Bi2Te3 nanoplates and nanoflowers: Synthesized by hydrothermal process and their enhanced thermoelectric properties

Abstract

Bi 2 Te 3 nanoplates with a thickness of 15-20 nm and self-assembled flower-like nanostructures using previous nanoplates as building blocks have been fabricated through a low-cost hydrothermal method with ethylenediamine tetraacetic acid (EDTA) as an additive. The structures and morphologies of the samples were characterized via X-ray diffraction (XRD), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectrometry (FT-IR) and transmission electron microscope (TEM) measurements. The growth mechanisms have been proposed based on the experimental results. The nanoplates and flower-like Bi 2 Te 3 nanocrystals (NCs) with no residual additives were consolidated by high pressure to an n-type nanostructured bulk material with preserved crystal grain sizes. Moreover, self-assembly NCs show higher thermoelectric properties than the nanoplates. The power factors and thermoelectric figure of merit (ZT) of chemically synthesized flowerlike Bi 2 Te 3 NCs were improved up to 8.6 mW cm À1 K À2 and 0.7, respectively, which possess the potential to design new materials and devices for thermoelectric applications.

Green synthesis and formation mechanism of nanostructured Bi2Te3 using ascorbic acid in aqueous solution

“…Besides, the XPS spectra in Fig. 3(b) and (c) from the Bi 2 -Te 3 rinsed with ethanol has one of the lowest ratio of oxide peak intensity to Bi 2 Te 3 peak intensity in previously reported XPS spectra of Bi 2 Te 3 NPs [2,7,8,[32][33][34][35]. This result suggests that hydrolyzed dehydroascorbic acid has an excellent oxidation resistance compared with other capping agents.…”

“…In both XPS spectra for Bi 4f region from the Bi 2 Te 3 NPs rinsed with ethanol or ethanol and water shown in Fig. 3(b), two peaks are observed at 162.5 eV and 157.2 eV which correspond to the reported values of Bi 4f5/2 and Bi 4f7/2 of Bi 2 Te 3 , respectively [7]. In addition, for Te 3d region in Fig.…”

“…In addition, for Te 3d region in Fig. 3(c), two peaks confirmed at 582.3 eV and 572.0 eV are attributed to Te 3d3/2 and Te 3d5/2 of Bi 2 Te 3 , respectively [7]. Peaks are clearly observed at 158.5 eV and 163.8 eV in the Bi 4f region, 586.2 eV and 575.7 eV in the Te 3d region from the Bi 2 Te 3 NPs rinsed with ethanol and water whereas the four peaks are barely detected from the Bi 2 Te 3 NPs rinsed with ethanol.…”

“…Peaks are clearly observed at 158.5 eV and 163.8 eV in the Bi 4f region, 586.2 eV and 575.7 eV in the Te 3d region from the Bi 2 Te 3 NPs rinsed with ethanol and water whereas the four peaks are barely detected from the Bi 2 Te 3 NPs rinsed with ethanol. These peaks are attributed to the oxidation of Bi 2 Te 3 surface [7]. Since FT-IR results show that hydrolyzed dehydroascorbic acid remains on the Bi 2 Te 3 NPs surfaces in the case of rinsing with ethanol, remaining hydrolyzed dehydroascorbic acid inhibits the surface oxidation.…”

“…Synthesis of Bi 2 Te 3 nanostructures with controllable morphology and size has attracted considerable attention because of the possibility of improving thermoelectric properties by tailoring the nanoparticle shape and size [2][3][4][5][6][7][8][9][10][11][12][13]. The popular synthesis procedures of nanocrystalline Bi 2 Te 3 is solvo(hydro)thermal reaction, which requires high temperature and high pressure, often together with toxic and hazardous reducing agent such as N 2 H 4 ÁH 2 O and NaBH 4 [3,7,8,[10][11][12]. Recently, for a facile and green synthesis of nanocrystalline Bi 2 Te 3 , aqueous chemical reduction syntheses near room temperature under atmospheric pressure have been reported [5,6,[13][14][15][16][17].…”