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The lithiation/delithiation in LiFePO4is highly anisotropicwith lithium-ion diffusion being mainly confined to channels alongthe b-axis. Controlling the orientation of LiFePO4crystals therefore plays an important role for efficientmass transport within this material. We report here the preparationof single crystalline LiFePO4nanosheets with a large percentageof highly oriented {010} facets, which provide the highest pore densityfor lithium-ion insertion/extraction. The LiFePO4nanosheetsshow a high specific capacity at low charge/discharge rates and retainsignificant capacities at high C-rates, which may benefit the developmentof lithium batteries with both favorable energy and power density. [ABSTRACT FROM AUTHOR]

Topologicalcrystalline insulators (TCIs) are a new class of topologicalmaterials that possess unique metallic surface states protected bycrystalline mirror symmetry. Their topological surface propertiesare expected to strongly depend on the surface orientation. By combiningdensity functional theory (DFT) calculations and synthesis experiments,we demonstrate the controlled growth of single crystalline nanostructuresof the prototypical TCI SnTe with distinct facets and morphologies.Our calculations suggest that the excess energy of the {111} surfacescan be either higher or lower than that of the {100} surfaces, dependingon the stoichiometry, while the {110} is always higher than the {100}.In our synthesis experiment, we qualitatively controlled the stoichiometryby tailoring the growth temperature and obtained two types of singlecrystalline nanowires: smooth nanowires dominated by {100} facetsat high temperatures and zigzag nanowires composed of both {100} and{111} surfaces at low temperatures. Notably, there is no {110} facetin our nanostructures, strongly supporting the DFT calculations. Ourdevice fabrication and electrical characterizations suggest that bothtypes of nanowires are suitable for transport studies of topologicalsurface states. [ABSTRACT FROM AUTHOR]

The dependence of the reaction initiation mechanism ofpentaerythritoltetranitrate (PETN) on shock orientation and shock strength is investigatedwith molecular dynamics simulations using a reactive force field andthe multiscale shock technique. In the simulations, a single crystalof PETN is shocked along the [110], [001], and [100] orientationswith shock velocities in the range 3–10 km/s. Reactions occurwith shock velocities of 6 km/s or stronger, and reactions initiatethrough the dissociation of nitro and nitrate groups from the PETNmolecules. The most sensitive orientation is [110], while [100] isthe most insensitive. For the [001] orientation, PETN decompositionvia nitro group dissociation is the dominant reaction initiation mechanism,while for the [110] and [100] orientations the decomposition is viamixed nitro and nitrate group dissociation. For shock along the [001]orientation, we find that CO–NO2bonds initiallyacquire more kinetic energy, facilitating nitro dissociation. Forthe other two orientations, C–ONO2bonds acquiremore kinetic energy, facilitating nitrate group dissociation. [ABSTRACT FROM AUTHOR]