22 research outputs found
Stress-Induced Transformations of Polarization Switching in CuInPS Nanoparticles
Using the Landau-Ginzburg-Devonshire approach, we study stress-induced
transformations of polarization switching in ferrielectric CuInP2S6
nanoparticles for three different shapes: a disk, a sphere, and a needle.
Semiconducting properties of a nanoparticle are modeled by a surface charge
layer, whose effective screening length can be rather small due to the
field-effect. We reveal a very strong and unusual influence of hydrostatic
pressure on the appearance of polarization switching in CuInP2S6 nanoparticles,
hysteresis loops shape, magnitude of the remanent polarization, and coercive
fields, and explain the effects by the anomalous temperature dependence and
"inverted" signs of CuInP2S6 linear and nonlinear electrostriction coupling
coefficients. In particular, by varying the sign of the applied pressure (from
tension to compression) and its magnitude (from zero to several hundreds of
MPa), quasi-static hysteresis-less paraelectric curves can transform into
double, triple, pinched, or single hysteresis loops. Due to the sufficiently
wide temperature and pressure ranges of double, triple, and pinched hysteresis
loop stability (at least in comparison with many other ferroelectrics),
CuInP2S6 nanodisks can be of particular interest for applications in energy
storage (in the region of double loops), CuInP2S6 nanospheres maybe suitable
for dynamic random access multibit memory, and CuInP2S6 nanoneedles are
promising for non-volatile multibit memory cells (in the regions of triple and
pinched loops). The stress control of the polarization switching scenario
allows the creation of advanced piezo-sensors based on CuInP2S6 nanocomposites.Comment: 43 pages, 8 figures, including Supplementary Material with 12 figure
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
Anomalous Polarization Reversal in Strained Thin Films of CuInPS
Strain-induced transitions of polarization reversal in thin films of a
ferrielectric CuInPS (CIPS) with ideally-conductive electrodes is
explored using the Landau-Ginzburg-Devonshire (LGD) approach with an
eighth-order free energy expansion in polarization powers. Due to multiple
potential wells, the height and position of which are temperature- and
strain-dependent, the energy profiles of CIPS can flatten in the vicinity of
the non-zero polarization states. This behavior differentiates these materials
from classical ferroelectrics with the first or second order
ferroelectric-paraelectric phase transition, for which potential energy
profiles can be shallow or flat near the transition point only, corresponding
to zero spontaneous polarization. Thereby we reveal an unusually strong effect
of the mismatch strain on the out-of-plane polarization reversal, hysteresis
loops shape, dielectric susceptibility, and piezoelectric response of CIPS
films. In particular, by varying the sign of the mismatch strain and its
magnitude in a narrow range, quasi-static hysteresis-less paraelectric curves
can transform into double, triple, and other types of pinched and single
hysteresis loops. The strain effect on the polarization reversal is opposite,
i.e., "anomalous", in comparison with many other ferroelectric films in that
the out-of-plane remanent polarization and coercive field increases strongly
for tensile strains, meanwhile the polarization decreases or vanish for
compressive strains. We explain the effect by "inverted" signs of linear and
nonlinear electrostriction coupling coefficients of CIPS and their strong
temperature dependence. For definite values of temperature and mismatch strain,
the low-frequency hysteresis loops of polarization may exhibit negative slope
in the relatively narrow range of external field amplitude and frequency.Comment: 26 pages, including 8 figures and 1 Appendi