51 research outputs found
Natural optical activity and its control by electric field in electrotoroidic systems
We propose the existence, via analytical derivations, novel phenomenologies,
and first-principles-based simulations, of a new class of materials that are
not only spontaneously optically active, but also for which the sense of
rotation can be switched by an electric field applied to them-- via an induced
transition between the dextrorotatory and laevorotatory forms. Such systems
possess electric vortices that are coupled to a spontaneous electrical
polarization. Furthermore, our atomistic simulations provide a deep microscopic
insight into, and understanding of, this class of naturally optically active
materials.Comment: 3 figure
Condensation of the atomic relaxation vibrations in lead-magnesium-niobate at
We present neutron diffraction, dielectric permittivity and photoconductivity
measurements, evidencing that lead-magnesium niobate experiences a diffuse
phase transformation between the spherical glass and quadrupole glass phases,
in the temperature interval between 400 K and 500 K, with the quadrupole phase
possessing extremely high magnitudes of dielectric permittivity. Our analysis
shows that the integral diffuse scattering intensity may serve as an order
parameter for this transformation. Our experimental dielectric permittivity
data support this choice. These data are important for the aplications desiring
giant dielectric responses, in a wide temperature intervals and not related to
electron's excitations.Comment: 6 figure
Energy storage properties of ferroelectric nanocomposites
An atomistic effective Hamiltonian technique is used to investigate the
finite-temperature energy storage properties of a ferroelectric nanocomposite
consisting of an array of BaTiO nanowires embedded in a SrTiO
matrix, for electric field applied along the long axis of the nanowires. We
find that the energy density \textit{versus} temperature curve adopts a
nonlinear, mostly temperature-independent response when the system exhibits
phases possessing an out-of-plane polarization and vortices while the energy
density more linearly increases with temperature when the nanocomposite either
only possesses vortices (and thus no spontaneous polarization) or is in a
paraelectric and paratoroidic phase for its equilibrium state. Ultrahigh energy
density up to 140 J/cm and an ideal 100% efficiency are also
predicted in this nanocomposite. A phenomenological model, involving a coupling
between polarization and toroidal moment, is further proposed to interpret
these energy density results.Comment: 7 pages, 5 figure
A new look at the temperature-dependent properties of the antiferroelectric model PbZrO3: an effective Hamiltonian study
A novel atomistic effective Hamiltonian scheme, incorporating an original and
simple bilinear energetic coupling, is developed and used to investigate the
temperature dependent physical properties of the prototype antiferroelectric
PbZrO3 (PZO) system. This scheme reproduces very well the known experimental
hallmarks of the complex Pbam orthorhombic phase at low temperatures and the
cubic paraelectric state of Pm 3m symmetry at high temperatures. Unexpectedly,
it further predicts a novel intermediate state also of Pbam symmetry, but in
which anti-phase oxygen octahedral tiltings have vanished with respect to the
Pbam ground state. Interestingly, such new state exhibits a large dielectric
response and thermal expansion that remarkably agree with previous experimental
observations and the x-ray experiments we performed. We also conducted direct
first-principles calculations at 0K which further support such low energy
phase. Within this fresh framework, a re-examination of the properties of PZO
is thus called for.Comment: 21 pages, 4 figures. This paper is submitted to Physical Review
Asymmetric dipolar ring
Describes a device having a dipolar ring surrounding an interior region that is disposed asymmetrically on the ring. The dipolar ring generates a toroidal moment switchable between at least two stable states by a homogeneous field applied to the dipolar ring in the plane of the ring. The ring may be made of ferroelectric or magnetic material. In the former case, the homogeneous field is an electric field and in the latter case, the homogeneous field is a magnetic field
Ferroelectric nanostructure having switchable multi-stable vortex states
A ferroelectric nanostructure formed as a low dimensional nanoscale ferroelectric material having at least one vortex ring of polarization generating an ordered toroid moment switchable between multi-stable states. A stress-free ferroelectric nanodot under open-circuit-like electrical boundary conditions maintains such a vortex structure for their local dipoles when subject to a transverse inhomogeneous static electric field controlling the direction of the macroscopic toroidal moment. Stress is also capable of controlling the vortex\u27s chirality because of the electromechanical coupling that exists in ferroelectric nanodots
Diffuse neutron scattering in relaxor ferroelectric PbMg1/3Nb2/3O3
High energy resolution neutron spin-echo spectroscopy has been used to
measure intrinsic width of diffuse scattering discovered earlier in relaxor
ferroelectric crystals. The anisotropic and transverse components of the
scattering have been observed in different Brillouin zones. Both components are
found to be elastic within experimental accuracy of 1 eV. Possible
physical origin of the static-like behavior is discussed for each diffuse
scattering contribution.Comment: Submitted to the "Physical Chemistry and Chemical Physics"
(Proceedings of the QENA2004
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