Embargoed until 2 P.M. EDT
NSF PR 99-51 - September 1, 1999
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Breakthrough Image of Atomic Bonding Will Advance
the Science of New Materials
Researchers funded by the National Science Foundation
have produced the first experimental image of atomic
bonding in copper oxide. Atomic bonds, or molecular
orbitals, are the "glue" that holds atoms together
and give materials most of their properties. The image
produced by scientists at Arizona State University,
to be published this week in the journal Nature, provides
a direct experimental mapping of the molecular orbitals
that connect atoms in a solid material, which has
never before been seen.
The image reveals covalent bonds between atomic nuclei
in copper oxide, or cuprite, a ceramic semiconducting
material. It resolves a long-standing controversy
about whether cuprite contains covalent as well as
ionic bonds, and shows that covalent bonds exist not
just between oxygen and copper atoms, but also between
pairs of copper atoms. Molecular orbitals are produced
by atomic nuclei sharing or competing for electrons.
In covalent bonds, atomic nuclei share electrons,
increasing a material's ability to conduct electricity.
In ionic bonds, nuclei compete for electrons, producing
insulators, or poor conductors.
"The evidence of covalent bonding between metals is
likely to make them rewrite the chemistry textbooks,"
said Arizona State University researcher John Spence,
who teamed with Jian-Min Zuo, Miyoung Kim, and Michael
O'Keefe to synthesize the image from measurements
of electron and X-ray scattering. "Chemistry has always
assumed that these are only possible between copper
and oxygen in this material."
In addition, Spence noted, the measurements are accurate
enough to test the latest theories that predict the
properties of new materials when they involve atoms
containing many electrons.
Spence and his colleagues expect to see similar orbitals
in high-temperature superconducting and colossal magnetoresistance
materials. Scientists have long known that some metals
are superconductors, which means they lose all resistance
to electricity at temperatures approaching absolute
zero. However, in 1986, scientists discovered that
ceramic oxides such as cuprates could reach this state
at higher temperatures, which are easier to achieve
and maintain. Still, scientists needed a better understanding
of the atomic bonds to understand the functional and
mechanical properties of superconducting materials.
Colossal magnetoresistance materials are those in which
the electrical conductivity can be changed dramatically
by the application of a magnetic field. Potential
applications for some of these materials include magnetic
media for computer disks, a new type of dynamic memory
for computers, and magnetic sensors that are useful
in medicine, environmental surveillance, and mine