Journal of Powder Materials

Research Articles

[Korean]
Fabrication of Multilayer Core-Shell Structure for High Power Factor in Bi₂Te_2.7Se_0.3 Thermoelectrics: Su Min Eun, Jin Kyeong Shin, Se Been Jeong, Eui Seon Lee, Sung-Tag Oh, Byung Joon Choi; J Powder Mater. 2026;33(4):299-309. Published online August 31, 2026; DOI: https://doi.org/10.4150/jpm.2026.00192

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Abstract PDF: Bi₂Te₃-based thermoelectric materials are attractive near room temperature, but their performance is constrained by sensitive carrier-concentration control, strong crystallographic anisotropy, and compositional instability from volatile Te. Here, a multilayer core-shell structure was fabricated by conformally coating Bi₂Te₂.₇Se₀.₃ (BTS) powders with ZnO–TiO₂ layers using rotary-type powder atomic layer deposition (pALD), followed by spark plasma sintering. Two configurations with the same ~4 nm total oxide thickness were prepared: a ZnO/TiO₂ bilayer (ZT) and a ZnO/TiO₂/ZnO/TiO₂ multilayer (DZT), where multilayer denotes the deposition scheme rather than a directly imaged layered architecture. Electron microscopy confirmed uniform amorphous shells that were retained as continuous interfacial films after sintering. The oxide interfaces donated electrons to the matrix, raising the carrier concentration and effective mass while preserving mobility and thereby enhancing the electrical conductivity and power factor; simultaneously they scattered phonons and suppressed bipolar conduction, lowering the lattice thermal conductivity. DZT achieved the highest power factor, attributed to its different deposition configuration, whereas ZT exhibited the lowest thermal conductivity; the two coated specimens reached comparable figures of merit (zT) within the measurement uncertainty, both markedly exceeding uncoated BTS. ALD-based interface engineering thus decouples electronic and phononic transport in n-type Bi₂Te₃.

[English]
Interfacial Characterization of Al₂O₃-Coated p-Type Bi–Sb–Te Powders by Thermal and UV-assisted Atomic Layer Deposition: Jin Kyeong Shin, Yeongtae Choi, Byung Joon Choi; J Powder Mater. 2026;33(3):221-229. Published online June 30, 2026; DOI: https://doi.org/10.4150/jpm.2026.00108

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Abstract PDF: Interface engineering is an effective strategy for enhancing thermoelectric performance by modulating carrier and phonon transport at interfaces. Atomic layer deposition (ALD), which enables uniform, conformal, and thickness-controlled coatings, is particularly well-suited for this purpose. In this study, p-type Bi0.35Sb1.6Te3 (BST) powders were coated with Al2O3 using thermal ALD and UV-assisted ALD (UV-ALD) at 85 °C. Scanning electron microscopy showed that neither process substantially altered the morphology of the BST powders. However, particle size analysis revealed that the UV-ALD sample exhibited a greater tendency toward partial agglomeration, which may be associated with the more pronounced OH-related band observed in the Fourier-transform infrared spectroscopy results. Cs-corrected scanning transmission electron microscopy and energy-dispersive X-ray spectroscopy mapping revealed continuous Al₂O₃-based coating layers approximately 2–3 nm thick on the BST particle surfaces, forming a core–shell structure. Fast Fourier transform analysis suggested that the coating layers were amorphous, and X-ray photoelectron spectroscopy indicated Al–O bond formation while the main chemical states of BST were preserved. These results demonstrate that both thermal ALD and UV-ALD can effectively deposit continuous amorphous Al₂O₃-based interfacial layers on BST powders, providing a structural basis for future studies of interface-engineered thermoelectric materials.

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