Browsing by Author "Yang, G"

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    Enhanced thermoelectric performance and mechanical strength of n-type BiTeSe materials produced via a composite strategy
    (Elsevier, 2022-01) Yang, G; Sang, L; Mitchell, DRG; Yun, FF; See, KW; Ahmed, AJ; Sayyar, S; Bake, A; Liu, P; Chen, L; Yue, ZJ; Cortie, DL; Wang, XL
    Zone-melted Bi2Te2.7Se0.3 (ZM BTS) alloys are typical n-type commercial thermoelectric (TE) materials and are utilized for refrigeration and power generation near room temperature. They usually suffer from poor mechanical performance, as well as having a low figure of merit (ZT). In this work, we report an effective composite strategy to improve both the TE and mechanical performance of n-type BTS materials by incorporating carbon microfibers. The introduction of carbon microfibers in BTS effectively reduces the lattice thermal conductivity due to phonon scattering at multi-scale boundaries and due to the large interfacial thermal resistance arising from phonon mismatch between the constituent phases. Simultaneously, it also gives rise to an enhancement of the electrical conductivity, which originates from the increased carrier density without significant limitation on its weighted mobility. Consequently, a high peak ZT of 1.1 at 400 K and an average ZTave value of 0.95 are achieved in the temperature range 300 ~ 550 K, yielding a calculated efficiency of η = 9%. Moreover, the BTS/carbon microfiber composites show superior compressive strength compared to a commercial ZM BTS sample. This improved strength is highly desirable for real-world TE applications. Our results demonstrate a novel way to produce high-performance TE materials, in which interfaces with large thermal resistance are used to achieve low thermal conductivity without significantly degrading the electrical properties of the materials. © 2021 Elsevier B.V.
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    Modulation of crystal and electronic structures in topological insulators by rare-earth doping
    (American Chemical Society, 2019-08-26) Yue, ZJ; Zhao, WY; Cortie, DL; Yang, G; Li, Z; Wang, XL
    We study magnetotransport in a rare-earth-doped topological insulator, Sm0.1Sb1.9Te3 single crystals, under magnetic fields up to 14 T. It is found that that the crystals exhibit Shubnikov-de Haas (SdH) oscillations in their magnetotransport behavior at low temperatures and high magnetic fields. The SdH oscillations result from the mixed contributions of bulk and surface states. We also investigate the SdH oscillations in different orientations of the magnetic field, which reveal a three-dimensional Fermi surface topology. By fitting the oscillatory resistance with the Lifshitz-Kosevich theory, we draw a Landau-level fan diagram that displays the expected nontrivial phase. In addition, the density functional theory calculations show that Sm doping changes the crystal structure and electronic structure compared with those of pure Sb2Te3. This work demonstrates that rare-earth doping is an effective way to manipulate the Fermi surface of topological insulators. Our results hold potential for the realization of exotic topological effects in magnetic topological insulators. Copyright © 2024 American Chemical Society.
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    Phonon engineering in thermal materials with nano-carbon dopants
    (AIP Publishing, 2024-06-01) Stamper, C; Cortie, DL; Nazrul-Islam, SMK; Rahman, R; Yu, DH; Yang, G; Al-Mamun, A; Wang, XL; Yue, ZJ
    The unique geometric and thermal properties of carbon nanoparticles (NPs)—including nanotubes, graphene, and nanodiamonds—have led to their use as additives in many composite material systems. In this review, we investigate the mechanisms behind the altered thermal conductivity (κ) of thermoelectric (TE) and other thermal materials that have been composited with carbon NPs. We provide a comprehensive overview and analysis of the relevant theoretical and applied literature, including a detailed review of the available thermal conductivity data across five common classes of TE materials (Bi2Te3 variants, skutterudites, metal–oxide, SnSe, Cu2Se) in combination with carbon additives, including graphene, nanotubes, carbon black, carbon fiber, and C60. We argue that the effectiveness of carbon NPs in reducing κ in TE composites generally arises due to a combination of the presence of the carbon NP interfaces and significant changes in the microstructure of the host material due to compositing, such as suppressed grain growth and the introduction of pores, dislocations, and strain. Carbon NPs themselves are effective phonon scatterers in TE composites due to a significant mismatch between their high-frequency phonon distribution and the lower-frequency phonon distribution of the host material. While carbon NP doping has proven itself as an effective way to increase the performance of TE materials, there is still a significant amount of work to do to precisely understand the fundamental thermal transport mechanisms at play. Rigorous material characterization of nanocomposites and spectroscopic studies of the precise lattice dynamics will greatly aid the development of a fully quantitative, self-consistent model for the thermal conductivity of carbon nanocomposites. © 2024 Author(s). All article content, except where otherwise noted, is licensed under a Creative Commons Attribution (CC BY) license (https://creativecommons.org/licenses/by/4.0/)
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    Topological insulator VxBi1.08-x Sn0.02Sb0.9Te2S as a promising n-type thermoelectric material
    (Elsevier, 2022-10) Chen, L; Zhao, WY; Li, M; Yang, G; Guo, L; Bake, A; Liu, P; Cortie, DL; Zheng, RK; Cheng, ZX; Wang, XL
    As one of the most important n-type thermoelectric (TE) materials, Bi2Te3 has been studied for decades, with efforts to enhance the thermoelectric performance based on element doping, band engineering, etc. In this study, we report a novel bulk-insulating topological material system as a replacement for n-type Bi2Te3 materials: V doped Bi1.08Sn0.02Sb0.9Te2S (V:BSSTS). The V:BSSTS is a bulk insulator with robust metallic topological surface states. Furthermore, the bulk band gap can be tuned by the doping level of V, which is verified by magnetotransport measurements. Large linear magnetoresistance is observed in all samples. Excellent thermoelectric performance is obtained in the V:BSSTS samples, e.g., the highest figure of merit ZT of ~ 0.8 is achieved in the 2% V doped sample (denoted as V0.02) at 530 K. The high thermoelectric performance of V:BSSTS can be attributed to two synergistic effects: (1) the low conductive secondary phases Sb2S3, and V2S3 are believed to be important scattering centers for phonons, leading to lower lattice thermal conductivity; and (2) the electrical conductivity is increased due to the high-mobility topological surface states at the boundaries. In addition, by replacing one third of costly tellurium with abundant, low-cost, and less-toxic sulfur element, the newly produced BSSTS material is inexpensive but still has comparable TE performance to the traditional Bi2Te3-based materials, which offers a cheaper plan for the electronics and thermoelectric industries. Our results demonstrate that topological materials with unique band structures can provide a new platform in the search for new high performance TE materials. © 2022 Elsevier B.V.