Study shows how sodium loses conductivity

LIVERMORE, Calif., Sept. 27 (UPI) -- U.S. government scientists have discovered the process by which sodium loses much of its electrical conductivity when melted at high pressures.

Lawrence Livermore National Laboratory researchers used a series of new calculations to describe the unusual melting behavior of dense sodium.

"We found that molten sodium undergoes a series of pressure-induced structural and electronic transitions similar to those observed in solid sodium but beginning at a much lower pressure," said researcher Eric Schwegler.

Schwegler and former colleagues Stanimir Bonev and Jeans-Yves Raty said that when a solid melts, its volume usually increases -- but sodium reacts differently.

As pressure is increased, liquid sodium initially evolves into a more compact local structure, with a transition associated with a threefold drop in electrical conductivity. The researchers subsequently determined that in addition to a rearrangement of the sodium atoms in the liquid under pressure, the electrons sometimes get trapped in interstitial voids of the liquid and the bonds between atoms adopt specific directions.

"This behavior is totally new in a liquid as we usually expect that metals get more compact with pressure," Raty said.

The study appears in the journal Nature.

Copyright 2007 by United Press International

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