High Density Of Domain Walls Research Articles

A strategy for improving piezoelectricity and thermal stability of Na0.25K0.25Bi2.5Nb2O9-based piezoceramics via A/B-site co-doping

Obviously improved piezoelectricity and thermal stability of Na0.25K0.25Bi2.5Nb2O9-based ceramics have been urgently required for high-temperature piezoelectric applications. In this work, Na0.25K0.25Bi2.5-xCexNb2-yWyO9 (NKBCxNWy, x = 0.01, 0.02, 0.03, 0.04; y = 0.02) piezoceramics were developed via a traditional solid-state reaction method. The effect of Ce/W co-doping on the crystal structure and microscopic morphology was systematically investigated, along with the ferroelectric domains and electrical properties. An optimum composition of Na0.25K0.25Bi2.48Ce0.02Nb1.98W0.02O9 was achieved, which shows a high curie temperature of 670 ℃, a good piezoelectric coefficient d33 of 24.4 pC/N. The enhanced d33 stems from small domain sizes and high domain wall density in NKBC0.02NW0.02 ceramics. More importantly, the maximum d33 can remain above 80 % of the d33 (@25 ℃), even if the annealing temperature increases to 500 ℃. This work provides a simple and viable method to obtain high piezoelectric properties and excellent thermal stability in Na0.25K0.25Bi2.5Nb2O9-based ceramics.

Enhanced piezoelectricity of Cu-doped K(Ta,Nb)O3 single crystals

As a class of solid solution material, K(Ta,Nb)O3 (KTN) single crystals have attracted significant interest due to their excellent piezoelectric and electro-optic performance. In this study, the piezoelectric properties of KTN were improved through Cu doping. Utilizing the advantages of composition-regulating phase transition, a large, high-quality Cu:KTN crystal measuring 30 mm × 25 mm × 20 mm in size was grown using the improved top seeded solution growth method. Cu-doped KTN exhibited better piezoelectric properties than pure KTN, and the full matrix parameters were investigated. Excellent dielectric, piezoelectric, and electromechanical coupling responses (ε11T∼ 2,136, d33∼303 pC/N, kt∼0.515, and k33∼0.672) were successfully obtained. To realize the optimized orientation of the piezoelectric properties, the orientation dependence of the single domain properties was investigated, and the mechanism of Cu doping to improve piezoelectric properties was explored. We found that 0.36% (in mass) Cu doped crystal consisted of A-site substitution, following ferroelectric and domain analysis. The small ferroelectric domain sizes led to a large domain wall mobility rate and high domain wall density, which contributed to high piezoelectric properties. This work revealed the effect of A-position doping on piezoelectric properties and provided a theoretical and experimental foundation for the performance optimization of KTN-based materials.

Performance enhancements of Pb(Mg1/3Nb2/3)O3-xPbTiO3 single crystal/epoxy 1–3 composite by alternating current polarization

Pb(Mg1/3Nb2/3)O3-xPbTiO3 single crystal/epoxy 1–3 piezoelectric composite was designed to decrease acoustic impedance and to improve the electromechanical property, which was vital to the ultrasound transducers. The piezo-/dielectric properties of the PMNT/epoxy 1–3 composites prepared by the different poling methods were measured. It was found that piezoelectric coefficient d33, dielectric constant ε33T/ε0, and electromechanical factor kt of composites exhibited the significant increases of 16.41%, 6.89%, and 1.97% under optimized alternating current polarization (ACP), compared with those of the samples using direct current polarization (DCP). The domain patterns suggested that the remarkable regular striped domain and high domain wall density of the ACP sample could result in performance enhancements. The ACP composite-based transducer's bandwidth (BW) and relative sensitivity (RS) were improved by 6.27% and 1.93 dB. These results indicated that the ACP effectively enhances the piezoelectric composite's performances, and BW and RS of the transducer based on ACP piezoelectric materials are improved simultaneously.

Grain Size Effects in Mn-Modified 0.67BiFeO3-0.33BaTiO3 Ceramics.

Grain size can have significant effects on the properties of electroceramics for dielectric, piezoelectric, and ferroelectric applications. Here, we systematically investigate the effect of grain size on the structure and properties of Mn-modified 0.67BiFeO3-0.33BaTiO3 ceramics, an important lead-free piezoelectric ceramic that exhibits both a high piezoelectric coefficient and a high Curie point. Ceramics with average grain sizes ranging from 0.46 to 6.85 μm were prepared using conventional and spark plasma sintering. It was found that the morphotropic phase boundary compositions are composed of two polar structures, rhombohedral and tetragonal, with DC poling inducing an increase in the fraction of the rhombohedral phase. All ceramics show relaxor behavior and their freezing temperature moves to higher temperatures with increasing grain size, although their Burns temperature is independent of grain size. In fine-grained ceramics, which show pronounced relaxor behavior, significant grain size dependency is seen in dielectric, piezoelectric, and ferroelectric properties, which is attributed to the presence of single ferroelectric domains and high concentrations of polar nanoregions. In coarse-grained ceramics, a critical grain size of 2.83 μm yields the highest dielectric permittivity at room temperature, with the piezoelectric coefficient plateauing at this grain size, which can be attributed to the contribution of both polar nanoregions and high domain wall density.

Hierarchical geometric designs for Fe-based amorphous materials with tunable soft magnetic properties

Tailoring the soft magnetic properties of magnetic materials is highly desired from both academic and technological standpoints. In this study, we propose an alternative approach to manipulate the magnetic susceptibility and related properties of soft magnetic materials by geometric designs. For example, porous honeycomb structures of Fe92.9C3.5Si3.6 amorphous ribbons are fabricated with control over the wall width, which ranges from 60 to 130 μm. The magnetic field dependence of the magnetization shows that the magnetic susceptibility strongly depends on the wall width of porous honeycomb structures, i.e., the smaller the width, the higher the susceptibility. In addition, the susceptibilities of porous honeycomb structures are larger than that of their continuous counterpart. The geometrical dependence of the magnetic susceptibility is confirmed by phase field modeling. The simulation results suggest that a high density of domain walls can be accommodated in a porous honeycomb structure with a small wall width. Thus, the transitions of domain configurations under the magnetic field can be tailored, which brings about a geometrical dependence of the magnetic susceptibility. The present work opens a broad avenue for the geometric design of magnetic properties.

Performance enhancement of 1–3 piezoelectric composite materials by alternating current polarising

The performances of 1–3 piezocomposite materials under various poling conditions were compared and analysed. The dielectric, piezoelectric, and electromechanical properties of 1–3 piezocomposite materials were studied with variations in the electric field amplitude (Ep), poling frequency (f), and number of cycles (C). It was found that the piezoelectric coefficient (d33), free dielectric constant (ε33T/ε0), and electromechanical coupling factor (kt) of 1–3 piezocomposite materials exhibit an increase of 21.4%, 13%, and 10.7%, respectively, under the optimum alternating current poling (ACP) condition (f = 1.25 Hz, Ep = 2 kV/mm, C = 16), compared with that of the samples poled using the direct current polarisation (DCP) method. The studies of the domain pattern indicate that the performance enhancement originates from the remarkable regularly striped domain structure and high domain wall density in ACP-poled samples. Our results suggest that the ACP method is effective in enhancing the performance of composite piezoelectric materials, which possess great benefits and potential for application in acoustic/medical transducers.

Domain wall contributions to piezoelectricity in relaxor-lead titanate single crystals

It is demonstrated that the dielectric permittivity and piezoelectric coefficients in relaxor-PbTiO3 single crystals close to the morphotropic phase boundary (MPB) can be augmented by contributions from domain walls. Landau-Ginzburg-Devonshire models, incorporating both polarization and strain gradients through the domain walls, show that wall contributions in domain engineered single crystals originate from enhanced, field-induced polarization rotation in static domain walls, unlike ceramics, in which piezoelectricity is enhanced by domain wall translation. For 71° domain walls in 0.7 Pb(Mg1/3Nb2/3)O3 – 0.3PbTiO3 the piezoelectric charge coefficient d33 at the center of the wall ranges from 5000 to >30,000 pC N−1 depending on the wall width. Thus, a sufficiently high domain wall density can account for the experimentally observed augmentation in the measured properties compared to single domain models. The symmetry of the domain walls explains both the variety of average symmetries observed close to the MPB and the experimentally observed switching of the [001]-oriented crystals into the tetragonal phase via a symmetry-improbable MC phase. For a crystal of rhombohedral ground state, the presence of domain walls will impart monoclinic symmetry, the predominance of which increases with increasing domain wall density.

Dielectric and piezoelectric properties of Pb[(Mg1/3Nb2/3)0.52(Yb1/2Nb1/2)0.15Ti0.33]O3 single-crystal rectangular plate and beam mode transducers poled by alternate current poling

The dielectric, piezoelectric and physical properties of the [001]-oriented rectangular plate and beam mode of Pb[(Mg1/3Nb2/3)0.52(Yb1/2Nb1/2)0.15Ti0.33]O3 (PMN-PYbN-PT) ternary single crystals (SC) poled by alternate current poling (ACP) were investigated. The dielectric permittivity and average piezoelectric coefficient d33 were 6800 and 2490 pC/N, respectively, for the rectangular plate sample after ACP, which were 31% and 41% larger than those of the same sample after conventional direct current poling. The highest value of d33 reached 2750 pC N−1. The dielectric loss was reduced by 31%; nevertheless, the d33 improved after ACP. The beam mode electromechanical coupling factor () was 91% by using ACP, showing the highest value among all relaxor-PT SC systems reported so far. The regular periodic stripe domains were observed in ACP samples, showing high domain wall density and uniform domain size. This work demonstrates that the high performance after ACP is an effective method of improving the relaxor-PT SC transducers.

On the origin of grain size effects in Ba(Ti0.96Sn0.04)O3 perovskite ceramics

Over the last 50 years, the study of grain size effects in ferroelectric ceramics has attracted great research interest. Although different theoretical models have been proposed to account for the variation in structure and properties of ferroelectrics with respect to the size of structural grains, the underlying mechanisms are still under debate. Here, we report the results of a study on the influence of grain size on the structural and physical properties of Ba(Ti0.96Sn0.04)O3 (BTS), a ferroelectric compound that represents a model perovskite system, where the effects of point defects, stoichiometry imbalance and phase transitions are minimized by chemical substitution. It was found that different microscopic mechanisms are responsible for the different grain size dependences observed in BTS. High permittivity is achieved in fine-grained BTS ceramics due to high domain wall density and polar nanoregions; high d33 is obtained in coarse-grained ceramics due to a high degree of domain alignment during poling; large electric field-induced strain in intermediate-grained ceramics is an outcome of a favorable interplay between constraints from grain boundaries and reversible reorientation of non-180° domains and polar nanoregions. These paradigms can be regarded as general guidelines for the optimization of specific properties of ferroelectric ceramics through grain size control.

The performance enhancement and temperature dependence of piezoelectric properties for Pb(Mg1/3Nb2/3)O3-0.30PbTiO3 single crystal by alternating current polarization

The comparison and analysis of piezoelectric properties for [001]-oriented PMN-0.30PT by different polarization conditions were investigated. It should be noticed that the average piezoelectric coefficients d33 of PMN-0.30PT crystals were 1860 pC/N by alternating current (AC) polarization and 1380 pC/N by direct current (DC) polarization, which indicates a promotion of 35.3%. The domain patterns in the [001] surface of PMN-0.30PT single crystals under different polarization conditions are obtained by piezo-response force microscopy. The enhancement of piezoelectric performance by AC polarization is attributed to the regular stripe domains with high domain wall density. With the temperature increased to TR-T, both the values of dielectric constant εrT and piezoelectric coefficients d33 under AC polarization condition maintain higher compared to traditional DC poled samples. In addition, both the values of e33 and ε33S under AC polarization retain higher than that of DC polarization, suggesting that the special domain structure with high domain wall density by AC polarization keeps a stable state as the temperature increased to TR-T. When the temperature increased from TR-T to TT-C, the piezoelectric properties of crystals (εrT and d33) under different polarization conditions become the same status, which indicates that the domain structure under the different conditions of polarization may tend to the similar state and the extrinsic contribution from the domain wall motion by AC polarization is disappeared.

Quantitative High‐Dynamic‐Range Electron Diffraction of Polar Nanodomains in Pb2ScTaO6

Highly B-site ordered Pb2 ScTaO6 crystals are studied as a function of temperature via dielectric spectroscopy and in situ high-dynamic-range electron diffraction. The degree of ordering is examined on the local and macroscopic scale and is determined to be 76%. Novel analysis of the electron diffraction patterns provides structural information with two types of antiferroelectric displacements determined to be present in the polar structure. It is then found that a low-temperature transition occurs on cooling at ≈210 K that is not present on heating. This phenomenon is discussed in terms of the freezing of dynamic polar nanodomains where a high density of domain walls creates a metastable state.

A glimpse at topological structures in multiferroic materials

A glimpse at topological structures in multiferroic materials

Colossal magnetoelectric effect in 3-1 multiferroic nanocomposites originating from ultrafine nanodomain structures

We investigate colossal magnetoelectric coupling through interactions between ferroelectric and ferromagnetic nanodomains in 3-1 multiferroic BaTiO3/CoFe2O4 nanocomposites using a recent real-space phase field model based on the Landau-Ginzburg theory. A hierarchical ultrafine domain structure is characteristically formed in the nanocomposites, resulting in an extremely high density of domain walls, which causes polarization domains to be more susceptible to an external magnetic field via interfacial strain-mediation. This leads to an anomalously large magnetoelectric coupling effect in the multiferroic nanocomposites. We further demonstrate that the domain configuration and consequent magnetoelectric effect are strongly dependent on the constituent phase distribution, suggesting a promising route for the rational design of multiferroic domains and magnetoelectric effects, reminiscent of recent nano-metamaterial concepts.

Ferroelectric Domain Structures in Low‐Strain BaTiO3

Epitaxial strain in ferroelectric films offers the possibility to enhance the piezoelectric performance utilizing low crystal symmetries and high density of domain walls. Ferroelectric BaTiO3 has been predicted to order in a variety of phases and domain configurations when grown under low strain on low mismatched substrates, but little experimental evidence of that region of the phase diagram exist. Here, epitaxial BaTiO3 thin films are grown on NdScO3 substrates under ≈0.1% strain. A monoclinic ca1/ca2 phase, with 90° periodic in‐plane domain configuration and small additional out‐of‐plane component of polarization, is stabilized at room temperature and investigated using piezoelectric force microscopy and X‐ray diffraction. Above 50 °C, this phase is transformed into an a/c phase with alternating in‐plane and out‐of‐plane polarizations and forming zigzag domain walls between up‐polarized and down‐polarized superdomains. Both types of domain patterns are highly anisotropic, giving rise to very long domain walls. Above 130 °C, the paraelectric phase is observed. The occurrence of a phase transition close to room temperature, a low symmetry ca1/ca2 phase, and the formation of periodic domains make of this material a promising candidate for high piezoelectric response.

Microstructure and electrical properties in Zn-doped Ba0.85Ca0.15Ti0.90Zr0.10O3 piezoelectric ceramics

Piezoelectric ceramics doped with small amounts of elements usually cause significant improvement in piezoelectric properties. In this study, we prepared Ba0.85Ca0.15Ti0.90Zr0.10O3–x wt% ZnO (0⩽x⩽0.16) ceramics via a conventional solid-state reaction method. The evolution of domain structure, relaxor behavior, ferroelectric and piezoelectric properties with Zn doping was systematically investigated. The ceramics with x=0.08 possess slender domain patterns and high domain wall density. The Ba0.85Ca0.15Ti0.90Zr0.10O3–8wt% ZnO ceramics show maximum remnant polarization and spontaneous polarization (Pr=10.14μC/cm2, Ps=19.68μC/cm2). A giant piezoelectric coefficient of d33=603pC/N and high planar electromechanical coupling factor of kp=0.56 were obtained for the sample of x=0.08, showing the potential possibilities for lead-free piezoelectric application.

Spatial modulation of in-plane magnetic anisotropy in epitaxial Co(111) films grown on macrostep-bunched Si(111)

We compared magnetic properties of epitaxial Co(111) films grown on microstep- and macrostep-bunched vicinal Si(111) substrates. A surface of the microstep-bunched Si(111) substrate represents regular array of step-bunches with height of 1.7 nm divided from each other by flat microterraces with a width of 34 nm. A surface of the macrostep-bunched Si(111) substrate is constituted by macrostep bunches with a height of 75–85 nm divided by atomically flat macroterraces. The average sum width of a macrostep bunch and a macroterrace is 2.3 μm. While in-plane magnetic anisotropy was spatially uniform in Co(111) films grown on the microstep-bunched Si(111), periodic macromodulation of the topography of the Si(111) substrate induced spatial modulation of in-plane magnetic anisotropy in Co(111) film grown on the macrostep-bunched Si(111) surface. The energy of uniaxial magnetic anisotropy in the areas of the Co(111) film deposited on the Si(111) macrosteps was higher more than by the order of magnitude than the energy of the magnetic anisotropy in the areas grown on macroterraces. Magnetization reversal in the areas with different energy of the magnetic anisotropy occurred in different magnetic fields. We showed the possibility of obtaining high density of domain walls in Co(111) film grown on the macrostep-bunched Si(111) by tuning the spatial step density of the Si(111) substrate.

Influence of excess Ba concentration on the dielectric nonlinearity in Mn and V-doped BaTiO3 multi layer ceramic capacitors

The effect of excess Ba concentration on the dielectric nonlinearity was investigated in Mn and V-doped BaTiO3 multi layer ceramic capacitors (MLCC) under the same grain size condition, which was described by the Preisach model utilizing the first order reversal curve (FORC) distribution. The high-field dielectric constant and its ac field dependence dramatically changed increasing to a maximum and then decreasing with the increase of Ba concentration. The saturation polarization which scales to the magnitude of spontaneous polarization also showed similar behavior. These results indicate that the dependence of the dielectric constant on the Ba concentration is associated with the variation of both domain wall contribution and the magnitude of the spontaneous polarization, which could be correlated with the same dependence on the Ba concentration of the reversible FORC distribution at zero bias and the irreversible FORC distribution near origin. In the corresponding bulk specimens of the dielectrics of MLCC, almost the same amount of the Ba2TiSi2O8 second phases were detected irrespective of Ba concentration, which shows that the excess Ba incorporate into BaTiO3. Thus, low and high Ba concentration corresponds to Ba-deficient and Ba-rich or Ti-deficient BaTiO3, respectively, which results in a small spontaneous polarization and low domain wall density. The intermediate Ba concentration for the maximum dielectric constant is supposed to be near stoichiometric condition in the ABO3 structure corresponding to large spontaneous polarization and high domain wall density. The excess Ba concentration and its resultant A/B stoichiometry is a crucial factor controlling dielectric properties.

Local properties of the surface layer(s) of BiFeO3 single crystals

The surface of BiFeO3 single crystals has been characterized at the local level using several AFM-based techniques. We have observed the presence of two different epilayers showing electrical and mechanical properties different from those of the bulk: a ferroelectrically “dead” outer skin of 5 nm sitting upon a subsurface layer that displays an extremely fine pattern of hierarchical self-ordered nanodomains. Based on the size of the nanodomains and applying a Kittel-like analysis, we argue that the nanotwinned region should be confined in a layer less than a micron deep. The superficial phase transition at T* = 275 °C is restricted to the outer skin layer (the “dead” layer), while the nanotwinned layer is insensitive to this transition. In view of the photovoltaic properties and spin-dependent transport of domain walls in BiFeO3, the existence of nanodomains (and thus a high density of domain walls) in bulk single crystals is likely to be relevant for understanding their functional properties.

ModulatedC60monolayers on Si(111)3×3-Au reconstructions

Adsorption of ${\mathrm{C}}_{60}$ onto the Si(111)-$\ensuremath{\alpha}$-$\sqrt{3}\ifmmode\times\else\texttimes\fi{}\sqrt{3}$-Au surface with a high density of domain walls and its In-induced modification, a domain-wall-free Si(111)$\sqrt{3}\ifmmode\times\else\texttimes\fi{}\sqrt{3}$-(Au,In) surface, has been studied using scanning tunneling microscopy (STM). Adsorbed ${\mathrm{C}}_{60}$ have been found to form close-packed hexagonal arrays displaying specific patterns of ${\mathrm{C}}_{60}$ having different dim-bright STM contrast. On the Si(111)-$\ensuremath{\alpha}$-$\sqrt{3}\ifmmode\times\else\texttimes\fi{}\sqrt{3}$-Au surface, the dim-bright ${\mathrm{C}}_{60}$ pattern replicates the domain-wall network of the substrate surface and has plausibly an electronic origin. On the homogeneous Si(111)$\sqrt{3}\ifmmode\times\else\texttimes\fi{}\sqrt{3}$-(Au,In) surface, a Moir\'e pattern of a two-dimensional lattice develops, which indicates periodic occupation of the same regular adsorption sites on the surface. Here, the dim-bright ${\mathrm{C}}_{60}$ contrast is associated plausibly with different topographic heights of the molecules. In the case of the multilayer ${\mathrm{C}}_{60}$ films, the dim-bright ${\mathrm{C}}_{60}$ patterns of the first ${\mathrm{C}}_{60}$ monolayer have been found to be inherited with gradual smearing in the next ${\mathrm{C}}_{60}$ layers.

Dielectric Properties of Barium Titanate Ceramics with Nano-Sized Domain

Barium titanate (BaTiO3) ceramics with various grain sizes from 0.7 to 13 μm on average were prepared by a conventional sintering method, a two-step sintering method and a rate controlled two-step sintering method. The permittivity of the ceramics was increased with decreasing grain size to 1.1 μm on average. However, the permittivity of the ceramics was decreased when the grain size was below 1 μm. The field emission scanning electron microscope (FE-SEM) observations revealed that the 90º domain width decreased with decreasing the grain size. By ultrawide range dielectric spectra from kHz to THz range of the BaTiO3 ceramics, the domain contribution to the permittivity was investigated. For the BaTiO3 ceramics with grain sizes over 1 μm, the dipole polarizability and the ionic polarizability were enhanced by high domain-wall density. In contrast, for the BaTiO3 ceramics with grain sizes below 1 μm, these polarizabilities were weakened.