measure for measure A defect determines strength When you start tearing a piece of aluminium foil apart, you create in the material. Suhas Eswarappa Prameela and Tim Weihs recount the story of the Burgers vector that is now an indispensable tool for describing dislocations.

rystalline materials, characterized by can be related to the nanoscale forces on an ordered and periodic arrangement 1 2 3 4 5 individual dislocations with the help of the Cof their atoms, are all around us, from b Burgers vector. With advanced computational snowflakes to salts or diamonds. The atoms 5 F S 1 tools such as dynamics, the in these crystals are usually arranged in a movement of hundreds of dislocations in lattice. In perfect crystals, atoms occupy 4 2 a crystal can be predicted, gaining insights ideal, periodic positions, with no disruptions into how other defects such as solute atoms, 3 3 or defects in their arrangement. If all the crystal boundaries, and intermetallic particles subatomic particles (for example, electrons) 2 4 can inhibit their motion. This, in turn, occupied the lowest energy states in such enhances our ability to design durable and perfect crystals, these would lack most 1 5 robust materials such as aluminium alloys for of their electronic, physical and chemical use in automobiles and aircraft. 1 properties : powdered iron cores used in 5 4 3 2 1 The Burgers vector is also employed transformers could not be magnetized when exploring material properties beyond without defects in their subatomic structure; strength and failure: phonons are scattered by silicon would lack its tunable electrical dislocations, and the Burgers vector is used conductivity without atomic defects such as back where you started. This is no longer heavily in formulating drag mechanisms. boron or phosphorus. Similarly, we could true if the crystal contains a dislocation, as Dislocations are also important to not form metallic alloys into unique shapes pictured; here, the dislocation in the centre electronic materials and the semiconductor for bridges, cars, or ships without line of the cubic aluminium crystal extends industry. They can explain the growth of defects lending them formability. in and out of the page’s plane. In this case, strained lattices or patterned structures in Imperfections thus bring life to many the equiatomic path around the line defect semiconductors and the failure of transistors materials by jostling atoms or sub-atomic yields a gap between the start (S) and because dislocations act as scattering centres particles off their ideal positions. Back in finish (F) points — the vector connecting for electrons and holes. Burgers’s description 1934, Egon Orowan, and them is called the Burgers vector b. Its of dislocations within a crystal has moved Geoffrey Taylor were trying to explain magnitude quantifies the displacement or well beyond its original intent of explaining why the theoretical or ideal strengths of deformation that is enabled by the movement material strength and continues to prove materials are much higher than observed of a single dislocation across the crystal, and useful in designing materials for applications experimentally. To account for this it is determined by the lattice spacing between ranging from the electronic chips in mobile discrepancy, they predicted what was then atoms for a given crystal and the atomic phones to the advanced metallic alloys5 in a new class of line defects or imperfections planes on which the dislocations move. aircraft engines and construction. ❐ called dislocations2, which occur when there Given that the magnitude of the Burgers is an abrupt change in the arrangement of a vector typically ranges between one and three Suhas Eswarappa Prameela 1,2 ✉ and row of atoms that affects translational order. ångströms, many millions of dislocations Timothy P. Weihs1,2 The defect is analogous to a bone dislocation are required to enable crystal deformation 1Department of Materials Science and Engineering, that we see during injuries to a joint, but a that is visible to the human eye. For example, Johns Hopkins University, Baltimore, MD, USA. billion times smaller. when we tear off a piece of aluminium foil to 2Hopkins Extreme Materials Institute, Johns Hopkins During the early stages of dislocation cover a dish in our kitchen, we force millions University, Baltimore, MD, USA. theory, the Dutch physicist Jan Burgers of dislocations to glide across the small ✉e-mail: [email protected] derived a simple but powerful way to indicate crystals in the foil near the torn surface, the the type and magnitude of dislocations — motion of each providing a displacement of Published online: 7 July 2020 a vector that is named after him, the Burgers approximately two ångströms. https://doi.org/10.1038/s41567-020-0961-2 vector3. But it took nearly two decades Today, the Burgers vector is used to before dislocations were observed directly, describe how crystalline defects determine References 4 1. Cai, W. & Nix, W. D. Imperfections in Crystalline Solids in experiments with aluminium using a the properties of materials and is related (Cambridge Univ. Press, 2016). transmission electron microscope. to the deformation, , and of 2. Hull, D. & Bacon, D. J. Introduction to Dislocations (Elsevier, 2011). If you were to travel a square path in a materials. In terms of deformation, when 3. Burgers, J. M. Proc. Phys. Soc. 52, 23–33 (1940). 4. Hirsch, P. B., Horne, R. W. & Whelan, M. J. Philos. Mag. J. Teor. perfect cubic crystal, moving equal atomic bulk mechanical stresses drive a crystal to Exp. Appl. Phys. 1, 677–684 (1956). distances along each side, you would end up deform, the macroscopic forces on the crystal 5. Prameela, S. E. et al. Materialia 9, 100583 (2019).

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