Scientists have long believed that while an atom's outer electrons are highly mobile and often behave somewhat chaotically, the inner electrons close to the nucleus are stable. They move steadily around the nucleus and stay out of each other's way. But new research reveals that if the pressure is really extreme, like double that found at the center of the Earth, the innermost electrons of an atom change their behavior.
The international team of researchers that observed this anomalous, unexpected phenomenon managed to put a metal called osmium, which is almost the densest of all known metals and almost as incompressible as diamond, under static pressure of over 770 gigapascals. That's more than twice as high as the pressure at the center of the Earth and 7.7 million times higher than the mean atmospheric pressure at the sea level.
The scientists were able to do this thanks to a device called a diamond anvil cell, which can put sub-millimeter-sized materials under pressure comparable to that which creates diamonds. The portion of the research team from Bayreuth University in Germany developed synthetic diamonds that could fit between two ordinary diamonds and on each side of the osmium crystal. These synthetic diamonds reduced the area in which the osmium could fit, thereby increasing the pressure to new extremes.
Osmium retained its hexagonal close-packed structure when extremely compressed, but both the inner-core and outer electrons behaved unexpectedly. Despite the extreme pressure, the outer, or valence, electrons behaved as normal, while the electrons in the atomic nuclei – which are normally predictable and tightly-bound to their nuclei – began to interact with one other. In other words, extreme compression changes the nature of core electrons.
"The phenomenon means that we can start searching for brand new states of matter," said project lead Igor Abrikosov. "We're really delighted, and it's exciting as it opens up a whole box of new questions for future research."
A paper describing the research was published in the journal Nature.
Source: Linköping University
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