Oak Ridge Today

ORNL researchers discover new state of water molecule

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berylCoverImage_horz

ORNL researchers discovered that water in beryl displays some unique and unexpected characteristics. (Photo by Jeff Scovil)

 

Neutron scattering and computational modeling have revealed unique and unexpected behavior of water molecules under extreme confinement that is unmatched by any known gas, liquid, or solid states.

In a paper published in Physical Review Letters, researchers at the U.S. Department of Energy’s Oak Ridge National Laboratory describe a new tunneling state of water molecules confined in hexagonal ultra-small channels—5 angstrom across—of the mineral beryl. An angstrom is 1/10-billionth of a meter, and individual atoms are typically about 1 angstrom in diameter.

The discovery, made possible with experiments at ORNL’s Spallation Neutron Source and the Rutherford Appleton Laboratory in the United Kingdom, demonstrates features of water under ultra confinement in rocks, soil, and cell walls, which scientists predict will be of interest across many disciplines.

“At low temperatures, this tunneling water exhibits quantum motion through the separating potential walls, which is forbidden in the classical world,” said lead author Alexander Kolesnikov of ORNL’s Chemical and Engineering Materials Division. “This means that the oxygen and hydrogen atoms of the water molecule are ‘delocalized’ and therefore simultaneously present in all six symmetrically equivalent positions in the channel at the same time. It’s one of those phenomena that only occur in quantum mechanics and has no parallel in our everyday experience.” [Read more…]

Helium ‘balloons’ offer new path to control complex materials

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Helium Atoms into Crystalline Film

Inserting helium atoms (visualized as a red balloon) into a crystalline film (gold) allowed Oak Ridge National Laboratory researchers to control the material’s elongation in a single direction. (Submitted image)

 

Researchers at Oak Ridge National Laboratory have developed a new method to manipulate a wide range of materials and their behavior using only a handful of helium ions.

The team’s technique, published in Physical Review Letters, advances the understanding and use of complex oxide materials that boast unusual properties such as superconductivity and colossal magnetoresistance but are notoriously difficult to control.

For the first time, ORNL researchers have discovered a simple way to control the elongation of a crystalline material along a single direction without changing the length along the other directions or damaging the crystalline structure. This is accomplished by adding a few helium ions into a complex oxide material and provides a never before possible level of control over magnetic and electronic properties.

“By putting a little helium into the material, we’re able to control strain along a single axis,” said ORNL’s Zac Ward, who led the team’s study. “This type of control wasn’t possible before, and it allows you to tune material properties with a finesse that we haven’t previously had access to.” [Read more…]

ORNL paper examines clues for superconductivity in an iron-based material

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FERMI Figure

A change of Hall and Seebeck effects point to large Fermi surface modification at the structural transition, preventing superconductivity at low temperatures. The change in the Fermi surface topology has been confirmed by angle-resolved photoemission spectroscopy. (Image courtesy ORNL)

For the first time, scientists have a clearer understanding of how to control the appearance of a superconducting phase in a material, adding crucial fundamental knowledge and perhaps setting the stage for advances in the field of superconductivity.

The paper, published in Physical Review Letters, focuses on a calcium-iron-arsenide single crystal, which has structural, thermodynamic, and transport properties that can be varied through carefully controlled synthesis, similar to the application of pressure. To make this discovery, researchers focused on how these changes alter the material’s Fermi surface, which maps the specific population and arrangement of electrons in materials.

“The Fermi surface is basically the ‘genetic code’ for causing a certain property, including superconductivity, in a material,” said Athena Safa-Sefat of the U.S. Department of Energy’s Oak Ridge National Laboratory, which led the research team. “We can make different phases of this material in single crystal forms and measure their structure and properties, but now we have Fermi surface signatures that explain why we can’t induce superconductivity in a certain structural phase of this material.” [Read more…]

‘Atomic switcheroo’ explains origins of thin-film solar cell mystery

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Current Maps

Cross-sectional electron beam-induced current maps show the difference in cadmium telluride solar cells before (pictured above) and after (below) cadmium chloride treatment. The increased brightness after treatment indicates higher current collection at the grain boundaries. (Submitted photo)

Treating cadmium-telluride (CdTe) solar cell materials with cadmium-chloride improves their efficiency, but researchers have not fully understood why. Now, an atomic-scale examination of the thin-film solar cells led by Oak Ridge National Laboratory has answered this decades-long debate about the materials’ photovoltaic efficiency increase after treatment.

A research team from ORNL, the University of Toledo, and the U.S. Department of Energy’s National Renewable Energy Laboratory used electron microscopy and computational simulations to explore the physical origins of the unexplained treatment process. The results are published in Physical Review Letters, or PRL.

Thin-film CdTe solar cells are considered a potential rival to silicon-based photovoltaic systems because of their theoretically low cost per power output and ease of fabrication. Their comparatively low historical efficiency in converting sunlight into energy, however, has limited the technology’s widespread use, especially for home systems. [Read more…]

ORNL study advances quest for better superconducting materials

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Superconductivity Pan Defects

Minghu Pan’s image of “clover-like” atomic defects—an example is circled—that result in strong superconductivity. (Photo courtesy ORNL)

Nearly 30 years after the discovery of high-temperature superconductivity, many questions remain, but an Oak Ridge National Laboratory team is providing insight that could lead to better superconductors.

Their work, published in Physical Review Letters, examines the role of chemical dopants, which are essential to creating high-temperature superconductors—materials that conduct electricity without resistance. The role of dopants in superconductors is particularly mysterious as they introduce non-uniformity and disorder into the crystal structure, which increases resistivity in non-superconducting materials.

By gaining a better understanding of how and why chemical dopants alter the behavior of the original (parent) material, scientists believe they can design superconductors that work at higher temperatures. This would make them more practical for real-world wire applications because it would lessen the extreme cooling required for conventional superconducting material. Existing “high-temperature superconductors” operate at temperatures in the range of negative 135 degrees Celsius and below. [Read more…]

ORNL electron microscopy unlocks graphene potential

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Silicon Atoms in Graphene

The atomic resolution Z-contrast images show individual silicon atoms bonded differently in graphene. (Photo by ORNL)

Electron microscopy at the Oak Ridge National Laboratory is providing unprecedented views of the individual atoms in graphene, offering scientists a chance to unlock the material’s full potential for uses from engine combustion to consumer electronics.

Graphene crystals were first isolated in 2004. They are two-dimensional (one-atom in thickness), harder than diamonds and far stronger than steel, providing unprecedented stiffness and electrical and thermal properties. By viewing the atomic and bonding configurations of individual graphene atoms, scientists are able to suggest ways to optimize materials so they are better suited for specific applications.

[Read more…]