Theory of Shock Waves Clears Up the Puzzling Graininess of Crystals.

CRYSTALS spectra; THERMAL properties of crystals; PHYSICAL & theoretical chemistry; PHYSICISTS; DISLOCATIONS in crystals; CRYSTALLOGRAPHY; RANDOM variables; FIELD theory (Physics); ATOMIC structure

This article focuses on a study conducted by Michael Zaiser, a theorist at the University of Edinburgh, which can lead to a deeper understanding of the grainy character of crystals. Within a crystal, atoms snuggle into orderly planes like checkers filling a checkerboard, and the planes stack to form a regular three-dimensional structure. A real crystal also contains many threadlike dislocations, which arise when, for example, one plane of atoms wedges partway between two others. The edge of the extra plane then creates a 1D irregularity running through the crystal. These 1D dislocations coalesce to form 2D walls that separate the grains and cells. Using a computer, the researchers then calculated how, starting from random variations, the tensor field interacts with itself and evolves. Wherever dislocations accumulate, stress within the crystal can jump significantly from one side of the accumulation to the other. Other physicists had attempted continuum models as much as 50 years ago, but all failed to produce walls.