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A D V A N C E D M A T E R I A L S & P R O C E S S E S | M A Y 2 0 1 5
1 0 METALS | POLYMERS | CERAMICS
SOLVING A 50-YEAR-OLD
VANADIUM DIOXIDE MYSTERY
At the transition temperature, va-
nadiumdioxide’s electrical conductivity
abruptly increases by a factor of 10,000
and the atomic lattice rearranges from
a monoclinic to a tetragonal structure.
A fundamental description of the phys-
ical and electronic properties during
the transition in VO2 has remained con-
troversial for more than 50 years. Now,
researchers at Oak Ridge National Lab-
oratory, Tenn., are using advanced neu-
tron and x-ray scattering experiments at
DOE facilities, coupled with large-scale
first-principles calculations with super
computers, to determine the detailed
mechanism for the transition.
Their studies reveal that the ther-
modynamic force driving the insula-
tor-to-metal transition is dominated by
the lattice vibrations (phonons) rather
than electronic contributions. In addi-
tion, adirect, quantitativedetermination
of the phonon dispersions was achieved,
as well as a description of how chang-
ing occupancies in the atomic orbitals
participate in the phase transition. The
low-energy phonons change the bonds
between atoms (i.e., electron orbitals),
allowing some electrons to travel freely
at higher temperatures leading to a me-
tallic state. This research demonstrates
that anharmonic lattice dynamics play
a critical role in controlling phase com-
petition in metal oxides, and provides
the complete physical model vital for
the predictive design of new materials
with unique properties. .
COOKING UP ANTIBACTERIAL
PLASTIC FOR HEALING
Bioplastics made from protein
sources such as albumin and whey show
significant antibacterial properties, find-
ings that could eventually lead to their
use in medical applications such as
wound healing dressings, sutures, cathe-
ter tubes, and drug delivery, according to
a recent study by the University of Geor-
gia College of Family and Consumer Sci-
ences, Athens. Researchers tested three
nontraditional bioplastic materials—al-
bumin, whey, and soy proteins—as alter-
natives toconventional petroleum-based
plastics that pose risks of contamination.
In particular, albumin, a protein found in
egg whites, demonstrates tremendous
antibacterial properties when blended
with a traditional plasticizer such as glyc-
erol.
Changes in the crystal structure and electronic properties of VO2 occur during its in-
sulator-to-metal phase transition (V blue; O red). Above 67°C (right), large-amplitude,
nonlinear lattice vibrations (phonons) lead to a tetragonal crystal structure with
mobile electrons (yellow) indicating that the vanadiumdioxide is a metal. At lower
temperatures (left), the electrons are localized in the atomic bonds in the distorted
monoclinic crystal structure indicating that the vanadiumdioxide is an insulator.
Courtesy of ORNL.
BRIEF
A new mountaineering shoe called the Edging Chassis from Salomon, France,
uses the high-performance, bio-based EcoPaXX polyamide from Royal DSM, the Netherlands.
EcoPaXX enables production of a chassis with an intricate design that is light and flexible yet rigid, retains its proper-
ties at low temperatures, and has reduced moisture uptake, despite being a polyamide. The material is suitable for
injection molding and certified as carbon neutral. .
Image courtesy of DSM Engineering Plastics.