The techniques the scientists used to observe this nanoscale atomic action were high-tech versions of x-ray vision, aided by mathematical and computer analysis of the results. First the lead materials were made in a purified powder form at Northwestern University. Then the scientists bombarded the samples with two kinds of beams - x-rays at the Advanced Photon Source at Argonne and neutrons at the Lujan Neutron Scattering Center at Los Alamos. Detectors gather information about how these beams scatter off the sample to produce diffraction patterns that indicate positions and arrangements of the atoms. Further mathematical and computational analysis of the data using computer programs developed at Brookhaven and Columbia allowed the scientists to model and interpret what was happening at the atomic level over a range of temperatures.
Brookhaven physicist Emil Bozin, first author on the paper, was the first to notice the odd behavior in the data, and he worked tenaciously to prove it was something new and not a data artifact. "If we had just looked at the average structure, we never would have observed this effect. Our analysis of atomic pair distribution functions gives us a much more local view - the distance from one particular atom to its nearest neighbors - rather than just the average," Bozin says. The detailed analysis revealed that, as the material got warmer, these distances were changing on a tiny scale - about 0.025 nanometers - indicating that individual atoms were becoming displaced.
The scientists have made an animation to illustrate the emergence of these displacements upon heating. In it, the displacements are represented by arrows to indicate the changing orientations of the atoms as they flip back and forth, or fluctuate, like tiny dipoles.
According to the scientists, it is th
|Contact: Karen McNulty Walsh|
DOE/Brookhaven National Laboratory