Beihang University

About: Beihang University is a education organization based out in Beijing, China. It is known for research contribution in the topics: Control theory & Microstructure. The organization has 67002 authors who have published 73507 publications receiving 975691 citations. The organization is also known as: Beijing University of Aeronautics and Astronautics.

Origin of low thermal conductivity in SnSe

Abstract: We provide direct evidence to understand the origin of low thermal conductivity of SnSe using elastic measurements. Compared to state-of-the-art lead chalcogenides $\mathrm{Pb}Q(Q=\mathrm{Te}$, Se, S), SnSe exhibits low values of sound velocity $(\ensuremath{\sim}1420\phantom{\rule{0.28em}{0ex}}\mathrm{m}/\mathrm{s})$, Young's modulus $(E\ensuremath{\sim}27.7\phantom{\rule{0.28em}{0ex}}\mathrm{GPa})$, and shear modulus $(G\ensuremath{\sim}9.6\phantom{\rule{0.28em}{0ex}}\mathrm{GPa})$, which are ascribed to the extremely weak Sn-Se atomic interactions (or bonds between layers); meanwhile, the deduced average Gr\"uneisen parameter \ensuremath{\gamma} of SnSe is as large as \ensuremath{\sim}3.13, originating from the strong anharmonicity of the bonding arrangement. The calculated phonon mean free path (l \ensuremath{\sim} 0.84 nm) at 300 K is comparable to the lattice parameters of SnSe, indicating little room is left for further reduction of the thermal conductivity through introducing nanoscale microstructures and microscale grain boundaries. The low elastic properties indicate that the weak chemical bonding stiffness of SnSe generally causes phonon modes softening which eventually slows down phonon propagation. This work provides insightful data to understand the low lattice thermal conductivity of SnSe.

Vacancy trapping mechanism for hydrogen bubble formation in metal

Abstract: We reveal the microscopic vacancy trapping mechanism for H bubble formation in W based on first-principles calculations of the energetics of H-vacancy interaction and the kinetics of H segregation. Vacancy provides an isosurface of optimal charge density that induces collective H binding on its internal surface, a prerequisite for the formation of ${\text{H}}_{2}$ molecule and nucleation of H bubble inside the vacancy. The critical H density on the vacancy surface before the ${\text{H}}_{2}$ formation is found to be ${10}^{19}--{10}^{20}\text{ }\text{H}$ atoms per ${\text{m}}^{2}$. We believe that such mechanism is generally applicable for H bubble formation in metals and metal alloys.

Surface structure dependent electrocatalytic activity of Co 3 O 4 anchored on graphene sheets toward oxygen reduction reaction

Abstract: Catalytic activity is primarily a surface phenomenon, however, little is known about Co3O4 nanocrystals in terms of the relationship between the oxygen reduction reaction (ORR) catalytic activity and surface structure, especially when dispersed on a highly conducting support to improve the electrical conductivity and so to enhance the catalytic activity. Herein, we report a controllable synthesis of Co3O4 nanorods (NR), nanocubes (NC) and nano-octahedrons (OC) with the different exposed nanocrystalline surfaces ({110}, {100}, and {111}), uniformly anchored on graphene sheets, which has allowed us to investigate the effects of the surface structure on the ORR activity. Results show that the catalytically active sites for ORR should be the surface Co2+ ions, whereas the surface Co3+ ions catalyze CO oxidation, and the catalytic ability is closely related to the density of the catalytically active sites. These results underscore the importance of morphological control in the design of highly efficient ORR catalysts.

Enhanced wave absorption of nanocomposites based on the synthesized complex symmetrical CuS nanostructure and poly(vinylidene fluoride)

Abstract: Complex symmetrical CuS nanostructures were synthesized in large scale by a simple wet chemical method at low temperature. As a semiconductor material with superstructure, CuS was well characterized and firstly introduced into PVDF to form nanocomposites. The substantial enhancement of wave absorption (−102 dB at 7.7 GHz) was observed by addition of CuS with a low filler loading (5 wt%). The mechanism for the enhanced wave absorbing properties was explained in detail.

Unidirectional water-penetration composite fibrous film via electrospinning

Abstract: An interesting “water diode” film is fabricated by a facile electrospinning technique. The fibrous film is a composite of hydrophobic polyurethane (PU) and hydrophilic crosslinked poly (vinyl alcohol) (c-PVA) fibrous layers. By taking advantages of the hydrophobic–hydrophilic wettability difference, water can penetrate from the hydrophobic side, but be blocked on the hydrophilic side.