6 research outputs found
Local Enhancement of Polarization at PbTiO<sub>3</sub>/BiFeO<sub>3</sub> Interfaces Mediated by Charge Transfer
Ferroelectrics
hold promise for sensors, transducers, and telecommunications.
With the demand of electronic devices scaling down, they take the
form of nanoscale films. However, the polarizations in ultrathin ferroelectric
films are usually reduced dramatically due to the depolarization field
caused by incomplete charge screening at interfaces, hampering the
integrations of ferroelectrics into electric devices. Here, we design
and fabricate a ferroelectric/multiferroic PbTiO<sub>3</sub>/BiFeO<sub>3</sub> system, which exhibits discontinuities in both chemical valence
and ferroelectric polarization
across the interface. Aberration-corrected scanning transmission electron
microscopic study reveals an 8% elongation of out-of-plane lattice
spacing associated with 104%, 107%, and 39% increments of δ<sub>Ti</sub>, δ<sub>O1</sub>, and δ<sub>O2</sub> in the PbTiO<sub>3</sub> layer near the head-to-tail polarized interface, suggesting
an over ∼70% enhancement of polarization compared with that
of bulk PbTiO<sub>3</sub>. Besides that in PbTiO<sub>3</sub>, polarization
in the BiFeO<sub>3</sub> is also remarkably enhanced. Electron energy
loss spectrum and X-ray photoelectron spectroscopy investigations
demonstrate the oxygen vacancy accumulation as well as the transfer
of Fe<sup>3+</sup> to Fe<sup>2+</sup> at the interface. On the basis
of the polar catastrophe model, FeO<sub>2</sub>/PbO interface is determined.
First-principles calculation manifests that the oxygen vacancy at
the interface plays a predominate role in inducing the local polarization
enhancement. We propose a charge transfer mechanism that leads to
the remarkable polarization increment at the PbTiO<sub>3</sub>/BiFeO<sub>3</sub> interface. This study may facilitate the development of nanoscale
ferroelectric devices by tailing the coupling of charge and lattice
in oxide heteroepitaxy
Unique Domain Structure of Two-Dimensional α‑Mo<sub>2</sub>C Superconducting Crystals
The
properties of two-dimensional (2D) materials such as graphene and
monolayer transition metal dichalcogenides are strongly influenced
by domain boundaries. Ultrathin transition metal carbides are a class
of newly emerging 2D materials that are superconducting and have many
potential applications such as in electrochemical energy storage,
catalysis, and thermoelectric energy conversion. However, little is
known about their domain structure and the influence of domain boundaries
on their properties. Here we use atomic-resolution scanning transmission
electron microscopy combined with large-scale diffraction-filtered
imaging to study the microstructure of chemical vapor deposited high-quality
2D α-Mo<sub>2</sub>C superconducting crystals of different regular
shapes including triangles, rectangles, hexagons, octagons, nonagons,
and dodecagons. The Mo atom sublattice in all these crystals has a
uniform hexagonal closely packed arrangement without any boundaries.
However, except for rectangular and octagonal crystals, the C atom
sublattices are composed of three or six domains with rotational-symmetry
and well-defined line-shaped domain boundaries because of the presence
of three equivalent off-center directions of interstitial carbon atoms
in Mo octahedra. We found that there is very small lattice shear strain
across the domain boundary. In contrast to the single sharp transition
observed in single-domain crystals, transport studies across domain
boundaries show a broad resistive superconducting transition with
two distinct transition processes due to the formation of localized
phase slip events within the boundaries, indicating a significant
influence of the boundary on 2D superconductivity. These findings
provide new understandings on not only the microstructure of 2D transition
metal carbides but also the intrinsic influence of domain boundaries
on 2D superconductivity
Large Scale Two-Dimensional Flux-Closure Domain Arrays in Oxide Multilayers and Their Controlled Growth
Ferroelectric
flux-closures are very promising in high-density
storage and other nanoscale electronic devices. To make the data bits
addressable, the nanoscale flux-closures are required to be periodic
via a controlled growth. Although flux-closure quadrant arrays with
180° domain walls perpendicular to the interfaces (V-closure)
have been observed in strained ferroelectric PbTiO<sub>3</sub> films,
the flux-closure quadrants therein are rather asymmetric. In this
work, we report not only a periodic array of the symmetric flux-closure
quadrants with 180° domain walls parallel to the interfaces (H-closure)
but also a large scale alternative stacking of the V- and H-closure
arrays in PbTiO<sub>3</sub>/SrTiO<sub>3</sub> multilayers. On the
basis of a combination of aberration-corrected scanning transmission
electron microscopic imaging and phase field modeling, we establish
the phase diagram in the layer-by-layer two-dimensional arrays versus
the thickness ratio of adjacent PbTiO<sub>3</sub> films, in which
energy competitions play dominant roles. The manipulation of these
flux-closures may stimulate the design and development of novel nanoscale
ferroelectric devices with exotic properties
Atomic Insight into the Successive Antiferroelectric–Ferroelectric Phase Transition in Antiferroelectric Oxides
Antiferroelectrics characterized by voltage-driven reversible
transitions
between antiparallel and parallel polarity are promising for cutting-edge
electronic and electrical power applications. Wide-ranging explorations
revealing the macroscopic performances and microstructural characteristics
of typical antiferroelectric systems have been conducted. However,
the underlying mechanism has not yet been fully unraveled, which depends
largely on the atomistic processes. Herein, based on atomic-resolution
transmission electron microscopy, the deterministic phase transition
pathway along with the underlying lattice-by-lattice details in lead
zirconate thin films was elucidated. Specifically, we identified a
new type of ferrielectric-like dipole configuration with both angular
and amplitude modulations, which plays the role of a precursor for
a subsequent antiferroelectric to ferroelectric transformation. With
the participation of the ferrielectric-like phase, the phase transition
pathways driven by the phase boundary have been revealed. We provide
new insights into the consecutive phase transformation in low-dimensional
lead zirconate, which thus would promote potential antiferroelectric-based
multifunctional devices
Atomic Insight into the Successive Antiferroelectric–Ferroelectric Phase Transition in Antiferroelectric Oxides
Antiferroelectrics characterized by voltage-driven reversible
transitions
between antiparallel and parallel polarity are promising for cutting-edge
electronic and electrical power applications. Wide-ranging explorations
revealing the macroscopic performances and microstructural characteristics
of typical antiferroelectric systems have been conducted. However,
the underlying mechanism has not yet been fully unraveled, which depends
largely on the atomistic processes. Herein, based on atomic-resolution
transmission electron microscopy, the deterministic phase transition
pathway along with the underlying lattice-by-lattice details in lead
zirconate thin films was elucidated. Specifically, we identified a
new type of ferrielectric-like dipole configuration with both angular
and amplitude modulations, which plays the role of a precursor for
a subsequent antiferroelectric to ferroelectric transformation. With
the participation of the ferrielectric-like phase, the phase transition
pathways driven by the phase boundary have been revealed. We provide
new insights into the consecutive phase transformation in low-dimensional
lead zirconate, which thus would promote potential antiferroelectric-based
multifunctional devices
Atomic Insight into the Successive Antiferroelectric–Ferroelectric Phase Transition in Antiferroelectric Oxides
Antiferroelectrics characterized by voltage-driven reversible
transitions
between antiparallel and parallel polarity are promising for cutting-edge
electronic and electrical power applications. Wide-ranging explorations
revealing the macroscopic performances and microstructural characteristics
of typical antiferroelectric systems have been conducted. However,
the underlying mechanism has not yet been fully unraveled, which depends
largely on the atomistic processes. Herein, based on atomic-resolution
transmission electron microscopy, the deterministic phase transition
pathway along with the underlying lattice-by-lattice details in lead
zirconate thin films was elucidated. Specifically, we identified a
new type of ferrielectric-like dipole configuration with both angular
and amplitude modulations, which plays the role of a precursor for
a subsequent antiferroelectric to ferroelectric transformation. With
the participation of the ferrielectric-like phase, the phase transition
pathways driven by the phase boundary have been revealed. We provide
new insights into the consecutive phase transformation in low-dimensional
lead zirconate, which thus would promote potential antiferroelectric-based
multifunctional devices