New theory provides answers to why metals have the structures that they do
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Loading... - Richard Patterson
- 02 Mar 2023
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A simple new theory that can explain why a metal forms a particular structure has been developed.1 The method allows researchers to understand and predict structures in solid compounds and alloys over a wide range of conditions. ‘This theory is based on our finding that the electrons in many metals occupy so-called quasi-atom orbitals, which are local quantum orbitals centred at the voids between atoms,’ explains Russell Hemley at the University of Illinois Chicago in the US, who led the study together with Maosheng Miao from California State University, Northridge. ‘The chemical interactions between such localised electrons control the metal structures,’ he adds.
‘This new chemical perspective of metals is [an] alternative to the traditional free electron gas model provided by physicists,’ comments Álvaro Lobato, a theoretical chemist at the Complutense University of Madrid in Spain who wasn’t involved in the study. He says that in the new chemical model, the metals behave like inorganic crystals with positive cores and quasi atoms interacting as cations and anions.
‘Determining the metal structures and their pattern across the periodic table is a puzzle that has remained unsolved since the first structure of metals was detected by x-ray diffraction about 100 years ago,’ points out Hemley. He notes that the structures of several classes of metals still can’t be described by the ‘physics’ or band–structure model. ‘Even though we can explain many advanced properties of metals and other compounds, such as superconductivity, we don’t understand why some metals crystallise in the face-centred cubic structure, others take on the hexagonal close-packed structure and some crystallise as body-centred cubic.’
But the structural changes that happen when metals are put under pressure are even more puzzling, adds Hemley. ‘Many metals give up high-symmetry structures and transform to lower symmetry and large voids, so there are many high-pressure structures that aren’t close-packed, which is counter-intuitive.’ Read More…
