High Quality Factor Enabled by Multiscale Phonon Scattering for Enhancing Thermoelectrics in Low-Solubility n-Type PbTe–Cu₂Te Alloys

Abstract

The fundamental challenge for enhancing the thermoelectric performance of n-type PbTe to match p-type counterparts is to eliminate the Pb vacancy and reduce the lattice thermal conductivity. The Cu atom has shown the ability to fill the cationic vacancy, triggering improved mobility. However, the relatively higher solubility of Cu2Te limits the interface density in the n-type PbTe matrix, leading to a higher lattice thermal conductivity. In particular, a quantitative relationship between the precipitate scattering and the reduction of lattice thermal conductivity in the n-type PbTe with low solubility of Cu2Te alloys still remains unclear. In this work, trivalent Sb atoms are introduced, aiming at decreasing the solubility of Cu in PbTe for improving the precipitate volumetric density and ensuring n-type degenerate conduction. Benefiting from the multiscale hierarchical microstructures by Sb and Cu codoping, the lattice thermal conductivity is considerably decreased to 0.38 W m–1 K–1. The Debye–Callaway model quantifies the contribution from point defects and nano/microscale precipitates. Moreover, the mobility increases from 228 to 948 cm2 V–1 s–1 because of the elimination of cationic vacancies. Consequently, a high quality factor is obtained, enabling a superior peak figure of merit ZT of ∼1.32 in n-type Pb0.975Sb0.025Te by alloying with only ∼1.2% Cu2Te. The present finding demonstrates the significant role of low-solubility Cu2Te in advancing thermoelectrics in n-type PbTe.

Enhancing Thermoelectrics for Small-Bandwidth n-Type PbTe–MnTe Alloys via Balancing Compromise

“…The integration of the reduced electrical conductivity and the improved Seebeck coefficient contributes to a tremendous enhancement of PF in the Cu-intercalated PbTe–MnTe samples, especially at room temperature, ranging from ∼2.37 mW m –1 K –2 (0.1% Cu) to ∼3.07 mW m –1 K –2 (0.5% Cu); the temperature-dependent PF for all samples can be seen in Figure S1 in Supporting Information. As shown in Figure c, compared with the experimental value reported in the literature, ,,,,, the PF of Cu-intercalated samples maintains a higher value in the whole temperature range, consistent with the theoretical prediction, but a value lower than the predicted value from another report due to the increased inertial effective mass in PbTe–MnTe alloys. In particular, the PF of Cu-doped PbTe–MnTe alloys in this work at room temperature is much higher than that of conventional np 3 donor Sb-doped PbTe–MnTe alloys, while the PF at an elevated temperature is still equivalent …”

“…However, all the black squares are consistent with the Pisarenko line with an effective mass of 0.36 m e . That is, there is no further enhancement in effective mass and the scattering factor in Cu-intercalated samples, indicating that the copper interstitial has little effect on the band structure and scattering mechanism, similar to other reports. ,− It is confirmed that the enhancement of PF of Cu-containing samples arises from the other factors and not the band structure or scattering mechanism.…”

“…It is noted that in Figure d, the Hall mobility of Cu-containing samples in this work is slightly lower than the predicted curve, which may be attributed to the underestimation of electron–phonon coupling or the existence of defect scattering sources . However, compared with the np 3 substitution element reported in the literature (blue area), the Cu-containing samples show higher carrier mobility (red area), further confirming that Cu interstitials have negligible effects on the band structure and charge scattering. − ,,,,− …”

“…Numerous explorations on the optimization of carrier mobility in n-type PbTe have conducted. Successful strategies include energy filtering, ,, the coherent/semicoherent interface, , and the band alignment and modulation doping. ,, Additionally, introducing small atomic elements such as Cu/Ag to eliminate Pb vacancy scattering sources and interstitial doping to avoid change on the conduction band structure are other effective measures to enhance carrier mobility. − More importantly, recent studies have revealed that sub-nanostructures such as interstitials can strongly impede heat phonons while scarcely scatter carriers . This means that Cu/Ag-intercalated MnTe–PbTe alloys may be beneficial to decouple the compromise between carrier mobility and lattice thermal conductivity (μ/κ l ) and alleviate the trade-off between the effective mass and carrier mobility (μ/ m b * ).…”

CuO/CuxS composites fabrication and their thermoelectric properties

“…Enhancements in thermoelectric performance have also been observed in polymer composites [28,29]. Similarly, many chaclogenide compounds are promising for thermoelectric applications [30][31][32][33][34].…”