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Inorganic semiconductors, such as silicon and gallium arsenide, are brittle materials. This property means that large single crystals are cleaved into thin sheets. Oshima et al. show that zinc sulfide is, in contrast, a plastic material if deformed in total darkness. Plastic deformation is likely inhibited when light is present because photoexcited charge carriers become trapped at these sites and pin them through electrostatic effects. Science , this issue p. 772 An inorganic semiconductor was plastic rather than brittle at room temperature when deformed in complete darkness. Inorganic semiconductors generally tend to fail in a brittle manner. Here, we report that extraordinary “plasticity” can take place in an inorganic semiconductor if the deformation is carried out “in complete darkness.” Room-temperature deformation tests of zinc sulfide (ZnS) were performed under varying light conditions. ZnS crystals immediately fractured when they deformed under light irradiation. In contrast, it was found that ZnS crystals can be plastically deformed up to a deformation strain of ε t = 45% in complete darkness. In addition, the optical bandgap of the deformed ZnS crystals was distinctly decreased after deformation. These results suggest that dislocations in ZnS become mobile in complete darkness and that multiplied dislocations can affect the optical bandgap over the whole crystal. Inorganic semiconductors are not necessarily intrinsically brittle.

Grain boundary (GB) migration plays an important role in modifying the microstructures and the related properties of polycrystalline materials, and is governed by the atomistic mechanism by which the atoms are displaced from one grain to another. Although such an atomistic mechanism has been intensively investigated, it is still experimentally unclear as to how the GB migration proceeds at the atomic scale. With the aid of high-energy electron-beam irradiation in atomic-resolution scanning transmission electron microscopy, we controllably triggered the GB migration in α-Al 2 O 3 and directly visualized the atomistic GB migration as a stop motion movie. It was revealed that the GB migration proceeds by the cooperative shuffling of atoms on GB ledges along specific routes, passing through several different stable and metastable GB structures with low energies. We demonstrated that GB migration could be facilitated by the GB structural transformations between these low-energy structures. The atomic process of grain boundary migration has been directly observed by scanning transmission electron microscopy, revealing transformations between different stable or metastable grain boundary structures.

Grain boundaries (GBs) serve as fast diffusion paths for dopant atoms, and the segregated dopants can significantly alter the materials’ properties. However, the exact mechanism of fast dopant diffusion along the GBs, particularly at atomic scale, is still unclear. Here we show direct observation of preferential GB diffusion of Hf dopant atoms along the Σ31 symmetric tilt GB in α -Al 2 O 3 , using time-resolved atomic-resolution scanning transmission electron microscopy and statistical tracking of Hf atom locations. Molecular dynamics simulations incorporating artificial neural network interatomic potentials reveal that Hf atoms preferentially diffuse along the GB by exchanging with co-segregated Al vacancies at the GB. Moreover, we demonstrate that GB interstitial diffusion can greatly enhance the diffusivity of Hf atoms along the GB, where shuffle motion plays a key role in lowering the activation energies for GB diffusion. Using electron microscopy, the authors demonstrate direct tracking of Hf dopant diffusion along the α-Al2O3 Σ31 grain boundary. Theoretical calculation elucidates that interstitial diffusion can greatly enhance diffusivity through shuffle motion.

Control of heterointerfaces in advanced composite materials is of scientific and industrial importance, because their interfacial structures and properties often determine overall performance and reliability of the materials. Here distinct improvement of mechanical properties of alumina-matrix tungsten-carbide composites, which is expected for cutting-tool application for aerospace industries, is achieved via interfacial atomic segregation. It is found that only a small amount of Zr addition is unexpectedly effective to significantly increase their mechanical properties, and especially their bending strength reaches values far beyond those of conventional superhard composite materials. Atomic-resolution STEM observations show that doped Zr atoms are preferentially located only at interfaces between Al 2 O 3 and WC grains, forming atomic segregation layers. DFT calculations indicate favorable thermodynamic stability of the interfacial Zr segregation due to structural transition at the interface. Moreover, theoretical works of separation demonstrate remarkable increase in interfacial strength through the interfacial structural transition, which strongly supports reinforcement of the interfaces by single-layer Zr segregation.

Zeolites have potential application as ion-exchangers, catalysts and molecular sieves. Zeolites are once again drawing attention in Japan as stable adsorbents and solidification materials of fission products, such as 137 Cs + from damaged nuclear-power plants. Although there is a long history of scientific studies on the crystal structures and ion-exchange properties of zeolites for practical application, there are still open questions, at the atomic-level, on the physical and chemical origins of selective ion-exchange abilities of different cations and detailed atomic structures of exchanged cations inside the nanoscale cavities of zeolites. Here, the precise locations of Cs + ions captured within A-type zeolite were analyzed using high-resolution electron microscopy. Together with theoretical calculations, the stable positions of absorbed Cs + ions in the nanocavities are identified and the bonding environment within the zeolitic framework is revealed to be a key factor that influences the locations of absorbed cations.

Low-dimensional structures, such as microclusters, quantum dots and one- or two-dimensional (1D or 2D) quantum wires, are of scientific and technological interest due to their unusual physical properties, which are quite different from those in the bulk 1 , 2 , 3 , 4 . Here we present a successful method for fabricating conducting nanowire bundles inside an insulating ceramic single crystal by using unidirectional dislocations. A high density of dislocations (10 9 cm −2 ) was introduced by activating a primary slip system in sapphire (α-Al 2 O 3 single crystal) using a two-stage deformation technique. Plate specimens cut out from the deformed sapphire were then annealed to straighten the dislocations. Finally, the plates on which metallic Ti was evaporated were heat-treated to diffuse Ti atoms inside sapphire. As a result of this process, Ti atoms segregated along the unidirectional dislocations within about 5 nm diameter, forming unidirectional Ti-enriched nanowires, which exhibit excellent electrical conductivity. This simple technique could potentially to be applied to any crystal, and may give special properties to commonly used materials.

Oxide materials have the potential to exhibit superior mechanical properties in terms of high yield point, high melting point, and high chemical stability. Despite this, they are not widely used as a structural material due to their brittle nature. However, this study shows enhanced room-temperature plasticity of strontium titanate (SrTiO3) crystals through the control of the chemical composition. It is shown that the deformation behavior of SrTiO3 crystals at room temperature depends on the Sr/Ti ratio. It was found that flow stresses in deforming SrTiO3 crystals grown from a powder with the particular ratio of Sr/Ti = 1.04 are almost independent of the strain rate because of the high mobility of dislocations in such crystals. As a result, the SrTiO3 crystals can deform by dislocation slip up to a strain of more than 10%, even at a very high strain rate of 10% per second. It is thus demonstrated that SrTiO3 crystals can exhibit excellent plasticity when chemical composition in the crystal is properly controlled.

Basal dislocations having a Burgers vector of 1/3<2 1 ¯ 1 ¯ 0> in zinc oxide (ZnO) with the wurtzite structure are known to strongly affect physical properties in bulk. However, the core structure of the basal dislocation remains unclear. In the present study, ZnO bicrystals with a 2 1 ¯ 1 ¯ 0/<01 1 ¯ 0> 2° low-angle tilt grain boundary were fabricated by diffusion bonding. The resultant dislocation core structure was observed by using scanning transmission electron microscopy (STEM) at an atomic resolution. It was found that a basal edge dislocation in α-type is dissociated into two partial dislocations on the (0001) plane with a separation distance of 1.5 nm, indicating the glide dissociation. The Burgers vectors of the two partial dislocations were 1/3<1 1 ¯ 00> and 1/3<10 1 ¯ 0>, and the stacking fault between the two partials on the (0001) plane has a formation energy of 0.14 J/m2. Although the bicrystals have a boundary plane of 2 1 ¯ 1 ¯ 0, the boundary basal dislocations do not exhibit dissociation along the boundary plane, but along the (0001) plane perpendicular to the boundary plane. From DFT calculations, the stacking fault on the (0001) plane was found to be much more stable than that on 2 1 ¯ 1 ¯ 0. Such an extremely low energy of the (0001) stacking fault can realize transverse dissociation of the basal dislocation of ZnO.

Impurity segregation at grain boundaries (GBs) often induces structural transformations at the atomic level and significantly influences materials’ properties, underscoring the importance of understanding the underlying mechanisms of GB segregation at the atomic scale. Here, the atomic structure of a Y‐segregated ∑13(104)/[20] GB is thoroughly studied in α‐Al 2 O 3 via scanning transmission electron microscopy and Monte Carlo and molecular dynamics simulations based on a neural network potential. It is found that the Y segregation at the GB involves not only the simple substitution of Y for Al atoms but also a structural adaptation with a change in GB atomic density. Such a change alters the local bonding environment at the GB so that the absolute excess volume is minimized for the lowest‐energy structure. This study offers a new insight into the atomic‐scale mechanism of GB structural transformation.

Impurity segregation at grain boundaries (GBs) often induces structural transformations at the atomic level and significantly influences materials' properties, underscoring the importance of understanding the underlying mechanisms of GB segregation at the atomic scale. Here, the atomic structure of a Y-segregated ∑13(10 1 ¯ $\\bar 1$ 4)/[ 1 ¯ $\\bar 1$ 2 1 ¯ $\\bar 1$ 0] GB is thoroughly studied in α-Al2O3 via scanning transmission electron microscopy and Monte Carlo and molecular dynamics simulations based on a neural network potential. It is found that the Y segregation at the GB involves not only the simple substitution of Y for Al atoms but also a structural adaptation with a change in GB atomic density. Such a change alters the local bonding environment at the GB so that the absolute excess volume is minimized for the lowest-energy structure. This study offers a new insight into the atomic-scale mechanism of GB structural transformation.Impurity segregation at grain boundaries (GBs) often induces structural transformations at the atomic level and significantly influences materials' properties, underscoring the importance of understanding the underlying mechanisms of GB segregation at the atomic scale. Here, the atomic structure of a Y-segregated ∑13(10 1 ¯ $\\bar 1$ 4)/[ 1 ¯ $\\bar 1$ 2 1 ¯ $\\bar 1$ 0] GB is thoroughly studied in α-Al2O3 via scanning transmission electron microscopy and Monte Carlo and molecular dynamics simulations based on a neural network potential. It is found that the Y segregation at the GB involves not only the simple substitution of Y for Al atoms but also a structural adaptation with a change in GB atomic density. Such a change alters the local bonding environment at the GB so that the absolute excess volume is minimized for the lowest-energy structure. This study offers a new insight into the atomic-scale mechanism of GB structural transformation.