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How electrons in transition metals get redistributed

The distribution of electrons in transition metals, which represent a large part of the periodic table of chemical elements, is responsible for many of their interesting properties used in applications. The magnetic properties of some of the members of this group of materials are, for example, exploited for data storage, whereas others exhibit excellent electrical conductivity. Transition metals also have a decisive role for novel materials with more exotic behaviour that results from strong interactions between the electrons. Such materials are promising candidates for a wide range of future applications.

In their experiment, whose results they report in a paper published today in Nature Physics, Mikhail Volkov and colleagues in the Ultrafast Laser Physics group of Prof. Ursula Keller exposed thin foils of the transition metals titanium and zirconium to short laser pulses. They observed the redistribution of the electrons by recording the resulting changes in optical properties of the metals in the extreme ultraviolet (XUV) domain. In order to be able to follow the induced changes with sufficient temporal resolution, XUV pulses with a duration of only few hundred attoseconds (10^-18 s) were employed in the measurement. By comparing the experimental results with theoretical models, developed by the group of Prof. Angel Rubio at the Max Planck Institute for the Structure and Dynamics of Matter in Hamburg, the researchers established that the change unfolding in less than a femtosecond (10^-15 s) is due to a modification of the electron localization in the vicinity of the metal atoms. The theory also predicts that in transition metals with more strongly filled outer electron shells an opposite motion – that is, a delocalization of the electrons – is to be expected.

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Alporas’ closed cell aluminium foam R…

Alporas’ closed cell aluminium foam

Reaction: Titanium hydride is used as a foaming agent

Processing: The ‘Alporas’ technique involves use of 1 to 3 wt% titanium hydride to a modified melt as a foaming agent

Applications: Closed cell aluminium foams are an ultra-light material, with potential structural applications in transport and construction. They may also be used in energy absorbing structures and heat exchangers

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Further information: Additions are made to molten aluminium or aluminium alloy to modify the melt viscosity and make it suitable for foaming. 1 to 3 wt% titanium hydride is then added to the melt, and this foams the melt by releasing hydrogen. The foamed melt solidifies to yield a closed cellular structure with an average cell size of 4.5 mm

Contributor: Dr V Gergely

Organisation: Department of Materials Science and Metallurgy, University of Cambridge

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Researchers capture microscopic manufacturin…

Researchers capture microscopic manufacturing flaws via high-speed X-ray movies

Microscopic defects that occur in laser-based manufacturing of metal parts can lead to big problems if undetected, and the process of fixing these flaws can increase the time and cost of high-tech manufacturing. But new research into the cause of these flaws could lead to a remedy.

Researchers from Missouri S&T, Argonne National Laboratory and the University of Utah created high-speed X-ray “movies” of a manufacturing phenomenon known as laserspattering. Laser spattering refers to the ejection of molten metal from a pool heated by a high-power laser during laser-based manufacturing processes, such as laser welding and laser-additive manufacturing. These laser manufacturing technologies are used to fabricate parts for use in a variety of industries, including aerospace, the automotive industry, healthcare and construction.

The researchers describe their findings in a paper published today (Friday, June 14, 2019) in the journal Physical Review X.

Using X-ray imaging, the researchers captured the spattering behavior of a titanium alloy known as Ti-6Al-4V during fabrication. Their microscopic movies reveal “a novel mechanism of laser spattering—the bulk explosion of a tongue-like protrusion” that forms in one region of the metal, the researchers say in their paper, titled “Bulk explosion induced metal spattering during laser processing.”

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Discovery of light-induced ferroelectricity …

Discovery of light-induced ferroelectricity in strontium titanate

Light can be used not only to measure materials’ properties, but also to change them. Especially interesting are those cases in which the function of a material can be modified, such as its ability to conduct electricity or to store information in its magnetic state. A team led by Andrea Cavalleri from the Max Planck Institute for the Structure and Dynamics of Matter in Hamburg have used terahertz frequency light pulses to transform a non-ferroelectric material into a ferroelectric one.

Ferroelectricity is a state in which the constituent lattice is polarized in one specific direction, forming a macroscopic electrical polarization. The ability to reverse polarization makes ferroelectric materialsparticularly suitable for digital information encoding and processing. The discovery of a light-induced ferroelectric is highly relevant for a new generation of high-speed devices, and is presented today in the journal Science.

Complex materials are special because their unusual macroscopic properties are determined by many competing tendencies. Unlike in more conventional compounds, such as the silicon crystals that make up current electronic devices, in complex materials one finds that more than one type of microscopic interaction favors more than one possible macroscopic phase.

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Bioinspired Materials—Graphene-enabled nicke…

Bioinspired Materials—Graphene-enabled nickel composites

Bioinspired engineering strategies rely on achieving the combined biological properties of strength and toughness inherent in nature. Tissue engineers and materials scientists therefore aim to construct intelligent, hierarchical biomimetic structures from limited resources. As a representative material, natural nacremaintains a brick-and-mortar structure that allows many viable toughening mechanisms on multiple scales. Such naturally occurring materials demonstrate an outstanding combination of strength and toughness, unlike any synthetic, engineered biomaterial.

In a recent study, Yunya Zhang and co-workers at the departments of Mechanical and Aerospace Engineering, Materials Science and Atom-Probe Tomography in the U.S. developed a bioinspired Ni/Ni3C composite to mimic nacre-like brick-and-mortar structure with Ni powders and graphene sheets. They showed that the composite achieved 73 percent increase in strength with only a 28 percent compromise in ductility to indicate a notable improvement in toughness.

In the study, the researchers developed optimized material of graphene-derived, nickel- (Ni), titanium- (Ti) and aluminum- (Al) based composites (Ni-Ti-Al/ Ni3C composite) that retained high hardness of up to 1000 °C. The materials scientistsunveiled a new method in the work to fabricate smart 2-D materials and engineer high-performance metal matrix composites. The composites displayed a brick-and-mortar structure via interfacial reactions to develop functionally advanced Ni-C based alloys for high-temperature environments. The results are now published in Science Advances.

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Heated crystal flakes can be sewn into cloth…

Heated crystal flakes can be sewn into clothing for thermotherapy

Heated gloves, bracelets, and even rings are some of the potential applications of highly conductive MXene, a 2-D material made of alternating atomic layers of titanium and carbon. In a new study, researchers have fabricated MXene flakes, then electrostatically adhered the flakes to threads, and finally sewed the threads into ordinary fabrics that can be safely heated under a low voltage.

The researchers, led by Chong Min Koo, at the Korea Institute of Science and Technology and Korea University, and Cheolmin Park, at Yonsei University, have published a paper on the shape-adaptable MXene heater in a recent issue of ACS Nano.

In recent years, researchers have been investigating different materials to be used as flexible, wearable heaters. Although materials such as carbon nanotubes and graphene have excellent electrical and optical properties, it has been challenging to process them for use in applications.

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Finding a needle in a haystack: Discovery of…

Finding a needle in a haystack: Discovery of Ti2InB2 for synthesizing layered TiB

Scientists at Tokyo Institute of Technology (Tokyo Tech) have used boron as the X element in a family of materials called MAX phases, for which only carbon and nitrogen could previously be used. A clever search strategy allowed them to avoid resorting to trial and error to design this novel material, from which layered TiB can be obtained for applications in Li- or Na-ion batteries.

Considering that there are dozens of elements in the periodic table and thousands of possible combinations, it is no surprise that researchers resort to ingenious ways to predict which compounds can be synthesized in practice and would have favorable properties. One class of useful materials is referred to as “MAX phases.” These are ternary compounds consisting of three elements represented by M, A and X that exhibit ceramic and metallic properties.

These compounds form layered structures from which the “A-layer” can be etched, leaving behind what is known as 2-D MXenes. MXenes have attracted a lot of attention because they can take a number of forms and structures and offer excellent chemical and mechanical stability. This makes them applicable in a wide variety of fields, such as batteries and catalysis.

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Tiny pinholes in thin film could pave the wa…

Tiny pinholes in thin film could pave the way for 3-D holographic displays

Researchers in Korea have designed an ultrathin display that can project dynamic, multi-colored, 3-D holographic images, according to a study published in Nature Communications.

The system’s critical component is a thin film of titanium filled with tiny holes that precisely correspond with each pixel in a liquid crystal display (LCD) panel. This film acts as a ‘photon sieve,’ whereby each pinhole diffracts light emerging from it widely, resulting in a high-definition 3-D image observable from a wide angle.

The entire system is very small: it comprises a 1.8-inch off-the-shelf LCD panel with a resolution of 1024 x 768. The titanium film, attached to the back of the panel, is a mere 300 nanometres thick.

“Our approach suggests that holographic displays could be projected from thin devices, like a cell phone,” says Professor YongKeun Park, a physicist at KAIST who led the research. The team demonstrated their approach by producing a hologram of a moving, tri-coloured cube.

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New discovery makes fast-charging, better pe…

New discovery makes fast-charging, better performing lithium-ion batteries possible

Materials could boost battery performance in consumer electronics, electric vehicles, and more

Creating a lithium-ion battery that can charge in a matter of minutes but still operate at a high capacity is possible, according to research from Rensselaer Polytechnic Institute just published in Nature Communications. This development has the potential to improve battery performance for consumer electronics, solar grid storage, and electric vehicles.

A lithium-ion battery charges and discharges as lithium ions move between two electrodes, called an anode and a cathode. In a traditional lithium-ion battery, the anode is made of graphite, while the cathode is composed of lithium cobalt oxide.

These materials perform well together, which is why lithium-ion batteries have become increasingly popular, but researchers at Rensselaer believe the function can be enhanced further.

“The way to make batteries better is to improve the materials used for the electrodes,” said Nikhil Koratkar, professor of mechanical, aerospace, and nuclear engineering at Rensselaer, and corresponding author of the paper. “What we are trying to do is make lithium-ion technology even better in performance.”

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