| 1. |
- Chen, Xiaozong, et al.
(författare)
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Preparation of nano-sized Bi2Te3 thermoelectric material powders by cryogenic grinding
- 2012
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Ingår i: Progress in Natural Science. - : Elsevier BV. - 1002-0071 .- 1745-5391. ; 22:3, s. 201-206
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Tidskriftsartikel (refereegranskat)abstract
- A novel method for rapid preparation of Bi2Te3 nano-sized powders with an average particle size of about 7nm was developed. A starting powder mixture consisting of Bi2Te3 coarse particles of similar to 5mm was ground using cryogenic grinding in the liquid nitrogen. For comparison, the conventional high-energy ball milling was used to prepare the Bi2Te3 nano-sized powders. Sintering properties of as-prepared powders was investigated by spark plasma sintering (SPS). The effects of the preparation procedure on the crystallinity, morphology and structure were examined by X-ray diffraction (XRD) and transmission electron microscopy (TEM). It was found that Bi2Te3 was not transformed into a non-equilibrium amorphous phase or decomposed during the cryogenic grinding process, and as-prepared nano-powders possessed excellent sinterability. This technique might also be applicable to other thermoelectric materials.
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| 2. |
- Chen, Xiaomeng, et al.
(författare)
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A Differentially Private Method for Distributed Optimization in Directed Networks via State Decomposition
- 2023
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Ingår i: IEEE Transactions on Control of Network Systems. - : Institute of Electrical and Electronics Engineers (IEEE). - 2325-5870. ; 10:4, s. 2165-2177
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Tidskriftsartikel (refereegranskat)abstract
- In this article, we study the problem of consensus-based distributed optimization, where a network of agents, abstracted as a directed graph, aims to minimize the sum of all agents' cost functions collaboratively. In the existing distributed optimization approaches (Push-Pull/AB) for directed graphs, all the agents exchange their states with neighbors to achieve the optimal solution with a constant step size, which may lead to the disclosure of sensitive and private information. For privacy preservation, we propose a novel state-decomposition-based gradient tracking approach (SD-Push-Pull) for distributed optimization over directed networks that preserves differential privacy, which is a strong notion that protects agents' privacy against an adversary with arbitrary auxiliary information. The main idea of the proposed approach is to decompose the gradient state of each agent into two substates. Only one substate is exchanged by the agent with its neighbors over time, and the other one is not shared. That is to say, only one substate is visible to an adversary, protecting the sensitive information from being leaked. It is proved that under certain decomposition principles, a bound for the suboptimality of the proposed algorithm can be derived, and the differential privacy is achieved simultaneously. Moreover, the tradeoff between differential privacy and the optimization accuracy is also characterized. Finally, a numerical simulation is provided to illustrate the effectiveness of the proposed approach.
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| 3. |
- Liang, Jiasheng, et al.
(författare)
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Crystalline Structure-Dependent Mechanical and Thermoelectric Performance in Ag2Se1-xSx System
- 2020
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Ingår i: RESEARCH. - : American Association for the Advancement of Science (AAAS). - 2639-5274. ; 2020
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Tidskriftsartikel (refereegranskat)abstract
- Self-powered wearable electronics require thermoelectric materials simultaneously with a high dimensionless figure of merit (zT) and good flexibility to convert the heat discharged by the human body into electricity. Ag-2(S,Se)-based semiconducting materials can well satisfy these requirements, and thus, they are attracting great attention in thermoelectric society recently. Ag-2(S,Se) crystalizes in an orthorhombic structure or monoclinic structure, depending on the detailed S/Se atomic ratio, but the relationship between its crystalline structure and mechanical/thermoelectric performance is still unclear to date. In this study, a series of Ag2Se1-xSx (x = 0, 0.1, 0.2, 0.3, 0.4, and 0.45) samples were prepared and their mechanical and thermoelectric performance dependence on the crystalline structure was systematically investigated. x = 0.3 in the Ag2Se1-xSx system was found to be the transition boundary between orthorhombic and monoclinic structures. Mechanical property measurement shows that the orthorhombic Ag2Se1-xSx samples are brittle while the monoclinic Ag2Se1-xSx samples are ductile and flexible. In addition, the orthorhombic Ag2Se1-xSx samples show better electrical transport performance and higher zT than the monoclinic samples under a comparable carrier concentration, most likely due to their weaker electron-phonon interactions. This study sheds light on the further development of flexible inorganic TE materials.
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| 4. |
- Peng, Liming, et al.
(författare)
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Phase-modulated mechanical and thermoelectric properties of Ag2S1-x Tex ductile semiconductors
- 2022
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Ingår i: Journal of Materiomics. - : Elsevier. - 2352-8478 .- 2352-8486. ; 8:3, s. 656-661
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Tidskriftsartikel (refereegranskat)abstract
- By virtue of the excellent plasticity and tunable transport properties, Ag2S-based materials demonstrate an intriguing prospect for flexible or hetero-shaped thermoelectric applications. Among them, Ag(2)S1-xTex exhibits rich and interesting variations in crystal structure, mechanical and thermoelectric transport properties. However, Te alloying obviously introduces extremely large order-disorder distributions of cations and anions, leading to quite complicated crystal structures and thermoelectric properties. Detailed composition-structure-performance correlation of Ag2S1-xTex still remains to be established. In this work, we designed and prepared a series of Ag2S1-xTex (x = 0-0.3) materials with low Te content. We discovered that the monoclinic-to-cubic phase transition occurs around x = 0.16 at room temperature. Te alloying plays a similar role as heating in facilitating this monoclinic-to-cubic phase transition, which is analyzed based on the thermodynamic principles. Compared with the monoclinic counterparts, the cubic-structured phases are more ductile and softer in mechanical properties. In addition, the cubic phases show a degenerately semiconducting behavior with higher thermoelectric performance. A maximum zT = 0.8 at 600 K and bending strain larger than 20% at room temperature were obtained in Ag2S0.7Te0.3. This work provides a useful guidance for designing Ag2S-based alloys with enhanced plasticity and high thermoelectric performance.
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| 5. |
- Wang, Lianjun, et al.
(författare)
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Formation of a unique glass by spark plasma sintering of a zeolite
- 2009
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Ingår i: Journal of Materials Research. - : Springer Science and Business Media LLC. - 0884-2914 .- 2044-5326. ; 24:10, s. 3241-3245
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Tidskriftsartikel (refereegranskat)abstract
- A simple approach, order–disorder transition (ODT), has been developed to synthesize a novel glass using ZSM-5 as starting materials. In this process, the ZSM-5 powders were pressed uniaxially in a graphite die and rapidly sintered using spark plasma sintering (SPS). High-resolution transmission electron microscopic images revealed that a few crystalline zeolite fragments were still preserved locally inside the SPS consolidated sample. Vickers microhardness and fracture toughness of this as-prepared transparent glass sample at room temperature reaches 7.3 ± 0.2 GPa and 2.0 ± 0.3MPa·m1/2, respectively. It is very interesting that these novel bulk transparent glasses exhibit ultraviolet photoluminescence (PL) properties at about ∼360 nm.
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| 6. |
- Xie, Jiaying, et al.
(författare)
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Atomistic study on the structure and thermodynamic properties of Cr7C3, Mn7C3, Fe7C3
- 2005
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Ingår i: Acta Materialia. - : Elsevier BV. - 1359-6454 .- 1873-2453. ; 53:9, s. 2727-2732
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Tidskriftsartikel (refereegranskat)abstract
- The crystal structures and stabilities of Cr7C3, Mn7C3, Fe7C3 have been investigated using the interatomic potentials obtained by the lattice inversion method. The calculated structures of Cr7C3, Mn7C3 and Fe7C3 are proposed to be hexagonal with P6(3)mc space group and the calculated lattice constants are in basic agreement with the experimental data. The calculated cohesive energies indicate that the increase in the atomic number of the metal is accompanied by the decrease in the stability of its carbides. The phonon density of states and vibrational entropy related to dynamic phenomena are also evaluated. This work provides a new method for studying the properties of carbides with complex structure.
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| 7. |
- Xie, J. Y., et al.
(författare)
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Study of Chromium Activity in the Cr-Fe-N System by Galvanic Cell Method
- 2010
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Ingår i: Metallurgical and Materials Transactions. A. - : Springer Science and Business Media LLC. - 1073-5623 .- 1543-1940. ; 41A:1, s. 172-180
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Tidskriftsartikel (refereegranskat)abstract
- In the present work, the Cr-Fe-N alloys with different compositions were synthesized by nitriding the Cr-Fe powder mixtures in the purified nitrogen gas (101,325 Pa) at 1473 K for 2 weeks. The phase relationships in the synthesized alloys and the alloys equilibrated at 1173 K were carried out by X-ray diffraction (XRD) and scanning electron microscopy (SEM) techniques. The nitrogen content in the alloys equilibrated in the nitrogen gas (101,325 Pa) at 1173 K was analyzed using the inert-gas fusion thermal conductivity (IGFTC) method. The thermodynamic activities of Cr in Fe-Cr-N alloys were measured in the temperature range 973 to 1123 K using the solid-state galvanic cell technique with CaF2 single crystal as the solid electrolyte. Based on the measured EMF values, the chromium activities in the alloys were calculated with respect to pure Cr with bcc structure as the standard state. The effect of nitrogen on Cr activities in the Cr-Fe-N system was examined by comparing the experimental results of the Cr activities in the Cr-Fe and Cr-Fe-C systems.
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| 8. |
- Yang, Qingyu, et al.
(författare)
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Flexible thermoelectrics based on ductile semiconductors
- 2022
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Ingår i: Science. - : American Association for the Advancement of Science (AAAS). - 0036-8075 .- 1095-9203. ; 377, s. 854-858
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Tidskriftsartikel (refereegranskat)abstract
- Flexible thermoelectrics provide a different solution for developing portable and sustainable flexiblepower supplies. The discovery of silver sulfide–based ductile semiconductors has driven a shift in thepotential for flexible thermoelectrics, but the lack of good p-type ductile thermoelectric materials hasrestricted the reality of fabricating conventional cross-plane p-shaped flexible devices. We report aseries of high-performance p-type ductile thermoelectric materials based on the composition-performance phase diagram in AgCu(Se,S,Te) pseudoternary solid solutions, with high figure-of-meritvalues (0.45 at 300 kelvin and 0.68 at 340 kelvin) compared with other flexible thermoelectricmaterials. We further demonstrate thin and flexible p-shaped devices with a maximum normalizedpower density that reaches 30 mW cm−2 K−2. This output is promising for the use of flexiblethermoelectrics in wearable electronics.
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