20 research outputs found
Screening-Induced Phase Transitions in Core-Shell Ferroic Nanoparticles
Using the Landau-Ginzburg-Devonshire approach, we study screening-induced
phase transitions in core-shell ferroic nanoparticles for three different
shapes: an oblate disk, a sphere, and a prolate needle. The nanoparticle is
made of a ferroic CuInP2S6 core and covered by a "tunable" screening shell made
of a phase-change material with a conductivity that varies as the material
changes between semiconductor and metallic phases. We reveal a critical
influence of the shell screening length on the phase transitions and
spontaneous polarization of the nanoparticle core. Since the tunable screening
shell allows the control of the polar state and phase diagrams of core-shell
ferroic nanoparticles, the obtained results can be of particular interest for
applications in nonvolatile memory cells.Comment: 22 pages, 6 figures, 1 Appendi
Light-Induced Transitions of Polar State and Domain Morphology of Photo-Ferroelectric Nanoparticles
Using the Landau-Ginzburg-Devonshire approach, we study light-induced phase
transitions, evolution of polar state and domain morphology in
photo-ferroelectric nanoparticles (NPs). Light exposure increases the free
carrier density near the NP surface and may in turn induce phase transitions
from the nonpolar paraelectric to the polar ferroelectric phase. Using the
uniaxial photo-ferroelectric Sn2P2S6 as an example, we show that visible light
exposure induces the appearance and vanishing of striped, labyrinthine or
curled domains and changes in the polarization switching hysteresis loop shape
from paraelectric curves to double, pinched and single loops, as well as the
shifting in the position of the tricritical point. Furthermore, we demonstrate
that an ensemble of non-interacting photo-ferroelectric NPs may exhibit
superparaelectric-like features at the tricritical point, such as strongly
frequency-dependent giant piezoelectric and dielectric responses, which can
potentially be exploited for piezoelectric applications.Comment: 42 pages, 7 figures, including 14 pages Supplement with 6 figure
The strain-induced transitions of the piezoelectric, pyroelectric and electrocaloric properties of the CuInPS films
The low-dimensional ferroelectrics, ferrielectrics and antiferroelectrics are
of urgent scientific interest due to their unusual polar, piezoelectric,
electrocaloric and pyroelectric properties. The strain engineering and strain
control of the ferroelectric properties of layered 2D Van der Waals materials,
such as CuInP(S,Se) monolayers, thin films and nanoflakes, are of
fundamental interest and especially promising for their advanced applications
in nanoscale nonvolatile memories, energy conversion and storage, nano-coolers
and sensors. Here, we study the polar, piezoelectric, electrocaloric and
pyroelectric properties of thin strained films of a ferrielectric
CuInPS covered by semiconducting electrodes and reveal an unusually
strong effect of a mismatch strain on these properties. In particular, the sign
of the mismatch strain and its magnitude determine the complicated behavior of
piezoelectric, electrocaloric and pyroelectric responses. The strain effect on
these properties is opposite, i.e., "anomalous", in comparison with many other
ferroelectric films, for which the out-of-plane remanent polarization,
piezoelectric, electrocaloric and pyroelectric responses increase strongly for
tensile strains and decrease or vanish for compressive strains.Comment: 16 pages, 5 figures, to be presented at the VI Lithuanian-Polish
Meeting on Physics of Ferroelectric
Bending-induced isostructural transitions in ultrathin layers of van der Waals ferrielectrics
Using Landau-Ginzburg-Devonshire (LGD) phenomenological approach we analyze
the bending-induced re-distribution of electric polarization and field, elastic
stresses and strains inside ultrathin layers of van der Waals ferrielectrics.
We consider a CuInP2S6 (CIPS) thin layer with fixed edges and suspended central
part, the bending of which is induced by external forces. The unique aspect of
CIPS is the existence of two ferrielectric states, FI1 and FI2, corresponding
to big and small polarization values, which arise due to the specific four-well
potential of the eighth-order LGD functional. When the CIPS layer is flat, the
single-domain FI1 state is stable in the central part of the layer, and the FI2
states are stable near the fixed edges. With an increase of the layer bending
below the critical value, the sizes of the FI2 states near the fixed edges
decreases, and the size of the FI1 region increases. When the bending exceeds
the critical value, the edge FI2 states disappear being substituted by the FI1
state, but they appear abruptly near the inflection regions and expand as the
bending increases. The bending-induced isostructural FI1-FI2 transition is
specific for the bended van der Waals ferrielectrics described by the eighth
(or higher) order LGD functional with consideration of linear and nonlinear
electrostriction couplings. The isostructural transition, which is revealed in
the vicinity of room temperature, can significantly reduce the coercive voltage
of ferroelectric polarization reversal in CIPS nanoflakes, allowing for the
curvature-engineering control of various flexible nanodevices.Comment: 26 pages, 7 figures and Appendices A-