Improved Thermoelectric Figure of Merit in Polyol Method-Prepared Cu_1–xBi_xS (x ≤ 0.06) Nanosheets

Abstract

The first thermoelectric (TE) properties of simple polyol method-synthesized Cu 1−x Bi x S (x = 0, 0.02, 0.04, 0.06) nanosheets are reported here. Various characterizations like Rietveld-refined X-ray diffraction (XRD), Raman spectroscopy, Xray photoelectron spectroscopy (XPS), and energy-dispersive X-ray (EDAX) data analysis confirm their single-phase nature of hexagonal crystal structure with space group P63/mmc, stoichiometric nature, valence states of the elements, and nominal elemental composition. Field emission scanning electron microscopy (FESEM) images show nanosheets (NSs) with an average thickness of 27 nm. The doping of Bi atoms in the CuS lattice has been evident from the systematic increase in its crystallite size, optical band gaps, photoluminescence peak intensities, Seebeck coefficients, resistivity, thermoelectric power factors (PFs), and thermoelectric figure of merits (ZTs) with increasing x. The selected area electron diffraction (SAED) pattern confirms that nanosheets are single crystalline in nature. Fourier transform infrared (FTIR) data confirms the absorption bands of the sulfides. The value of the Seebeck coefficient increases with increasing x without deteriorating the electrical conductivity too much due to the energy-dependent scattering of the carriers at the interfaces and the modulation doping. An enhancement of 231% in the thermoelectric power factor and a 6-fold increase in ZT, both at 300 K for x = 0.06 compared to x = 0, are found that show interesting outcomes for these toxic-and rare-earth element-free TE materials.

Dispersion stability analysis of copper sulphide nanoparticles in different medium

“…The strong peak detected at 474.6 cm -1 in figure 1b is due to S-S stretching vibrational mode of A 1g symmetry for S atoms at 4e sites, which indicates that 2/3 of sulfur atoms in the covellite structure of CuS form covalent S−S bonds. In addition, two weaker peaks are identified at 139 cm -1 and 268 cm -1 (associated with the Cu-S vibrational mode), which is in agreement with previous studies [2].…”

“…A standard procedure for synthesizing CuS NPs using the modified polyol method involves combining 2 mmol of Cu(NO 3 ) 2 .3H 2 O (99% , MERCK) and 5 mmol of CH 4 N 2 S (99%, MERCK) in a roundbottom flask with three necks with 40 ml of ethylene glycol (EG) (99%, MERCK). An excess amount of CH 4 N 2 S was used in the synthesis due to the volatile nature of sulfur [2]. The mixture was heated to a temperature of 160-165ºC for a period of 2 hours, during which continuous argon gases flow of was maintained.…”

“…Copper sulphides, are a type of metal chalcogenides that are chemically stable under ambient conditions, such as at room temperature. Examples of copper sulfides include CuS 2 (villamaninite), Cu 9 S 8 (yarrowite), Cu 1.8 S (digenite), Cu 1.75 S (anilite), Cu 1.96 S (djurleite), CuS (covellite), and Cu 2 S (chalcocite) etc [2]. CuS is of particular interest among these sulfides due to its low toxicity, affordability, natural abundance, and metallic properties down to ~5 K. With an energy band gap ranging from 1.55 to 2.15 eV, it functions as an indirect ptype semiconductor [2].…”

Impact of Copper Intercalation on Thermoelectric Properties in Polyol Method-Prepared CuxBi2Se3, x = 0, 0.05, 0.10, and 0.15 Nanosheets

“…The high-resolution spectrum of Bi 4f is fitted successfully with two peaks for Bi 4f 7/2 and 4f 5/2 at 157.6 and 163 eV for BS1, respectively (Figure d), and at 158.2 and 163.6 eV for BS3, respectively (Figure e). Here, the spin–orbit splitting of Bi 4f 7/2 and 4f 5/2 for both samples is 5.4 eV, which is near that of pure bulk Bi 4f . Therefore, Bi retained its Bi 3+ oxidation state after the introduction of Cu in the Bi 2 Se 3 lattice.…”