Abstract
Nanostructured bulk silicon (bulk nano-Si) has attracted attention as an advanced thermoelectric (TE) material due to its abundance and low toxicity. However, oxidization will occur easily when bulk nano-Si is synthesized by a conventional method, which deteriorates the TE performance. Various methods to prevent such oxidation have been proposed but they need specific techniques and are thus expensive. Here, we propose a simple and cost-effective method named Surface Diffusion/Sintering Doping (SDSD) to synthesize bulk nano-Si for TEs. SDSD utilizes Si nanoparticles whose surface is coated with a native thin oxide layer. SDSD is composed of two steps, (1) a molecular precursor containing a doping element is added onto the oxide layer of Si nanoparticles and (2) the nanoparticles are sintered into a bulk state. During sintering, the doping element diffuses through the oxide layer forming conductive paths, which results in a high carrier concentration as well as high mobility. Furthermore, owing to the nanostructures, low lattice thermal conductivity (κlat) is also achieved, which is an ideal situation for TEs. In this study, we show that P-doped bulk nano-Si synthesized by SDSD shows good TE performance due to its high carrier concentration, high carrier mobility, and low κlat. Since SDSD takes advantage of oxidization, it is cost-effective and suitable for mass production to synthesize bulk nano-Si for TEs.
Highlights
Thermoelectrics (TEs) can convert heat gradients into electricity and vice versa, making them important to the future of power generation from waste heat.[1]
The average particle diameter determined by dynamic light scattering (DLS) and the crystallite size determined from the XRD pattern are 0.6 mm and 25 nm, respectively
The powder XRD pattern of a bulk sample (Fig. 1b) whose doping level is 9% molar parts to Si shows sharp peaks compared with the Si nanoparticles, meaning that grain growth occurs during spark plasma sintering (SPS)
Summary
Thermoelectrics (TEs) can convert heat gradients into electricity and vice versa, making them important to the future of power generation from waste heat.[1]. A traditional method to synthesis nanostructured bulk Si (bulk nano-Si) is consolidating ne nanoparticles of highly doped Si through ball milling (BM) followed by hot pressing or spark plasma sintering (SPS). This method has been demonstrated to synthesis various nanostructured bulk TE materials, including Bi2Te3-based alloys.[8] the procedure should be done under a carefully controlled inert atmosphere to prevent oxidization of the surface of nanoparticles, because the oxide layer scatters charge carriers signi cantly, results in poor electrical conduction. During the SPS, sintering and diffusing of the doping element from the precursor into Si occur, which realizes to synthesize bulk nanoSi with desired carrier type and concentration
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