Electrical and Thermal Transport Properties of Ge1–xPbxCuySbyTeSe2y

Balancing the contradictory relationship between thermoelectric parameters, such as effective mass and carrier mobility, is a challenge to optimize thermoelectric performance. Herein, the exceptional thermoelectric performance is realized in GeTe through collaboratively optimizing the carrier and phonon transport via stepwise alloying Pb and CuSbSe₂. The formation energy of Ge vacancy is efficiently bolstered by alloying Pb, which reduces carrier density and carrier scattering to maintain superior carrier mobility in GeTe. Additionally, CuSbSe₂, acting as an n-type dopant, further modulates carrier density and validly equilibrates carrier mobility and effective mass. Accordingly, the promising power factor of 45 µW cm⁻¹ K⁻² is achieved at 723 K. Meanwhile, point defects are found to significantly suppress phonons transport to descend lattice thermal conductivity by Pb and CuSbSe₂ alloying, which barely impacts the carrier mobility. A combination with superior carrier mobility and lower lattice thermal conductivity, a maximum ZT of 2.2 is attained in Ge_0.925Pb_0.075Cu_0.005Sb_0.005TeSe_0.01, which corresponds to a 100% promotion compared with that of intrinsic GeTe. This study provides a new indicator for optimizing carrier and phonon transport properties by balancing interrelated thermoelectric parameters.     

Enhancing the Thermoelectric Properties via Modulation of Defects in P-Type MNiSn-Based (M = Hf,Zr, Ti) Half-Heusler Materials

The thermoelectric figure-of-merit (zT) of p-type MNiSn (M = Ti, Zr, or Hf) half-Heusler compounds is lower than their n-type counterparts due to the presence of a donor in-gap state caused by Ni occupying tetrahedral interstitials. While ZrNiSn and TiNiSn, have been extensively studied, HfNiSn remains unexplored. Herein, this study reports an improved thermoelectric property in p-type HfNi_1−xCo_xSn. By doping 5 at% Co at the Ni sites, the Seebeck coefficient becomes reaching a peak value exceeding 200 µV K⁻¹ that breaks the record of previous reports. A maximum power factor of ≈2.2 mW m⁻¹ K⁻² at 973 K is achieved by optimizing the carrier concentration. The enhanced p-type transport is ascribed to the reduced content of Ni defects, supported by first principle calculations and diffraction pattern refinement. Concomitantly, Co doping also softens the lattice and scatters phonons, resulting in a minimum lattice thermal conductivity of ≈1.8 W m⁻¹ K⁻¹. This leads to a peak zT of 0.55 at 973 K is realized, surpassing the best performing p-type MNiSn by 100%. This approach offers a new method to manipulate the intrinsic atomic disorder in half-Heusler materials, facilitating further optimization of their electronic and thermal properties.     

Enhanced Thermoelectric Performance in GeTe by Synergy of Midgap state and Band Convergence

The good co-existence of midgap state and valence band degeneracy is realized in Bi-alloyed GeTe through the In-Cd codoping to play different but complementary roles in the valence band structure modification. In doping induces midgap state and results in a considerably improved Seebeck coefficient near room temperature, while Cd doping significantly increases the Seebeck coefficient in the mid-high temperature region by promoting the valence band convergence. The synergistic effects obviously increase the density of state effective mass from 1.39 to 2.65 m₀, and the corresponding carrier mobility still reaches 34.3 cm² V⁻¹ s⁻¹ at room temperature. Moreover, the Bi-In-Cd co-alloying introduces various phonon scattering centers including nanoprecipitates and strain field fluctuations and suppresses the lattice thermal conductivity to a rather low value of 0.56 W m⁻¹ K⁻¹ at 600 K. As a result, the Ge_0.89Bi_0.06In_0.01Cd_0.04Te sample obtains excellent thermoelectric properties of zT_max ≈2.12 at 650 K and zT_avg ≈1.43 between 300 and 773 K. This study illustrates that the thermoelectric performance of GeTe can be optimized in a wide temperature range through the synergy of midgap state and valence band convergence.     

High Thermoelectric Performance of ZnO by Coherent Phonon Scattering and Optimized Charge Transport

ZnO is identified as a potentially attractive n-type oxide thermoelectric material due to its abundance, nontoxicity, and a high degree of stability. However, working with ZnO is challenging due to its high thermal conductivity from its strong ionic bonds and low electrical conductivity due to its low charge concentrations. Here, it is demonstrated that the electrical and thermal transport properties of ZnO can be simultaneously improved via the successful doping of Al and ZnS coating. The ZnS coating in Al-doped ZnO is observed and analyzed through microstructure and spectroscopic studies. The power factor for 1% ZnS-coated Zn_0.98Al_0.02O is increased to ≈0.75 mW m⁻¹ K⁻² at 1073 K, 161% higher than pure ZnO. This enhancement in the power factor can be explained by the aliovalent Al³⁺ doping and modifications in intrinsic defects, leading to an increased carrier concentration. Interestingly, ZnS coating significantly reduces lattice thermal conductivity to ≈2.31 W m⁻¹ K⁻¹ at 1073 K for 2% ZnS-coated Zn_0.98Al_0.02O, a 62% decrease over pure ZnO. This large reduction in lattice thermal conductivity can be elucidated based on coherent phonon scattering via Callaway's model. Overall, the figure of merit, zT, increases to 0.2 in 2% ZnS-coated Zn_0.98Al_0.02O, which is 272% higher than pure ZnO at 1073 K.     

Superior Thermoelectric Performance of Textured Ca3Co4−xO9+δ Ceramic Nanoribbons

Calcium cobaltite Ca₃Co_4−xO_9+δ (CCO) is a promising p-type thermoelectric (TE) material for high-temperature applications in air. The grains of the material exhibit strong anisotropic properties, making texturing and nanostructuring mostly favored to improve thermoelectric performance. On the one hand multitude of interfaces are needed within the bulk material to create reflecting surfaces that can lower the thermal conductivity. On the other hand, low residual porosity is needed to improve the contact between grains and raise the electrical conductivity. In this study, CCO fibers with 100% flat cross sections in a stacked, compact form are electrospun. Then the grains within the nanoribbons in the plane of the fibers are grown. Finally, the nanoribbons are electrospun into a textured ceramic that features simultaneously a high electrical conductivity of 177 S cm⁻¹ and an immensely enhanced Seebeck coefficient of 200 µV K⁻¹ at 1073 K are assembled. The power factor of 4.68 µW cm⁻¹ K⁻² at 1073 K in air surpasses all previous CCO TE performances of nanofiber ceramics by a factor of two. Given the relatively high power factor combined with low thermal conductivity, a relatively large figure-of-merit of 0.3 at 873 K in the air for the textured nanoribbon ceramic is obtained.     

Vacancy Manipulation Induced Optimal Carrier Concentration,Band Convergence and Low Lattice Thermal Conductivity in Nano-Crystalline SnTe Yielding Superior Thermoelectric Performance

Synergetic optimization of electrical and thermal transport properties is achieved for SnTe-based nano-crystalline materials. Gd doping is able to suppress the Sn vacancy, which is confirmed by positron annihilation measurements and corresponding theoretical calculations. Hence, the optimal hole carrier concentration is obtained, leading to the improvement of electrical transport performance and simultaneous decrease of electronic thermal conductivity. In addition, the incremental density of states effective mass m* in SnTe is realized by the promotion of the band convergence via Gd doping, which is further confirmed by the band structure calculation. Hence, the enhancement of the Seebeck coefficient is also achieved, leading to a high power factor of 2922 µW m⁻¹ K⁻² for Sn_0.96Gd_0.04Te at 900 K. Meanwhile, substantial suppression of the lattice thermal conductivity is observed in Gd-doped SnTe, which is originated from enhanced phonon scattering by multiple processes including mass and strain fluctuations due to the Gd doping, scattering of grain boundaries, nano-pores, and secondary phases induced by Gd doping. With the decreased phonon mean free path and reduced average phonon group velocity, a rather low lattice thermal conductivity is achieved. As a result, the synergetic optimization of the electric and thermal transport properties contributes to a rather high ZT value of ≈1.5 at 900 K, leading to the superior thermoelectric performance of SnTe-based nanoscale polycrystalline materials.     

Hierarchical Architectural Structures Induce High Performance in n-Type GeTe-Based Thermoelectrics

Compatible p- and n-type materials are necessary for high-performance GeTe thermoelectric modules, where the n-type counterparts are in urgent need. Here, it is reported that the p-type GeTe can be tuned into n-type by decreasing the formation energy of Te vacancies via AgBiTe₂ alloying. AgBiTe₂ alloying induces Ag₂Te precipitates and tunes the carrier concentration close to the optimal level, leading to a high-power factor of 6.2 µW cm⁻¹ K⁻² at 423 K. Particularly, the observed hierarchical architectural structures, including phase boundaries, nano-precipitates, and point defects, contribute an ultralow lattice thermal conductivity of 0.39 W m⁻¹ K⁻¹ at 423 K. Correspondingly, an increased ZT of 0.5 at 423 K is observed in n-type (GeTe)_0.45(AgBiTe₂)_0.55. Furthermore, a single-leg module demonstrates a maximum η of 6.6% at the temperature range from 300 to 500 K. This study indicates that AgBiTe₂ alloying can successfully turn GeTe into n-type with simultaneously optimized thermoelectric performance.     

Intrinsically Low Lattice Thermal Conductivity and Anisotropic Thermoelectric Performance in In-doped GeSb2Te4 Single Crystals

Layer-structured GeSb₂Te₄ is a promising thermoelectric candidate, while its anisotropy of thermal and electrical transport properties is still not clear. In this study, Ge_1–xIn_xSb₂Te₄ single crystals are grown by Bridgman method, and their anisotropic thermoelectric properties are systematically investigated. Lower electrical conductivity and higher Seebeck coefficient are observed in the c-axis due to the higher effective mass in this direction. Intrinsically low lattice thermal conductivity is also observed in the c-axis due to the weak chemical bonding and the strong lattice anharmonicity proved by density functional theory calculation. Indium doping introduces an impurity band in the bandgap of GeSb₂Te₄ and leads to the locally distorted density of states near the Fermi level, which contributes to enhanced Seebeck coefficient and improved power factor. Ultimately, a peak zT value of 1 at 673 K and an average zT value of 0.68 within 323–773 K are obtained in Ge_0.93In_0.07Sb₂Te₄ along the c-axis direction, which are 54% and 79% higher than that of the pristine GeSb₂Te₄ single crystal, respectively. This study clarified the origin of intrinsic low lattice thermal conductivity and anisotropy transport properties in GeSb₂Te₄, and shed light on the performance optimization of other layered thermoelectric materials.     

Modulation Doping Leads to Optimized Thermoelectric Properties in n-Type Bi6Cu2Se4O6 due to Interface Effects

Heterogeneous composites consisting of Bi₆Cu₂Se_3.6Cl_0.4O₆ and Bi₂O₂Se are prepared according to the concept of modulation doping. With prominently increased carrier mobility and almost unchanged effective mass, the electrical transport properties are considerably optimized resulting in a peak power factor ≈1.8 µW cm⁻¹ K⁻² at 873 K, although the carrier concentration is slightly deteriorated. Meanwhile, the lattice thermal conductivity is lowered to ≈0.62 W m⁻¹ K⁻¹ due to the introduction of the second phase. The modified Self-consistent Effective Medium Theory is utilized to explain the deeper mechanism of modulation doping. The enhancement of apparent carrier mobility is derived from the highly active phase interfaces as fast carrier transport channels, while the reduced apparent thermal conductivity is ascribed to the existence of thermal resistance at the phase interfaces. Ultimately, an optimized ZT ≈0.23 is obtained at 873 K in Bi₆Cu₂Se_3.6Cl_0.4O₆ + 13% Bi₂O₂Se. This research demonstrates the effectiveness of modulation doping for optimizing thermoelectric properties once again, and provides the direct microstructure observation and consistent theoretical model calculation to emphasize the role of interface effects in modulation doping, which should be probably applicable to other thermoelectrics.     

Improved Thermoelectric Properties in Ga2Te3-GaSb Vacancy Compounds

Thermoelectric materials with high figure of merit, which requires large Seebeck coefficient, large electrical conductivity, and low thermal conductivity, are of great importance in solid-state cooling and power generation. Solid-solution formation is one effective method to achieve low thermal conductivity by phonon scattering due to mass and strain field fluctuations. This type of scattering is maximized in structures containing vacancies. The thermoelectric properties of Ga₂Te₃-GaSb vacancy compounds were studied in this work. We find that the lattice thermal conductivity is reduced by over an order of magnitude with the addition of only very moderate amounts of Ga₂Te₃. Additionally, both the carrier type and concentration can be modified. While the vacancy structure induced by Ga₂Te₃ addition to GaSb can effectively reduce phonon conductivity, carrier mobility is also degraded, and optimized thermoelectric properties require careful control of the vacancy content in these solid solutions.     

Rational Electronic and Structural Designs Advance BiCuSeO Thermoelectrics

In this work, a record high thermoelectric figure-of-merit ZT of 1.6 ± 0.2 at 873 K in p-type polycrystalline Bi_0.94Pb_0.06CuSe_1.01O_0.99 by a synergy of rational band manipulation and novel nanostructural design is reported. First-principles density functional theory calculation results indicate that the density of state at the Fermi level that crosses the valence band can be significantly reduced and the measured optical bandgap can be enlarged from 0.70 to 0.74 eV by simply replacing 1% O with 1% Se, both indicating a potentially reduced carrier concentration and in turn, an improved carrier mobility and a boosted power factor up to 9.0 µW cm⁻¹ K⁻². Meanwhile, comprehensive characterizations reveal that under Se-rich condition, Cu₂Se secondary microphases and significant lattice distortions triggered by Pb-doping and Se-substitution can be simultaneously achieved, contributing to a reduced lattice thermal conductivity of 0.4 W m⁻¹ K⁻¹. Furthermore, a unique shear exfoliation technique enables an effective grain refinement with higher anisotropy of the polycrystalline pellet, leading to a further improved power factor up to 10.9 µW cm⁻¹ K⁻² and a further reduced lattice thermal conductivity of 0.30 W m⁻¹ K⁻¹, which gives rise to record high ZT.     

Thermoelectric Properties of <Emphasis Type="Italic">n</Emphasis>-Type Multiple-Filled Skutterudites

Filled skutterudites are prospective intermediate temperature materials for␣thermoelectric power generation. CoSb₃-based n-type filled skutterudites have good electrical transport properties with power factor values over 40 μW/cm K² at elevated temperatures. Filling multiple fillers into the crystallographic voids of skutterudites would help scatter a broad range of lattice phonons, thus resulting in lower lattice thermal conductivity values. We report the thermoelectric properties of n-type multiple-filled skutterudites between 5 K and 800 K. The combination of different fillers inside the voids of the skutterudite structure shows enhanced phonon scattering, and consequently a strong suppression of the lattice thermal conductivity. Very good power factor values are achieved in multiple-filled skutterudite compared with single-element-filled materials. The dimensionless thermoelectric figure of merit for n-type filled skutterudites is improved through multiple-filling in a wide temperature range.     

Electrical Property Enhancement in Orientation-Modulated Perovskite La-Doped SrTiO3 Thermoelectric Thin Films

Thermoelectric oxide thin films are promising in chip cooling. The issues on the orientation of thin films are essential as they are related to the structures, morphologies, and thermoelectric properties. In this regard, the orientation modulation is conducted on La-doped SrTiO₃ thin films on (LaAlO₃)_0.3(Sr₂TaAlO₆)_0.7 (LSAT) single crystal substrates. Layer-by-layer growth mode is found in (001)- and (110)- oriented thin films, resulting in few grain boundaries (GBs). In (111)-oriented films, island growth mode leads to columnar grain boundaries that build up potential barriers for electrons to be strongly scattered and filtered, suppressing electron mobility and increasing effective mass. In addition, the GBs serve as oxygen vacancy diffusion paths when annealing, causing increased carrier concentration and lattice contraction. The weighted mobility of 71.9 cm² V⁻¹ s⁻¹ and electrical conductivity of ≈600 S cm⁻¹ are realized in the (001)-oriented film at room temperature. Ultimately, outstanding power factor values of ≈569 µW m⁻¹ K⁻² (room temperature) and ≈791 µW m⁻¹ K⁻² (573 K) are successfully achieved, outperforming those in polycrystalline ceramics and (111)-oriented films. This study systematically investigates the influence of grain boundaries and orientations on SrTiO₃-based thermoelectric films, which lays a solid foundation for improving thermoelectric performance in other oxide thin films.     

High Entropy Semiconductor AgMnGeSbTe4 with Desirable Thermoelectric Performance

A new p-type high entropy semiconductor AgMnGeSbTe₄ with a band gap of ≈0.28 eV is reported as a promising thermoelectric material. AgMnGeSbTe₄ crystallizes in the rock-salt NaCl structure with cations Ag, Mn, Ge, and Sb randomly disordered over the Na site. Thus, a strong lattice distortion forms from the large difference in the atomic radii of Ag, Mn, Ge, and Sb, resulting in a low lattice thermal conductivity of 0.54 W m⁻¹ K⁻¹ at 600 K. In addition, the AgMnGeSbTe₄ exhibits a degenerate semiconductor behavior and a large average power factor of 10.36 µW cm⁻¹ K⁻² in the temperature range of 400–773 K. As a consequence, the AgMnGeSbTe₄ has a peak figure of merit (ZT) of 1.05 at 773 K and a desirable average ZT value of 0.84 in the temperature range of 400–773 K. Moreover, the thermoelectric performance of AgMnGeSbTe₄ can be further enhanced by precipitating of Ag₈GeTe₆, which acts as extra scatting centers for holes with low energy and phonons with medium wavelength. The simultaneous optimization in power factor and lattice thermal conductivity yields a peak ZT of 1.27 at 773 K and an average ZT of 0.92 (400–773 K) in AgMnGeSbTe₄-1 mol% Ag₈GeTe₆.     

Zintl Phases as Thermoelectric Materials: Tuned Transport Properties of the Compounds CaxYb1–xZn2Sb2

Zintl phases are ideal candidates for efficient thermoelectric materials, because they are typically small‐bandgap semiconductors with complex structures. Furthermore, such phases allow fine adjustment of dopant concentration without disrupting electronic mobility, which is essential for optimizing thermoelectric material efficiency. The tunability of Zintl phases is demonstrated with the series Ca_xYb_1–xZn₂Sb₂ (0 ≤ x ≤ 1). Measurements of the electrical conductivity, Hall mobility, Seebeck coefficient, and thermal conductivity (in the 300–800 K temperature range) show the compounds to behave as heavily doped semiconductors, with transport properties that can be systematically regulated by varying x. Within this series, x = 0 is the most metallic (lowest electrical resistivity, lowest Seebeck coefficient, and highest carrier concentration), and x = 1 is the most semiconducting (highest electrical resistivity, highest Seebeck coefficient, and lowest carrier concentration), while the mobility is largely independent of x. In addition, the structural disorder generated by the incorporation of multiple cations lowers the overall thermal conductivity significantly at intermediate compositions, increasing the thermoelectric figure of merit, zT. Thus, both zT and the thermoelectric compatibility factor (like zT, a composite function of the transport properties) can be finely tuned to allow optimization of efficiency in a thermoelectric device.     

Enhanced power factor of poly (3,4-ethyldioxythiophene):poly (styrene sulfonate) (PEDOT:PSS)/RTCVD graphene hybrid films

The thermoelectric generator has been an attractive alternative power source to operate a wireless sensor node. Usually, inorganic compounds are most often used in thermoelectric devices, and hence, are extensively studied due to their superior thermoelectric performance. We have investigated a novel interfacial technique to fabricate a hybrid film of highly conductive PEDOT:PSS (poly 3,4-ethylenedioxythiophene):poly(4-styrenesulfonate) and graphene. Organic materials PEDOT doped with PSS exhibits outstanding electrical properties due to its high conductivity, low bandgap, and energy migration. Furthermore, we utilized graphene fabricated by rapid thermal chemical vapor deposition (RTCVD) as a thermoelectric material. Our results show that the interfacial technique between substrate and hybrid film could be clearly improved due to the UV plasma treatment. The thermoelectric hybrid film of PEDOT:PSS and RTCVD graphene (P/RTG) exhibited an enhanced power factor of 56.28 μW m⁻¹ K⁻² with a Seebeck coefficient of 54.0 μV K⁻¹.     

Interstitial Cu: An Effective Strategy for High Carrier Mobility and High Thermoelectric Performance in GeTe

Dense point defects can strengthen phonon scattering to reduce the lattice thermal conductivity and induce outstanding thermoelectric performance in GeTe-based materials. However, extra point defects inevitably enlarge carrier scattering and deteriorate carrier mobility. Herein, it is found that the interstitial Cu in GeTe can result in synergistic effects, which include: 1) strengthened phonon scattering, leading to ultralow lattice thermal conductivity of 0.48 W m⁻¹ K⁻¹ at 623 K; 2) weakened carrier scattering, contributing to high carrier mobility of 80 cm² V⁻¹ s⁻¹ at 300 K; 3) optimized carrier concentration of 1.22 × 10²⁰ cm⁻³. Correspondingly, a high figure-of-merit of ≈2.3 at 623 K can be obtained in the Ge_0.93Ti_0.01Bi_0.06Te-0.01Cu, which corresponds to a maximum energy conversion efficiency of ≈10% at a temperature difference of 423 K. This study systematically investigates the doping behavior of the interstitial Cu in GeTe-based thermoelectric materials for the first time and demonstrates that the localized interstitial Cu is a new strategy to enhance the thermoelectric performance of GeTe-based thermoelectric materials.     

Improvement in Thermoelectric Properties of Se-Free Cu3SbS4 Compound

Recently, Cu-based chalcogenides such as Cu₃SbSe₄, Cu₂Se, and Cu₂SnSe₃ have attracted much attention because of their high thermoelectric performance and their common feature of very low thermal conductivity. However, for practical use, materials without toxic elements such as selenium are preferable. In this paper, we report Se-free Cu₃SbS₄ thermoelectric material and improvement of its figure of merit (ZT) by chemical substitutions. Substitutions of 3 at.% Ag for Cu and 2 at.% Ge for Sb lead to significant reductions in the thermal conductivity by 37% and 22%, respectively. These substitutions do not sacrifice the power factor, thus resulting in enhancement of the ZT value. The sensitivity of the thermal conductivity to chemical substitutions in these compounds is discussed in terms of the calculated phonon dispersion and previously proposed models for Cu-based chalcogenides. To improve the power factor, we optimize the hole carrier concentration by substitution of Ge for Sb, achieving a power factor of 16 μW/cm K² at 573 K, which is better than the best reported for Se-based Cu₃SbSe₄ compounds.     

Al-doped ZnO and N-doped CuxO thermoelectric thin films for self-powering integrated devices

With the use of a thermoelectric material, terrestrial heat can be harvested then converted to electrical power. The advent of these devices has led to the idea of self-powering wherein devices are driven by heat from their working environment. The focus of this study is to fabricate low cost thermoelectric materials, such as aluminum-doped ZnO (ZnO:Al) and nitrogen-doped Cu_xO (Cu_xO:N) that can effectively harvest heat for power generation.ZnO:Al (n-type) and Cu_xO:N (p-type) thin films with nanocrystallites were deposited in (1.27×0.64) cm² glass substrates via spray pyrolysis technique. These materials exhibit significantly high thermoelectric properties, which is comparable to previous works on thermoelectric materials. ZnO:Al showed to have a maximum Seebeck coefficient (S) of 448 μV/K ranging from 300 to 330 K. Cu_xO:N exhibited a significantly much larger |S| of 1002 μV/K at the same temperature range. A prototype of a thermoelectric device was constructed based from these grown thin films and showed to generate a maximum of 32.8 mV at 28 K temperature difference.     

Contrasting Cu Roles Lead to High Ranged Thermoelectric Performance of PbS

To obtain high-performance PbS-based thermoelectric materials, this study introduces Cu with different contrasting roles in p-type PbS, which can effectively decrease the lattice thermal conductivity and simultaneously optimize the electrical transport properties. Experimental results illustrate that Cu substitutions and Cu interstitials can improve carrier mobility through lowering effective mass (m*) and carrier concentration (n_H) in a low temperature range (300–450 K), and further optimize temperature-dependent n_H in a high temperature range (450–823 K). Both decreased m* and n_H shift the peak power factor to low temperature range, leading to an ultrahigh power factor ≈23 µW cm⁻¹ K⁻² at 423 K for Pb_0.99Cu_0.01S-0.01Cu. Additionally, the special dynamic-doping behaviors of Cu can continuously promote n_H to approach the temperature-dependent relationship of (n_{H, opt}) ≈ (m*T)^1.5, which brings about an eminent average power factor (PF_ave) ≈ 18 µW cm⁻¹ K⁻² among 300–823 K in Pb_0.99Cu_0.01S-0.01Cu. Furthermore, the microstructure characterizations unclose that the atomic and nanoscale Cu-containing defects can effectively intensify the phonon scattering and suppress the lattice thermal conductivity. Consequently, both high ZT (≈0.2 at 300 K) and peak ZT (≈1.2 at 773 K) result in a record-high average ZT (ZT_ave) of ≈0.79 at 300–823 K for Pb_0.99Cu_0.01S-0.01Cu.