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As an earth‐abundant, environment‐friendly, and cost‐effective material, tetrahedrite Cu12Sb4S13 has attracted much attention in thermoelectrics (TEs). However, the TE performance of the pristine Cu12Sb4S13 (CSS) is mediocre, thereby much improvement is required. In this work, both the electronic and phonon transports of the CSS are engineered using Ga2Te3 as a dopant. In the results, it is indicated that dual substitutions of Ga for Cu and Te for Sb not only cause the enhancement of power factor via electronic band structure tuning, but also leads to a drop in both the electronic and lattice thermal conductivities. As a result, the total thermal conductivity (κ) decreases to 0.98 W m−1 K−1 at 770 K, which is about 58% that of the pristine CSS, thus improving the TE performance with the highest dimensionless figure of merit value increasing to 0.95 for (Cu12Sb4S13)0.9(Ga2Te3)0.1 at 773 K, 1.9 times that of the pristine CSS (≈0.5 at 770 K). [ABSTRACT FROM AUTHOR]

Thermoelectric (TE) materials allow us to harvest energy practically from any heat source, including heat that would be otherwise wasted. This huge promise of energy harvesting is contingent on identifying/designing materials having higher efficiency than presently available ones. However, due to the vastness of the chemical space of materials, only a small fraction of potential candidates has been experimentally and/or computationally scanned thus far. By employing an artificial intelligence (AI) approach based on compressed-sensing symbolic regression analysis of experimental data in an active-learning framework, we have not only identified a trend in the materials composition for superior TE performance, but also predicted and experimentally synthesized several high-performing TE chalcogenides. In particular, p-type Cu0.45Ag0.55GaTe2 shows a very high experimental figure of merit (zT) ∼1.90 at 770 K using experimentally measured heat capacity (Cp). The present work demonstrates not only experimental realization of AI-predicted high-zT TE, but also the importance and potential of physically informed descriptors in material science, particularly for relatively small but well-controlled datasets typically available from experiments. [ABSTRACT FROM AUTHOR]

In this work, we design and synthesize a hybrid structure consisting of Sn-incorporated Cu3SbSe4 and a second phase CuSe, that is, (Cu3Sb1 − xSnxSe4)(CuSe)y (x = 0–0.04, y = 0.3–0.08), and explore the role of each phase on the improvement of the thermoelectric (TE) performance. In the Cu3Sb1 − xSnxSe4 phase, the element Sn residing at the Sb site provides p-type holes while at the same time increasing the point defects and crystal structure distortion. The presence of the second phase CuSe, which is in situ formed within the Cu3Sb1 − xSnxSe4 matrix, not only improves the electrical conductivity but also increases the phonon scattering on the phase boundaries. As a result, the hybrid structure allows the improvement in TE performance with the highest ZT value of 0.37 at ∼600 K for the samples at x = 0.02–0.03 and y = 0.11–0.09, which is about 42% higher than that of pristine Cu3SbSe4. This work reveals us a new method of improving TE performance, that is, through organizing a hybrid structure in Cu3SbSe4-based composites. [ABSTRACT FROM AUTHOR]

Wingtip vortex is the initial phase of aircraft wake flow that jeopardizes flight safety. Previous studies have focused on the effect of incidence angle on tip vortex flow; thus, investigations on tip vortex in the roll-up stage under crosswind conditions are limited. In the present study, two NACA0012 wings with different tip shapes (round and square) were numerically analyzed to explore the effects of wingtip configurations on tip vortex. In addition, the effects of crosswinds on wingtip vortex evolution were also investigated. It was found that sharp edges of the square wingtip generated a multi-vortex system, resulting in a larger turbulent wake vortex core radius. The lift and vortex strength of the square wingtip were 23% higher and only 12% stronger than those of the round wingtip, respectively. Furthermore, crosswinds changed both the pressure distribution and the vortex structure. Crosswinds made the flow field unstable; hence, upwind lower edge vortices of the square wingtip burst earlier and merged faster. Consequently, the tightness of the upwind vortex of the square wingtip increased, and the corresponding vortex strength was enhanced. The downwind vortex of the square wingtip was weakened by 2.7% under a crosswind velocity of 4 m/s, whereas the downwind tip vortex of the round wingtip was strengthened under the same conditions. [ABSTRACT FROM AUTHOR]

The carrier transport mechanism in most thermoelectric semiconductors is governed by conventional band transport, however, there is an exception in ternary Cu2SnSe4 (CTS) or its based counterparts in which the transport mechanism is dominated by a small polaron hoping model. The sluggish movement of the small polaron greatly suppresses the mobility of the carrier due to the strong coupling of the electron with the phonon, therefore, a proper decoupling is highly necessary. To achieve this goal, herein, InSe bonds are created by incorporating some indium into the cation vacancy in CTS, which effectively balances the transports between electron and phonon. As a consequence, both the electrical property (σ) and thermal conductivity (κ) are optimized in the sample Cu2Sn1−xInxSe4 (x = 0.1), and its thermoelectric performance improves with the highest figure of merit (ZT) of 0.5. This value is ≈52% higher than that of the pristine CTS, proving that incorporation of In in the cation vacancy in CTS is an alternative way to balance the transports between electron and phonon. [ABSTRACT FROM AUTHOR]

AgBiSe2 is a promising thermoelectric (TE) candidate because of its intrinsically low thermal conductivity (κ = 0.4–0.5 W K−1 m−1 at ∼770 K) and optimal n-type carrier concentration (5.85 × 1018 cm−3 at 300 K). However, its TE figure of merit (ZT) is still low (0.3 at ∼770 K). Therefore, it is necessary to further improve its ZT. In this work, the solid solutions (AgBiSe2)1−x(Ag2Te)x (x = 0–0.125) have been designed through simple alloying Ag2Te inspired by the entropy engineering concept, and the TE performance has been further regulated. The analyses show that the exothermic effects related to α/β and β/γ phase transitions weaken, and the transition temperature of β/γ decreases as the Ag2Te content increases, which indicates the stabilization of the cubic γ-phase at high temperatures. Aside from that, the power factor (PF) enhances from 2.91 μW/cm K2 (x = 0) to 3.49 μW/cm K2 (x = 0.075), and at the same time, the lattice thermal conductivity reduces from 0.3 W K−1 m−1 to 0.1 W K−1 m−1 at ∼760 K. This directly improves the TE performance with the highest ZT value of 1.0, which is almost double that of the pristine AgBiSe2. The result suggests that the entropy engineering is a very effective screening method in thermoelectrics. [ABSTRACT FROM AUTHOR]

The rational synthesis of high‐performance thermoelectric (TE) materials guided by theoretical design is still in its infancy. Here by computationally exploiting the possibilities of materials' dopability and hence the electron–phonon transport/scattering, a new defective compound, AgGaTe2, with simultaneous Ag deficiency and isoelectronic substitution of In on Ga‐site (InGa) is predicted, and its high performance is then confirmed via experiments. Using density functional theory and density functional perturbation theory calculations, it is identified that controlled defects viz. Ag vacancy and In substitution in AgGaTe2 system can lead to extremely low lattice thermal conductivity (κL) of around 0.13 WK−1 m−1 at 850 K. This ultralow κL results from both the Ag vacancy that serves as a better rattler and the extra phonon scattering due to the defect induced internal lattice distortion (ψ). The synthesized compounds Ag0.85Ga1−xInxTe2 (x = 0–0.3) indeed achieve the extremely low κL (0.08 WK−1 m−1 for x = 0.15). As a result, the highest TE figure of merit (ZT) of 1.44 is obtained, which is the highest recorded value for silver‐based ternary chalcopyrite semiconductors to date. [ABSTRACT FROM AUTHOR]

In this work the crystal structure and bandgap in the Cu3+δIn5Te9 material system were engineered through modifying the copper vacancy concentration (Vc). The results reveal that the crystal distortion parameter (ψ) increases as the Vc value decreases, which plays a fundamental role in enhancing the phonon scattering, thereby reducing the lattice part (κL) to the minimum value 0.21 W K−1 m−1 at ∼830 K. Although the electrical properties degrade due to the reduced Hall carrier concentration (nH) caused by the widened bandgap (Eg) as the Vc value increases, the mobility (μ) increases. As a consequence, the thermoelectric performance remarkably improves with a highest ZT value of ∼1.0 for the sample Cu3+δIn5Te9 (δ = 0.1). This value doubles that of the pristine Cu3In5Te9. The work gives insight into the potential phonon scattering in the distorted crystal structure in Cu-ternary systems and sheds some light on the design of high performance thermoelectric materials. [ABSTRACT FROM AUTHOR]

AgInTe2 compound has not received enough recognition in thermoelectrics, possibly due to the fact that the presence of Te vacancy (VTe) and antisite defect of In at Ag site (InAg) degrades its electrical conductivity. In this work, we prepared the Ag1-xInTe2 compounds with substoichiometric amounts of Ag and observed an ultralow lattice thermal conductivity (κL = 0.1 Wm−1K−1) for the sample at x = 0.15 and 814 K. This leads to more than 2-fold enhancement in the ZT value (ZT = 0.62) compared to the pristine AgInTe2. In addition, we have traced the origin of the untralow κL using the Callaway model. The results attained in this work suggest that the engineering of the silver vacancy (VAg) concentration is still an effective way to manipulate the thermoelectric performance of AgInTe2, realized by the increased point defects and modified crystal structure distortion as the VAg concentration increases. [ABSTRACT FROM AUTHOR]

α-In2Se3 is of large bandgap (∼1.4 eV) semiconductor and its structure is based on two-layer hexagonally packed arrays of selenium atoms with 1/3 of the sites of indium atoms being empty. Here we report a bandgap Eg reduction due mainly to the formation of a Cu2Se slab in the host In2Se3, which is responsible for the remarkable improvement of thermoelectric performance of bulk polycrystalline In2-xCuxSe3 (x = 0.1-0.2). When x = 0.2 the dimensionless figure of merit ZT and power factor were increased by a factor of 2 and 3, respectively, at 846 K if compared to those of Cu-free In2Se3. Interestingly, an incorporation of Cu into the lattice of In2Se3 results in a change in morphology from amorphouslike structure represented by In2Se3 to a visible polycrystalline form attributed to partial crystallization of the structure. This change enhances lattice thermal conductivities κL over the very low values of In2Se3. However, the enhancement is only moderate because of the effective scattering of phonons in the polycrystalline nanostructure. [ABSTRACT FROM AUTHOR]

In this paper we reported the thermoelectric (TE) properties in nanostructured homologous series alloys GamSbnTe1.5(m+n) over the temperature range of 318–482 K and observed the maximum TE figure of merit (ZT) value of 0.98 for the alloy with m:n=1:10 at 482 K, which is approximately 0.24 higher than that of undoped Sb2Te3 at the corresponding temperature. This improvement is mainly attributed to the substantial reduction in lattice thermal conductivity due to the phonon scattering caused partly by the nanograins (<30 nm) and amorphous structure conceived in the matrix and partly by the lattice distortion resulted from an occupation of some Ga atoms in the Sb sites and a certain amount of Ga2Te3 precipitation. If in comparison with the TE properties for Ga directly doped Bi–Sb–Te solid solutions, we conclude that these Bi-free nanostructured homologous series alloys GamSbnTe1.5(m+n) with proper compositions are of great potentiality for the improvement of TE performance. [ABSTRACT FROM AUTHOR]

In this paper we reported the thermoelectric (TE) properties in nanostructured homologous series alloys GamSbnTe1.5(m+n) over the temperature range of 318–482 K and observed the maximum TE figure of merit (ZT) value of 0.98 for the alloy with m:n=1:10 at 482 K, which is approximately 0.24 higher than that of undoped Sb2Te3 at the corresponding temperature. This improvement is mainly attributed to the substantial reduction in lattice thermal conductivity due to the phonon scattering caused partly by the nanograins (<30 nm) and amorphous structure conceived in the matrix and partly by the lattice distortion resulted from an occupation of some Ga atoms in the Sb sites and a certain amount of Ga2Te3 precipitation. If in comparison with the TE properties for Ga directly doped Bi–Sb–Te solid solutions, we conclude that these Bi-free nanostructured homologous series alloys GamSbnTe1.5(m+n) with proper compositions are of great potentiality for the improvement of TE performance. [ABSTRACT FROM AUTHOR]

Cu4Te3 substituted (Cu4Te3)x–(Bi0.5Sb1.5Te3)1-x (x=0–0.2) alloys were prepared using spark plasma sintering technique and their thermoelectric properties were evaluated. Measurements show that the alloy with x=0.025 reveals very high electrical conductivity and low lattice thermal conductivity, the Seebeck coefficient that increases linearly with temperature is dependent on Cu4Te3 concentration. The maximum ZT value of 1.26 for the alloy with x=0.025 is achieved at 474 K, whereas that of the state-of-the-art thermoelectric material Bi0.5Sb1.5Te3 is only 0.58 at 318 K, thus indicating that the currently prepared pseudobinary alloy is very encouraging. [ABSTRACT FROM AUTHOR]

Controlling the chemical and physical structure at the atomic level is of paramount importance for decreasing the thermal conductivity by enhancing phonon scattering in thermoelectric materials. Additional enhancement in the figure of merit (ZT) can be achieved by improving the electron transport properties. Cu-deficient ternary I–III–VI compounds have received increasing attention because they can easily form solid solutions and thereby their thermoelectric performance can be readily engineered. In this work, we present a novel thermoelectric compound Cu1.15In2.29Te4 with the dimensionless figure of merit ZT∼ 1.0 through alloying with Cu2Te. The enhanced ZT value is mainly attributed to the ultralow lattice thermal conductivity (κL = 0.24 W K−1 m−1 at 825 K), caused by a pronounced local lattice disorder as a result of the interstitial residing of extra Te. Density functional theory based first-principles calculations further elucidate that the creation of the resonant states at the Fermi level and impurity levels near the valence band edge has increased the effective mass and carrier concentration, resulting in the improved electrical properties. Moreover, the localized modes of the Te interstitial defects hybridize with the acoustic modes of stoichiometric In and Te and lead to the enhanced scattering of the thermal phonons resulting in the significantly low κL. The above findings substantiate that appropriate doping of Cu2Te in the newly developed Cu1.15In2.29Te4 compound can effectively manipulate both electron and phonon transport and thereby promises high thermoelectric performance. [ABSTRACT FROM AUTHOR]

Our previous work demonstrated that the ternary Cu18Ga25Te50 compound is a good thermoelectric candidate. However, its thermal stability is unsatisfactory, which suppresses the improvement of thermoelectric performance at high temperatures. In this work, we have tuned the chemical composition through the addition of Sb to the Cu-deficient Cu4−δGa4Te8 (δ = 1.12) compound. The first-principles calculations reveal that Sb prefers the Te site, and the replaced Te occupies the copper vacancy (TeVCu) in Cu4−δGa4SbxTe8. These occupancies enable the creation of Sb–Te bonds with higher bond dissociation energies; hence the thermal stability increases, and the lattice thermal conductivity reduces at high temperatures significantly. Besides, the defect TeVCu contributes to the formation of impurity levels within the gap, which narrows the bandgap, and also increases the density of states in the vicinity of the Fermi level (Ef). Accordingly, the Hall carrier concentration is enhanced by more than one order of magnitude compared with that in Sb-free Cu4−δGa4Te8. As a result, the highest thermoelectric (TE) figure of merit ZT at x = 0.6 reaches 1.51 at ∼870 K, which substantiates that direct addition of Sb is an effective way to improve the TE performance of Cu4−δGa4Te8 ternary chalcogenides. [ABSTRACT FROM AUTHOR]

A newly developed chalcopyrite semiconductor Cu18Ga25Te50 (Cu/Ga = 0.72) has an inherent deficiency in Cu. Therefore, it is taken as a thermoelectric candidate due to a high vacancy rate of copper. In this work, we have observed that after Sb substitution for Te in Cu18Ga25SbxTe50−x, the active Sb-5p orbital hybridizes with those of Cu-4s and Te-5p in the valence band, which makes the Fermi level (Ef) unpin and move toward the inner side of the valence band as Sb content increases. The alteration in the band structure, which is the determining factor, causes the Hall carrier concentration (nH) to rise by more than one order of magnitude compared with those in pristine Cu18Ga25Te50, thereby significantly increasing the power factor (PF). Combined with the relatively low thermal conductivity, caused by the increased lattice disorder and general diminution of the crystal structure distortion as the x value increases, we have attained the best TE performance, where ZT reaches the highest value of 1.2 for the Sb-incorporated Cu18Ga25SbxTe50−x (x = 2.5) at 854 K. This result suggests that the coordination of energy band and crystal structures is a good approach to achieving high TE performance via the appropriate distortion of the crystal structure of ternary chalcopyrite semiconductors. [ABSTRACT FROM AUTHOR]

Improving the thermoelectric (TE) performance of Cu3SnS4 is challenging because it exhibits a metallic behavior, therefore, a strategy should be envisaged to coordinate the carrier concentration (nH) and Seebeck coefficient (α). The coordination in this work has been realized through the Fermi level (Ef) unpinning and shifting towards the conduction band (CB) via addition of excess Sn in Cu3SnS4. As a result, the solid solution Cu3Sn1+xS4 (x = 0.2) has a moderate α (178.0 μV K−1) at 790 K and a high nH (1.54 × 1021 cm−3) value. Along with the lowest lattice thermal conductivity κL (0.39 W K−1 m−1) caused by the increased phonon scattering by carriers, the highest ZT value of 0.75 is attained at ∼790 K. This value is 2.8 times that of the stoichiometric Cu3SnS4, and stands among the highest for ternary Cu–Sn–S sulfide thermoelectrics at the corresponding temperatures. More importantly, this approach used in the case of ternary Cu3SnS4 provides a guidance or reference to improve the TE performance of other materials. [ABSTRACT FROM AUTHOR]

In this work, we have investigated the band structures of ternary Cu4Sn7+xS16 (x = 0–1.0) compounds with an excess of Sn, and examined their thermoelectric (TE) properties. First principles calculations reveal that the excess Sn, which exists as Sn2+ and is preferentially located at the intrinsic Cu vacancies, unpins the Fermi level (Fr) and allows Fr to enter the conduction band (CB) at x = 0.5. Accordingly, the Hall carrier concentration (nH) is enhanced by about two orders of magnitude when the x value increases from x = 0 to x = 0.5. Meanwhile, the lattice thermal conductivity (κL) is reduced significantly to 0.39 W K−1 m−1 at 893 K, which is in reasonably good agreement with the estimation using the Callaway model. As a consequence, the dimensionless TE figure of merit (ZT) of the compound Cu4Sn7+xS16 with x = 0.5 reaches 0.41 at 863 K. This value is double that of the stoichiometric Cu4Sn7S16, proving that excess Sn in Cu4Sn7S16 is beneficial for improving the TE performance. [ABSTRACT FROM AUTHOR]

In this work we have observed the beneficial effect from the solid solution formation on the thermoelectric performance of (Cu 2(1 − x ) Sb 2 x Te)(Ga 2 Te 3 ) 3 upon Sb substitution for Cu. This substitution allows the different occupations of Sb in the crystal lattice, i.e. Sb at Cu sites with x ≤ 0.05 and at Ga sides with x ≥ 0.05, which has resulted in the Pisarenko relation does not exactly capture the measured Seebeck coefficient under assumed effective masses m *. The reduction of the lattice thermal conductivity ( κ L ) has been quantified within the temperature range from room temperature to 723 K. Over the entire composition range, the κ L value is reduced by 33% and 25% at temperature 723 K and 580 K, respectively. This observation is in a good agreement with the theoretical calculation based on the Callaway model used in the solid solutions. Along with the increasing of the mobility and electrical conductivity, the thermoelectric performance has been improved with the highest ZT value of 0.58 at 723 K, which is about double the value of intrinsic (Cu 2 Te)(Ga 2 Te 3 ) 3 . [ABSTRACT FROM AUTHOR]

Cu3Ga5Te9-based compounds Cu3−xGa5MnxTe9 (x = 0–0.2) with Mn substitution for Cu have been synthesized. The engineered energy gap (ΔEA) between impurity and valence bands is reduced from 44.4 meV at x = 0 to 25.7 meV at x = 0.1, which is directly responsible for the reduction of the potential barrier for thermal excitation of carriers and the increase in carrier concentration. However, the Seebeck coefficient shows an increasing tendency with the increase of determined Hall carrier concentration (n). This anomalous behavior suggests that the Pisarenko plots under assumed effective masses do not fit the current relationship between the Seebeck coefficient and the carrier density. With the combination of enhanced electrical conductivities and reduced thermal conductivities at high temperatures, the maximum thermoelectric (TE) figure of merit (ZT) of 0.81 has been achieved at 804 K with x = 0.1, which is about 1.65 and 2.9 times the value of current and reported intrinsic Cu3Ga5Te9. The remarkable improvement in TE performance proves that we have succeeded in engineering the energy gap near the valence band edge upon Mn incorporation into Cu3Ga5Te9. [ABSTRACT FROM AUTHOR]

In this work we have observed a remarkable improvement in the thermoelectric (TE) performance of In6- xSn xSe7 ( ZT = ∼0.28 at x = 0.1, 833 K) compared to that of pristine In6Se7 ( ZT = 0.015 at 640 K). This improvement is mainly attributed to the creation of active donor defects SnIn3+ as Sn(4+) is energetically favorable to In+ sites. Although Sn (2+), which generates a defect SnIn− as an acceptor when it is incorporated into the In3+ sites, has a negative effect on the transport properties, the counter effect from Sn(4+) and Sn(2+) suggests that In6Se7-based alloys are prospectively good thermoelectric candidates if their chemical compositions are well optimized. [ABSTRACT FROM AUTHOR]

In this work, we have observed the enhancement of carrier concentration in α-In2Se3 at a specific S content. This enhancement results from avoiding the annihilation of defects, such as VIn and interstitial Ini acting as donors, via the rearrangement of both the cationic and anionic disorders. Therefore, there is a remarkable improvement in electrical conductivity ( σ). For example, the sample α-In2S0.05Se2.95 perpendicular to the pressing direction ( C┴) gives the highest σ value of 5.56 × 103 Ω−1 m−1 at 923 K, while the virgin α-In2Se3 gives only 9.17 × 102 Ω−1 m−1. In addition, there are dual effects on the lattice thermal conductivity ( κL) resulting from the stabilization of the lattice structure caused by the rearrangement of defect disorder and the lattice distortion from the formation of defect SSe. Therefore, the lattice contribution ( κL) in S-incorporated α-In2Se3 remains relatively high at high temperatures. As a consequence, we have improved the thermoelectric performance, achieving a ZT value of 0.67 for α-In2S0.05Se2.95 at 923 K, which is about 2.8 times that of virgin α-In2Se3 ( ZT = 0.24 at C┴). [ABSTRACT FROM AUTHOR]

In this project, we have successfully manipulated the lattice defects in α-In2Se3-based solid solutions (In2−xZnxSe3) by appropriate substitution of Zn for In, via a non-equilibrium fabrication technology (NEFT) of materials. The manipulation of the defect centers involves reduction of the number of interstitial In atoms (Ini) and Se vacancies (VSe), and creation of a new antisite defect ZnIn as a donor. Through this technique, the lattice structure tends to be ordered, and also more stabilized than that of pure α-In2Se3. In the meantime, the carrier concentration (n) and mobility (μ) have increased by 1–2 orders of magnitude. As a consequence, the solid solution at x = 0.01 gives the highest TE figure of merit (ZT) of 1.23(±0.22) in the pressing direction at 916 K, which is about 4.7 times that of pure α-In2Se3 (ZT = 0.26). This achieved TE performance is mainly due to the remarkable improvement in the electrical conductivity from 0.53 × 103 (Ω−1 m−1) at x = 0 to 4.88 × 103 (Ω−1 m−1) at x = 0.01 at 916 K, in spite of the enhancement in the lattice thermal conductivity (κL) from 0.26 (W m−1 K−1) to 0.32 (W m−1 K−1). [ABSTRACT FROM AUTHOR]

We present two series of Cu2Ga4Te7-based compounds with Zn substituting for Cu (Cu-poor) and Ga (Ga-poor), and have observed enhanced thermoelectric performance. Generally, the Seebeck coefficient ( α) and lattice thermal conductivity ( κL) increase and electrical conductivity ( σ) decreases with the Zn content increasing. The variation in electrical properties might be mainly due to the formation of antisite defects ( [ABSTRACT FROM AUTHOR]