Search

Tetradymite-structured chalcogenides, such as Bi2Te3 and Sb2Te3, are quasi-two-dimensional (2D) layered compounds, which are significant thermoelectric materials applied near room temperature. The intercalation of guest species in van der Waals (vdW) gap implemented for tunning properties has attracted much attention in recent years. We attempt to insert Ga atoms in the vdW gap between the Te layers in p-type Bi0.3Sb1.7Te3 (BST) for further improving thermoelectrics. The vdW-related defects (including extrinsic interstitial and intrinsic defects) induced by Ga intercalation can not only modulate the carrier concentration but enhance the texture, thereby yielding excellent electrical properties, which is reflected in the power factor PF ~4.43 mW m-1 K-2. Furthermore, the intercalation of Ga produces multi-scale lattice imperfections such as point defects, Te precipitations, and nanopores, realizing the low lattice thermal conductivity in BST-Ga samples. Ultimately, a peak zT ~1.1 at 373 K is achieved in the BST-1%Ga sample and greatly improved by ~22% compared to the pristine BST. The weak bonding of vdW interlayer interaction can boost the synergistic effect for advancing BST-based or other layered thermoelectrics.

The synergistic effect of band convergence and lattice disorder optimizes SnTe electron–phonon transport. The alloy scattering and ionized impurity scattering are important for heavily defective materials.

The highly electronegative halogen element Br can promote the dissolution of high-melting Gd in PbSe, thereby enhancing its band modification effect, leading to a realization of high thermoelectric performance for n-type Pb0.997Gd0.003Br0.003Se0.997.

The lamellar structure of (Bi,Sb)2(Te,Se)3 alloys makes it difficult to achieve isotropic thermoelectric properties in the directions along and perpendicular to the c-axis, especially for n-type samples. In this work, by introducing Cu in polycrystalline n-type CuxBi2Te2.7Se0.3 and applying the traditional synthesis process of high-energy ball milling and hot pressing, substantial enhancement of the thermoelectric figure of merit zT is obtained in both in-plane and out-of-plane directions. The intercalated Cu not only provides electron transport media for mobility improvement but also reduces the lattice thermal conductivity owing to the strain fluctuation. Typically, the van der Waals gap in the out-of-plane direction leads to relatively slower mobility and lower lattice thermal conductivity. Taking into account the same average density-of-state effective mass (mavg* ∼ 1.5me) predicted based on a single parabolic model, the obtained quality factor β is comparable in both directions. As a result, a peak zT ∼ 1.05 at 420 K and the average zT approaching to 1.0 in the temperature range 300-500 K are obtained in both directions for the Cu0. 02Bi2Te2.7Se0.3 sample. The simple synthesis process and isotropic thermoelectric properties in this work make n-type Bi2Te3 more convenient for potential production and application.

The discovery of band convergence has opened an effective avenue for significantly enhancing thermoelectric performance of SnTe, while alloying CdTe in SnTe is evidenced efficient for improving the valley degeneracy. However, the thermoelectric transport properties are limited due to the low solubility of CdTe in SnTe (∼3%). Inspired by the improvement of dimensionless figure of merit zT in Cu or Se-doped SnTe, investigating the effect of Cu2Se on the electronic and phonon transport properties of SnTe-CdTe alloys is highly desired. Traditionally, improving the quality factor can trigger an increase of the potential of a compound for higher zT, which is of importance for design of thermoelectric materials. Here, alloyed 3% Cu2Se in SnTe-3%CdTe system enables an increased peak zT, which is attributed by the optimization of electronic performance (∼21 μW cm−1 K-2 at 800 K), as well as the decreased lattice thermal conductivity owing to the enhanced mass and strain fluctuations. More importantly, alloying Cu2Se not only improves the quality factor from ∼0.25 to ∼0.45, resulting in a higher maximum potential zT, but also effectively preserves the Fermi energy in a relative optimized level. The current findings demonstrate the role of Cu2Se for manipulating thermoelectrics in SnTe.

Bi

The traditional thermoelectric material GeTe has drawn much attention recently because of the reported high thermoelectric performance of the rhombohedral phase in low-temperature ranges, where the split L and Σ band can be reconverged to have a small energy offset and thus high density of state effective mass according to the rhombohedral angle. In addition, In doping in GeTe is also reported to enhance the density of effective mass and therefore increase the Seebeck coefficient because of the induced resonant levels. In this work, In and Pb are doped in GeTe, and In doping leads to an increase in the rhombohedral angle and thus enhanced density of state effective mass in addition to the resonant effect. However, the improved Seebeck coefficient result from In doping is compensated for by a sharp reduction of Hall mobility, leading to no significant enhancement of electronic performance in the rhombohedral phase. By further Pb/Ge doping in the matrix Ge0.95In0.05Te for the optimization of carrier concentration and reduction of lattice thermal conductivity (as low as 0.7 W/mK), a zT as high as ∼1.2 at 550 K and average zT of ∼0.75 between 300 and 550 K are realized in this work, demonstrating GeTe as a promising candidate for near-room-temperature application.

Liquid-like materials have attracted increasing attention, owing to their phonon-liquid electron-crystal feature. As a typical representative, the superionic conductor AgCrSe2 is regarded as a promising thermoelectric for its intrinsic ultralow lattice thermal conductivity. The primary challenge for achieving high thermoelectric performance is to enhance the inferior electronic performance in AgCrSe2 compounds. Thus, it is very significant to manipulate band effective mass to achieve a higher power factor. In this work, the Sb/Bi elements are doped at Cr sites in Ag0.97CrSe2, i.e., Ag0.97Cr1-x(Sb/Bi)xSe2, aiming at producing a better overlap of electron orbits between different atoms for sharpening the valence band and decreasing the effective mass. In comparison to pristine AgCrSe2, a considerable improvement (>50%) in the power factor (∼387 μW m-1 K-2 at 750 K) is realized upon 3% Sb doping. The single parabolic band model clarifies that the decreased effective mass and optimized carrier concentration contribute to the enhanced electronic property. Furthermore, an ultralow lattice thermal conductivity (∼0.2 W m-1 K-1) is well-maintained for the sample with 3% Sb doping as a result of the nearly unchanged superionic conduction. Eventually, a high peak figure of merit zT (∼0.7 at 750 K) is obtained in Ag0.97Cr0.97Sb0.03Se2. The current finding provides an excellent avenue for advancing thermoelectrics in AgCrSe2 materials.

AgCrSe2-based compounds have attracted much attention as an environmentally friendly thermoelectric material in recent years due to the intriguing liquid-like properties. However, the ultra-low carrier concentration and the high AgCr deep-level defects limit the overall thermoelectric performance. Here, we successfully introduced Pb into Ag-deficient Ag0.97CrSe2 alloys to tune the carrier concentration across a broad temperature range. The Pb2+ as an acceptor dopant preferentially occupies Cr sites, boosting the hole carrier concentration to 1.77 × 1019 cm−3 at room temperature. Furthermore, the Pb strongly inhibits the creation of intrinsic AgCr defects, weakens the increased thermal excited ionization with the increasing temperature and slowed the rising trend of the carrier concentration. The designed carrier concentration matches the theoretically predicted optimized one over the entire temperature range, leading to a remarkable enhancement in power factor, especially the maximum power factor of ∼ 500 μW⋅m−1⋅K−2 at 750 K is superior to most previous results. Additionally, the abundant point defects promote phonon scattering, thus reducing the lattice thermal conductivity. As a result, the maximum figure of merit zT (∼ 0.51 at 750 K) is achieved in Ag0.97Cr0.995Pb0.005Se2. This work confirms the feasibility of manipulating deep-level defects to achieve temperature-dependent optimal carrier concentration and provides a valuable guidance for other thermoelectric materials.

Breaking the thermoelectric figure of merit zT barrier of SnTe enables it to become a promising alternative to PbTe; however, the inferior and strongly coupled physicochemical properties of pristine SnTe severely restrict the efficient optimization. Herein, we doped trivalent Sb in SnTe and incorporated SnS particles to achieve high quality factor B through a two-step optimization strategy of tuning the valence band structure and intercalating heterostructural precipitates, and well predicted the potential prospects. The high solubility limit of Sb not only reduced the carrier concentration nH but also significantly optimized the valence band structure and improved the Seebeck coefficient, thereby enhancing the weight mobility μw in the all-temperature region. Furthermore, the additional SnS, which tends to exist as precipitates with different micrometer-scale sizes, enhanced low-medium-frequency phonon scattering in a wider frequency range except for point defects scattering, suppressing the lattice thermal conductivity to 0.55 W m−1 K−1. As a result of this synergistic effect, a high B-factor of ∼0.82 greater than triple pure SnTe was obtained in Sn0.91Sb0.09Te-10%SnS, with an enhanced zT of ∼1.15 at 850 K. More importantly, the high B-factor accurately predicted an excellent zT value of ∼1.65 at the optimal Fermi level, which highlights the great potential of Sn1- xSb xTe- y%SnS-based materials. This work provides an effective route for stepwise optimization of electrical and thermal performance from the B-factor perspective and has guiding significance for other thermoelectric materials.

The lamellar structure of (Bi,Sb)

PbS is identified as a potential alternative candidate material for thermoelectric power generation and refrigeration, owing to the resemblance with PbTe in crystal and band structures. However, the thermoelectric performance has reached a bottleneck because of its inferior electronic structure and high lattice thermal conductivity. This work focuses on optimizing the electron–phonon transport by the synergistic effect of Ti and Cu2S in n-type PbS. The first-principles calculation, single Kane band model, and Debye model reveal the physical origin of thermoelectric enhancement. The Ti doping introduces a donor-defect state, leading to a high electrical conductivity and a suppression of bipolar diffusion. However, the band structure of PbS is not ideally optimized due to the localization effect of the Ti resonant impurity states. Furthermore, the co-added Cu2S induces additional point defects, multiscale secondary phases, and Cu-rich precipitates at grain boundaries, which significantly scatter phonons in a wide frequency range and reduce the lattice thermal conductivity. As a result, the maximum zT of ∼0.8 at 823 K and the average zTave of ∼0.46 from 300 to 623 K are achieved in n-type Pb0.99Ti0.01S–2%Cu2S, demonstrating the important roles of Ti and Cu2S on improving thermoelectrics in n-type PbS.

Small-bandwidth n-type PbTe-MnTe alloys effectively modify the valley shape, while it also inevitably aggravates the deterioration of carrier mobility as nonpolar phonons dominate the scattering. It is found that a trace amount of Cu doping can alleviate the compromises among thermoelectric parameters, thereby significantly optimizing the electrical-transport performance near room temperature of n-type PbTe-MnTe alloys. The single-Kane model reveals that the physical origin of performance improvement lies in the carrier mobility enhancement and self-optimization of carrier concentration. The Debye-Callaway model further quantifies the contribution of copper defect scattering to the lattice thermal conductivity. Notably, the high thermoelectric quality factor obtained in this work rationalizes their superior properties and reveals immense potential for achieving higher zT. Herein, an extremely high zT of ∼0.52 at room temperature and a maximum zTmax of ∼1.2 at 823 K are achieved in 0.3% Cu-intercalated n-type PbTe-MnTe. The mechanism in balancing compromise elaborated in principle contributes to an improvement of thermoelectric properties of the n-type PbTe alloys in a broad temperature range.

We revisit a superconducting phase diagram and electronic structures across the charge density wave (CDW) phase transition of Cu-underdoped $1T\text{\ensuremath{-}}{\mathrm{Cu}}_{\ensuremath{\delta}}\mathrm{Ti}{\mathrm{Se}}_{2}$ ($\ensuremath{\delta}\ensuremath{\sim}0.03$) under hydrostatic pressure. Superconductivity appears right after the complete collapse of the long-range CDW at a critical pressure of ${P}_{\mathrm{c}}\ensuremath{\sim}2.48\phantom{\rule{0.16em}{0ex}}\mathrm{GPa}$, apart from the reported superconducting phase diagrams; it is found that the superconducting transition temperature shows a domelike pressure dependence covering a narrow pressure range with a maximum of ${{T}_{\mathrm{c}}}^{\mathrm{max}}\ensuremath{\sim}2.80\phantom{\rule{0.16em}{0ex}}\mathrm{K}$ at 4.80 GPa. Accordingly, the residual resistivity ${\ensuremath{\rho}}_{0}$ and temperature exponent $n$ of normal-state resistivity (from \ensuremath{\sim}3.30 at ambient pressure to \ensuremath{\sim}2.38 at ${P}_{\mathrm{c}}$ and \ensuremath{\sim}4.0 at 6.50 GPa) reduce sizably while the quadratic temperature coefficient $A$ of normal-state resistivity is enhanced by one order in magnitude; these results indicate the importance of CDW quantum fluctuation in superconducting pairing; low-$T$ resistivity upwarps with a \ensuremath{-}ln$T$ dependence below a characteristic temperature ${T}^{*}$ which has a domelike shape in the pressure range of 2.82--4.80 GPa. Based on two-band analysis of Hall conductivity and Kohler-fitting of magnetotransport (MR), energy bands are dominated by electron-type carriers across the CDW phase transition for $Pl{P}_{\mathrm{c}}$, and they reverse into hole-type for $Pg{P}_{\mathrm{c}}$; interestingly, the mobility of carriers increases up to five times at ${P}_{\mathrm{c}}$, but carrier concentration shows a weak pressure dependence. The MR value increases with the pressure for $Pl{P}_{\mathrm{c}}$ and then jump up to a saturated value after the collapse of the CDW. Our results show that the collapse of the CDW is accompanied by the reconstruction of the Fermi surface, and the enhancement in MR can be mainly attributed to the change of mobility. Possible mechanisms are discussed.

Conventional PbTe-based semiconductors have been leading the developments in the thermoelectrics community due to their rich capabilities in optimizing the electronic and phonon transport properties. However, growing environmental concerns related to Pb toxicity is guiding thermoelectrics research toward the lead-free route. As an alternative analog of PbTe, SnTe has recently attracted increasing research interest for thermoelectric energy conversion. The key challenges for enhancing the thermoelectric performance of SnTe to be comparable with that of p-type PbTe include decreases in the carrier concentration, energy offset between the light valence band (L band) and heavy valence band (Σ band), and lattice thermal conductivity. In this review, the recent progresses made in SnTe alloys are first outlined. Based on the insights gained into the intrinsic nonstoichiometry as well as the electronic and phonon transport properties of SnTe materials, fundamental and successful strategies focusing on confronting the challenges faced by figure-of-merit zT enhancement in SnTe are discussed and highlighted, aiming at providing a straightforward overview on the underlying physics of these effective strategies. Eventually, future challenges and outlook are summarized for boosting advancements in environment-friendly SnTe thermoelectric materials.

Texturization tuning is of crucial significance for designing and developing high-performance thermoelectric materials and devices. Here, we report for the first time that a strong texturization effect induces an in-plane high-performance thermoelectric and an out-of-plane low lattice thermal conductivity in Sb-substituted misfit-layered (SnS)1.2(TiS2)2 alloys. In the in-plane direction, the oriented texture promotes a high carrier mobility, contributing to the maximization of the power factor (∼0.90 mW K-2 m-1). Moreover, the in-plane lattice thermal conductivity dramatically reduces deriving from the point defects due to the Sb substitution and weakened transverse sound velocity owing to the softening of bonding, ultimately leading to one of the highest thermoelectric performances ever reported among misfit-layered chalcogenides. In particular, in the out-of-plane direction, the texturization triggers the lowest lattice thermal conductivity (∼0.39 W K-1 m-1), exceeding the theoretical limit of the Debye-Cahill model, which provides a precious opportunity to investigate this real Sb-substituted (SnS)1.2(TiS2)2 material. The present finding in misfit-layered chalcogenides provides a novel strategy for manipulating thermoelectrics via texturization engineering.

As an environment-friendly alternative to traditional PbTe, many attempts have recently been made to improve thermoelectric SnTe. Effective strategies are mainly focused on valence band convergence, nanostructuring, interstitial defects, and alloying solubility. In particular, alloying SnTe with CdTe/GeTe triggers an inherent decline of valence band offset effectively owing to a high solubility of ∼20% of CdTe. However, to what level an additional element doping in low-solubility SnTe-CdTe alloys can play a role in enhancing the thermoelectric performance still remains a mystery. Here, a new strategy is shown that unexpected Bi doping, by alloying with only ∼3% CdTe, induces a significant enhancement of the thermoelectric figure of merit ZT to be ∼240% (ZT up to ∼1.3) at 838 K, which is mainly determined by the dramatically reduced lattice thermal conductivity above 800 K deriving from the exotic Bi doping and Cu-interstitial defects. More interestingly, combining experimental and theoretical evidences, the Bi-doping-driven band convergence is also beneficial to the improvement of thermoelectric performance below 800 K. The present findings demonstrate the extraordinary role of Bi for advancing the thermoelectric performance in SnTe alloys.

Semiconducting manganese selenide (MnSe), crystalizing in a cubic structure with a wide band gap, is focused on in this work for its potential as an ecofriendly thermoelectric material. Pristine MnSe exhibits a low carrier concentration of ∼1.3 × 1017 cm−3 at room temperature, which can be dramatically increased to ∼2.6 × 1021 cm−3 primarily resulting from the Mn-vacancy introduced by Na-doping at Mn site. The broad range of carrier concentration not only enables a reliable prediction of the electrical transport properties using a single parabolic band (SPB) model with the acoustic scattering, but also provides a well understanding of its underlying material physics. Such a doping and the simultaneously induced Mn-vacancies provide additional phonon scattering, leading to a reduced lattice thermal conductivity of ∼1.2 W/m-K at high temperatures.

The misfit layer compound (SnS)1.2(TiS2)2 is a promising low-cost thermoelectric material because of its low thermal conductivity derived from the superlattice-like structure. However, the strong covalent bonds within each constituent layer highly localize the electrons thereby it is highly challenging to optimize the power factor by doping or alloying. Here, we show that Bi doping at the Sn site markedly breaks the covalent bonds networks and highly delocalizes the electrons. This results in a high charge carrier concentration and enhanced power factor throughout the whole temperature range. It is highly remarkable that Bi doping also significantly reduces the thermal conductivity by suppressing the heat conduction carried by phonons, indicating that it independently modulates phonon and charge transport properties. These effects collectively give rise to a maximum ZT of 0.3 at 720 K. In addition, we apply the single Kane band model and the Debye–Callaway model to clarify the electron and phonon transport mechanisms in the misfit layer compound (SnS)1.2(TiS2)2.

The fact that the thermoelectric performance is far inferior to that of p-type PbTe has inspired many strategies to develop n-type PbTe thermoelectrics. Alloying PbS in n-type PbTe effectively changes the shape of a valley to trigger a heavier conduction band for improving the Seebeck coefficient, while the resulting small orbital overlap inevitably leads to phase separation hindering electron transport. The effect of vacancies on the solubility of sulfur in n-type PbTe is ambiguous; especially, the heterostructure due to phase separation in high-content PbS-alloyed PbTe also requires sufficient modification to optimize the electroacoustic transport. This motivates the current work on the introduction of vacancies by charge-balancing doping via Sb2Te3 and discovers striking new insight that the introduced vacancies can induce a new heterostructure of Pb2Sb2S5 and suppress the aggregation of Sb and PbS in high-solubility n-type PbTe–PbS. The modification of the band structure and optimization of the electron transport give rise to a prominent enhancement in electronic performance. Furthermore, the Debye–Callaway model validates the dramatic contribution of vacancy aggregation and heterostructures to lattice thermal conductivity. As a result, the synergistic modulation of electroacoustic characteristics achieves a significant improvement in both the maximum zT and the near-room-temperature zT. Understanding such unique findings is critical for applicability to other thermoelectric materials.

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 Cu

p-Type and n-type thermoelectric semiconductor materials with compatible performance are key components for thermoelectric devices. Great improvement in thermoelectric performance has been achieved in p-type PbTe, whereas the n-type counterpart still shows much inferior thermoelectric performance compared to that of the p-type PbTe. This inspires many strategies focused on advancing n-type PbTe thermoelectrics. Herein, not only effective mass engineering, resonance states, point defects, and nanostructures but also newly developed concepts including dynamic doping for stabilizing the optimal carrier concentration and introducing dislocations for reducing lattice thermal conductivity are summarized. In addition, the synergistic effects for further enhancing the thermoelectric performance are outlined, together with a discussion and outlook for boosting the advancement in n-type PbTe thermoelectric materials. Strategies discussed here are expected to be applicable to other thermoelectric materials.

In strongly correlated electron system, the impact of elementary substitution or intercalation plays a crucial role in determining electronic ground state among various macroscopic quantum phases such as charge order and superconductivity. Here, we report that simultaneous Cu intercalation and Ta substitution at Ti site in 1T-Cu

Liquid-like materials have attracted increasing attention, owing to their phonon-liquid electron-crystal feature. As a typical representative, the superionic conductor AgCrSe

Intermetallic clathrates are materials characterized by a large cage structure where guest atoms can move anharmonically, providing these materials exotic thermoelectric properties. Unfortunately, the dynamical and atomic nature of the rattling phonons, and their interactions with the electronic structure, are not fully understood. Here, we report that a germanium isotope effect can trigger an inherent guest rattling and cage distortion in clathrate Ba8Ga16Ge30 (BGG). Raman-scattering spectroscopy and advanced electron microscopy demonstrate that the atomic germanium isotope effect induces an off-centre rattling at the 6d sites as well as a tetrakaidecahedron deformation which is anisotropic for n-type BGG but isotropic for p-type BGG. The present findings indicate that the large n-type germanium isotope effect arises from the strong electron-phonon coupling, which opens up a novel avenue for manipulating dynamical motions of phonons via atomic isotope engineering. Keywords: Thermoelectric, Clathrate, Isotope effect, Electron-phonon coupling

P-type lead telluride (PbTe) emerged as a promising thermoelectric material for intermediate-temperature waste-heat-energy harvesting. However, n-type PbTe still confronted with a considerable challenge owing to its relatively low figure of merit ZT and conversion efficiency η, limiting widespread thermoelectric applications. Here, we report that Ga-doping in n-type PbTe can optimize carrier concentration and thus improve the power factor. Moreover, further experimental and theoretical evidence reveals that Ga-doping-induced multiphase structures with nano- to micrometer size can simultaneously modulate phonon transport, leading to dramatic reduction of lattice thermal conductivity. As a consequence, a tremendous enhancement of ZT value at 823 K reaches ∼1.3 for n-type Pb0.97Ga0.03Te. In particular, in a wide temperature range from 323 to 823 K, the average ZTave value of ∼0.9 and the calculated conversion efficiency η of ∼13% are achieved by Ga doping. The present findings demonstrate the great potential...

Introducing resonant levels is a potent strategy to improve the thermoelectric properties of the thermoelectric systems. However, the beneficial effect of resonant levels tends to be weakened with rising temperature for the PbTe system. This motivates us to introduce dynamic doping of Cu into Cr-doped n-type PbTe to achieve the fully optimized carrier transport over a wide temperature range. As a consequence, an extraordinary figure of merit, ZT of ∼ 0.55 at room temperature, a peak ZT of ∼ 1.31 at 773 K and an average ZT of ∼ 1.02 in the range of 323 to 823 K are obtained in the Pb0.975Cr0.025Te-0.2%Cu. Additionally, how co-doped of Cr and Cu contributes to suppressing thermal transports is still ambiguous. Herein, we employ comprehensive electron microscopy investigations to reveal that the synergistic incorporation of Cr and Cu into the PbTe matrix results in a series of phonon scattering sources, including massive point defects, high-density of nanoscale precipitates, microscale secondary phases, and dense grain boundaries, which can significantly reduce the lattice thermal conductivity by enhancing phonon scattering. This work clarifies the fundamental Cr-doping mechanism in PbTe and demonstrates that dynamic Cu-doping engineering is an effective approach to boosting thermoelectric performance, which should be applied in other thermoelectric materials.

The development of n-type high-performance PbTe thermoelectric materials for matching its p-type counterparts is an urgent matter to expand its practical applications. Here, we introduce Ag2Te into n-type Pb0.975Cr0.025Te for achieving a high peak figure of merit of 1.5 at 773 K. Such a high value is attributed to the synergistic optimization of carrier and phonon transports by Ag2Te introducing and the dynamic doping of Ag. From the detailed structure and property analysis, we found that Ag2Te nanoprecipitates establish coherent interfaces and hence potential barriers with the matrix to induce energy-dependent carrier scattering and maintain relatively high carrier mobility, leading to an optimal electrical-transport properties over a wide temperature range. Moreover, we employ comprehensive electron microscopy investigations and approximate Debye-Callaway model to reveal the origin of the significantly reduced lattice thermal conductivity in Ag2Te-alloyed Pb0.975Cr0.025Te. The strategies used here provide an effective method for designing high-performance thermoelectric material systems.

Understanding the alloying effect is of critical significance for rationally designing highly efficient thermoelectric materials. Here, we report that a Co- and Cu-substituted alloying effect in misfit-layered (SnS)1.2(TiS2)2 can directly enhance the thermoelectric performance with the highest dimensionless figure of merit ZT of ∼ 0.42 at 720 K until now. The substitution of Co3+ and Cu2+ for Ti4+ ions reduces the electron carrier concentration of the n-type material, thereby contributing to the increase of the Seebeck coefficient, which is clearly evidenced by the Hall measurement. In addition, the introduction of point defects due to the Co and Cu substitution gives rise to the decrease of phononic thermal conductivity. Consequently, the Co- and Cu-substituted alloying effect triggers an optimized carrier concentration, local mass fluctuation, and local strain variation, which inherently lead to the enhancement of thermoelectric properties owing to the combined effect of improved electrical transport properties and increased phonon scattering. The present misfit-layered chalcogenide provides an excellent platform for modulating the thermoelectric performance via an element-substituted alloying effect.

A decrease in valence band energy offset can considerably improve the thermoelectric performance of SnTe, and alloying CdTe in SnTe has been confirmed to be efficient for inducing band convergence. However, the low solubility of CdTe in SnTe severely limits the further decrease in the energy offset and the reduction of lattice thermal conductivity. Inspired by the high solubility of Sb in SnTe-based thermoelectric materials, the trivalent Sb is introduced into SnTe–CdTe alloys, aiming at manipulating the thermoelectric transport properties. Combined with the valence band model, it is demonstrated that high concentration of Sb in SnTe–CdTe enables a further optimization in valence band structures, resulting in an improvement in density-of-state effective mass, thus significantly reinforces the power factor in the whole temperature range. Meanwhile, we propose the solid solution mode of Sb in SnTe, which always generates vacancies to balance the valence state, and the introduction of vacancies explains the reduced lattice parameters and almost constant carrier concentration. Particularly, the Debye–Callaway model quantitatively compares the contribution of Sb substitutional defects and vacancy defects. As a result, an enhanced zT of ∼1.1 has been achieved for Sn0.83Cd0.05Sb0.12Te at 823 K. This work clearly shows the critical role of Sb for enhancing the thermoelectric performance of SnTe–CdTe materials.

Thermoelectric generator (TEG) has been proved as a promising technology for directly converting heat into electricity based on Seebeck effect. On the contrary, this electricity can trigger a solid-state cooling based on conventional Peltier effect. However, these two effects induce a coupling between heat and electric flux, especially for the quantitative relationship still remaining a mystery. Here, we show experimental evidence and theoretical calculation for the coupling by monitoring transient response of fluid temperature and output power. The experimental maximum heat flow in open circuit is 1162 W at cold fluid flow rate V c = 0.3 m3/h and fluid temperature difference ΔTf = 70 °C, enhanced by 13% owing to heat compensation from intrinsic coupling in closed-loop circuit. Meanwhile, the measured maximum output power of TEG is 18.2 W, and subsequently decreases to 15.4 W due to the objective existence of coupling. This double-edged sword in coupling vigorously inspires the potential applications in heat-dissipation situation such as spacecraft, electronic components, photovoltaic, refrigerator and etc. Present findings open a novel avenue for manipulating heat-electricity conversion in practical engineering.

Rhombohedral GeTe can be approximated as the directional distortion of the cubic GeTe along [111]. Such a symmetry-breaking of the crystal structure results in an opposite arrangement in energy of the L and Σ valence bands, and a split of them into 3L+1Z and 6Σ+6η, respectively. This enables a manipulation of the overall band degeneracy for thermoelectric enhancements through a precise control of the degree of crystal structure deviating from a cubic structure for the alignment of the split bands. Here, we show the effect of AgBiSe2-alloying on the crystal structure as well as thermoelectric transport properties of rhombohedral GeTe. AgBiSe2-alloying is found to not only finely manipulate the crystal structure for band convergence and thereby an increased band degeneracy, but also flatten the valence band for an increased band effective mass. Both of them result in an increased density of state effective mass and therefore an enhanced Seebeck coefficient along with a decreased mobility. Moreover, a remarkably reduced lattice thermal conductivity of ∼0.4 W/m-K is obtained due to the introduced additional point defect phonon scattering and bond softening by the alloying. With the help of Bi-doping at the Ge site for further optimizing the carrier concentration, thermoelectric figure of merit, zT, of ∼1.7 and average zTave of ∼0.9 are achieved in 5% AgBiSe2-alloyed rhombohedral GeTe, which demonstrates this material as a promising candidate for low-temperature thermoelectric applications.

Binary group II–V antimonides, especially Zn4Sb3 and ZnSb, have shown great potential for thermoelectric applications because of the intrinsic low lattice thermal conductivity. Another member from ...

Much progress on highly efficient thermoelectric materials have been made in the p-type PbTe. However, the n-type PbTe only shows a relatively low figure of merit ZT and conversion efficiency η, which is urgently required to be strengthened and compatible with p-type counterpart from the viewpoint of large-scale applications. Here, we report that n-type Sb-doped PbTe alloys can directly improve the power factor owing to the optimized carrier concentration. Moreover, the unexpected synergistic effect, deriving from alloying and nano-precipitates scattering due to Sb doping, triggers a dramatic reduction of lattice thermal conductivity. Consequently, a remarkable ZT of ~ 1.3 at 673 K in n-type Pb0.98Sb0.02Te and the average ZTave of ~ 0.83 with the calculated conversion efficiency η of ~ 12.3% in a wide temperature range from 323 to 823 Κ are achieved. The present findings demonstrate the excellent potential in n-type Sb-doped PbTe thermoelectric materials through a synergetic carrier tuning and multiple phonon scattering strategy, which provides a new avenue for exploring high-performance thermoelectric materials in n-type PbTe and/or other materials.

Mn alloying in thermoelectrics is a long-standing strategy for enhancing their figure-of-merit through optimizing electronic transport properties by band convergence, valley perturbation, or spin-orbital coupling. By contrast, mechanisms by which Mn contributes to suppressing thermal transports, namely thermal conductivity, is still ambiguous. A few precedent studies indicate that Mn introduces a series of hierarchical defects from the nano- to meso-scale, leading to effective phonon scattering scoping a wide frequency spectrum. Due to insufficient insights at the atomic level, the theory remains as phenomenological and cannot be used to quantitatively predict the thermal conductivity of Mn-alloyed thermoelectrics. Herein, by choosing the SnTe as a case study, aberration-corrected transmission electron microscopy (TEM)/scanning transmission electron microscopy (STEM) to characterize the lattice complexity of Sn1.02−xMnxTe is employed. Mn as a “dynamic” dopant that plays an important role in SnTe with respect to different alloying levels or post treatments is revealed. The results indicate that Mn precipitates at x = 0.08 prior to reaching solubility (≈10 mol%), and then splits into MnSn substitution and γ-MnTe hetero-phases via mechanical alloying. Understanding such unique crystallography evolution, combined with a modified Debye-Callaway model, is critical in explaining the decreased thermal conductivity of Sn1.02−xMnxTe with rational phonon scattering pathways, which should be applicable for other thermoelectric systems.

AgCrSe2, which crystallizes in alternative layers of Ag+ and CrSe2− octahedral structure, has shown great potential as good thermoelectric material due to its unique ultralow lattice thermal conductivity. In this work, compound Cr2/3Te is alloyed with the matrix Ag0.97CrSe2 and the carrier concentration ranges within 1018–1020 cm−3, enabling a reliable assessment of transport properties based on single parabolic band model at room temperature. Moreover, homogeneous nanoprecipitate is observed in the matrix for high Cr2/3Te content samples, which leads to the scattering of main heat carrier of long-wavelength phonons, and thus a slight reduction of lattice thermal conductivity (∼0.3 W/m K) compared with intrinsic AgCrSe2. Combined with the optimized carrier concentration and the low lattice thermal conductivity, a figure of merit zT of 0.6 at 650 K is achieved, exceeding other reported AgCrSe2 systems, demonstrating the current Ag0.97CrSe2(Cr2/3Te)x materials as good potential thermoelectrics.