Magazine article Science News

Soft Crystal Shows off Its Many New Facets

Magazine article Science News

Soft Crystal Shows off Its Many New Facets

Article excerpt

A beautifully faceted diamond may be forever, but there are many types of facets in crystals that, until now, seemed to be never.

In most chunks of crystalline material, facets correspond to a few, highly favored planes within the lattice of atoms. Theorists have long postulated, however, that crystals with more mobile atoms or molecules could develop other, less readily formed facets, too. Those surfaces would lie at shallow angles relative to the main crystal planes.

In the 1980s, scientists searched for such facets in lead, gold, and solid helium. They came up empty-handed, however, observing no more than a half-dozen different facet types, none shallowly oriented.

In the March 13 PHYSICAL REVIEW LETTERS, a French research team reports the discovery of the long-sought facets. The finding verifies a fundamental prediction dating to the 1950s about the shapes that samples of crystalline substances can assume, the scientists say.

Russian physicist Lev Landau had predicted then that a crystal at 0 kelvin could manifest an almost endless number of facets of different orientations. Researchers in the 1970s and 1980s extended the theory to include the possibility of such a zoo of facets appearing under the right conditions at higher temperatures.

Such facet production would subdivide the crystal surface into an array of different-size plates, in which the successively smaller ones are often set at increasingly shallow angles. The unlimited facet proliferation that was expected can be depicted by a graph that traces, ideally, an infinite number of steps. …

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