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.
Crystal transformations that reduce symmetry are called "distortions". ISODISTORT (iso.byu.edu) is a powerful group-theoretical tool that can generate, parameterize, and interactively visualize virtually any crystal distortion involving atomic displacements, magnetic moments, occupational orderings, or lattice strains. Figure based on La2CoRuO6 (J. Mater. Chem. 15, 715-720, 2005).
The irreducible representations (IRs) of the parent symmetry of a system provide a symmetry-motivated parameter set for describing any periodic or aperiodic distortion. The IRs of complete crystallographic space groups and their extensions to (3+d)-dimensional superspace, including all special and non-special k-vectors, commensurate and incommensurate, have now been exhaustively tabulated for the first time. Photo (Wikipedia): Table Mountain, Capetown, South Africa.
Wave-like modulations with non-lattice periodicities accompany a variety of important physical phenomena (e.g. magnetism and superconductivity). Though such a material is not properly crystalline in three dimensions, it does have a regular crystal lattice in a higher dimensional superspace. The superspace symmetry groups in (3+1), (3+2) and (3+3) dimensions have now been exhaustively tabulated, which will make it easier to solve modulated structure and understand their properties.
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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28 April, Thursday
29 April, Friday
Blaine Harker, Kent Gee, and Traci Neilsen recently published an article titled "Application of Beamforming Methods to Extended Partially Correlated Sources" in Sixth Berlin Beamforming Conference, BeBeC-2016-S6, (Berlin, Germany, February 2016).. Click on the image above to read it.
A Dust Angel Nebula: The combined light of stars along the Milky Way are reflected by these cosmic dust clouds that soar some 300 light-years or so above the plane of our galaxy. Dubbed the Angel Nebula, the faint apparition is part of an expansive complex of dim and relatively unexplored, diffuse molecular clouds....
This photograph and Description come from NASA's Astronomy Picture of the Day web site.