Thermoelectric properties of Ag-doped CuS nanocomposites synthesized by a facile polyol method

Abstract

We report the first thermoelectric properties of CuAgS, x = 0-0.75 nanocomposites, synthesized by using a facile polyol method. Systematic characterizations using powder XRD, Rietveld refinement of XRD, EDAX, XPS and Raman spectroscopy confirmed their single phase, hexagonal crystal structure with the space group P6/mmc, nominal elemental composition, valence states of the constituent elements and stoichiometric nature. The TEM images showing the CuS formation of nearly perfect hexagonal disk-like particles of average thickness 26.7 nm and breadth ranging in a few hundreds of nanometers with nanorods stacked from these hexagonal nanodisks (NDs) elongated along the c axis corroborate the FESEM images. Attributed to structural phase transition, an anomaly at 55 K is clearly observed in both the thermopower and Hall resistivity data. By increasing x, a systematic reduction in thermal conductivity was observed near 300 K. Consequently, a 50% enhancement in figure of merit was observed for CuAgS as compared to pure CuS at 300 K. These results therefore are expected to provide a new direction in improving ZT near 300 K.

Enhanced thermoelectric performance of Ag2S nanoparticles by Ag-nanoinclusions

“…Faleev et al [1] proposed metal nanoparticles (NPs) inclusion into semiconducting TE materials can be a useful tool to increase the power factor due to formation of metal-semiconductor interfaces which acts as potential barriers to filter low energy charge carriers. This concept is demonstrated in many reports experimentally [2][3][4]6]. Sumithra et al [2] reported 100 % enhancement in ZT value for Bi 2 Te 3 with 2 vol% Bi nanoinclusins.…”

“…This resulting solution with black ppt was washed using steps followed in Ref. 4 for proper removal of DEG. Finally, it was dried at 60 o C in vacuum for 5 hrs to get powder product which was directly used for all characterizations.…”

“…In furtherance, Zhang et al [3] also demonstrate a 304% enhancement in ZT value of Bi 2 Te 3 with 2% Ag-nanoinclusions due to combine effect of low energy charge carrier filtering and phonon scattering from the metal-semiconductor interface. In our previous work [4], we demonstrated the introduction of 10 vol% of Ag 2 S NPs in metallic CuS results in an enhancement of ~ 37 % in ZT at 300 K due to low energy charge carrier filtering and phonon scattering at Ag 2 S -CuS interfaces. But single phase pure Ag 2 S shows very high ρ and consequently not possible to collect Seebeck coefficient data for it.…”

“…For this high efficiency is needed which determined by a dimensionless figure of merit, ZT = S 2 σTκ -1 , where S, σ, κ and T are the Seebeck coefficient, electrical conductivity, total thermal conductivity and absolute temperature, respectively. Therefore, S 2 σ (power factor) should be high and κ should be low in the TE samples for better efficiency and these can be easily achieved by nanoinclusion in TE host materials [1][2][3][4].…”

Copper Sulfides: Earth‐Abundant and Low‐Cost Thermoelectric Materials

“…The highest zT value of ≈5.45 10 −3 obtained for pure CuS improved slightly to 8.3 × 10 −3 (with S = 11 µV K −1 and k = 1.13 W m −1 K −1 ) at 362 K for one of the doped samples with x = 0.4, and these values were extremely low. An important investigation is made on the effects of Ag doping in CuS by Okram's group . CuS‐ and Ag‐doped CuS samples with composition Cu 1− x Ag x S have been fabricated by a polyol method.…”