Jacob
L.
Jones
Department
of
Materials Science
and
Engineering,
North
Carolina
State University,
Raleigh,
NC
Seeing
the unseen:
Local
atomic
disorder
of ferroelectric
oxides
from
pair distribution
functions
and local
structure
response
to
electric
fields
Dielectric
and
ferroelectric
materials
are used
to store
and convert
electrical
and mechanical
energy,
making them
essential
to a
broad range
of applications
and devices
including impact
and displacement
sensors,
actuators,
capacitors, piezoelectric
microelectromechanical
systems
(MEMS),
vibrational
energy
harvesters,
and ultrasound
imaging devices.
In these
materials,
changes in
the crystallographic
structure under
application of
externally
applied
electric
fields
(e.g., phase
transitions,
lattice strain)
significantly
influence
the properties.
However,
most
established
characterization techniques
such
as diffraction
cannot resolve
the structures
of many
newly
explored material
compounds and
systems
because
the structures
exhibit
local-scale chemical
or positional
disorder
that does
not influence
the diffraction
patterns.
New
characterization
techniques
are required
in order
to fully
characterize
increasing
structural complexity
at the
nanoscale in
these
functional
materials.
One
such
approach, the
pair distribution
function
(PDF)
which describes
atom-atom distances
from
~2
Å to
>50 Å,
has gained
attention as
a method
to study
the local
structure of
such
complex
materials.
In this
talk, I
first
introduce several
prior studies
demonstrating
the ability
of PDF
to obtain
structural information
inaccessible
via
conventional
Bragg diffraction.
We
then present our
own
measurements
on Na0.5Bi0.5TiO3
(NBT)
and
(1-x)BaTiO3-
xBi(Zn0.5Ti0.5)O3
(BT-BZT)
which
evidence
significant
local structure
distortions
from
the average
structure.
In NBT, PDF
studies
have revealed
the effect
of unique
local environments
of Bi3+
and
Na+.
In BT-BZT,
a high
energy
density
dielectric at
x >0.10,
a unique
behavior
of permittivity vs.
temperature is
linked to
local structure effects
that are
observable
in the
PDF.
Results
from
a newly
developed
technique of
in situ
electric-field
PDF are
then
presented for
several
established
and emerging
compositions.
The
local structure
response
of various
systems
is found
to be
different,
reflecting
unique electromechanical
behaviors
in different
systems.
Notably,
we
observe
the reorientation
of disordered
Bi3+
displacements
in
NBT during
application of
electric field,
a dipolar
mechanism
that has
not been
previously
characterized in
situ.
Dr.
Jacob
Jones
(Purdue
BSME
’99, MSME
’01, PhD
Materials ’04)
is a
Professor
in the
Department
of Materials
Science and
Engineering
and Director
of the
Analytical Instrumentation
Facility
at North
Carolina
State University.
His research
interests
include electromechanics,
mechanical behavior
of materials,
and crystallography.
Jones’
group
applies advanced
in situ
X-ray
and neutron
scattering
methods in
order
to study
real-time processing-structure-property
relationships
of materials.
Much of
his recent
work
has focused
on the
mechanics of
electrically- active
domain walls
in solids
and their
contribution to
the piezoelectric,
dielectric and
elastic properties.
However,
the X-ray
tools and
techniques developed
in pursuit
of these
efforts
are
also
widely applied
to materials
synthesis
and the
response
of solids
to other
perturbing
fields
(e.g.,
magnetic, mechanical).
Since 2004, Jones
has published
130 papers
on these
topics and
his research
has been
supported
by the
National Science
Foundation, the
Army
Research
Office,
National Institute
of Standards
and Technology,
and various
industrial
and other
laboratory
sponsors.
He has
received
numerous
research
awards
including the
National Science
Foundation CAREER
award
(2007),
a PECASE
- Presidential
Early
Career
Award
for
Scientists and
Engineers
(2009), the
IEEE Ferroelectrics
Young
Investigator Award
(2011), and
the 2010 and
2012 Edward
C.
Henry
“Best Paper”
awards
from
the Electronics
Division
of the
American
Ceramic
Society. Jones
has
also
been selected
to be
elevated to
the grade
of Fellow
of The
American
Ceramic
Society, a
recognition
to be
given October
5, 2015
at the
117th Annual Meeting
of the
American
Ceramic
Society.
Friday, Sept. 25th 3:30 pm Seminar ARMS 1010