Intrinsic Low Thermal Conductivity Research Articles

Enhancement of Thermoelectric Performance for CuCl Doped P-Type Cu2Sn0.7Co0.3S3

Cu2SnS3 (CSS) has gained great attraction due to its constitutive earth-abundant elements and intrinsic low lattice thermal conductivity, κl, potentially providing high quality factor, B, and high zT value. However, the lack of band convergence is the bottleneck to enhancing the thermoelectric performance of Cu2SnS3 when performing the band engineering. To study the doping effect on the band structure and the thermoelectric performance, the composite Cu2Sn0.7Co0.3S3-xCuCl (x = 0, 0.1, 0.2, 0.3) (CSCS-xCuCl) has been investigated for the first time. The samples showed excellent data repeatability at high temperatures of up to 700 K. It was found that CuCl could compensate the Cu loss, enhance the phonon scattering and minimize the adverse effect on the power factor, PF. The ultralow lattice thermal conductivity could reach 0.38 W m-1 K-1 for the nominal composition of CSCS-0.3CuCl at 700 K. A peak zT of 0.56 (evaluated with no cold finger effect) was realized at 700 K when x = 0.3, which is almost double the performance of pristine samples.

New class of high‐entropy rare‐earth niobates with high thermal expansion and oxygen insulation

AbstractTailoring the structure and properties of materials using the high‐entropy (HE) effect is of significant interest in the fields of environmental and thermal barrier coatings (TBCs). In this work, a new class of dense HE rare‐earth niobates was successfully prepared by a solid‐phase reaction method, including (Sm1/5Dy1/5Ho1/5Er1/5Yb1/5)NbO4 (5HERN), (Sm1/6Dy1/6Ho1/6Er1/6Yb1/6Lu1/6)NbO4 (6HERN), (Sm1/7Dy1/7Ho1/7Er1/7Yb1/7Lu1/7Gd1/7)NbO4 (7HERN), and (Sm1/8Dy1/8Ho1/8Er1/8Yb1/8Lu1/8Gd1/8Tm1/8)NbO4 (8HERN), along with eight single rare‐earth niobates (RENbO4, RE = Sm, Dy, Ho, Er, Yb, Lu, Gd, and Tm). X‐ray diffraction analysis showed that 5–8HERN are single‐phase solid solutions with a monoclinic structure (space group C12/c1). The thermal expansion coefficients of 7HERN and 8HERN exceed 11 × 10−6 K−1 at 1200°C and are much higher than those of the RENbO4 compositions (10.13–10.74 × 10−6 K−1) and other some HE rare‐earth oxides (10.27–10.87 × 10−6 K−1). Importantly, 5–8HERN have lower oxygen‐ion conductivity and higher activation energy than yttrium‐stabilized zirconia (YSZ) and the RENbO4 compositions. The oxygen‐ion conductivity of 5HERN (7.52 × 10−7 S cm−1, 900°C) was 105 times lower than that of YSZ (0.01 S cm−1, 750°C). The hardness of 5–8HERN is ∼7.81–8.46 GPa and these compositions have low intrinsic lattice thermal conductivity at high temperature (1.28–1.69 W m−1 K−1 at 900°C). The mechanism by which the HE effect improved the material properties was elucidated. Young's modulus, hardness, thermal expansion coefficient, and intrinsic lattice thermal conductivity are linearly related to the mass, size, and distortion degree of samples. In contrast, the oxygen‐ion conductivity depends on both the degrees of disorder and distortion and the oxygen‐ion vacancy concentration. Based on their overall performance, especially their high thermal expansion coefficients and excellent oxygen‐barrier performance, HE rare‐earth niobates show potential for further development as TBC materials.

Revealing the promising near-room-temperature thermoelectric performance in Ag2Se single crystals

With high carrier mobility and intrinsic low lattice thermal conductivity, Ag2Se compounds have attracted increasing attention for thermoelectric application near room temperature. Due to its phase transition at ∼406 K and resulting thermal volume expansion, the growth and thermoelectric properties of large-sized Ag2Se single crystals have seldom been reported so far. In this work, the vertical Bridgeman method was used for growing bulk Ag2Se single crystal, with an orientation preference along low-symmetric (201) plane. The Hall mobility as high as 2 000 cm2/(V·s) and weak electron-phonon coupling contributes to a high electronic quality BE of ∼7.0 in near-room-temperature β-Ag2Se single crystals, which is superior to the high-temperature phase α-Ag2Se. The observed low lattice thermal conductivity of 0.8 W/(m·K) at 300 K is due to the low group speeds and strong anharmonicity. A promising peak zT of 0.66 at 375 K and an average zT of 0.65 at 300–375 K were realized in β-Ag2Se crystals. The low Vickers hardness and good ductile properties were confirmed by experiment and theoretical analysis. This work not only synthesized large-sized and highly-orientated Ag2Se crystals, but also revealed its great potential of thermoelectric performance and mechanical properties for various applications near room temperature.

Thermoelectric properties of ductile Ag2S0.7Te0.3 prepared via zone melting method

Recently, the discovery of ductility inorganic semiconductors Ag2S-based alloys have drawn significant interest in hetero-shaped thermoelectric applications. In this work, Ag2S0.7Te0.3 inorganic thermoelectric compound was prepared using the zone melting technique. The crystal structure of Ag2S0.7Te0.3 is similar to that of the cubic-structured Ag2S compound, in which S and Te atoms are randomly occupied at the anionic sites. The observed high hall carrier mobility of ∼410 cm2V−1s−1 and intrinsic low lattice thermal conductivity of ∼0.2 Wm−1K−1 lead to a maximum zT of 0.30 at 600 K for Ag2S0.7Te0.3. In addition, its mechanical properties including microhardness Hv and fracture toughness Kc are measured, showing great potential for thermoelectric application.

Janus γ-GeSSe Monolayer as a High-Performance Material for Photocatalysis and Thermoelectricity

Two-dimensional Janus materials have attracted increasing attention in recent years because of their potential as materials for energy applications, such as photocatalysis and thermoelectricity (TE). Here, for the first time, we propose a monolayer Janus structure with the Mexican-hat band, γ-GeSSe, by replacing the S atoms on one side of the synthesized γ-GeS with Se atoms. Using first-principles calculations based on density functional theory (DFT), we show that γ-GeSSe is mechanically, dynamically, and thermally stable. The mechanical, electronic, optical, and transport properties of monolayer Janus γ-GeSSe are also investigated in the DFT calculations. We find that the ideal strengths of the Janus γ-GeSSe are 6.08, 8.6, and 10.08 GPa for the armchair, zigzag, and biaxial directions, respectively. The Janus γ-GeSSe is an indirect-gap semiconductor with a band gap of 1.131 eV. Our results show the Janus γ-GeSSe as a photocatalysis material for water splitting with a high solar-to-hydrogen efficiency of up to 28.78%. This is because the combination of features includes an intrinsic electric field, high optical absorption coefficient, and carrier mobility. In addition, with the γ-structure, the Janus γ-GeSSe shows an intrinsic low lattice thermal conductivity of 3.33 W/mK at room temperature, which will contribute to obtaining high TE efficiency. By using the Boltzmann transport theory, we find that the maximum TE power factor and figure of merit of the Janus γ-GeSSe reach 55–85 mW/mK2 and 0.7–0.9 in the temperature range from 300 to 900 K, respectively. Thus, our findings not only contribute to proposing a Janus material but also suggest that it can be used as an energy material with high-performance photocatalysis and TE.

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

AbstractLayer‐structured GeSb2Te4 is a promising thermoelectric candidate, while its anisotropy of thermal and electrical transport properties is still not clear. In this study, Ge1–xInxSb2Te4 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 Ge0.93In0.07Sb2Te4 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.

Flexible composite structures with controlled physical and mechanical characteristics

The article presents the results of theoretical and experimental studies that are the basis for the development of a new class of aerospace engineering structures that allow implementing approaches to create structures with variable morphological and functional characteristics of products. Condensed soft substances, such as elastomers, gels, gradually become functional elements on the basis of which the creation of soft machines and electronics develops [1-3]. Research in this direction has led to the creation of structures with a special architecture that are mechanically compatible, deformable and capable, with a certain combination, of perceiving and transmitting a signal, changing their shapes and physical characteristics (thermal conductivity, electrical conductivity, etc.). The use of such structures in a certain sense models the multifunctionality observed in biological objects and structures (skin, muscles, nervous tissue) [4-7]. The creation of structures that change their shape, structure and change their functional and operational characteristics in the process of work, taking into account changing external and internal conditions, is an urgent task for many systems of aerospace technology. In this paper, morphologically changeable structures are considered, which include reconfigurable antennas, aircraft wings with variable shape and geometry, flexible robotic systems [8]. The use of such systems with flexible structural elements makes it possible to create structures capable of overcoming unpredictable obstacles due to their adaptive geometry, fit into limited spaces and withstand significant loads and vibrations. One of the most important tasks in the development of such systems is the organization of a distributed actuation system associated with the problem of creating an internal structure of actuators integrated into a flexible composite design of actuators made of elastic materials. In a number of works for the operation of thermoactive actuators, the use of rigid nanoparticles as surface heating elements or as fillers for composites that are electrically sensitive, magnetically sensitive and/or photoreactive has been investigated [9-13]. However, surface heating elements are limited in use beyond a thickness of several hundred micrometers due to their low intrinsic thermal conductivity [14]. In addition, rigid components significantly change the mechanical properties of the structure being created, which limits the morphological capabilities of the structures being created. For example, in [15], it is shown that reducing the electrical resistance for a thermal heater to acceptable values requires an increase in the filler to 15% of the mass of the structure, while the deformation of the actuation of the structure is reduced by 35.0%. In this paper, overcoming the above limitations is carried out by creating a material architecture that dramatically expands the range of properties and dynamic functions of the heating element being developed for the actuator. Multifunctionality is achieved by embedding metal fibers of a certain configuration into an elastic medium based on polydimethylsiloxane elastomer, which provide mobility and conformality of the deformable structure of the actuator during its operation. It is shown that the inclusion of metal fibers of a certain configuration in the structure of the actuator does not interfere with its ability to change shape and perform mechanical work in response to external stimuli. Shape morphing in the absence of an external load can be programmed in the composite structure by including fibers with certain stiffness and thermal characteristics in it so that it can reversibly switch between programmed morphologies using electrical or thermal stimulation. Together, these properties allow the composite to demonstrate a rich variety of functionality, which allows it to simultaneously realize sensory and dynamic characteristics.

Synergistically optimizing thermoelectric performance of ZnO ceramics by interfacial band alignment and self-doping defects

ZnO is a promising thermoelectric ceramic material due to non-toxicity and abundance in resources. However, its thermoelectric performance is limited by the intrinsic low carrier concentration and high thermal conductivity. In this work, we synthesized the (1 − x)ZnO/xZnS (x = 0–0.05) powders by a two-step solution method followed by microwave sintering in an oxygen-deficient environment at 1000 ℃, and then produced the self-doped ZnO ceramics with ZnO/ZnS interfaces. The electrical and thermal properties was investigated from room temperature to 900 K. The ZnO/ZnS interface and self-doping significantly increased the electrical properties of ZnO ceramics, the electrical conductivity (σ) and Seebeck coefficient (α) increased simultaneously with temperature for (1 − x)ZnO/xZnS (x > 0), and the highest power factor (PF, 3675 µW·m−1·K−2) was obtained from 0.98ZnO/0.02ZnS at 900 K. At the same time, the ZnO/ZnS interfaces and self-doped defects greatly reduced the lattice thermal conductivity. Finally, the highest ZT value of 0.94 has been reached in 0.95ZnO/0.05ZnS at 900 K.

Defect engineering synergistically modulates power factor and thermal conductivity of CuGaTe2 for ultra-high thermoelectric performance

• The vacancy of Cu atom can increase the band gap and reduce the sound velocity. • Cu vacancies increase the density of the samples, and significantly increase the carrier concentration. • Cu vacancies generate many defects, which scatter phonons at multiple scales and realize thermoelectric decoupling. • The highest ZT value of Cu 0.96 GaTe 2 reaches 1.23 at 823 K, and the average ZT value reaches 0.575. The ternary chalcopyrite CuGaTe 2 has emerged as a promising p -type thermoelectric material with its advantages of low cost, good stability, and non-toxic elements. However, its thermoelectric performance is limited by the intrinsic low electrical conductivity and high lattice thermal conductivity. In this work, A deficiency of Cu in Cu 1– x GaTe 2 semiconductors can be used to optimize the electrical properties by improving the carrier concentration and to reduce thermal conductivity through multi-scale phonon scattering, which is predicted and guided by the First-principles density functional theory calculations. The carrier concentration is increased to 10 20 , which compensates for the low electrical performance caused by the intrinsic low n H of CuGaTe 2 . The average power factor of Cu 0.96 GaTe 2 reaches 106.3% higher than that of the original CuGaTe 2 . In addition, the lattice thermal conductivity of the defective samples is greatly reduced at high temperatures, which is mainly due to the reduction of sound speed and phonon scattering. All the above factors contribute to the highest dimensionless figure of merit (ZT) value of 1.23 at 823 K in Cu 0.96 GaTe 2 , which is 114% higher than the pristine CuGaTe 2 , and the average ZT is 171.4% higher.

Synergistically optimized electron and phonon transport of p-type BiCuSeO oxyselenides via Pb dopant and Te composite

Layer-structured BiCuSeO oxyselenides with intrinsic low lattice thermal conductivity, non-toxicity, non-pollution and outstanding thermal stability is regarded as a promising thermoelectric material, but its application is limited by the poor electrical conductivity. In this paper, Pb-doped BiCuSeO (Bi1-xPbxCuSeO) was fabricated via a fast preparation method combined self-propagating high-temperature synthesis (SHS) with spark plasma sintering (SPS). Although Pb doping could greatly improve the electrical conductivity of BiCuSeO, the thermal conductivity increased as well, and it limits the thermoelectric performance. To further optimize the electron and phonon transport properties, Te powders and Te nanowires were introduced in Bi0·9Pb0·1CuSeO by ball milling, respectively. As a result, the thermal conductivity largely decreased with a maintained electrical performance. Ultimately, a maximum ZT value of 1.0 at 873 K was achieved for the 5 vol% Te nanowire + Bi0·9Pb0·1CuSeO sample, which is about 2.5 times as large as that for pristine BiCuSeO. Our work paves an alternative strategy for tuning the thermoelectric performance of BiCuSeO through Bi site doping combined low-dimension nanocomposites.

Enhanced energy management performances of passive cooling, heat storage and thermoelectric generator by using phase change material saturated in metal foam

In this study, a thermal energy management system that combines passive cooling, heat storage and electrical energy harvest is proposed by using foam/PCM composite and thermoelectric generator (TEG), which are separately fixed upon and under the heat source as the coolers of heat source. Foam/PCM composite is also aimed to enhance the latent-heat energy storage and passive cooling. Results show that the control case of using solitary metal foam harvests the most thermoelectric energy, but has the risk of leading heat source to thermal failure. Using pristine PCM can reduce the wall temperature and prolong the thermal management time during phase change. However, the intrinsic low thermal conductivity of pure PCM still results in high temperature of heat source when the PCM is in solid stage. Attributed to high thermal conductivity and latent heat storage, the foam/PCM composite presents the lowest heat-source temperature, but at the cost of delivering the least thermoelectrical power.

Preparation and thermoelectric transport properties of BiSe and Sb-doped BiSe single crystals

<p indent="0mm">Exploring high thermoelectric performance in single crystal materials with intrinsic low lattice thermal conductivity has become an important field for thermoelectric research. BiSe, as a member of (Bi₂Se₃)_{<italic>m</italic>}(Bi₂)_{<italic>n</italic>} series superlattice compounds, has a very low intrinsic thermal conductivity due to the existence of Bi₂ bilayer in its layered crystal structure. Moreover, it is a new and promising thermoelectric material due to the non-toxic and environmentally friendly chemical compositions. The special layered structure of BiSe makes its thermoelectric transport properties significantly anisotropic. In this paper, BiSe single crystal was prepared by Bridgman method, and its anisotropic thermoelectric transport properties were investigated. The results show that the sample has higher conductivity and thermal conductivity in the in-plane direction, while the lower Seebeck coefficient makes the thermoelectric figure of merit <italic>ZT</italic> value in this direction lower than that in the interlamellar direction. The maximum values of <italic>ZT</italic> in the two directions are 0.11 <sc>(573 K)</sc> and 0.16 <sc>(623 K),</sc> respectively. Compared with polycrystalline BiSe, the single crystal sample exhibits lower electric transport performance, which can be attributed to the difference of scattering coefficient. The carrier concentration of BiSe single crystal is regulated by Sb doping, which effectively improves the Seebeck coefficient of the samples and optimizes the electrical transport performance. In the meanwhile, Sb doping can produce lattice distortion and reduce the lattice thermal conductivity. The final <italic>ZT</italic> value of Bi_0.8Sb_0.2Se single crystal increases by about 1 fold, reaching 0.34 <sc>(573 K)</sc> in the interlamellar direction and 0.20 <sc>(573 K)</sc> in the in-plane direction.

Enhanced average thermoelectric properties of n‑type Mg3Sb2 based materials by mixed-valence Ni doping

Due to their high band degeneracy and intrinsic low lattice thermal conductivity, n-type Mg3Sb2-based thermoelectric materials have drawn a lot of attention in thermoelectric applications in recent years. By using simple and efficient fast induction melting and hot pressing, the n-type Mg3.5−xNixSbBi0.96Te0.04 (x = 0, 0.015, 0.02, 0.03, 0.04, 0.05, and 0.06) samples have been successfully synthesized. The structure of Mg3.5−xNixSbBi0.96Te0.04 samples is examined, as well as their thermoelectric properties. The findings demonstrate that the mixed valence of Ni2+ and Ni3+ that occupied distinct Mg sites occurred as the Ni doping level grew in the Mg3.5−xNixSbBi0.96Te0.04 samples. The trivalent Ni3+ increases carrier concentrations dramatically, while the divalent Ni2+ increases the effective mass. The mixed valence of Ni causes lattice disorder, which enhances phonon scattering and reduces lattice thermal conductivity. As a result, the Mg3.485Ni0.015SbBi0.96Te0.04 sample has a high ZT value of 1.58 at 743 K and an average ZT value of 1.22 from 323 to 743 K. This work suggests that the mixed valence of cationic dopant effectively improve the thermoelectric performance of n-type Mg3Sb2-based compounds.

Ni doping and rational annealing boost thermoelectric performance of nanostructured double perovskite Pr1.8Sr0.2CoFeO6

Pr2CoFeO6-based double perovskite exhibits intrinsic low thermal conductivity and high Seebeck coefficient, but its low electrical conductivity induces unsatisfied thermoelectric performance. Here, we employ a synergistic strategy of rational annealing and Ni doping to achieve an improved ZT of ∼0.085 at 573 K in Pr1.8Sr0.2CoFe0.95Ni0.05O6, which is ∼425 % higher than that of pristine Pr2CoFeO6. The annealing process effectively reduces pores in the as-sintered bulk material, leading to an enhanced electrical conductivity without damaging the Seebeck coefficient, and the Ni doping further effectively improves the hole carrier concentration and in turn enhances the electrical conductivity, leading to a peak power factor of ∼113 μW m−1 K−2 at 573 K. Besides, Ni doping induces localized crystal imperfections including point defects, dislocations, and lattice distortions, contributing to an ultra-low thermal conductivity of <0.6 W m−1 K−1. As a result, the as-achieved Pr1.8Sr0.2CoFe0.95Ni0.05O6 has a ZT of ∼0.085 at 573 K, which is highly competitive to reported thermoelectric double perovskites, indicating its potential applications in high-performance thermoelectric devices.

Band engineering and improved thermoelectric performance in p-type SmMg2Sb2: A first-principles study

The thermoelectric properties of p-type SmMg2Sb2 are investigated by using the density functional theory and the Boltzmann transport equation method. It is found that SmMg2Sb2 shows a narrow band gap characteristic, and the crystal field splitting and spin-orbital coupling effect result in a singly degenerate valence band maximum. Meanwhile, SmMg2Sb2 exhibits an intrinsic low lattice thermal conductivity owing to the obvious phonon softening in the low-frequency acoustic branches. Based on a careful analysis of the band structure, we propose a scheme of metallic dopant at Sm site to promote the valence band convergence and improve the Seebeck coefficient. The improved thermoelectric properties are numerically confirmed in the Ba-doped p-type SmMg2Sb2, where a significantly improved ZT of 1.6 at 750 K is predicted with the synergistical effects of band engineering and enhanced phonon scattering.

Improvement of anisotropic thermoelectric performance in polycrystalline SnSe by metallic AgSnSe2 compositing

SnSe is an emerging star material in thermoelectric community owing to its attractive electronic band structure and ultralow intrinsic lattice thermal conductivity. By now, aliovalent doping is often employed to be a route strategy to optimize the thermoelectric properties of SnSe via improving its poor electrical conductivity. In this work, AgSnSe2, as a metallic composite, is introduced with the aim to increase the hole concentration of SnSe via metal-semiconductor contact. It is demonstrated that compositing of AgSnSe2 can effectively increase the hole concentration of polycrystalline SnSe hosts by two orders of magnitude (from 1017 to 1019 cm−3) without deteriorating the carrier mobilities. Therefore, a lager power factor of 5.72 μW cm−1 K−2 is achieved at 773 K for the SnSe + 0.020AgSnSe2 sample perpendicular to the hot-pressing direction. Combined with the intrinsic low thermal conductivity, the maximum zT value of the sample can be boosted to 0.68 at 773 K, which is increased by 124% compared to that of the uncomposited counterpart. This work proves that composite engineering should be an efficient alternative strategy in optimizing the thermoelectric performance of polycrystalline SnSe and can be synergistically used with other sophisticated approaches.

Thermoelectric performance of hydrothermally synthesized micro/nano Cu2-xS

Among the state-of-the-art thermoelectric materials, copper sulfides (Cu2S) have been predicted as promising thermoelectric materials due to their low intrinsic thermal conductivity. However, they still confront the problems with lower electrical properties, which distinctly restrict their thermoelectric application. Significant enhancement of thermoelectric properties is a great challenge owing to the common interdependence of electrical and thermal conductivity. Herein, a micro/nano Cu2-xS composite, with significantly enhanced thermoelectric properties, is prepared via a simple hydrothermal method. Due to the synergistic effect of the introduced nanostructure and the increased Cu1.96S contents, the micro/nano Cu2-xS bulk samples present a power factor of 10.1 μW cm−1 K−2 at 773 K. Meanwhile, a decrease of the thermal conductivity to 0.69 W m−1 K−1 is obtained, originating from the strong phonon scattering of micro/nano structure. Remarkably, a ZTmax value of 1.1 at 773 K is obtained, which is higher than the reported Cu2-xS thermoelectric material using chemical methods. This study proposes a facile microstructure engineering strategy for the development of high-performance thermoelectric materials.

Phonon Symphony of Stacked Multilayers and Weak Bonds Lowers Lattice Thermal Conductivity.

Controlling lattice vibrations to obtain intrinsic low thermal conductivity play a critical role in thermal management of electronic and photonic devices, energy converters, and thermal insulation, which necessitates exploring new compounds and a thorough understanding of their chemical structure, bonding, and lattice dynamics. Herein, a new chalcogenide, Ga6 Cr5 Se16 , shows intrinsic low lattice thermal conductivity κlat , which crystallizes in the monoclinic phase (C2/m) with the stacked inverse GaSe4 layers (g'), close-packed Cr3+ Se6 layers (c), GaSe4 layers (g) and loosely-stacked Cr2+ Se6 layers (c') along the c-axis. In this structure, a wide variety of chemical bonding is arranged in each layer, such as covalent Ga-Se, covalent Cr3+ -Se, and weaker Cr2+ -Se bonding, which endow it with a large phonon symphony by strong coupling of soft acoustic and low-lying optical phonons. As a result, Ga6 Cr5 Se16 realizes an intrinsic low κlat of 0.79 W m- 1 K- 1 at 323 K, which is almost four times, or twice lower than that of Cr3 Se4 (2.95 W m- 1 K- 1 ), or Cr2 Se3 (1.56 W m- 1 K- 1 ), Ga2 Se3 (1.36 W m- 1 K- 1 ) at 323 K, respectively. These insights will offer comprehensive understanding of the phonon propagation in complex layered chalcogenides, andalso shed useful light on future design of low-κlat solids.

A new poly(3,4-ethylenedioxythiophene)-poly (styrene sulfonate)/nickel oxide nanoparticles (PEDOT:PSS/NiO) thermoelectric system with a promising thermoelectric power factor

Recently, the thermoelectric (TE) functions of Poly(3,4-ethylene-dioxythiophene):Poly(styrenesulphonate) (PEDOT:PSS) polymer have been extensively progressed, owing to its processability, flexibility, and its low intrinsic thermal conductivity. In this regards, nickel oxide (NiO) nano-particles have been mixed with PEDOT:PSS to design a new thermoelectric (PEDOT:PSS/NiO) system. The anisotropic (parallel // and vertical ⊥) TE functions as a function of the NiO content (10–40 wt%) have been investigated in the temperature range 300–390 K. The anisotropic conductivity (σ) of the systems is reduced while their anisotropic Seebeck coefficients (S) have increased with the increase in the NiO content. The anisotropic conductivity of the systems is reduced while their anisotropic Seebeck coefficients have increased firstly and then decrease with the growth of temperature. The optimal PF//~24.61 ± 0.3 μW/mK2 and PF⊥~ 3.40 ± 0.03 μW/mK2 are achieved at 340 K for 30 wt% with S// ~39.07 ± 1.7 μV/K and S⊥~27.34 ± 2 μV/K owing to the spin Seebeck coefficient, the reduction in the carrier concentration and the energy filtering effects. Interestingly, the impact of H2SO4 acid post-treatment on the PEDOT:PSS/NiO (30 wt%) has been done to obtain the highest PF values (PF//~ 54.59 ± 1 μW/mK2, PF⊥~ 5.64 ± 2 μW/mK2) owing to the growth in the anisotropic σ as a result of the removal of PSS polymers. Finally, the achieved PEDOT:PSS/NiO system offers a promising TE functions for potential applications in temperature sensors, wearable electronics and harvest technology.

Paving 3D interconnected Cring-C3N4@rGO skeleton for polymer composites with efficient thermal management performance yet high electrical insulation

Polymer-based thermal interface materials (TIMs) with good electrical insulation property is essential in the thermal management of microelectronic devices. A common approach to increasing the polymer's low intrinsic thermal conductivity is to introduce thermally conductive fillers. In most cases, those fillers are also electrically conductive, which destroys the origin electrical insulation property. In this work, we develop a novel heterogeneous two-dimensional hybrid filler by assembling circular carbon nitride (Cring-C3N4) and graphene oxide (GO), aiming to bring the insulation property via Cring-C3N4. With an ordered 3D interconnected structure, the assembled filler shows enlarged sheet size and compact sheet stacking, which facilitates heat conduction. Additionally, the adopted ice-templated method further arranges the filler with the largest thermal conductivity reaching 4.12 W/mK. Meanwhile, it also shows a lower electrical conductivity of 3.6 × 10−7 S/m, meeting most electrical insulation required occasions. Practical heat dissipation performance tests reveal that both larger temperature change rate and maximum attainable temperature are observed for ice-templated treated composite, indicating the reduced thermal contact resistance (TCR) is responsible for the overall improved heat conduction process. This viewpoint is also supported by the practical application of the material functioning as TIMs from both experimental and simulative aspects.