PbS–Pb–Cu_xS Composites for Thermoelectric Application

Abstract

Composite materials offer numerous advantages in a wide range of applications, including thermoelectrics. Here, semiconductor−metal composites are produced by just blending nanoparticles of a sulfide semiconductor obtained in aqueous solution and at room temperature with a metallic Cu powder. The obtained blend is annealed in a reducing atmosphere and afterward consolidated into dense polycrystalline pellets through spark plasma sintering (SPS). We observe that, during the annealing process, the presence of metallic copper activates a partial reduction of the PbS, resulting in the formation of PbS−Pb− Cu x S composites. The presence of metallic lead during the SPS process habilitates the liquid-phase sintering of the composite. Besides, by comparing the transport properties of PbS, the PbS−Pb−Cu x S composites, and PbS−Cu x S composites obtained by blending PbS and Cu x S nanoparticles, we demonstrate that the presence of metallic lead decisively contributes to a strong increase of the charge carrier concentration through spillover of charge carriers enabled by the low work function of lead. The increase in charge carrier concentration translates into much higher electrical conductivities and moderately lower Seebeck coefficients. These properties translate into power factors up to 2.1 mW m −1 K −2 at ambient temperature, well above those of PbS and PbS + Cu x S. Additionally, the presence of multiple phases in the final composite results in a notable decrease in the lattice thermal conductivity. Overall, the introduction of metallic copper in the initial blend results in a significant improvement of the thermoelectric performance of PbS, reaching a dimensionless thermoelectric figure of merit ZT = 1.1 at 750 K, which represents about a 400% increase over bare PbS. Besides, an average ZT ave = 0.72 in the temperature range 320−773 K is demonstrated.

Lattice expansion enables interstitial doping to achieve a high average ZT in n‐type PbS

“…With the optimized carrier density and mobility after Cu interstitial doping in PbS 0.6 Se 0.4 , the power factor undergoes a remarkable increase at wide temperature. The peak power factor increases from 3.88 μW cm −1 K −2 in PbS 0.6 Se 0.4 to 20.58 μW cm −1 K −2 in PbS 0.6 Se 0.4 − 1%Cu, as shown in Figure 3A, and the average power factor (PF ave ) in Supporting Information: Figure undergoes substantial increase, from 2.01 μW cm −1 K −2 in PbS 0.6 Se 0.4 to 18.38 μW cm −1 K −2 in PbS 0.6 Se 0.4 − 1%Cu at 300–773 K. Compared with other n ‐type PbS, including PbS–Cl–Sb, [ 39 ] PbS–In–Ga, [ 20 ] PbS–Te–Sn, [ 17 ] PbS–Se–Sb, [ 21 ] PbS–Pb–Cu x S [ 18 ] , and PbS–Se–Te–Ga, [ 22 ] PbS 0.6 Se 0.4 − 1%Cu in this study exhibits a superior power factor, as shown in Figure 3B, and also a highest PF ave at 300–773 K as seen in Supporting Information: Figure .…”

“…(A) Thermal conductivity in PbS 0.6 Se 0.4 – x %Cu ( x = 0–2), and (B) comparison of lattice thermal conductivity between PbS 0.6 Se 0.4 – 1%Cu and previous works, including PbS–Cl–Sb, [ 39 ] PbS–In–Ga, [ 20 ] PbS–Te–Sn, [ 17 ] PbS–Se–Sb, [ 21 ] PbS–Pb–Cu x S, [ 18 ] and PbS–Se–Te–Ga. [ 22 ] …”

Insights into the Classification of Nanoinclusions of Composites for Thermoelectric Applications

“…The SEM micrograph of the Yb 14 MnSb 11 /W composite and the homogeneous distribution of W nanoinclusions are shown in Figure a and b. Srivastava et al demonstrated that Fe nanoinclusions exhibit a higher α and lower σ than do Cu nanoinclusions in the SrTiO 3 -based composite because Fe has a lower σ than does Cu, as shown in Figure e and f. However, both Cu and Fe nanoinclusions enhance the total thermal conductivity of the composite due to the high thermal conductivity of both of the metals and still improve the overall ZT of the composites, as shown in Figure g and h. Li et al added Cu metallic nanoinclusions to the PbS matrix, Cu dissoluted and formed Pb domains, and Cu x S precipitates improved the ZT . The addition of Ag/Cu nanoparticles in the TE matrix material enormously improved the carrier concentration, employing spontaneous doping of the Ag/Cu atoms .…”

“…The size and shape of the metallic nanoinclusions affect the energy filtering effect . The composite’s enhanced κ is due to the electron thermal conductivity contribution from the metallic nanoinclusions. ,,, Metallic inclusions such as Cu, ,, Fe, , Zn, , B, Pt, Ag, ,,,, Bi, , Au, W, Si, ,, Sn, Ge, Yb, Te, and In , were used to improve the thermoelectric properties.…”

“…125 The composite's enhanced κ is due to the electron thermal conductivity contribution from the metallic nanoinclusions. 58,106,121,126 Metallic inclusions such as Cu, 42,58,80 Fe, 58,121 Zn, 106,127 B, 124 Pt, 128 Ag, 24,49,66,125,129 Bi, 34,122 Au, 130 W, 126 Si, 47,69,131 Sn, 42 Ge, 132 Yb, 133 Te, 22 and In 70,75 were used to improve the thermoelectric properties.…”