Oxygen Vacancy Diffusion and Condensation in Lithium‐Ion Battery Cathode Materials

Oxygen vacancies (OV) are native defects in transition metal (TM) oxides and their presence has a critical effect on the physicochemical properties of the oxide. Metal oxides are commonly used in lithium‐ion battery (LIB) cathodes and there is still a lack of understanding of the role of OVs in LIB research field. Here, we report on the behavior of OVs in a single‐crystal LIB cathode during the non‐equilibrium states of charge and discharge. We found that microcrack evolution in a single crystal occurs due to OV condensation in specific crystallographic orientations generated by the continuous migration of OVs and TM ions. Moreover, understanding the effects of the presence and diffusion of OVs in metal oxides enables the elucidation of most of the conventional mechanisms of capacity fading in LIBs and provides new insights for new electrochemical applications.     

Thin-thick surface phase coexistence and boundary tension of the square-well fluid on a weak attractive surface

Prewetting transition is studied for the square-well fluid of attractive-well diameter lambda(ff)sigma(ff)=1.5 in the presence of a homogeneous surface modeled by the square-well potential of attractive well from 0.8sigma(ff) to 1.8sigma(ff). We investigate surface phase coexistence of thin-thick film transition using grand-canonical transition matrix Monte Carlo (GC-TMMC) and histogram reweighting techniques. Molecular dynamics (MD) and GC-TMMC are utilized to predict the properties of the fluid for various surface fluid affinities. Occurrences of prewetting transition with the variation of surface affinity are observed for a domain of reduced temperature from T(*)=0.62 to 0.75. We have used MD and GC-TMMC+finite size scaling (FSS) simulations to calculate the boundary tension as a function of temperature as well as surface affinity. Boundary tensions via MD and GC-TMMC+FSS methods are in good agreement. The boundary tension increases with the decrease of wall-fluid affinity. Prewetting critical properties are calculated using rectilinear diameter approach and scaling analysis. We found that critical temperature and density increase with the decrease of wall-fluid affinity.     

Near‐infrared spectroscopic studies on the cure behaviors of the CAE/DGEBA blend system initiated by a thermal latent catalyst

The latent properties and cure behaviors of an epoxy blend system based on cycloaliphatic epoxy (CAE) and diglycidyl ether of bisphenol A (DGEBA) epoxy containing N‐benzylpyrazinium hexafluoroantimonate (BPH) as a thermal latent initiator were investigated with near‐infrared (N‐IR) spectroscopy. The assignments of the latent properties and cure kinetics were performed by the measurements of the N‐IR reflectance for epoxide and hydroxyl functional groups at different temperatures and compositions. As a result, this system showed more than one type of reaction, and BPH was an excellent thermal latent catalyst without any coinitiator. The cure behaviors were identified by the changes in the absorption intensity of the hydroxyl groups at 7100 cm⁻¹ with different composition ratios. Moreover, characteristic N‐IR band assignments were used to evaluate the reactive kinetics and were shown to be an appropriate method for studying the cure behaviors of the CAE/DGEBA blend system containing a thermal latent catalyst. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 39: 326–331, 2001     

Structural,Raman, and photoluminescence properties of double‐shelled coaxial nanocables of In2O3 core with ZnO and AZO shells

We synthesized In₂O₃/ZnO/Al‐doped ZnO (AZO) core‐double shell nanowires, in which the inner shell (ZnO) and the outer shell (AZO) have been subsequently deposited on the core In₂O₃ nanowires. With their one‐dimensional morphology being preserved, the X‐ray diffraction (XRD), lattice‐resolved transmission electron microscopy (TEM) image, selected area electron diffraction, and Raman spectrum coincidentally revealed that the shell was comprised of hexagonal ZnO phase. In addition, TEM‐EDX investigation revealed the presence of Al elements in the shell region. The thermal annealing at 700 °C did not significantly change the nanowire morphology, however, the XRD spectrum indicated that the ZnO phase was crystallized by the annealing. PL spectrum of the 700 °C‐annealed In₂O₃/ZnO/AZO core‐double shell nanowires was comprised of three Gaussian bands at approximately 2.1 eV, 2.4 eV, and 3.0 eV, respectively. The integrated intensities of 2.1 eV‐, 2.4 eV‐, and 3.0 eV‐bands were decreased by the thermal annealing. This study will pave the road to the preparation and applicaition of double‐shelled nanowires. (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Investigation of crystal/electronic structure effects on the photoluminescence properties in the BaO–SiO2:Eu2+ systems

BaO–SiO₂:Eu²⁺ phosphors with different Ba/Si mole ratio were prepared using a solid-state reaction method, and their crystal structure dependent-photoluminescence properties were investigated. The prepared phosphor powders were characterized using X-ray diffraction (XRD), field-emission electron microscopy (FE-SEM) and fluorescence spectroscopy. The emission band of the Eu²⁺ activator varied from orange to blue with varying crystal structure of the host materials, which was related to the crystal field splitting of the Eu 5d orbitals. These emission color changes were examined by calculating the electronic band structure properties such as the density of the state. Moreover, the host material with Ba/Si=1 (BaSiO₃) for Eu²⁺, which exhibited a yellow emission when excited with near UV light, was further characterized for enhancing its emission intensity.     

s‐Regular cubic graphs as coverings of the complete bipartite graph K3,3

A graph is s‐regular if its automorphism group acts freely and transitively on the set of s‐arcs. An infinite family of cubic 1‐regular graphs was constructed in [10], as cyclic coverings of the three‐dimensional Hypercube. In this paper, we classify the s‐regular cyclic coverings of the complete bipartite graph K_3,3 for each ≥ 1 whose fibre‐preserving automorphism subgroups act arc‐transitively. As a result, a new infinite family of cubic 1‐regular graphs is constructed. © 2003 Wiley Periodicals, Inc. J Graph Theory 45: 101–112, 2004     

Synthesis and properties of blue light‐emitting,silicon‐containing,regio‐ and stereoregular conjugated polymers

This article concerns the hydrosilylation polyaddition of 1,4‐bis(dimethylsilyl)benzene ( 1 ) with 4,4′‐diethynylbiphenyl, 2,7‐diethynylfluorene ( 2b ), and 2,6‐diethynylnaphthalene with RhI(PPh₃)₃ catalyst. Trans‐rich polymers with weight‐average molecular weights (M_w's) ranging from 19,000 to 25,000 were obtained by polyaddition in o‐Cl₂C₆H₄ at 150–180 °C, whereas cis‐rich polymers with M_w's from 4300 to 34,000 were obtained in toluene at 0 °C–r.t. These polymers emitted blue light in 4–81% quantum yields. The cis polymers isomerized into trans polymers upon UV irradiation, whereas the trans polymers did not. The device having a layer of polymer trans‐ 3b obtained from 1 and 2b demonstrated electroluminescence without any dopant. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 2774–2783, 2004