dc.description.abstract | In this study, magnesium silicide (Mg2Si) synthesized from low-cost, non-toxic silicon and magnesium was selected. The doping of Bi has been proven to increase the conductivity of pure magnesium silicide and reduce the thermal conductivity. However, doping of Bi has its solubility limit, and magnesium bismuthide (Mg3Bi2) will be precipitated if the solubility is exceeded. Adding nanostructures, such as nanoprecipitation or nanocomposite, to the above powders can further reduce thermal conductivity by increasing phonon scattering on the interface.
The common nanocomposites in the literature are mostly oxides, such as silicon dioxide (SiO2) and titanium dioxide (TiO2). Vanadium dioxide (VO2) has been studied and pointed out that it has the characteristics of metal-insulator phase transition (MIT) at 68 ℃. Metallic vanadium dioxide has the advantage that the electrical conductivity is greatly increased, but the thermal conductivity is almost unchanged. Therefore, in this work, we tried to use vanadium dioxide as nanocomposite and mixed with magnesium silicide. The addition of vanadium dioxide nanoparticle in different proportions will further reduce its thermal conductivity and effectively increase the figure of merit(ZT).
Bi-doped magnesium silicide compounds(Mg2SiBi0.02) were prepared by solid state reaction in tube furnace under argon atmosphere after mixing starting materials with the rolling machine. The vanadium dioxide powder needs to be refined by planetary ball milling. The vanadium dioxide and magnesium silicide powders are weighed in proportions and mixed with the rolling machine. Spark plasma sintering (SPS) was later operated after grinding and sieving for densification.
The composition and microstructure of the sample were measured and observed by using X-ray diffraction and SEM, respectively. The thermoelectric properties were studied by Laser flash apparatus (LFA), Archimedes, ZEM-3, and Differential scanning calorimetry (DSC) to obtain the parameter including thermal conductivity, electrical conductivity, and Seebeck coefficient in order to get the figure of merit(ZT).
The final result of this study is that the addition of 3% vanadium dioxide has the highest thermoelectric performance ZT = 0.0857 at room temperature, which is twice that without addition.. The final goal is to manufacture magnesium silicide compounds with high ZT values as thermoelectric materials with high-performance conversion efficiency. | en_US |