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A New Family of Quasicrystals

Researchers have discovered a new family of stable quasicrystals made from only two elements, a rare earth and cadmium. The family includes the first magnetic binary quasicrystals. Quasicrystals are metallic alloys that lack the periodic order seen in conventional crystals. Instead, they exhibit aperiodic, long-range order and have “forbidden” rotational symmetries (for example, five-fold).

Imperfections at Boundaries Key to Understanding Nanostructured Materials

Nanoscale twin boundaries — where one side of the boundary is a mirror image of the other — are not straight as thought, but instead have "kinks". Researchers used a newly developed transmission electron microscopy technique to resolve the orientation of features along these boundaries with 1 nanometer resolution. Twin boundaries that appear straight at lower resolution, actually contain many kink-like steps. These kinks are distributed non-uniformly from twin boundary to twin boundary.

Predicting Unusual Deformation Behavior in Materials

For the first time, researchers can now both explain and predict the behavior of different materials while they are being pulled apart.  Some materials are ductile, meaning they will deform without losing their toughness, and others are brittle.  The results explain even the unexpected ductility of a material within a class of rare-earth-containing materials that are otherwise known to be brittle.  To predict the behavior requires two maps.  The first map reveals whether a system has the ability to slip in a particular

The Long and the Short of It: Nanostructure of Thermoelectric Materials

A study of thermoelectrics, materials that convert heat to electricity, demonstrates the importance of characterizing materials using several different methods. According to Vegard’s Law of Alloys, the size of a crystalline lattice (lattice parameter) changes linearly with composition. It is actually not a law, but an empirical observation that has been found to hold true for a majority of alloys.

A Mystery at Cryogenic Temperatures

Scientists have discovered a fascinating secret about praseodymium aluminide. When PrAl2 is cooled, its crystal structure changes from high symmetry cubic to low symmetry tetragonal below -400 °F (32 K). However, when the cooling is done in a high magnetic field, the material retains the cubic structure. This change is not observed in other rare-earth aluminides. Furthermore, PrAl2 has an anomalous heat capacity per unit mass at low temperatures.  It is 10x higher than pure praseodymium.

Crystal Growth at the Nanoscale yields Unexpected Shapes

Scientists have discovered that the rare earth element dysprosium grown on graphene — a one atom thick layer of carbon — forms triangular-shaped islands, whereas other magnetic metals form hexagonal-shaped islands. Based on the hexagonal closed packed (hcp) bulk crystal structure of dysprosium, hexagonal islands would also have been expected. Researchers used scanning tunneling microscopy to identify the crystal structure of dysprosium on graphene. The results indicate that dysprosium grows as face centered cubic (fcc) crystals on graphene rather than hcp.

BCS Theory of Superconductivity Explains Universal Behavior

A recent discovery suggested to be a universal behavior of superconductors does not require a fancy new explanation; it elegantly falls out from the BCS theory of superconductivity, first published in 1957.The universal behavior is scaling relationship, known as Homes scaling, that relates the penetration depth of the magnetic field to the superconducting transition temperature and conductivity. It is valid over many orders of magnitude from the so-called “dirty”, short mean-free path, superconductors up to as clean materials as one can synthesize.

Neutron Spin Resonance in Iron-based Superconductors

The propagation of a novel magnetic excitation in the superconducting state, called a spin resonance, has been observed in iron arsenide superconductors for the first time. How the resonance disperses depends upon the direction probed within the single crystals studied. Propagation of the spin resonance reveals details about the superconducting state and highlights qualitative differences between iron arsenide and cuprate superconducting materials. The magnetic excitation appears in the superconducting state with upwards dispersion in iron arsenide superconductors.

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