BUFFALO, N.Y. -- In the search for superconductors, finding ways
to compress hydrogen into a metal has been a point of focus ever
since scientists predicted many years ago that electricity would
flow, uninhibited, through such a material.
Liquid metallic hydrogen is thought to exist in the high-gravity
interiors of Jupiter and Saturn. But so far, on Earth, researchers
have been unable to use static compression techniques to squeeze
hydrogen under high enough pressures to convert it into a metal.
Shock-wave methods have been successful, but as experiments with
diamond anvil cells have shown, hydrogen remains an insulator even
under pressures equivalent to those found in the Earth's core.
To circumvent the problem, a pair of University at Buffalo
chemists has proposed an alternative solution for metallizing
hydrogen: Add sodium to hydrogen, they say, and it just might be
possible to convert the compound into a superconducting metal under
significantly lower pressures.
The research, published June 10 in Physical Review Letters,
details the findings of UB Assistant Professor Eva Zurek and UB
postdoctoral associate Pio Baettig.
Using an open-source computer program that UB PhD student David
Lonie designed, Zurek and Baettig looked for sodium polyhydrides
that, under pressure, would be viable superconductor candidates.
The program, XtalOpt, is an
evolutionary algorithm that incorporates quantum mechanical
calculations to determine the most stable geometries or crystal
structures of solids.
In analyzing the results, Baettig and Zurek found that NaH9,
which contains one sodium atom for every nine hydrogen atoms, is
predicted to become metallic at an experimentally achievable
pressure of about 250 gigapascals -- about 2.5 million times the
Earth's standard atmospheric pressure, but less than the pressure
at the Earth's core (about 3.5 million atmospheres).
"It is very basic research," says Zurek, a theoretical chemist.
"But if one could potentially metallize hydrogen using the addition
of sodium, it could ultimately help us better understand
superconductors and lead to new approaches to designing a
By permitting electricity to travel freely, without resistance,
such a superconductor could dramatically improve the efficiency of
power transmission technologies.
Zurek, who joined UB in 2009, conducted research at Cornell
University as a postdoctoral associate under Roald Hoffmann, a
Nobel Prize-winning theoretical chemist whose research interests
include the behavior of matter under high pressure.
In October 2009, Zurek co-authored a paper with Hoffman and
other colleagues in the Proceedings of the National Academy of
Sciences predicting that LiH6 -- a compound containing one lithium
atom for every six hydrogen atoms -- could form as a stable metal
at a pressure of around 1 million atmospheres.
Neither LiH6 and NaH9 exists naturally as stable compounds on
Earth, but under high pressures, their structure is predicted to be
"One of the things that I always like to emphasize is that
chemistry is very different under high pressures," Zurek says. "Our
chemical intuition is based upon our experience at one atmosphere.
Under pressure, elements that do not usually combine on the Earth's
surface may mix, or mix in different proportions. The insulator
iodine becomes a metal, and sodium becomes insulating. Our aim is
to use the results of computational experiments in order to help
develop a chemical intuition under pressure, and to predict new
materials with unusual properties."
The University at Buffalo is a premier research-intensive
public university, a flagship institution in the State University
of New York system and its largest and most comprehensive campus.
UB's more than 28,000 students pursue their academic interests
through more than 300 undergraduate, graduate and professional
degree programs. Founded in 1846, the University at Buffalo is a
member of the Association of American Universities.