The Li 4 Ti 5 O 12 defect spinel is a promising anode material for lithium ion batteries because it transforms to/from Li 7 Ti 5 O 12 with a negligible volume change during charging/discharging. Ab initio calculation is a powerful approach for modern materials design and mechanistic studies. However, the atomistic models of the stoichiometric Li 4 Ti 5 O 12 and Li 7 Ti 5 O 12 defect spinel have not been optimized due to the requirements of large unit cells and numerous atomistic arrangements of Li and Ti ions at the 16d sites of the defect spinel. In this study, ab initio calculations were systematically performed and the most energetically favorable full supercell models were constructed for both Li 4 Ti 5 O 12 and Li 7 Ti 5 O 12 defect spinel. The equilibrium lattice parameter of Li 4 Ti 5 O 12 was 8.4257 Å, while a slight lattice shrinkage of 0.77% and an average intercalation voltage of 1.41 V during charging/discharging were obtained. Moreover, the Li 4 Ti 5 O 12 phase shows insulating property with a wide bandgap of around 2.3 eV, while the Li 7 Ti 5 O 12 phase exhibits metallic property. All the calculated structural and electrochemical properties agree closely with the experimental findings in literature. Further theoretical studies on the Li 4 Ti 5 O 12 defect spinel or other defect spinel in general can be realized according to the full supercell models proposed in this study.
Nano-indentation is a sophisticated method to characterize mechanical properties of materials. This method samples a very small amount of material during each indentation. Therefore, this method is extremely useful to measure mechanical properties of nano-materials. The measurements using nanoindentation is very sensitive to the surface topology of the indenter and the indenting surfaces. The mechanisms involved in the entire process of nanoindentation require an atomic level understanding of the interplay between the indenter and the substrate. In this paper, we have used atomistic simulation methods with empirical potentials to investigate the effect of various types of pristine indenter on the defect nucleation and growth. Using molecular dynamics simulations, we have predicted the load-depth curve for conical, vickers, and sperical tip. The results are analyzed based on the coherency between the indenter tip and substrate surface for a fixed depth of 20 Å. The depth of defect nucleation and growth is observed to be dependent on the tip geometry. A tip with larger apex angle nucleates defects at a shallower depth. However, the type of defect generated is dependent on the crystalline orientation of the tip and substrate. For coherent systems, prismatic loops were generated, which released into the substrate along the close-packed directions with continued indentation. For incoherent systems, pyramidal shaped dislocation junctions formed in the FCC systems and disordered atomic clusters formed in the BCC systems. These defect nucleation and growth process provide the atomistic mechanisms responsible for the observed load-depth response during nanoindentation.
In a stirred batch reaction, Fe(phen) 3 2ϩ ion behaves differently from Ce(III) or Mn(II) ion in catalyzing the bromate-driven oscillating reaction with ethyl hydrogen malonate [CH 2 COOHCOOEt, ethyl hydrogen malonate (EHM)]. The effects of N 2 atmosphere, concentrations of bromate ion, EHM, metal ion catalyst, sulfuric acid, and additive (bromide ion or bromomalonic acid) on the pattern of oscillations were investigated. The kinetic study of the reaction of EHM with Ce(IV), Mn(III), or Fe(phen) 3 3ϩ ion indicates that under aerobic or anaerobic conditions the order of reactivity toward reacting with EHM is Mn(III) Ͼ Ce(IV) Ͼ Ͼ Fe(phen) 3 3ϩ , which follows the same trend as that of the malonic acid system. The presence of the ester group in EHM lowers the reactivity of the two methylene hydrogen atoms toward bromination or oxidation by Ce(IV), Mn(III), or Fe(phen) 3 3ϩ ion. No good oscillations were observed for the BrO 3--CH 2 (COOEt) 2 reaction catalyzed by Ce(III), Mn(II), or Fe(phen) 3 2ϩ ion.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.