|
New
Release -- Superconductor Week does not edit or endorse the following
news release:
Under pressure, vanadium won’t turn down the volume
Washington, DC, 20 February 2007: Scientists
at Carnegie’s
Geophysical Laboratory have discovered a new type of phase transition—a change
from one form to another—in vanadium, a metal that is commonly added to steel to
make it harder and more durable. Under extremely high pressures, pure vanadium
crystals change their shape but do not take up less space as a result, unlike
most other elements that undergo phase transitions. The work appears in the
February 23 issue of Physical Review Letters.
Led by High Pressure Collaborative Access Team (HPCAT)
research scientist Yang Ding, the team* used a diamond anvil cell to subject
vanadium crystals to pressures more than 600 thousand times higher than the
atmospheric pressure at sea level (which is about one bar). Using the
high-resolution HPCAT x-ray facility, the scientists were able to detect that
the basic atomic packing units of vanadium crystals had changed from a cube to a
rhombohedron, which resembles a cube whose sides have been squashed from squares
into diamond shapes.
“Trying to understand why high-pressure vanadium
uniquely has the record-high superconducting temperature of all known elements
inspired us to study high-pressure structure of vanadium,” Ding said. “We had no
idea that we would discover a completely new type of phase transition.”
The most familiar phase transitions are those
between gas, liquid, and solid forms. In general, increasing pressure and
decreasing temperature will cause a substance to take up less space and
eventually form a solid. But as a result of their atoms packing in closer
together at extremely high pressures, some solids undergo further changes in
their physical properties and can even change shape, which usually results in a
change in volume. But in this respect, vanadium is unique.
Though it is expensive to mine and refine, vanadium
is extremely important in the industrial world, where its main use is as a steel
additive. Steel that contains vanadium is exceptionally strong and resistant to
metal fatigue, making it ideal for kitchen knives that stay sharp almost
indefinitely, and jet turbine blades that can withstand high speed and abrasion.
Pure vanadium crystals in cubic form were thought to
be able to resist pressures over several million bars. Recent theoretical
calculations, however, suggested that pressure could cause unusual electronic
interactions in vanadium that would destroy the cubic crystals. Instead,
vanadium avoids this collapse by changing to a rhombohedron.
“Although this type of transition was first observed
in vanadium, it suggests that we should reexamine many other elements we thought
were very stable,” Ding explained. “Moreover, the transition provides a new
explanation for the continuous rising of superconducting temperature in
high-pressure vanadium, and could lead us to the next breakthrough in
superconducting materials.”
Return
to industry news releases |
