Atoms rattle in Boron due to frustration
Could an elemental crystal prefer to be defective rather than
perfectly ordered? A recent study shows that this is indeed the case
for Boron, and that its defects arrange in a very peculiar geometry.
This geometry and the way defects interact are related to a very well
know concept in the physics of disordered systems: frustration. So in
addition to being a defective solid, boron is also a frustrated element
In general chemistry classes we learn that all elements, with the
exception of helium, solidify into an ordered crystal structure at
low temperature and that defects destabilize ordered solids, making
their energy higher. Therefore it has been a mystery for decades why
the fifth element, boron, has an extraordinarily complicated crystal
structure with 4 percent atomic defects.
Research now shows that it is precisely the presence of these
defects that stabilizes the complex phase of boron against all the
other allotropes, by providing a geometry where the number of bonds
is commensurate to the number of electrons. Most surprisingly, the
geometrical arrangement of these defects forms a very specific two-
dimensional geometrical lattice known as a double layer expanded
kagome lattice. The hopping or “rattling” of boron defects between
nearly degenerate configurations appears to be responsible for the
peculiar transport properties of boron that have puzzled scientists
for the past four decades.
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BK10995
The strength of diamond at extreme conditions.
New measurements using intense laser pulses show that diamond - the strongest solid- becomes even stronger during rapid compression, supporting almost a million times atmospheric pressure before being crushed (dynamic strength exceeding 60-80 billion Pascals, depending on crystal orientation). Diamond has been characterized at high pressures and temperatures using shock waves generated by the intense laser pulses. Diamond is found to exhibit considerable strength right up to the point that it melts, at around 6 million atmospheres pressure and 14,000 degrees Fahrenheit (8000 Kelvin). These findings underscore the remarkable properties and technological utility of diamond: for example, as a capsule material for fusion-energy experiments at the new National Ignition Facility, the world's largest laser. They may also provide insights into the ancient history of natural diamonds found on Earth and in meteorites, where shock waves caused by impact are common.
