A team led by Oak Ridge
National Laboratory’s Ho Nyung Lee has discovered a strain relaxation
phenomenon in cobaltites that has eluded researchers for decades and may lead
to advances in fuel cells, magnetic sensors, and a host of energy-related
materials.
The finding, published in Nano Letters, could change the
conventional wisdom that accommodating the strain inherent during the formation
of epitaxial thin films necessarily involves structural defects, says Lee, a
member of the U.S. Department of Energy laboratory’s Materials Science and
Technology Division. Instead, the researchers found that some materials, in
this case cobaltite, form structurally well-ordered atomic patterns that can
change their magnetic properties and effectively minimize the size mismatch with
the crystalline substrate.
Epitaxial thin films, used in
nanotechnology and semiconductor fabrication, are created by growing a crystal
layer of one material on another in such a way that the crystalline structures
align. The challenge is to grow the film coherently with minimal defects, which
can have a catastrophic effect on a material’s performance.
“We discovered
properties that were not readily apparent in crystal, or bulk, form, but in
thin-film form we were able to clearly see the atomically ordered lattice
structure of lanthanum cobaltite,” Lee says. “With this knowledge, we
hope to be able to tailor the physical properties of a material for many information
and energy technologies.”
The researchers studied the
material in different strain states using scanning transmission electron
microscopy complemented by X-ray and optical spectroscopy. Using these
instruments, the scientists could see unconventional strain relaxation behavior
that produced stripe-like lattice patterns. The result is a material with
useful magnetic properties and highly suitable for sensors and ionic conductors
used in, for example, batteries.
This discovery and the
ability to engineer the structure of materials could lead to advanced cathode
materials in solid oxide fuel cells and batteries that can be charged much
faster.
“Since cobaltites are
promising candidates for magnetic sensors, ionic conductors and surface
catalysts, this discovery provides a new understanding that can be used for
artificial tuning of magnetism and ionic activities,” Lee says.
Source: Oak Ridge National Laboratory