University of Science and Technology Beijing

About: University of Science and Technology Beijing is a education organization based out in Beijing, China. It is known for research contribution in the topics: Microstructure & Alloy. The organization has 41558 authors who have published 44473 publications receiving 623229 citations. The organization is also known as: Beijing Steel and Iron Institute.

Tailored Dielectric Properties based on Microstructure Change in BaTiO3-Carbon Nanotube/Polyvinylidene Fluoride Three-Phase Nanocomposites

Abstract: The carbon nanotube (CNT) has been chosen as an excellent candidate for acquiring high dielectric constant polymer matrix composites according to percolation theory. However, its nanometer-scale dimension makes it naturally form bundles, which makes it difficult to use. Compared with chemical modification of multiwalled carbon nanotube (MWNT), the incorporation of the third component (nanosized BaTiO3 (NBT)) particles into MWNT/polymer composites would realize the uniform dispersion of MWNT without sacrificing the inherent properties of MWNT. We reported a three-phase (NBT-MWNT)/polyvinylidene fluoride nanocomposite with a significantly enhanced dielectric constant (643 at 103 Hz) and a gradually decreased loss, which was extremely hard to be realized at the same time for composites only filled by conductive MWNT filler. Adjustable dielectric properties were discovered by employing the three-phase system due to the nanocomposites microstructure change. Furthermore, impedance analysis and simulated circuit...

A Study of Three Intrinsic Problems of the Classic Discrete Element Method Using Flat-Joint Model

Abstract: Discrete element methods have been proven to offer a new avenue for obtaining the mechanics of geo-materials. The standard bonded-particle model (BPM), a classic discrete element method, has been applied to a wide range of problems related to rock and soil. However, three intrinsic problems are associated with using the standard BPM: (1) an unrealistically low unconfined compressive strength to tensile strength (UCS/TS) ratio, (2) an excessively low internal friction angle, and (3) a linear strength envelope, i.e., a low Hoek–Brown (HB) strength parameter m i . After summarizing the underlying reasons of these problems through analyzing previous researchers’ work, flat-joint model (FJM) is used to calibrate Jinping marble and is found to closely match its macro-properties. A parametric study is carried out to systematically evaluate the micro-parameters’ effect on these three macro-properties. The results indicate that (1) the UCS/TS ratio increases with the increasing average coordination number (CN) and bond cohesion to tensile strength ratio, but it first decreases and then increases with the increasing crack density (CD); (2) the HB strength parameter m i has positive relationships to the crack density (CD), bond cohesion to tensile strength ratio, and local friction angle, but a negative relationship to the average coordination number (CN); (3) the internal friction angle increases as the crack density (CD), bond cohesion to tensile strength ratio, and local friction angle increase; (4) the residual friction angle has little effect on these three macro-properties and mainly influences post-peak behavior. Finally, a new calibration procedure is developed, which not only addresses these three problems, but also considers the post-peak behavior.

Manipulation of facet orientation in hybrid perovskite polycrystalline films by cation cascade

Abstract: Crystal orientations in multiple orders correlate to the properties of polycrystalline materials, and it is critical to manipulate these microstructural arrangements to enhance device performance. Herein, we report a controllable approach to manipulate the facet orientation within the ABX3 hybrid perovskites polycrystalline films by cation cascade doping at A-site. Two-dimensional synchrotron radiation grazing incidence wide-angle X-ray scattering is employed to probe the crystal orientations in multiple orders in mixed perovskites thin films, revealing a general pattern to guide crystal planes stacking upon extrinsic doping during crystallization. Different from previous studies, this method enables to adjust the crystal stacking mode of certain crystallographic planes in polycrystalline perovskites. Moreover, the preferred facet orientation is found to facilitate photocarrier transport across the absorber and pertaining interface in the resultant PV device, which provides an exemplary paradigm for further explorations that relate to the microstructures of hybrid perovskite materials and relevant optoelectronics. Crystal facet orientations of the polycrystalline hybrid lead halide perovskite thin films play a crucial role in determining the device performance. Here Zheng et al. demonstrate effective control of the crystal stacking mode by cation cascade doping, which promotes the charge transport in the photovoltaic device.