Scientists have managed to strong-arm the superlight element boron into taking on a couple of unnatural attributes: those of both a metal and a superconductor.

The new experiments not only confirm theoretical predictions of boron's pressure-induced metallicity but should also help flesh out little-understood periodic trends in superconductivity.

Physicist Russell J. Hemley and colleagues at the Carnegie Institution of Washington first squeezed samples of boron under pressures more than a million times that of Earth's atmosphere and then measured the samples' electrical conductivity--a difficult experimental feat.

Andrew McMahan, a high-pressure physicist at Lawrence Livermore National Laboratory, calls the experiments "excellent work," citing the extraordinarily high pressures needed to overcome the strong covalent bonds that hinder metal transformation.

The results show that the element becomes metallic at pressures of about 175 gigapascals at room temperature, close to the theoretically predicted pressure of 200 GPa. The element becomes superconducting at 6 K and 175 GPa and at 11.2 K and 250 GPa [Science, 293, 272 (2001)].

Boron is the latest on the list of lighter main-group elements, such as oxygen and sulfur, that become superconducting under high pressures and at low temperatures.

Boron is particularly interesting in light of the recent discovery that magnesium boride is a superconductor at relatively high temperatures. But the behavior still perplexes scientists, who hope that an understanding of individual elements' superconductivity will solve this and other mysteries.

And James S. Schilling, physics professor at Washington University in St. Louis, hints that boron is not the only recent addition to the roster of superconductors: Soon-to-be-published work shows superconductivity in another, as-yet-undisclosed element, he says.

[Previous Story] [Next Story]

Chemical & Engineering News
Copyright © 2001 American Chemical Society