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    Transient Defects Caught in the Act

    The anisotropic x-ray diffuse scattering pattern surrounding this Bragg reflection from La1.8Sr2.2Mn2O7 at 125 K provides evidence that Jahn-Teller polarons (football-shaped lattice distortions that follow hopping electrons from site to site) play a role in this material's exotic phase transition from paramagnetic insulator to ferromagnetic metal. This data was used to perform a quantitative three-dimensional structural analysis of transient polaronic distortions.

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    Slab-Stacking in Gd5(Si,Bi)4

    Structures based on stacking sequences of Gd5T4 slabs are determined by the directionality of interslab T-T dimers. These include giant-magnetocaloric compounds like Gd5Si2Ge2. In the T = (Si,Bi) system, substituting Si for Bi not only leads to the complete electronic/geometric cleavage of the interslab dimers, it removes the directionality of residual nearest-slab interactions, which facilitates novel stacking sequences and extensive stacking faults.

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    Defect-Free Superconductors

    solved. Unlike their hole-doped cousins, these crystals do not superconduct when newly grown, but only after a high-temperature treatment in a reducing environment. Using a combination of x-ray diffuse scattering and neutron powder diffraction techniques, their copper-oxide sheets were found to be initially riddled with copper-vacancy defects, which were then reversibly repaired during heat treatments.

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    Stellar Diffuse X-ray Scattering

    Not astronomy! This is actually single-crystal diffuse x-ray scattering from an important industrial isomerization catalyst called mordenite, where the L = 0 plane of reciprocal space was reconstructed using portions from over 1000 CCD X-ray camera images. The broad patches, open diamonds, and star-shaped distributions are clues that reveal a complex architecture of framework defects with implications for this zeolite’s unusual adsorptive and catalytic properties.

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    Gamma-Alumina Nanoparticles

    Nanoparticles of gamma-alumina obtained from a novel synthetic solvent-deficient method show promise as improved industrial catalyst-supports. X-ray PDF analysis reveals that they are born with a high concentration of defects that locally resemble boehmite. As the nanoparticles are annealed to successively higher temperatures, the boehmite-like defects heal gradually rather than disappearing in an abrupt phase transition, which explains several previously misunderstood of properties of the gamma phase.

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Recently Published Research

Elizabeth Jeffery Kraczek et al. recently published an article titled "Deriving the Ages of Field White Dwarfs" in Astronomical Society of the Pacific Conference Series. Click on the image above to read it.

Astronomy Picture of the Day

M31: The Andromeda Galaxy : What is the nearest major galaxy to our own Milky Way Galaxy? Andromeda. In fact, our Galaxy is thought to look much like Andromeda. Together these two galaxies dominate the Local Group of galaxies. The diffuse light from Andromeda is caused by the hundreds of billions of stars that compose it....

This photograph and Description come from NASA's Astronomy Picture of the Day web site.