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Sodium Loses Its Luster: A Liquid Metal That's Not Really Metallic

Date:
October 1, 2007
Source:
DOE/Lawrence Livermore National Laboratory
Summary:
When melting sodium at high pressures, the material goes through a transition in which its electrical conductivity drops threefold. Usually when a solid melts, its volume increases. In addition, when pressure is increased, it becomes increasingly difficult to melt a material. However, sodium tells a different story. As pressure is increased, liquid sodium initially evolves into a more compact local structure.
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FULL STORY

Unlike other solid metals, sodium melts differently when additional pressure is added.
Credit: Kwei-Yu Chu/LLNL

When melting sodium at high pressures, the material goes through a transition in which its electrical conductivity drops threefold.

In a series of new calculations, Lawrence Livermore National Laboratory scientists 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 LLNL's Eric Schwegler.

Schwegler and former colleagues Stanimir Bonev, now at Dalhousie University in Nova Scotia, and Jeans-Yves Raty at FNRS-University of Liège in Belgium report the new findings in the Sept. 27 edition of the journal, Nature.

Earlier experimental measurements of sodium's melting curve have shown an unprecedented pressure-induced drop in melting temperature from 1,000 K at 30 GPa (30,000 atmospheres of pressure) down to room temperature at 120 GPa (120 million atmospheres of pressure).

Usually when a solid melts, its volume increases. In addition, when pressure is increased, it becomes increasingly difficult to melt a material.

However, sodium tells a different story.

As pressure is increased, liquid sodium initially evolves into a more compact local structure. In addition, a transition takes place at about 65 GPa that is associated with a threefold drop in electrical conductivity.

The researchers carried out a series of first-principle molecular dynamic simulations between 5 and 120 GPa and up to 1,500 K to investigate the structural and electronic changes in compressed sodium that are responsible for the shape of its unusual melting curve.

The team discovered that in addition to a rearrangement of the sodium atoms in the liquid under pressure, the electrons were transformed as well. The electronic cloud gets modified; 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.


Story Source:

The above story is based on materials provided by DOE/Lawrence Livermore National Laboratory. Note: Materials may be edited for content and length.


Cite This Page:

DOE/Lawrence Livermore National Laboratory. "Sodium Loses Its Luster: A Liquid Metal That's Not Really Metallic." ScienceDaily. ScienceDaily, 1 October 2007. <www.sciencedaily.com/releases/2007/09/070926155621.htm>.
DOE/Lawrence Livermore National Laboratory. (2007, October 1). Sodium Loses Its Luster: A Liquid Metal That's Not Really Metallic. ScienceDaily. Retrieved May 22, 2015 from www.sciencedaily.com/releases/2007/09/070926155621.htm
DOE/Lawrence Livermore National Laboratory. "Sodium Loses Its Luster: A Liquid Metal That's Not Really Metallic." ScienceDaily. www.sciencedaily.com/releases/2007/09/070926155621.htm (accessed May 22, 2015).

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