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.
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.
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.
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.
In this image of from BYU's x-ray diffraction facility, x-rays arriving from the left scatter in all directions from a tiny crystal at the center, and are then imaged by a 16-megapixel x-ray camera. The often beautiful scattering patterns that result contain a wealth of information about the atomic structure of the sample. The speed and sensitivity of state-of-the-art instruments like this have revolutionized the study of crystalline materials.
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6 October, Tuesday
7 October, Wednesday
Kent Harrison recently published an article titled "Book Review: Even Unto Bloodshed: An LDS Perspective on War, by Duane Boyce" in SquareTwo. Click on the image above to read it.
Flying Past Pluto : What would it look like to fly past Pluto? The robotic New Horizons spacecraft did just this in late July and continues to return stunning pictures of the dwarf planet. Some well-chosen flyby images have now been digitally sequenced to create the featured video....
This photograph and Description come from NASA's Astronomy Picture of the Day web site.