8 research outputs found
Self-Polarization in Epitaxial Fully Matched Lead-Free Bismuth Sodium Titanate Based Ferroelectric Thin Films
The
Bi<sub>0.5</sub>Na<sub>0.5</sub>TiO<sub>3</sub>-based ferroelectric
is one of the most promising candidates for environment-friendly lead-free
ferroelectric/piezoelectric materials for various applications such
as actuators and micro-electromechanical systems. The understanding
and tailoring of the ferro-(piezo-)Âelectric properties of thin films,
however, are strongly hindered by the formation of the defects such
as dislocations, ion vacancies in the film, as well as by the complexity
of the interface between the film and the substrate. An ideal system
for the study of the polarization behavior in the ferro-(piezo-)Âelectric
film would be a fully matched system. In this work, monocrystalline
0.89Bi<sub>0.5</sub>Na<sub>0.5</sub>TiO<sub>3</sub>–0.11BaTiO<sub>3</sub> thin films were epitaxially grown on (001)-oriented Nb-doped
SrTiO<sub>3</sub> substrates using a sol–gel technique. The
films were almost fully lattice- and thermally matched with the substrate,
thus avoiding the impact of dislocations and thermal stress. The films
were self-poled by a built-in electric field, originating from the
sedimentation of heavier atoms during the film preparation. As a consequence,
an upward self-polarization was introduced into the films, giving
rise to asymmetric phase hysteresis loops and domain switching current
responses. These results highlight the importance of the interface
complexity for the self-polarization of piezoelectric thin films,
even for fully matched films, which will therefore facilitate the
control of properties of piezoelectric films and their applications
for various functional devices
Recoverable Self-Polarization in Lead-Free Bismuth Sodium Titanate Piezoelectric Thin Films
Bismuth
sodium titanate, Bi<sub>0.5</sub>Na<sub>0.5</sub>TiO<sub>3</sub> (BNT),
is a promising lead-free ferroelectric material. However, its potential
applications have not been fully explored, mainly because of the complex
domain structure arising from its intricate phase transitions. A deep
and thorough study of its domain structure and polarization switching
behavior will greatly help with understanding the polarization nature
and with promoting future applications. In this work, we demonstrate
that BNT polycrystalline films possess a highly ordered out-of-plane
polarization (self-polarization) and randomly oriented in-plane polarizations.
Interestingly, the inherent nature of polarization in the BNT films
does not allow for the nonvolatile domain writing, as the switched
polarization spontaneously and rapidly reverses to the initial orientation
state once the external poling electric field is removed, making the
self-polarization recoverable. Such a stable self-polarization vanishes
gradually with temperature increasing over 150 °C but starts
to recover to its initial state upon cooling down to 250 °C,
and entirely recovers once the temperature is reduced to below 200
°C. Such interesting properties of BNT films are attributed to
the combined effects of the free charges at the Pt electrode, (detected)
cation vacancies at the oxide/Pt interface and the defects in oxide
lattices. Our results make a step closer to fully understand the nature
of polarization and related piezoelectricity in BNT. Such films with
recoverable self-polarization are of great interest for applications
as sensors, actuators, and transducers that can operate particularly
under high temperatures and high electric field conditions
Large Piezoelectric Strain with Superior Thermal Stability and Excellent Fatigue Resistance of Lead-Free Potassium Sodium Niobate-Based Grain Orientation-Controlled Ceramics
Environment-friendly
lead-free piezoelectric materials with high piezoelectric response
and high stability in a wide temperature range are urgently needed
for various applications. In this work, grain orientation-controlled
(with a 90% ⟨001⟩<sub>c</sub>-oriented texture) (K,Na)ÂNbO<sub>3</sub>-based ceramics with a large piezoelectric response (<i>d</i><sub>33</sub>*) = 505 pm V<sup>–1</sup> and a high
Curie temperature (<i>T</i><sub>C</sub>) of 247 °C
have been developed. Such a high <i>d</i><sub>33</sub>*
value varies by less than 5% from 30 to 180 °C, showing a superior
thermal stability. Furthermore, the high piezoelectricity exhibits
an excellent fatigue resistance with the <i>d</i><sub>33</sub>* value decreasing within only by 6% at a field of 20 kV cm<sup>–1</sup> up to 10<sup>7</sup> cycles. These exceptional properties can be
attributed to the vertical morphotropic phase boundary and the highly
⟨001⟩<sub>c</sub>-oriented textured ceramic microstructure.
These results open a pathway to promote lead-free piezoelectric ceramics
as a viable alternative to lead-based piezoceramics for various practical
applications, such as actuators, transducers, sensors, and acoustic
devices, in a wide temperature range
Ferroelectric Phase Transition Induced a Large FMR Tuning in Self-Assembled BaTiO<sub>3</sub>:Y<sub>3</sub>Fe<sub>5</sub>O<sub>12</sub> Multiferroic Composites
Yttrium
iron garnet (YIG) is of great importance in RF/microwave devices for
its low loss, low intrinsic damping, and high permeability. Nevertheless,
tuning of YIG-based multiferroics is still a challenge due to its
near-zero magnetostriction and the difficulty of building epitaxial
interface between ferromagnetic garnet and ferroelectric perovskite
phases. In this work, the vertically aligned heterostructure of YIG:BTO/STO(001)
with local epitaxial interface between BTO and YIG is well-constructed,
where the single crystal BTO pillars are embedded in YIG matrix. A
large magnetoelectric coupling effect that drives YIG’s FMR
shift up to 512 and 333 Oe (1–2 order greater than those of
all state-of-the-art progresses) is obtained through BTO ferroelectric
phase changes induced by temperature variation at 295 and 193 K, correspondingly.
This record high magnetoelectric tunability of YIG paves a way toward
thermal/electrical tunable YIG devices
Discovery of Enhanced Magnetoelectric Coupling through Electric Field Control of Two-Magnon Scattering within Distorted Nanostructures
Electric
field control of dynamic spin interactions is promising
to break through the limitation of the magnetostatic interaction based
magnetoelectric (ME) effect. In this work, electric field control
of the two-magnon scattering (TMS) effect excited by in-plane lattice
rotation has been demonstrated in a La<sub>0.7</sub>Sr<sub>0.3</sub>MnO<sub>3</sub> (LSMO)/PbÂ(Mn<sub>2/3</sub>Nb<sub>1/3</sub>)-PbTiO<sub>3</sub> (PMN-PT) (011) multiferroic heterostructure. Compared with
the conventional strain-mediated ME effect, a giant enhancement of
ME effect up to 950% at the TMS critical angle is precisely determined
by angular resolution of the ferromagnetic resonance (FMR) measurement.
Particularly, a large electric field modulation of magnetic anisotropy
(464 Oe) and FMR line width (401 Oe) is achieved at 173 K. The electric-field-controllable
TMS effect and its correlated ME effect have been explained by electric
field modulation of the planar spin interactions triggered by spin–lattice
coupling. The enhancement of the ME effect at various temperatures
and spin dynamics control are promising paradigms for next-generation
voltage-tunable spintronic devices
Thermal Driven Giant Spin Dynamics at Three-Dimensional Heteroepitaxial Interface in Ni<sub>0.5</sub>Zn<sub>0.5</sub>Fe<sub>2</sub>O<sub>4</sub>/BaTiO<sub>3</sub>‑Pillar Nanocomposites
Traditional
magnetostrictive/piezoelectric laminated composites
rely on the two-dimensional interface that transfers stress/strain
to achieve the large magnetoelectric (ME) coupling, nevertheless,
they suffer from the theoretical limitation of the strain effect and
of the substrate clamping effect in real ME applications. In this
work, 3D NZFO/BTO-pillar nanocomposite films were grown on SrTiO<sub>3</sub> by template-assisted pulsed laser deposition, where BaTiO<sub>3</sub> (BTO) nanopillars appeared in an array with distinct phase
transitions as the cores were covered by NiZn ferrite (NZFO) layer.
The perfect 3D heteroepitaxial interface between BTO and NZFO phases
can be identified without any edge dislocations, which allows effective
strain transfer at the 3D interface. The 3D structure nanocomposites
enable the strong two magnon scattering (TMS) effect that enhances
ME coupling at the interface and reduces the clamping effect by strain
relaxation. Thereby, a large FMR field shift of 1866 Oe in NZFO/BTO-pillar
nanocomposite was obtained at the TMS critical angle near the BTO
nanopillars phase transition of 255 K
Achieving Higher Strength and Sensitivity toward UV Light in Multifunctional Composites by Controlling the Thickness of Nanolayer on the Surface of Glass Fiber
The
interphase between fiber and matrix plays an essential role in the
performance of composites. Therefore, the ability to design or modify
the interphase is a key technology needed to manufacture stronger
and smarter composite. Recently, depositing nanomaterials onto the
surface of the fiber has become a promising approach to optimize the
interphase and composites. But, the modified composites have not reached
the highest strength yet, because the determining parameters, such
as thickness of the nanolayer, are hardly controlled by the mentioned
methods in reported works. Here, we deposit conformal ZnO nanolayer
with various thicknesses onto the surfaces of glass fibers via the
atomic layer deposition (ALD) method and a tremendous enhancement
of interfacial shear strength of composites is achieved. Importantly,
a critical thickness of ZnO nanolayer is obtained for the first time,
giving rise to a maximal relative enhancement in the interfacial strength,
which is more than 200% of the control fiber. In addition, the single
modified fiber exhibits a potential application as a flexible, transparent,
in situ UV detector in composites. And, we find the UV-sensitivity
also shows a strong correlation with the thickness of ZnO. To reveal
the dependence of UV-sensitivity on thickness, a depletion thickness
is estimated by a proposed model which is an essential guide to design
the detectors with higher sensitivity. Consequently, such precise
tailoring of the interphase offers an advanced way to improve and
to flexibly control various macroscopic properties of multifunctional
composites of the next generation
Deterministic Switching of Perpendicular Magnetic Anisotropy by Voltage Control of Spin Reorientation Transition in (Co/Pt)<sub>3</sub>/Pb(Mg<sub>1/3</sub>Nb<sub>2/3</sub>)O<sub>3</sub>–PbTiO<sub>3</sub> Multiferroic Heterostructures
One of the central
challenges in realizing multiferroics-based
magnetoelectric memories is to switch perpendicular magnetic anisotropy
(PMA) with a control voltage. In this study, we demonstrate electrical
flipping of magnetization between the out-of-plane and the in-plane
directions in (Co/Pt)<sub>3</sub>/(011) PbÂ(Mg<sub>1/3</sub>Nb<sub>2/3</sub>)ÂO<sub>3</sub>–PbTiO<sub>3</sub> multiferroic heterostructures
through a voltage-controllable spin reorientation transition (SRT).
The SRT onset temperature can be dramatically suppressed at least
200 K by applying an electric field, accompanied by a giant electric-field-induced
effective magnetic anisotropy field (Δ<i>H</i><sub>eff</sub>) up to 1100 Oe at 100 K. In comparison with conventional
strain-mediated magnetoelastic coupling that provides a Δ<i>H</i><sub>eff</sub> of only 110 Oe, that enormous effective
field is mainly related to the interface effect of electric field
modification of spin–orbit coupling from Co/Pt interfacial
hybridization <i>via</i> strain. Moreover, electric field
control of SRT is also achieved at room temperature, resulting in
a Δ<i>H</i><sub>eff</sub> of nearly 550 Oe. In addition,
ferroelastically nonvolatile switching of PMA has been demonstrated
in this system. E-field control of PMA and SRT in multiferroic heterostructures
not only provides a platform to study strain effect and interfacial
effect on magnetic anisotropy of the ultrathin ferromagnetic films
but also enables the realization of power efficient PMA magnetoelectric
and spintronic devices