Twins and grain boundaries are a powerful way to manipulate the properties of materials, including their catalytic activity. Combined with the interest in nanoparticles (NPs) as catalysts, twinning in nanostructures promises an additional opportunity for efficient catalyst design.<br/>Most metals crystallise with face-centred cubic (FCC), body-centred cubic (BCC) or hexagonal close-packed (HCP) symmetry. Twinned NPs are well known in FCC systems, where bulk growth twins are common, and have recently been shown in HCP metals. To the best of our knowledge, no conclusive experimental evidence of BCC NPs has ever been published, but this does not mean they do not exist. Meanwhile, NPs of BCC metals such as Cr, Fe, Mo and W are becoming increasingly popular for catalytic, medical, and sensing applications.<br/>We developed and used a suite of modelling tools to unravel the shape, diffraction, and electron microscopy signatures of twinned BCC NPs. We report here that 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 in the literature.<br/>This analysis has been further expanded to a full shape and diffraction understanding of tetragonal systems, which include the metal indium. These are known to form singly and multiply-twinned nanoparticles, however their exact shapes are often poorly understood and characterized. We show that various shapes, some strikingly different from the FCC counterparts, are possible and lead to unique sets of exposed facets relevant to surface science and catalysis.

Identification of twinning in body-centred cubic and tetragonal nanoparticles

ACS Spring Meeting 2021

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