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'Keeffe 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 detection.
Editors: The image is available at: http://clasdean.la.asu.edu/news/images/cuprite/