Fabircaiton And Thermoelectric Performance Of The SiNWs-Mg₂Si Nanocomposites

Thermoelectric materials can transform heat to electricity directly as onekind of functional materials, and it can be utilized for power generation orrefrigeration. Thermoelectric device made from thermoelectric materials has avariety of advantages such as briefness, lightness，good durability’ sensitiveresponse, reliable environmental protection and so on, thus rendering it widelyapplication prospect. Magnesium silicon thermoelectric materials attractsconsiderable attention in recent years due to its abundant raw materials,non-toxicity and excellent thermoelectric properties.In this paper2at.%Bi doped SiNWs-Mg^Si nanocomposites were preparedby vibratingBi powder and the chemical-etched single crystal Si wafersynchronously in anhydrous ethanol using a ultrasonic oscillator andsubsequently consolidating the dried mixed powder by the field activation-pressure auxiliary sintering (FAPAS). The microstmcture of the composites wasobserved by scanning electron microscope and transmission electronmicroscope, and the thermoelectric properties was measured by thermoelectrictesters, and the mechanical properties of the composites was characteirzed andanalyzed by shear test and shear fracture microscopic observation. The main results of this research were as below:By using mixture of0.035mol/L AgNOs solution and20wt%HF acid aschemical etching liquid,3h for ambient temperature etching, SiNWs arrays of50-500nm in diameter and dozens of micrometers in length can be obtained.And SiNWs-Mg2Si nanocomposites with good density can be fabricated byFAPAS sintering using Mg^Si powder, Bi powder and the chemically etchedsilicon wafer as raw materials, which were blent in anhydrous ethanol imderultrasound oscillating and vacuum-dryed straight atfer.After ultrasonic oscillation and FAPAS rapid sintering process, SiNWs canbe kept intact and distribute uniformly in the matrix. It is indicated that theelectrical conductivity of the composites decreased greatly for the drop ofboth carrier concentration and mobility, and the Seebeck coefficient remainedroughly the same, and the thermal conductivity reduced obviously. With theincrease of the dosage of SiNWs, the electrical conductivity furtherly decreased,and the Seebeck coefficient slightly improved, while the thermal conductivityhad a rising trend. When the content of SiNWs increased from O.lat.%to0.3at.%, the carrier mobility decreased by14.2%, leading to a28.2%drop inelectrical conductivity; and the Seebeck coefficient increased by12.1%, and thethermal conductivity increases by13.7%. Conclusively, the sample with O.lat.%SiNWs embedded obtained a highest ZT value of0.5at800K.The shear strength of Mg2SiBioith.o2block materals increased remarkably withe dosage of SiNWs, reaching8.43MPa for the sample with0.3at.%SiNWs embedded, promoting nearly twice than that of the unembedded. It was alsodiscovered that the shear fracture mode of the materials transformed from amixed mode of cleavage fracture and intergranular fracture to the mixed modeof quasi-cleavage fracture and the intergranular fracture with the increase of thecontent of SiNWs, indicating that the strength-toughness properties of thematerials were improved for some extent.