Search

The n-type sulfur-based material MnBi 4 S 7 exhibits intrinsically low thermal conductivity, which is well explained by double well potential. Se alloying can enlarge the carrier concentration and reduce lattice thermal conductivity, resulting in a peak zT value of 0.31, which reveals a record high value among earth-abundant ternary n-type sulfides. • Systematic investigation of the thermoelectric properties of MnBi 4 S 7-x Se x solid solutions. • Elucidation of low lattice thermal conductivity by first-principle calculations and other advanced experimental techniques. • Potential as competitive n type thermoelectric candidate demonstrated by a peak zT of 0.31. We report self-doped MnBi 4 S 7-x Se 7x solid solution as a novel n-type sulfide thermoelectric material with weak anisotropic transport properties. These compounds feature intrinsically low lattice thermal conductivity of 0.5–0.8 W m−1K−1 in the temperature range of 300–800 K, which is well explained by strong lattice anharmonic vibration, mainly from Bi atoms as verified by theoretical calculations. Intentionally introduced sulfur deficiency acts as an efficient electron donor that enhances the electrical conductivity of MnBi 4 S 7 while alloying with Se can promote electrical conductivity and further reduce thermal conductivity by 25% in the whole temperature region. As a result, the sample of with nominal composition of MnBi 4 S 5.46 Se 1.4 shows a peak zT of ~0.31 at 770 K vertical to the pressing direction. [ABSTRACT FROM AUTHOR]

Continuous and robust filler network is very critical in improving thermal conductivity of the thermally conductive yet electrically insulating composite. Regrettably, such network is commonly constructed by large amount of thermally conductive while electrically insulating fillers with sacrificing mechanical properties of the final composite. In the present work, to address this issue and further improve the thermally conductive property, the robust 3D thermally conductive while electrically insulating hybrid filler network with high orientation and ordered distribution was constructed successfully through strong shear and extension flow field in confined space during the multilayer co-extrusion. In the hybrid filler network with the 32-layer alternating structure, along the extrusion direction, graphite (Gt) flakes were highly oriented; meanwhile, along the thickness direction, the local Gt-MWCNTs network was confined between two adjacent SiC-filled layers. As a result, thermal conductivity of the final composite reached as high as 2.05 W/(m × K). Furthermore, significantly anisotropic electrical resistivities were also obtained, which endowed the final composite with excellent electrical insulation, great anti-static and electromagnetic interference shielding properties. Moreover, compared with commonly compounded composites, mechanical properties of the multilayered composite were also enhanced significantly. As a consequence, the multifunctional composite with robust thermally conductive while electrically insulating filler network and excellent mechanical properties can be obtained based on this strategy, thus it plays a critical role in facilitating the development of the thermal management materials. [ABSTRACT FROM AUTHOR]

To fabricate thermally conductive while electrically insulating composites with excellent antistatic property is a huge challenge in the region of packaging materials of electronic devices due to the contradiction between the electrical insulation and the antistatic property. In the present work, the peculiar multilayer structures with alternating high efficiency thermally, electrically conductive layers and thermally conductive, electrically insulating layers were constructed successfully through a simple, one-step melt extrusion method. Such thermally conductive and electrically insulating composites possessed significant anisotropic electrical resistivity; for example, the in-plane electrical resistivities (parallel to the layer direction) were below 117 Ω × cm, while the through-plane electrical resistivities were over 5 × 10 13 Ω × cm. Meanwhile, with increasing the layer number, thermal conductivity of the composite with the same filler loading was improved monotonously, and reached as high as 1.45 W/(m × K) in the composite with 32 layers. In addition, tensile strength and elongation at break of the composites were also enhanced due to the different deformation mechanisms of separate layers. Furthermore, to give a deep insight into the enhancement mechanism of thermally conductive property, finite element analysis was applied and the results indicated that high efficiency thermally, electrically conductive layers possessed magnified effects on the heat dissipation. Therefore, the multilayer structure with alternating high efficiency thermally, electrically conductive layers and thermally conductive, electrically insulating layers can endow the composite with excellent comprehensive properties effectively, and it also sheds light on the design and fabrication of high performance materials for the applications of thermal management or other energy harvesting fields. [ABSTRACT FROM AUTHOR]

• Growth of large-sized Ge 1– x In x Bi 2 Te 4 single crystals by Bridgman method. • Ultralow κ L of GeBi 2 Te 4 driven by cation disorder and low phonon velocity. • Resonant level introduced by In-doping greatly improves electrical performance. • Achieving zT ave of 0.36 in the range of 323–573 K for Ge 0.97 In 0.03 Bi 2 Te 4 sample. Resonant level, the impurity level located inside the valence/conduction band, is an effective strategy for decoupling the electrical conductivity and Seebeck coefficient and enhancing the thermoelectric power factor. In this work, we show that In doping induces resonant level and enhances the thermoelectric performance of GeBi 2 Te 4 , a promising n-type thermoelectric material with layered structure. Single crystals grown by Bridgman method were used in this study to take the advantage of its anisotropic transport properties. An ultralow lattice thermal conductivity of ∼0.51 W m−1 K−1 at 323 K was found along the c -axis of GeBi 2 Te 4 , driven by intrinsic cation disorder and the low phonon group velocity from the relatively weak chemical bonds as well as the strong lattice anharmonicity caused by hierarchical bond orders. Both enhanced electrical conductivity and Seebeck coefficient were observed in the In-doped samples, indicating that In-doping not only increases the carrier concentration, but also introduces the resonant level that was further confirmed by the first-principles calculation. A maximum zT of ∼0.42 at 523 K and an average zT of 0.36 over 323 to 573 K were achieved in Ge 0.97 In 0.03 Bi 2 Te 4 crystal sample, ∼100% and ∼89% enhancement compared to those of pristine single crystal sample, respectively. This study demonstrates another example of resonant level for thermoelectric performance enhancement, which may be applied to other related materials. [ABSTRACT FROM AUTHOR]

• Constructing fiber reinforced segregated structure. • BN orient along the fiber surface forming robust thermally conductive network. • Simultaneously enhanced thermal conductivity and mechanical properties. Segregated structure with continuous filler network but isolated matrix is a classic prototype to increase the thermal conductivity (TC) of the composites. However, such prototype only finds limited applications due to both the poor mechanical properties originated from the discontinuity of the polymer matrix and the mediately improved TC of the continuous filler network arising from the random contact of the fillers. In this work, a reinforced segregated structure in which the continuous phase is made with boron nitride (BN) wrapped a trace amount of PP fiber (PF), is first proposed in order to enhance the TC and mechanical properties simultaneously. In such reinforced segregated structure, BN aligns on the surfaces of PF thus forms a long-range ordered, high thermal conductive pathway. As expected, an enhancement of 244%, 133% and 103% in the TC, elongation at break and tensile strength of the composite with reinforced segregated structure are successfully achieved compared with typical segregated structure. Therefore, this work offers some new insights into the design of a segregated structure to balance the TC and mechanical properties. [ABSTRACT FROM AUTHOR]

• PVA/MXene alternating multilayered films were fabricated via multilayered casting. • The multilayered films exhibited high EMI SE of 44.4 dB and SSE t of 9343 dB cm2 g−1. • The multilayered films exhibited a high thermal conductivity of 4.57 W/mK. • The multilayered films showed remarkable anti-dripping performance. With the miniaturized and high-frequency development in electronic products, polymeric films synchronously with high electromagnetic interference (EMI) shielding effectiveness (SE) and thermal conductivity (TC) are urgently needed. In this work, poly (vinyl alcohol)/transition metal carbide (PVA/MXene) films featured with alternating multilayered structure were fabricated through multilayered casting. The continuous MXene layer provided a compact network for conducting heat and electron, endowing the multilayered film with excellent EMI SE and TC synchronously. In particular, the 27-μm-thick PVA/MXene multilayered film (containing 19.5 wt% MXene in total) exhibited an electrical conductivity of 716 S/m, a maximum EMI SE of 44.4 dB and a specific EMI SE (SSE t) of 9343 dB cm2 g−1. Meanwhile, the multilayered film showed a high in-plane TC of 4.57 W/mK, enhanced by almost 23-fold compared with that of neat PVA. Moreover, the multilayered architecture endowed the film with remarkable anti-dripping performance. This work provides a novel and feasible strategy for fabricating flame-retardant polymeric thermal conductive and EMI shielding films, which will have enormous prospect in advanced electrical devices. [ABSTRACT FROM AUTHOR]