Preparation And Thermoelectric Transport Properties Of In-situ SiNWs-Mg₂Si Composite Materials

At present,energy and environmental issues have become the focus of the world.As energy conversion materials,thermoelectric?TE?materials have attracted much attention,which can directly recycle low-grade heat sources under the driving of temperature difference.It has great application prospects in the field of industrial waste heat,space,medical treatment,microelectronics and so on.Compared with bulk TE materials,nanowires composites TE materials have better TE properties because of their unique structure.In this work,Mg₂Si-based TE materials were used to prepare SiNWs-Mg₂Si composites in which SiNWs grows in-situ instead of additive mix.The Si coated by Ni powder were prepared by mechanical alloying?MA?process,which then was used as the precursor powder of Si NWs.In-situ compositeSiNWs-Mg₂SiwerepreparedbyField-Activatedand Pressure-Assisted Synthesis?FAPAS?in one-step.The TE properties of the materials were further optimized by adjusting the procedure and dopant.The main results are summarized as following:Si NWs-Mg₂Si composited were prepared successfully in one-step in-situ synthesis method through FAPAS and its TE properties were improved by 20%,which provides a new approach for the preparation of nanowire composites.This method can effectively avoid the secondary pollution of samples,simplify the procedure,and keep high repeatability of the data.The co-doping of both heavy metal elements Sb and Si NWs into Mg₂Si matrix has better TE properties than that with Sb alone based on the synergistic effect of lattice distortion and SiNWs transport channels,the effective scattering of phonons will be further enhanced.The introduction of Si NWs did not change the scattering mechanism of Mg₂Si matrix material but improve its electrical properties.With the increase of SiNWs,the resistivity of Mg₂Si_0.99Sb_0.01.01 samples decreased and then increased,while the change of the Seebeck coefficient and thermal conductivity was not obvious.When the content of SiNWs is 1.5at.%,the ZT value of the sample reaches 0.6 at 775K,which is 20%higher than that of the undoped SiNWs.It has also been found that the Sb-doped composites has higher power factor,2.5 mWm^-1K^-2@775K,than that Bi-doped,while the difference of thermal conductivity is not obvious.The ZT value of Sb-doped composites materials is higher than that of Bi-doped samples,0.6@775K for the sample of Mg₂Si_0.99Sb_0.01SiNWs_0.015,which is more than 33%higher than that of the Bi-doped samples.The results show that the Si NWs composite can effectively improve the TE properties of Mg₂Si materials through the decoupling effect between the resistivity and the Seebeck coefficient and the interface filter effect.The SiNWs-Mg₂Si composite materials obtained by in-situ synthesis have better TE properties than those obtained by additive mix.Compared with Bi-doped samples,Sb-doped ones improve the TE properties of SiNWs-Mg₂Si composite materials more effectively.