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Some recent studies:
''Nature of
dynamical coupling between polarization and strain in nanoscale
ferroelectrics from first principles,''
I. Ponomareva
and L. Bellaiche, Physical Review Letters 101, 197602 (2008).
Snapshots at different times of a (x,y) cross-section of the dipole pattern in a PZT film initially possessing low-density
nanobubbles (Pattern III). This cross-section corresponds to the most inner (001) B-plane, and the x- and y-axis lie along the [100] and [010] directions, respectively. Red (respectively, blue) areas show areas with dipoles pointing
''up'' (respectively,
''down'') along the z-direction.
These data correspond to the intermediate strain pulse (dashed lines in Fig.1(a) and (c)), and an initial nanobubble volume
of 5.3 nm3."
''Controlling
double vortex states in
low-dimensional dipolar systems,''
S. Prosandeev
and L. Bellaiche, Physical Review Letters 101, 097203 (2008).
Schematization
of the dipole arrangement in a (x, y)
plane for magnetic states playing a key role in the reversal of the hypertoroidal
moment. Crosses represent the vortex centers.
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''Coexistence
of the Phonon and Relaxation Soft Modes in the Terahertz Dielectric Response
of Tetragonal BaTiO3,''
J. Hlinka, T.
Ostapchuk, D. Nuzhnyj, J. Petzelt, P. Kuzel, C. Kadlec, P. Vanek, I.
Ponomareva and L. Bellaiche,
Physical Review
Letters bf 101, 167402 (2008).
Dipole moment pz of
an arbitrarily chosen unit cell as a function of time in MD simulations at
T=TC-10K. The inset shows
the 8 possible off-center Ti
sites. The Ti ion mostly fluctuates around and among the 4 sites preferred by
the molecular
field (full circles, pz>
0). Occasionally, it also hops towards the excited site (dashed circles, pz<0).
These hops correspond to the few
negative spikes encountered on the pz trajectory.
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"Control
of vortices by homogeneous fields in asymmetric low-dimensional dipolar
systems,"
S. Prosandeev, I. Ponomareva, I. Kornev, and L. Bellaiche, Phys. Rev.
Lett. 100, 047201 (2008).
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Predicted
hysteresis loops in asymmetric ferromagnetic rings [Panels (a) and (b)] and
in asymmetric ferroelectric rings [Panels
(c)
and (d)]. Panels (a) and (b) display the behavior of the magnetization and
magnetic toroidal moment, respectively, as a
function
of the applied homogeneous ac magnetic field. Panels (c) and (d) show the
evolution of the polarization and electric
toroidal
moment, respectively, versus the applied homogeneous ac electric field.
Insets schematize the rings' geometry and the
dipole
arrangement in the (x,y) plane for eight important states: vortex states (states
(1), (3), (5), and (7)), onion states (states (2) and (4)), and
antiferrotoroidic pair states (states (6) and (8)).
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Internal
dielectric susceptibility χint of a PZT60 film [part
(a)], wire [part (b)], and dot [part (c)] vs the screening parameter
β. The vertical lines characterize the transition from
short-circuit-like conditions to open-circuit-like conditions. Note
that χintxx(yy)=χextxx(yy)
in the film, while χintzz=χextzz
in the wire - since no depolarizing field exists along these
directions.
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"Terahertz
dielectric response of cubic BaTiO3,"
I. Ponomareva, L. Bellaiche, T. Ostapchuk, J. Hlinka and J. Petzelt, Phys.
Rev. B 77, 012102 (2008).
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Complex
dielectric response of cubic BaTiO3 versus frequency at
T=440 (bold lines) and 470 K (thin lines). Panels (a) and (b) displays
the ε' real and ε'' imaginary parts, respectively. Solid
lines show our predictions, while the dashed lines report our
measurements. Arrows emphasize the frequencies of the two peaks of
ε''.
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Real-space
decomposition, χ''(ν=ν'i,x,y,z=0)/(ε''(ν=ν')-1)
(for i=1 and 2, expressed in percent and for three different
temperatures), of the two peaks of the imaginary part of the dielectric
constant. The x, y and z-axes are chosen along the [100], [010] and
[001] directions, respectively, and their coordinates are expressed in
terms of the 5-atom unit cell lattice's constant (that is, a=0.39 nm).
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"Properties
of ferroelectric nanodots embedded in a polarizable medium: Atomistic
simulations",
S. Prossandeev and L. Bellaiche, Phys. Rev. Lett. 97,
167601 (2006)
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Temperature-versus-Δ&kappa
phase diagram of a 12x12x12 AB''O3 dot embedded in a AB'O3 medium within a
16x16x16
periodic
supercell.The positive Δκ part of this diagram corresponds to a
soft ferroelectric dot immersed in a medium that is
ferroelectrically
harder than the dot and that has a decreasing ferroelectric instability as
Δ&kappa increases. The negative
Δ&kappa
part of this diagram corresponds to a dot (having a ferroelectric
instability that is weaker than those of the medium
and
that decreases, and then vanishes, as Δ&kappa increases in
magnitude) embedded in a ferroelectrically-soft medium. The
lines
with symbols represent the phases’ boundaries. The insets show a
(001) cross-section of the dipole configuration in the
different
phases. Specifically, these insets correspond to atomistic calculations
with the following (Δ&kappa temperature)
combination:
(-0.0212 a.u., 1K), (-0.0212 a.u., 500K), (0.0062 a.u., 1K), (0.0087 a.u.,
1 K) and (0.0112 a.u., 1K) for the FE3,
FE2, FE1, FE1+FT and FT phases,
respectively. The dot surfaces are indicated via thick continuous lines in
these insets.
The
x- and y-axes are chosen along the pseudo-cubic [100] and [010] directions,
respectively.
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"Phase
diagram of Pb(Zr,Ti)O3 solid solutions from first
principles", Igor A. Kornev, L. Bellaiche, P.-E. Janolin, B.Dkhil, and
E. Suard, Phys. Rev. Lett. 97, 157601 (2006)
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Phase
diagram of Pb(Zr1-xTix)O3 near its
MPB, as predicted by the present scheme with an applied pressure of
-4.68 GPa. Symbols display the direct results of our simulations, while
lines are guide for the eyes. Indices 1, 2 and 3 indicate the
multiphase points. The uncertainty on the transition temperatures is
typically around 13K, except close to the multiphase points 2 and 3 for
which this uncertainty is around 3K.
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"Influence
of the growth direction on properties of ferroelectric ultrathin
films",
I. Ponomareva and L. Bellaiche, Phys. Rev. B 74,
064102 (2006)
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Cartesian
components of the ground-state spontaneous polarization in Pb(Zr0.4Ti0.6)O3
(4.6-4.8-nm-thick) films as a
function
of the screening coefficient β and expressed in the xyz coordinate
system, when choosing 16 and 24 unit cells
for
the periodicity of the (in-plane) x' and y' directions for [110] and [111]
films under compressive strain and 12 unit
cells
for the periodicity of the x' and y' directions for all other films (see
text for the definition of the xyz and x'y'z'
coordinate
systems). Parts (a), (b), and (c): [001] films under stress free, 2.65%
tensile strain, and -2.65% compressive
strain,
respectively. Parts (d)-(f): same as parts (a)-(c) but for a [110] film.
Parts (g)-(i): same as parts (a)-(c) but for a
[111]
film. The vertical lines characterize the transition of the dipoles pattern
from short-circuit-like conditions to
open-circuit-like
conditions. The schematization of these two different patterns is given
above each part. The width
of
the stripe domains is given in Angstrom.
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"Controlling
Toroidal Moment by Means of an Inhomogeneous Static Field: An Ab Initio
Study",
S. Prossandeev, I. Ponomareva, I. Kornev, I. Naumov, and L. Bellaiche, Phys.
Rev. Lett. 96, 237601 (2006)
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Schematization
of the two set-ups considered in this study, the resulting inhomogeneous
electric fields at the sites of the dot and the ground-state dipole
pattern.
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Dependency
of the Cartesian components of the ground-state toroidal moment and
polarization (in the top inset) on the angle of rotation about the
x-axis of the dipolar source associated with the setup of Fig. (a). For
each angle, the calculations are first performed at high temperature
and then slowly cooled down until 1 K. The bottom inset reports the
dependency of the ground-state toroidal moment for the setup of Fig.
(b) (for which no polarization exists) with respect to the angle of
rotation about the x-axis of the two dipolar sources.
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"Ferroelectricity
of perovskites under pressure",
I.A. Kornev, L. Bellaiche, P. Bouvier, P.-E. Janolin, B. Dkhil, and J.
Kreisel, Phys. Rev. Lett. 95, 196804 (2005).
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Electronic-related
properties of PbTiO3under pressure. Panels (a), (b) and (c)
display the partial electronic density of occupied states in the cubic
phase at 3.6, 40 and 103 GPa, respectively, for the O 2s, O 2p and Ti
3d orbitals. The zero in energy is chosen at the top of the valence
band. Panels (d), (e) and (f) show the electronic charge density of the
valence bands located between -22 and -15 eV in the vertical (100)
plane passing through Ti (center), Oparallel (top and bottom
sides), and Operpend (left and right sides) atoms for the
cubic state at 3.6, 40, and 103 GPa, respectively. Panels (g)-(i) display
the same information as Panels (d)-(f), respectively, but for the P4mm
equilibrium - for which Ti moves towards the bottom oxygen atom.
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"Electric-field
induced domain evolution in ferroelectric ultrathin films ,"
Bo-Kuai Lai, I Ponomareva, I. I. Naumov, Igor A. Kornev, Huaxiang Fu, L.
Bellaiche and G. J.Salamo,
Phys. Rev. Lett. 96, 137602 (2006).
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Nanobubbles
in ferroelectric ultrathin films under external electric field. Yellow
lines indicate plane of y=8,
which
cross-sectional view is shown in inset.
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CCMP web page: Wei
Ren
Last updated : 07 Jan, 2009
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