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.
The laser intensity at the center of this laser focus is an astounding billion gigawatts (a billion billion watts) per square centimeter. This easily makes it most intense spot on campus. The laser pulse which creates the spot lasts only 30 femtoseconds, and is used to rip electrons from helium and study the radiation they emit in this intense field.
Group theory provides the most natural parameter set for describing a distorted crystal structure, since a relatively small number of parameters normally exhibit non-zero values. These symmetry modes are also the ideal parameter set for determining a complicated structural distortion and determining its symmetry without prior assumptions. This was demonstrated in a combined x-ray/neutron study of monoclinic room-temperature tungsten oxide.
To uniquely identify the superspace-group (SSG) symmetry of a modulated crystal, one needs a way to test the equivalence of two distinct sets of superspace-group operators. A highly efficient and robust algorithm, which was recently developed for tabulating SSGs, has now been employed to identify the symmetries of each of the (3+2)D and (3+3)D modulated structures published in the literature to date.
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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27 June, Monday
28 June, Tuesday
Gus Hart et al. recently published an article titled "First principles thermodynamical modeling of the binodal and spinodal curves in lead chalcogenides" in Physical Chemistry Chemical Physics. Click on the image above to read it.
Anticrepuscular Rays over Colorado II: What's happening over the horizon? Although the scene may appear somehow supernatural, nothing more unusual is occurring than a setting Sun and some well placed clouds. Pictured above are anticrepuscular rays....
This photograph and Description come from NASA's Astronomy Picture of the Day web site.