12 In Mo, first-principles calculations and bond-cutting calculations yield differently proportioned Bijinski dodecahedra. In Fe NPs, truncated cuboctahedra have been observed and modelled 24 truncated nanocubes have also been seen. The relative surface energies/growth velocities differ widely under varying experimental conditions, and in turn so do the shapes obtained. Complementarily, relative surface energies were extracted from matching published NP shapes from ref 12 ( Fig. Wulffmaker 26 and Crystal Creator 19,27 were used to predict single crystalline NP shapes based on the relative surface energies or growth velocities reported for Fe and Mo 24,25 ( Fig. ![]() To establish realistic shapes and surface energies, we modelled shapes inspired by numerical and experimental results. (b, d, f and h) Analytical thermodynamic and (c, e, g and i) numerical kinetic shapes from the surface energies/growth velocities listed twin planes are shown as a black line, viewing directions are or these and the x, y, z directions refer to the parent crystal, on, for, the bottom left of and, for, behind the crystal. (a) Dense crystallographic planes in BCC and their color-coding. 6–8 For instance, twinned icosahedral Pd and Pt–Ni NPs have higher activities than single crystal octahedra for formic acid oxidation and oxygen reduction, respectively, despite both being bound exclusively by facets with their relative values depending on reaction conditions. the presence of one or more planar crystallographic defects, leads to not only novel shapes but also strain that influences catalytic properties. 5 Twinning and grain boundaries are known to affect catalytic activity, 6–10 yet there is little recorded evidence for or against the presence of twinning in BCC NPs.Ĭatalytic properties are controlled by NP shape, composition, and crystallinity. Nanoparticles (NPs) of these metals are finding applications in strain sensing, 1 catalysis, 2–5 and, for Fe, medical diagnosis, treatment, and electronic media. About one third of metallic elements crystallise in a body-centred cubic (BCC) structure, including the transition metals Cr, Mo, W and Fe. We conclude by outlining how nanoparticles can be characterized to conclusively prove the presence or absence of twinning. BCC single crystal and twinned shapes often appear similar and diffraction patterns along common, low-index zone axes are often indistinguishable, casting doubt on many claims of single crystallinity. Here, we explore the potential shapes of twinned BCC nanoparticles, and predict their electron microscopy and diffraction signatures. Twinning has a marked effect on catalytic activity, yet there is little evidence for or against the presence of twinning in BCC nanoparticles. However even removing half the lattice points wouldn't make much difference because the in phase reflection is so much stronger than the background.Many metals and alloys, including Fe and W, adopt body-centred cubic (BCC) crystal structures and nanoparticles of these metals are gaining significant scientific and industrial relevance. But you'd still see a strong reflection at the same angle.Īs you removed more and more of the lattice points the contrast would decrease, and eventually you'd no longer see a pattern. ![]() At the same time the destructive interference in other directions is less complete, so the background reflection goes up. The remaining lattice points still radiate in phase, so there's still a strong reflection at the same angle, but since there's fewer points radiating the intensity of the reflection is decreased. making the biggest decrease possible in the structure factor. Now imagine randomly removing some of the lattice points i.e. At other angles the lattice points don't radiate in phase so there is destructive interference and no reflection. If you take some plane then this creates a bright reflection at a certain angle because along a line at that angle all the lattice points radiate in phase, so we get constructive interference. Yes you will see the usual BCC pattern and I think it's fairly easy to see why.
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