Superior Thermoelectric Properties Research Articles

High entropy alloy particle reinforced 6061 aluminum matrix composites: An investigation of mechanical strength and thermoelectric properties

The relentless pursuit of advanced materials characterized by superior mechanical and thermoelectric properties has spurred significant research into metal matrix composites (MMCs), particularly aluminum matrix composites (AMCs). This study investigates the development of 6061 aluminum alloy composites reinforced with varying concentrations (4–10 wt%) of AlCoCrFeNi high-entropy alloy (HEA) particles via Spark Plasma Sintering (SPS). Key findings underscore the positive impact of HEA reinforcement on the density and hardness of AMCs, while revealing a complex relationship between HEA content and strength. The composite incorporating 6 wt% HEA exhibited optimal properties, characterized by a density of 2.85 g/cm³, Vickers hardness of 85 HV, ultimate tensile strength of 174 MPa, and elongation of 13.7 %. A corresponding peak in thermal conductivity was observed at this composition, while electrical conductivity diminished due to increased phonon scattering.

Suppressed Lattice Thermal Conductivity in Haeckelite Compounds for High-Performance Thermoelectric Applications.

Traditional semiconductors are known to exhibit excellent electrical properties but oversized lattice thermal conductivities, thus limiting their thermoelectric performance. Herein, we have discovered a low-energy allotrope of those traditional semiconductors. Compared with the wurtzite structure, the lattice thermal conductivity is reduced by more than five times in the haeckelite structure. This is attributed to the softening of acoustic phonon modes and concurrently enhanced anharmonicity in the haeckelite structure. Benefiting from the suppressed lattice thermal conductivity while retaining the excellent electrical properties of wurtzite structure, haeckelite compounds have been proven to be a novel category of high-performance thermoelectric materials. As an excellent representative, haeckelite CdTe exhibits a peak figure of merit approaching 1.3 at n-type doping and high temperature, which experiences a 3-fold improvement compared with its wurtzite counterpart. This work provides an alternative pathway of engineering the lattice thermal conductivities of traditional semiconductors toward superior thermoelectric properties.

Magnetothermopower of Nodal-Line Semimetals

The search for materials with large thermopower is of great practical interest. Dirac and Weyl semimetals have recently proven to exhibit superior thermoelectric properties, particularly when subjected to a quantizing magnetic field. Here, we consider whether a similar enhancement arises in nodal-line semimetals, for which the conduction and valence band meet at a line or ring in momentum space. We compute the Seebeck and Nernst coefficients for arbitrary temperature and magnetic field and we find a wealth of different scaling regimes. Most strikingly, when a sufficiently strong magnetic field is applied along the direction of a straight nodal line or in the plane of a nodal ring, the large degeneracy of states leads to a large linear-in-B thermopower that is temperature independent even at low temperatures. Our results suggest that nodal-line semimetals may offer significant opportunity for efficient low-temperature thermoelectrics. Published by the American Physical Society 2024

High Thermoelectric Performance in Bismuth Telluride via Constructing MoSe2-2D Heterojunction.

Currently, the only thermoelectric (TE) materials commercially available at room temperature are those based on bismuth telluride. However, their widespread application is limited due to their inferior thermoelectric and mechanical properties. In this study, a strategy of growing a rigid second phase of MoSe2 is employed, in situ within the matrix phase to achieve n-type bismuth telluride-based materials with exceptional mechanical and thermoelectric properties. The in situ grown second phase contributes to both the electronic and lattice thermal conductivities. This is primarily attributed to the strong energy filtering effect, as the second phase forms a semi-common lattice interfacial structure with the matrix phase during growth. Furthermore, for composites containing 2wt% MoSe2, a maximum zT value of 1.24 at 373K can be achieved. On this basis, 8-pair TE module is fabricated and 1-pair TE module is optimized using a homemade p-type material. The optimized 1-pair TE module generates a maximum output power of 13.6µW, which is twice that of the 8-pair TE module and four times more than the 8-pair TE module fabricated by commercial material. This work facilitates the development of the TE module by presenting a novel approach to obtaining bismuth telluride-based thermoelectric materials with superior thermoelectric and mechanical properties.

Exploring layer thinning of exfoliated β-tellurene and room temperature photoluminescence with large exciton binding energy revealed in β-TeO2

Due to its tunable bandgap, anisotropic behavior, and superior thermoelectric properties, device applications using layered tellurene (Te) are becoming more attractive. Here, we report a thinning technique for exfoliated tellurene nanosheets using thermal annealing in an oxygen environment. We characterize different thinning parameters, including temperature and annealing time. Based on our measurements, we show that controlled layer thinning occurs in the narrow temperature range of 325–350 °C. We also show a reliable method to form β-tellurene oxide (β-TeO2), which is an emerging wide bandgap semiconductor with promising electronic and optoelectronic properties. This wide bandgap semiconductor exhibits a broad photoluminescence (PL) spectrum with multiple peaks covering the range of 1.76–2.08 eV. This PL emission, coupled with Raman spectra, is strong evidence of the formation of 2D β-TeO2. We discuss the results obtained and the mechanisms of Te thinning and β-TeO2 formation at different temperature regimes. We also discuss the optical bandgap of β-TeO2 and show the existence of pronounced excitonic effects evident by the large exciton binding energy in this 2D β-TeO2 system that reach 1.54–1.62 eV for bulk and monolayer, respectively. Our work can be utilized to have better control over the Te nanosheet thickness. It also sheds light on the formation of well-controlled β-TeO2 layered semiconductors for electronic and optoelectronic applications.

High thermoelectric performance in Ti2OX2 (X = F, Cl) MOene: A first-principles study incorporating electron–phonon coupling

MXenes exhibit significant potential in thermoelectric materials owing to their exceptional electrical conductivity; however, their limited number of semiconductors restricts their application. Thus, it is highly desirable to expand the MXene family beyond carbides and nitrides to broaden their applications in thermoelectricity. In this work, we systematically investigate the thermoelectric transport of Ti2OX2 (X = F, Cl) MOene through comprehensively evaluating the electron–phonon coupling (EPC) from first principles. Our findings first emphasize the limitations of the deformation potential theory method and stress the importance of considering EPC. Ti2OF2 (Ti2OCl2) monolayer exhibits exceptional electronic transport, with Seebeck coefficients reaching 1483.87 (1206.22) μV/K and electrical conductivity reaching 9.5 × 105 (7.6 × 105) Ω−1 m−1 at room temperature for its N-type counterpart. Additionally, the presence of degenerate multiple valleys and peaks significantly enhances their electronic transport. For phonon transport, EPC results in a significant reduction in lattice thermal conductivity (kL) [e.g., at 300 K with 1.44 × 1015 (1.68 × 1015) cm−2 of hole, the reduction is 86.3% (73.3%) for Ti2OF2 (Ti2OCl2)]. Additionally, their kL demonstrates a strong correlation with the density of states at corresponding Fermi levels. Moreover, the kL and total thermal conductivity of P-type Ti2OF2 show T-independence, making it suitable for applications in aviation and thermal insulation materials. Finally, N-type Ti2OF2 and Ti2OCl2 demonstrate superior zT values of 0.63 and 0.9 at 900 K, respectively. This study provides in-depth insights into the superior thermoelectric properties of Ti2OX2 (X = F, Cl) MOene with considering EPC, providing a novel platform for the next-generation thermoelectric field.

Superior optical and thermoelectric properties of bilayer β12-like phase borophene synthesized on Cu(111) film

In this work we theoretically investigate the electronic properties, optical properties, and thermoelectric characteristics of bilayer (BL) β12-like phase borophene synthesized on a Cu(111) substrate.

Efficient stepwise carrier concentration optimization in Ge(1+x)−ySbyTe

Owing to superior thermoelectric properties, GeTe shows practical applications in power generation and refrigeration.

A first-principles study on the promising thermoelectric properties of SnX (X = S, Se, Te) compounds.

SnSe has emerged as an outstanding thermoelectric material due to its exceptional performance. In this study, first-principles calculations are employed to investigate the thermoelectric properties of materials within the SnX family, where X can be either S, Se, or Te. Initially, we assessed the stability of SnX (X = S, Se, Te). We found that SnS exhibits better mechanical and thermal stability than SnSe and SnTe. We then conduct phonon and electronic transport analysis. Following the general rule that heavier atoms have lower thermal conductivity, SnTe demonstrates lower thermal conductivity due to its low group velocity compared with SnS and SnSe. Regarding electrical transport properties, the band gaps for SnS, SnSe, and SnTe are 0.56, 0.54, and 0.35 eV, respectively. Notably, the small band gap and higher degeneracy in its band valleys for SnTe make it more effective for achieving a high power factor. The maximum ZT values are determined to be 1.41, 1.41, and 1.87 for SnS, SnSe, and SnTe, respectively. Remarkably, ZTmax of SnTe exceeds that of SnSe by 32.6%. Overall, the results clearly demonstrate that SnTe exhibits superior thermoelectric properties compared to SnSe and SnS. This study provides valuable insights into the electronic structure, thermal conductivity, and mechanical and thermal stability of materials within the SnSe family, such as SnS or SnTe, without the need for extensive and costly experimental work.

Experimental evaluation of thermal efficiency, electrical efficiency, and power production of low-concentrating photovoltaic-thermal system with micro-jet channel

The efficient behavior of a low-concentrating photovoltaic-thermal system with a micro-jet channel (LCPV/T-JET) and booster mirror reflector is experimentally evaluated here. Micro-jets promote the thermal management of PV solar cells by implementing jet water as active cooling, which is still in the early stages of development. The booster mirror reflector concentrates solar irradiance into solar cells and improves the thermal, electrical, and combined efficiencies of the LCPV/T-JET system. The LCPV/T-JET system was tested under ambient weather conditions in the city of Bangi, Selangor, Malaysia, and all data was recorded between 10:00 a.m. and 4:00 p.m. Parametric studies were conducted to compare the performance of the LCPV/T-JET system to that of a conventional PV module. It is found that the short-circuit current of a standard PV module could be increased by 28% and 11.7%, with and without the use of jet water and booster mirror reflectors, respectively. Moreover, the power supplied by the PV component increases to 31% and 16%, respectively, with and without jet water and a booster mirror reflector. The characteristic curves for current–voltage and power–voltage curves also confirmed the superior thermoelectric properties of the LCPV/T-JET system. The measurements reveal a drop in the electrical efficiency of solar cells from 14.5% to 12.25% as the temperature of the cells increases from 32.5 °C to 66.5 °C between 10:00 a.m. and 1:00 p.m. Meanwhile, the thermal and overall efficiencies declined from 84% to 81.5% and 96% to 93%, respectively.

Lead-free and scalable GeTe-based thermoelectric module with an efficiency of 12.

GeTe-based materials with superior thermoelectric properties promise great potential for waste heat recovery. However, the lack of appropriate diffusion barrier materials (DBMs) limits not only the energy conversion efficiency but also the service reliability of the thermoelectric devices. Here, we propose a design strategy based on phase equilibria diagrams from first-principles calculations and identify transition metal germanides (e.g., NiGe and FeGe2) as the DBMs. Our validation experiment confirms the excellent chemical and mechanical stabilities of the interfaces between the germanides and GeTe. We also develop a process for scaling up the GeTe production. Combining with module geometry optimization, we fabricate an eight-pair module using mass-produced p-type Ge0.89Cu0.06Sb0.08Te and n-type Yb0.3Co4Sb12 and achieve a record-high efficiency of 12% among all reported single-stage thermoelectric modules. Our work thus paves the way for waste heat recovery based on completely lead-free thermoelectric technology.

Electrical conductivity, Seebeck coefficient, and crystal growth of p-type tellurium films through temperature dependent RF sputtering

Te thin films have recently received considerable attention owing to its superior electrical and thermoelectric properties. During the deposition process, if the temperature of the substrate is raised, high crystallinity and improved electrical properties can be expected. In this study, we used radio frequency sputtering for Te deposition to study the relationship between the deposition temperature, crystal size, and electrical performance. As the deposition temperature is increased from room temperature to 100 °C, we observed an increase in crystal size from the x-ray diffraction patterns and full-width half maximum calculations. With this grain size increment, the Hall mobility and Seebeck coefficient of the Te thin film increased significantly from 16 to 33 cm2 V−1 s−1 and 50 to 138 μV K−1, respectively. This study reveals the potential of a facile fabrication method for enhanced Te thin films using temperature control and highlights the importance of the Te crystal structure in determining the electrical/thermoelectrical properties. These findings are particularly significant for the development of semiconductor material systems for various applications, including thermoelectric devices, CMOS, FET, and solar devices.

Quasi-random distribution of distorted nanostructures enhances thermoelectric performance of high-entropy chalcopyrite

Here, we suggest that the quasi-random distribution of distorted nanostructures (QDDN), which is unique in high-entropy materials, is the reason for superior thermoelectric properties. The general high entropy material consists of several atoms with disordered lattice in atomic scale. Our QDDN showed nanoscale disorder because the consisting atoms were not distributed fully randomly. The order of compositional distribution was found as 40–60 nm, which causes high level of lattice-strain-induced distortion. The underlying mechanism of phonon scattering by QDDN was clarified by theoretical analysis. The high level of lattice strain induced by QDDN causes strong phonon scattering in entire phonon spectrum. A low κlat of ∼0.38 W/m-K at 850 K was achieved in a CuGaTe2-based high-entropy chalcopyrite material. However, the power factor was not significantly affected due to ther high crystallinity, despite the QDDN. Therefore, a zT of ∼1.56 at 850 K was attained in a Cu0.8Ag0.2[Ga0.8In0.2]0.99Zn0.01Te2 compound, which represented a 132% enhancement from pure CuGaTe2. These results elucidate recent zT increases in high-entropy materials and can be a step towards further enhancements of zT in thermoelectric materials.

Superior Thermoelectric Properties of Twist-Angle Superlattice Borophene Induced by Interlayer Electrons Transport.

In this paper, the energy bands, interlayer interactions and thermoelectric effects of twisted bilayer borophene (TBB) synthesized on Ag (111) are studied theoretically. The results manifest the advantages of twistronics, where the high electrical conductivity and the large Seebeck coefficient are regulated to the same range, which lead to the significantly increase of figure of meritZT than that of bilayer borophene (BB) without twist, where the BB without twist is successfully synthesized on Ag (111) film is recently experimental report [Nat. Mater. 2022, 21, 35]. For the TBB synthesized of on Ag (111) film, theoretical analysis demonstrates that TBB and Ag are relatively strongly coupled, and TBB becomes a metallic 2D material, where the top and bottom borophene layers are semiconducting and metallic, respectively. TBB exhibits excellent thermoelectric efficiency due to the charge transfer bonding between the layers, less electron localization, and the regulation of Seebeck coefficient, electrical conductivity, and ZT at the same region of chemical potential and the same temperature by twistronics. The structure-property relationship offers the possibility of applying TBB in thermoelectric devices.

Revealing the Enhanced Thermoelectric Properties of Controllably Doped Donor-Acceptor Copolymer: The Impact of Regioregularity.

Albeit considerable attention to the fast-developing organic thermoelectric (OTE) materials due to their flexibility and non-toxic features, it is still challenging to design an OTE polymer with superior thermoelectric properties. In this work, two "isomorphic" donor-acceptor (D-A) conjugated polymers are studied as the semiconductor in OTE devices, revealing for the first time the internal mechanism of regioregularity on thermoelectric performances in D-A type polymers. A higher molecular structure regularity can lead to higher crystalline order and mobility, higher doping efficiency, order of energy state, and thermoelectric (TE) performance. As a result, the regioregular P2F exhibits a maximum power factor (PF) of up to 113.27µWm-1 K-2 , more than three times that of the regiorandom PRF (35.35µWm-1 K-2 ). However, the regular backbone also implies lower miscibility with a dopant, negatively affecting TE performance. Therefore, the trade-off between doping efficiency and miscibility plays a vital role in OTE materials, and this work sheds light on the molecular design strategy of OTE polymers with state-of-the-art performances.

Superior thermoelectric properties through triangular triple quantum dots (TTQD) attached to one metallic and one superconducting lead.

We theoretically investigate the thermoelectric transport properties of triangular triple quantum dots (TTQD) with the central quantum dot coupled to one metallic and one superconducting lead. The system shows significantly superior thermoelectric performance over parallel coupled triple quantum dots and those coupled to two conventional metallic leads. The thermoelectric coefficients strongly depend on the ratio of superconducting gap to interdot coupling, as well as asymmetry and interference effects. The thermopower exhibits single-platform and double-platform structures for different ratios of superconducting gap to interdot coupling. The thermopower and figure of merit achieve quite remarkable values near the superconducting gap edges where the single-particle tunnelling occurs. For symmetric coupling, the maximal figure of merit might reach the order of 102 when the superconducting gap is about half that of the interdot coupling. Moreover, the figure of merit can be further greatly enhanced by appropriately matching the electrode coupling asymmetry and interdot coupling asymmetry.

Superior thermoelectric properties of bulk and monolayer fullerene networks

The structure, electronic energy band, and thermoelectric properties of bulk and monolayer fullerene (C60) networks were analyzed in detail, stimulated by the successful experimental synthesis of C60 networks [Hou L., et al., Synthesis of a monolayer fullerene network, Nature, 2022, 606, 507].

Twisted grain boundary leads to high thermoelectric performance in tellurium crystals

A twisted grain boundary is introduced in the tellurium crystal to effectively block phonon propagation while maintaining high electron mobility for superior thermoelectric properties.

Substituted (P, As, Sb, S and Se) two-dimensional Bi2Te3 monolayer under stress at high temperature: achieving high thermoelectric performance

The group-VA (X = P, As, Sb)-substituted Bi2Te3 alloys of BiPTe3, BiSbTe3 and BiAsTe3 are promising candidates for thermoelectric applications near room temperature, and compressive strain can effectively improve the ZT value of the n-type structure.

Thermoelectric Figure of Merit of a Superatomic Crystal Re6Se8I2 Monolayer

Superatomic materials are newly emerging candidates for high-performance thermoelectric (TE) devices due to their intrinsic ultralow thermal conductivities. However, the low TE power factor becomes a huge obstacle to reaching the required dimensionless figure of merit (ZT) values for practical applications. Here, motivated by the recently synthesized superatomic ${\mathrm{Re}}_{6}{\mathrm{Se}}_{8}{\mathrm{I}}_{2}$ monolayer [He et al. J. Am. Chem. Soc. 144, 74 (2022)], we study its superior TE properties by using density functional theory combined with phonon Boltzmann transport theory and deep potential molecular dynamics. We show that the large mass and anharmonic $\mathrm{Re}---\mathrm{I}$ bonds introduce strong phonon scattering and result in a low lattice thermal conductivity of 1.20 W m${}^{\ensuremath{-}1}$ K${}^{\ensuremath{-}1}$ at 300 K, while the strong and harmonic $\mathrm{Re}---\mathrm{Se}$ network ensures a high TE power factor of 4344 \textmu{}W m${}^{\ensuremath{-}1}$ K${}^{\ensuremath{-}2}$ in the b direction for n-type doping. This is an order of magnitude higher than those of other cluster-based materials. Owing to the low thermal conductivity and high TE power factor, ${\mathrm{Re}}_{6}{\mathrm{Se}}_{8}{\mathrm{I}}_{2}$ exhibits higher ZT values of 1.20 (500 K) and 1.43 (900 K) with n-type doping along the b direction compared with other cluster-based TE materials reported so far.