This discovery could improve everything from medical devices to electronics.
From:
University of Minnesota
November 17, 2021 -- An international
team of researchers from the University of Minnesota Twin Cities and Kiel
University in Germany have discovered a path that could lead to shape-shifting
ceramic materials.
The research is published open access
in Nature, the world's leading multidisciplinary science journal.
Anyone who has ever dropped a coffee cup
and watched it break into several pieces, knows that ceramics are brittle.
Subject to the slightest deformation, they shatter. However, ceramics are used
for more than just dishes and bathroom tiles, they are used in electronics
because, depending on their composition, they may be semiconducting,
superconducting, ferroelectric, or insulating. Ceramics are also non corrosive
and used in making a wide variety of products, including spark plugs, fiber
optics, medical devices, space shuttle tiles, chemical sensors, and skis.
On the other end of the materials
spectrum are shape memory alloys. They are some of the most deformable or
reshapable materials known. Shape memory alloys rely on this tremendous
deformability when functioning as medical stents, the backbone of a vibrant
medical device industry both in the Twin Cities area and in Germany.
The origin of this shape-shifting
behavior is a solid-to-solid phase transformation. Different from the process
of crystallization-melting-recrystallization, crystalline solid-solid
transitions take place solely in the solid state. By changing temperature (or
pressure), a crystalline solid can be transformed into another crystalline
solid without entering a liquid phase.
In this new research, the route to producing
a reversible shape memory ceramic was anything but straightforward. The
researchers first tried a recipe that has worked for the discovery of new
metallic shape memory materials. That involves a delicate tuning of the
distances between atoms by compositional changes, so that the two phases fit
together well. They implemented this recipe, but, instead of improving the
deformability of the ceramic, they observed that some specimens exploded when
they passed through the phase transformation. Others gradually fell apart into
a pile of powder, a phenomenon they termed "weeping."
With yet another composition, they
observed a reversible transformation, easily transforming back and forth
between the phases, much like a shape memory material. The mathematical conditions
under which reversible transformation occurs can be applied widely and provide
a way forward toward the paradoxical shape-memory ceramic.
"We were quite amazed by our
results. Shape-memory ceramics would be a completely new kind of functional material,"
said Richard James, a co-author of the study and a Distinguished McKnight
University Professor in the University of Minnesota's Department of Aerospace
Engineering Mechanics. "There is a great need for shape memory actuators
that can function in high temperature or in corrosive environments. But what
excites us most is the prospect of new ferroelectric ceramics. In these
materials, the phase transformation can be used to generate electricity from
small temperature differences."
The team from Germany was responsible
for the experimental part and the chemical and structural investigation at the
nanoscale.
"For the explanation of our
experimental discovery that, contrary to expectation, the ceramics are
extremely incompatible and explode or decay, the collaboration with Richard
James' group at the University of Minnesota was very valuable," says
Eckhard Quandt, a co-author of the study and a professor in the Institute for
Materials Science, at Kiel University. "The theory developed on this basis
not only describes the behavior, but also shows the way to get to the desired
compatible shape memory ceramics."
James also highlighted the importance of
the collaboration between the University of Minnesota and Kiel University.
"Our collaboration with Eckhard Quandt's
group at Kiel University has been tremendously productive," added James.
"As in all such collaborations, there is sufficient overlap that we
communicate well, but each group brings plenty of ideas and techniques that
expand our collective ability to discover."
In addition to James and Quandt, the
research team included Lorenz Kienle from Kiel University Andriy Lotnyk from
the Leibniz Institute of Surface Engineering, and graduate students Hanlin Gu,
Jascha Romer, and Justin Jetter.
The researchers were supported by the
U.S. National Science Foundation, a Vannevar Bush Faculty Fellowship on the
`Mathematical Design of Materials' from the U.S. Department of Defense, a
Multidisciplinary University Research Initiatives (MURI) grant from the Office
of Naval Research, a Mercator Fellowship from the German Research Foundation,
and the Reinhart Koselleck Project from the German National Science Foundation.
https://www.sciencedaily.com/releases/2021/11/211117211559.htm
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