers films were prepared by alternately depositing and diffusion reaction on interface between metal Mg target and Mg-Sn alloy target by high vacuum magnetron sputtering.The influence of Mg,Sn and Si content and modulation period on the crystal structure,surface morphology and thermoelectric properties of Mg₂Sn-based films and Mg₂Sn/Mg nano-multilayers films were investigated.The experimental results showed that the carrier concentration increased first and then decreased slightly and the migration decreased first and then increased with the increase of Mg content in the deposited films.The resistivity and Seebeck coefficient increased first and then decreased with increasing Mg content.The deposited film with 76.57at%Mg content had the higher power factor due to the higher Seebeck coefficient and moderate resistivity in the measured temperature range.The deposited Mg₂Sn films containing appropriate metal Mg phase can obtain a higher power factor.With the increase of Sn phase content of the deposited Mg₂Sn films,the carrier concentration increased first and then decreased slightly and the carrier mobility decreased first and then increased.The resistivity and Seebeck coefficient of the deposited Mg₂Sn films increased first and then decreased with increasing Sn content.The deposited film with 39.78 at%Sn content had the higher power factor due to the higher Seebeck coefficient and moderate resistivity in the measured temperature range.The thermoelectric properties of Mg₂（Sn,Si）films doped with different Si contents were studied.It was found that Si replaced Sn in Mg₂Sn lattice to form Mg₂（Sn,Si）substitute solid solution.With the increase of Si content,the carrier concentration first increased and then decreased and the mobility decreased continuously.With the increase of Si content,both the resistivity and Seebeck coefficient increased.The deposited film with Si content of 4.40 at.%had the higher power factor due to the higher Seebeck coefficient and moderate resistivity in the measured temperature range.Mg₂Sn/Mg nano-multilayers films with different modulation periods can be prepared by adjusting the sputtering time of Mg and Mg-Sn targets simultaneously.With the decrease of the modulation period,carrier concentration,carrier mobility and thermal conductivity decreased,but the resistivity,Seebeck coefficient and figure of merit ZT value increased significantly.The Mg₂Sn/Mg nano-multilayers films with the minimum modulation period（0.17μm）possessed the higher power factor due to the higher Seebeck coefficient and moderate resistivity in the measured temperature range.At room temperature,the film had the higher power factor and the lower thermal conductivity,resulting in the higher figure of merit value ZT of 1.52.