Abstract
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. Twinning has a marked effect on catalytic activity, yet there is little evidence for or against the presence of twinning in BCC nanoparticles. Here, we explore the potential shapes of twinned BCC nanoparticles, and predict their electron microscopy and diffraction signatures. 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. We conclude by outlining how nanoparticles can be characterized to conclusively prove the presence or absence of twinning.
Highlights
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
We explore the potential shapes of twinned BCC nanoparticles, and predict their electron microscopy and diffraction signatures
The shapes and diffraction signatures of twinned BCC NPs can resemble that of their single crystal counterparts, making experimental identification elusive
Summary
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. The presence and density of related, strain-inducing defects such as grain boundaries increase the catalytic activity of Au for the reduction of CO2 to CO and of Cu for the electrochemical reduction of CO to ethanol, acetate, propanol, and ethylene.[9,10] Scanning electrochemical cell microscopy directly confirmed the increase in local activity at grain boundaries of Au electrodes for the reduction of CO2.11 The characterization, understanding, and control of twinning and polycrystallinity is, crucial for designing catalysts Fuelled by their exciting catalytic and magnetic properties, an increasing number of syntheses of ( presumed) single-crystalline NPs of Fe12–14 and W,15,16 both BCC, are emerging. The NPs have diameters as small as 10 nm, and their single-crystallinity is typically supported by shape observation and a single low-index electron diffraction pattern, which we demonstrate is insufficient evidence
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