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Bismuth Layer-Structured Ferroelectric (BLSF) materials with Bi 4 Ti 3 O 12 composition exhibit high ferroelectricity, potential for high-temperature piezoelectricity, and the puzzle of low polarizability, explored via textured ceramics and domain configurations. Here, we show that a distinctive stripe configuration of 90° domains emerges for large platelet-like grains, while the smallest grains, possessing a more equiaxial morphology, exhibit a needle-like domain structure that significantly impacts the ferroelectric properties of the ceramics. The observed hysteresis loops suggest that polarization is effectively clamped, owing to reduced mobility along the needle-like domain walls, thereby leading to a reduction in remnant polarization as grain size diminishes. It is elucidated that the domain structure is intricately linked to both internal stress within the grains and the presence of defects, notably oxygen vacancies, at the domain walls. Consequently, these multifaceted factors are identified as key determinants of the ferroelectric activity within ceramics bearing such a distinctive crystalline structure. [Display omitted] • Confocal Raman Microscopy reveals detailed domain structures in BLSF ceramics. • Grain morphology, domain structures, and internal stresses dictate polarization behavior. • Large platelet-like grains exhibit distinctive 90° stripe domain configuration. • Smallest equiaxial grains show impactful needle-like domain structure. • Reduced grain size leads to clamped polarization, diminishing remnant polarization. [ABSTRACT FROM AUTHOR]

Ferroelectric Bi2SiO5 (BSO) thin films were deposited by pulsed laser deposition on Nb‐doped (100), (110) and (111) SrTiO3 (Nb:STO) substrates, resulting in (001)‐, (113)‐ and (204)‐oriented epitaxial films. Due to the crystallinity of BSO, in which the Bi2O2 layers are formed perpendicular to the c‐axis direction, the (001)‐oriented epitaxial BSO thin film showed the lowest remanent polarization and the best leakage current characteristics. On the other hand, the (113)‐ and (204)‐oriented films showed an increase in remanent polarization due to the improvement of a‐oriented crystallinity. Through experiments using vertical and lateral piezoresponse force microscopy, it has been confirmed that the distribution of in‐plane‐oriented domains reducing remanent polarization decreases in the order of (001)‐, (113)‐ and (204)‐oriented epitaxial BSO thin films. The epitaxial BSO thin films that exhibit ferroelectric hysteresis loops similar to the relaxor ferroelectric thin films tended to have improved energy storage characteristics as a result of improved remanent polarization and saturation polarization. In particular, the (113)‐oriented epitaxial BSO thin film showed a high recoverable energy density of about 41.6 J cm−3 and an energy storage efficiency of about 85.6%. [ABSTRACT FROM AUTHOR]

BiFeO3 represents the most extensively investigated multiferroic due to its fascinating ferroelectric domain structures, large polarization, and multiferroic coupling, among many other emergent phenomena. Nevertheless, much less concern with the piezoelectricity has been raised while all these well addressed properties are identified in thin film BiFeO3, and bulk ceramic BiFeO3 has never been given priority of attention. In this paper, we report our experiments on the ferroelectric and piezoelectric properties as well as domain structures of BiFeO3 bulk ceramics synthesized by rapid hot-press sintering. It is revealed that these properties are strongly dependent on the microstructural quality, and the largest piezoelectric coefficient d33 = 55 pC/N with electric polarization as large as 45 μC/cm2 is obtained for the sample sintered at 800 °C, while they are only 30 pC/N and 14 μC/cm2 for the samples sintered in normal conditions at 800 °C. The two-level hierarchical stripe-like and irregular dendrite-like domain structures are observed in these hot-press sintered samples. It is suggested that the enhanced piezoelectric property is ascribed to the two-level hierarchical stripe-like domain structure which may respond more easily to electrical and strain stimuli than those irregular dendrite-like domains. The enhanced remnant polarization should be owing to the improved sample quality and large grains in the properly hot-press sintered samples. [ABSTRACT FROM AUTHOR]

The possibility to control the charge, type, and density of domain walls allows properties of ferroelectric materials to be selectively enhanced or reduced. In ferroelectric–ferroelastic materials, two types of domain walls are possible: pure ferroelectric and ferroelastic–ferroelectric. In this paper, we demonstrated a strategy to control the selective ferroelectric or ferroelastic domain wall formation in the (111) single-domain rhombohedral PMN-PT single crystals at the nanoscale by varying the relative humidity level in a scanning probe microscopy chamber. The solution of the corresponding coupled electro-mechanical boundary problem allows explaining observed competition between ferroelastic and ferroelectric domain growth. The reduction in the ferroelastic domain density during local switching at elevated humidity has been attributed to changes in the electric field spatial distribution and screening effectiveness. The established mechanism is important because it reveals a kinetic nature of the final domain patterns in multiaxial materials and thus provides a general pathway to create desirable domain structure in ferroelectric materials for applications in piezoelectric and optical devices. [ABSTRACT FROM AUTHOR]

We investigated the ferroelectric, piezoelectric, and domain wall current properties affected by the distribution of a -oriented domains and c -oriented domains in flexible SrBi 2 Ta 2 O 9 (SBT) thin films on flexible Pt/mica substrates. On the flexible Pt/mica substrates, the SBT thin films with a mixed crystallinity of a -oriented and c -oriented crystallinities exhibited the domain structures mixed with a -oriented domains and c -oriented domains. The SBT thin films with excellent a -oriented crystallinity showed improved ferroelectric and piezoelectric properties due to the polar axis perpendicular to the c -axis. In particular, 90o domain walls composed of a -domain and c -domain have larger domain wall currents than 180o domain walls composed of c -domains, which increases the leakage current of the SBT thin films. • Flexible polycrystalline SrBi 2 Ta 2 O 9 thin films on Pt/mica substrates. • Ferroelectric domain structures with rectangular a -domains and elongated c -domains. • Enhanced ferroelectric and piezoelectric properties with c -domain distribution. • Leakage current characteristics improved by increasing distribution of a -domains. • Domain wall currents of 90o domain walls and 180o domain walls. [ABSTRACT FROM AUTHOR]

The possibility to control the charge, type, and density of domain walls allows properties of ferroelectric materials to be selectively enhanced or reduced. In ferroelectric–ferroelastic materials, two types of domain walls are possible: pure ferroelectric and ferroelastic–ferroelectric. In this paper, we demonstrated a strategy to control the selective ferroelectric or ferroelastic domain wall formation in the (111) single-domain rhombohedral PMN-PT single crystals at the nanoscale by varying the relative humidity level in a scanning probe microscopy chamber. The solution of the corresponding coupled electro-mechanical boundary problem allows explaining observed competition between ferroelastic and ferroelectric domain growth. The reduction in the ferroelastic domain density during local switching at elevated humidity has been attributed to changes in the electric field spatial distribution and screening effectiveness. The established mechanism is important because it reveals a kinetic nature of the final domain patterns in multiaxial materials and thus provides a general pathway to create desirable domain structure in ferroelectric materials for applications in piezoelectric and optical devices.

Confocal Raman spectroscopy is applied to identify ferroelectric domain structure sensitive phonon modes in potassium titanyl phosphate. Therefore, polarization-dependent measurements in various scattering configurations have been performed to characterize the fundamental Raman spectra of the material. The obtained spectra are discussed qualitatively based on an internal mode assignment. In the main part of this work, we have characterized z-cut periodically poled potassium titanyl phosphate in terms of polarity- and structure-sensitive phonon modes. Here, we find vibrations whose intensities are linked to the ferroelectric domain walls. We interpret this in terms of changes in the polarizability originating from strain induced by domain boundaries and the inner field distribution. Hence, a direct and 3D visualization of ferroelectric domain structures becomes possible in potassium titanyl phosphate. [ABSTRACT FROM AUTHOR]

Incommensurate and commensurate structural modulations of Ba5RTi3Nb7O30 (R=La, Nd) tungsten bronze ceramics were investigated by using a cooling holder equipped transmission electron microscopy in the temperature range from 100K to 363 K. The incommensurate modulation was observed in both Ba5LaTi3Nb7O30 and Ba5NdTi3Nb7O30 at room temperature, while there was a transition from incommensurate tilted structure to commensurate superstructure for Ba5NdTi3Nb7O30 with decreasing temperature. The incommensurate and commensurate modulations were determined by the A-site occupancy of Ba and R cations. The A-site disorder resulted in larger incommensurability parameter d and the diffusion of the satellite reflection spots. The effect of A-site disorder on the coupling between long-range dipolar order and the commensurate modulation was also discussed. The obvious ferroelectric 180° domains with spike-like shape parallel to c axis were observed for Ba5NdTi3Nb7O30, while no macroferroelectric domain was determined for Ba5LaTi3Nb7O30. [ABSTRACT FROM AUTHOR]

We report a piezo-response force microscopy study of the effect of thermal annealing on ferroelectric domain structures in 6 to 20 monolayer (11 to 36 nm) polycrystalline poly(vinylidene-fluoridetrifluorethylene) thin films prepared using the Langmuir-Blodgett approach. Stripe-shape domains have been created at room temperature and subjected to thermal annealing at progressively higher temperatures up to the ferroelectric Curie temperature TC of approximately 110 °C. The static configuration of the domain walls exhibits no appreciable temperature dependence after thermal annealing, with the domain-wall roughness exponent ζ ranging from 0.4 to 0.5. Above 80 °C, we observed spontaneous polarization reversal at randomly scattered local sites in both polarization states. The number of domain nucleation centers increases rapidly as a function of temperature. We compared the thermally driven domain formation in ferroelectric polymers with those observed in ferroelectric oxides and attributed the difference to the distinct mechanisms for domain formation in these two systems. [ABSTRACT FROM AUTHOR]

Crystal structure, microstructure, local ferroelectric, and magnetic properties of the Bi0.9Nd0.1Fe1-xTixO3 samples have been investigated at room temperature to reveal the effect of Ti4+ doping on the multiferroic behavior of the lanthanide-modified compound representing a polar (space group R3c) antiferromagnetic phase of the Bi1-xLnxFeO3 perovskites. Ti doping results in a gradual suppression of the rhombohedral distortions, however, symmetry of the crystal structure remains the same in the entire concentration range allowing the single-phase perovskites to be obtained (x⩽0.08). The doping tends to reduce existing lone-pair cation-driven polar displacements, thus giving rise to a decrease of the ferroelectric polarization in the Bi0.9Nd0.1Fe1-xTixO3 (x→0.08) series. A drastic (from ~10 μm for x=0 to ~1 μm for 0.02⩽x⩽0.08) decrease of the average grain size induced by the doping is accompanied by the formation of a ferroelectric domain structure with the average domain width of ~40 nm. Finally, the doping was shown to induce an antiferromagnetic to weak ferromagnetic transformation. The maximum remanent magnetization observed in the Bi0.9Nd0.1Fe1-xTixO3 series at x~0.05 coincides with the locked magnetization releasing upon the magnetic field-induced suppression of the magnetic cycloid in pure BiFeO3. [ABSTRACT FROM AUTHOR]

With the trend of device miniaturization, ultrathin ferroelectric films are gaining more and more attention. However, understanding ferroelectricity in this nanoscale context remains a formidable challenge, primarily due to the heightened relevance of surface effects, which often leads to the loss of net polarization. Here, the influence of surface effects on the polarization as a function of thickness in ultrathin BiFeO 3 films is investigated using phase-field simulations. The findings reveal a notable increase in ferroelectric polarization with increasing thickness, with a particularly discernible change occurring below the 10 nm threshold. Upon accounting for surface effects, the polarization is marginally lower than the case without such considerations, with the disparity becoming more pronounced at smaller thicknesses. Moreover, the hysteresis loop and butterfly loop of the ultrathin film were simulated, demonstrating that the ferroelectric properties of films remain robust even down to a thickness of 5 nm. Our investigations provide valuable insights into the significance of ferroelectric thin films in device miniaturization.

An experimental method for three-dimensional (3D) imaging of ferroelectric domain patterns using digital holographic tomography is presented. The implementation of this method employs the curvilinear filtered back-projection. Our experimental method has been demonstrated on the imagining of the domain structure in a periodically poled lithium niobate single crystal. The developed method allows fast and accurate 3D observations of ferroelectric domain structures in the whole volume of the ferroelectric single crystals on the millimeter scale. [ABSTRACT FROM AUTHOR]

The effects of domain wall shape instabilities and the formation of nanodomains in front of moving walls obtained in various uniaxial ferroelectrics are discussed. Special attention is paid to the formation of self-assembled nanoscale and dendrite domain structures under highly non-equilibrium switching conditions. All obtained results are considered in the framework of the unified kinetic approach to domain structure evolution based on the analogy with firstorder phase transformation. [ABSTRACT FROM AUTHOR]

Ferroelectric domain structure has been formed under the action of electron beam scanning in congruent lithium niobate single crystal covered by surface dielectric layer. The obtained types of the domain patterns have been considered as subsequent stages of domain structure evolution. The dependence on irradiated charge density of domain density, length, and period of domain rays and stripe domain width was used for characterization of the domain structure evolution. The threshold irradiated charge density necessary for the formation of solid stripe domain has been revealed. All obtained results have been discussed in terms of kinetic approach based on the analogy between domain structure evolution and first-order phase transition. [ABSTRACT FROM AUTHOR]

We report on domain pattern transfer from a ferroelectric BaTiO 3 substrate to a CoFeB wedge film with a thickness of up to 150 nm. Strain coupling to domains in BaTiO 3 induces a regular modulation of uniaxial magnetic anisotropy in CoFeB via an inverse magnetostriction effect. As a result, the domain structures of the CoFeB wedge film and BaTiO 3 substrate correlate fully and straight ferroelectric domain boundaries in BaTiO 3 pin magnetic domain walls in CoFeB. We use X-ray photoemission electron microscopy and magneto-optical Kerr effect microscopy to characterize the spin structure of the pinned domain walls. In a rotating magnetic field, abrupt and reversible transitions between two domain wall types occur, namely, narrow walls where the magnetization vectors align head-to-tail and much broader walls with alternating head-to-head and tail-to-tail magnetization configurations. We characterize variations of the domain wall spin structure as a function of magnetic field strength and CoFeB film thickness and compare the experimental results with micromagnetic simulations. [ABSTRACT FROM AUTHOR]

Epitaxial BiFeMnO (BFMO) thin films were deposited on Nb-dopedSrTiO(Nb:STO) substrates via pulsed laser deposition. The 100-nm-thick BFMO thin films had a relatively high tetragonality with a high c/ a ratio of 1.04, confirmed by X-ray diffraction. The BFMO thin film had low leakage currents and good ferroelectric properties along with an enhanced remanent polarization of about 25.0 μC/cm. The BFMO thin films had large ferroelectric domain structures compared to conventional ferroelectric thin films, such as PbTiO thin films, which is due to their high domain wall energy. [ABSTRACT FROM AUTHOR]

Polycrystalline YMnO 3 (YMO) thin films were deposited on (111) Pt/Ta/glass substrates via pulsed laser deposition (PLD). The low PLD deposition rate made it possible to reduce the leakage currents of the YMO thin film due to the resulting high level of crystallinity. The YMO thin film exhibited a strong ferroelectric response, including a remnant polarization of 4.2 μC/cm 2 . The piezoresponse force microscopy study revealed that the YMO thin films had a mosaic domain structure and a ferroelectric domain wall energy lower than that of PbTiO 3 thin films. It is suggested that the fast switching speed of YMO capacitors, which is below 85 ns, originates from this low domain wall energy. [ABSTRACT FROM AUTHOR]

We apply here spectral-domain optical coherence tomography (SD-OCT) for the precise detection and temporal tracking of ferroelectric domain walls (DWs) in magnesium-doped periodically poled lithium niobate (Mg:PPLN). We reproducibly map static DWs at an axial (depth) resolution down to ∼ 0.6 μm, being located up to 0.5 mm well inside the single crystalline Mg:PPLN sample. We show that a full 3-dimensional (3D) reconstruction of the DW geometry is possible from the collected data, when applying a special algorithm that accounts for the nonlinear optical dispersion of the material. Our OCT investigation provides valuable reference information on the DWs' polarization charge distribution, which is known to be the key to the electrical conductivity of ferroelectric DWs in such systems. Hence, we carefully analyze the SD-OCT signal dependence both when varying the direction of incident polarization, and when applying electrical fields along the polar axis. Surprisingly, the large backreflection intensities recorded under extraordinary polarization are not affected by any electrical field, at least for field strengths below the switching threshold, while no significant signals above noise floor are detected under ordinary polarization. Finally, we employed the high-speed SD-OCT setup for the real-time DW tracking upon ferroelectric domain switching under high external fields. [ABSTRACT FROM AUTHOR]

The effect of abrasive polishing on the surface topography and domain structure of relaxor and non-relaxor ferroelectric ceramics was studied with the aid of atomic force microscopy (AFM). Two-fold effect of the surface layers on the properties of the samples was revealed: firstly, polishing treatment removes the non-ferroelectric passive layers formed during the preparation of the material; secondly, polishing results in a formation of a new surface layer having properties different from those in the bulk. [ABSTRACT FROM PUBLISHER]

In this work, the ferroelectric domain structure of (PbLa)TiO transparent ceramics and its response to an applied electric field were investigated by piezoresponse force microscopy (PFM). A qualitative three-dimensional reconstruction of the domains by PFM measurements revealed that the domain structure consists in stripes in two size scales (micro and nanometer) separated by 90° domain walls coexisting with 180° domains. While the nanoscale 90° domains were found arranged in organized structures, (e.g., lamellas, herringbones, and other unusual configurations), the 180° domains form a 'labyrinth' structure, typical of ferroelectrics with a degree of disorder. Local application of an electric field reveals different coercive voltages to reorient 180° and the two types of 90° domains and the appearance of a different nanoscale 90° domain structure after poling. While the labyrinth structure is destroyed with relative low voltages, the created 90° domains structure persists, avoiding the formation of a single-domain structure. [ABSTRACT FROM AUTHOR]

Revealing strains on the unit-cell level is essential for understanding the particular performance of materials. Large-scale strain variations with a unit-cell resolution are important for studying ferroelectric materials since the spontaneous polarizations of such materials are strongly coupled with strains. Aberration-corrected high-angle-annular-dark-field scanning transmission electron microscopy (AC-HAADF-STEM) is not so sensitive to the sample thickness and therefore thickness gradients. Consequently it is extremely useful for large-scale strain determination, which can be readily extracted by geometrical phase analysis (GPA). Such a combination has various advantages: it is straightforward, accurate on the unit-cell scale, relatively insensitive to crystal orientation and therefore helpful for large-scale. We take a tetragonal ferroelectric PbTiO 3 film as an example in which large-scale strains are determined. Furthermore, based on the specific relationship between lattice rotation and spontaneous polarization ( P s ) at 180° domain-walls, the P s directions are identified, which makes the investigation of ferroelectric domain structures accurate and straightforward. This method is proposed to be suitable for investigating strain-related phenomena in other ferroelectric materials. [ABSTRACT FROM AUTHOR]

YCrO 3 thin films were deposited on Pt/Ta/glass substrates by pulsed laser deposition. X-ray diffraction experiments revealed that the YCrO 3 thin films were polycrystalline. The ferroelectric polarization of polycrystalline YCrO 3 thin films on glass substrate was smaller than that of polycrystalline YCrO 3 thin films on single crystalline Rh substrate. However, the ferromagnetism of YCrO 3 thin films on glass substrate was better than that of YCrO 3 thin films on the Rh substrate. The ferroelectric switching speed of the YCrO 3 thin films on glass substrate was faster than that of YCrO 3 thin films on Rh substrate. Atomic Force Microscopy (AFM) and Piezoelectric Force Microscopy (PFM) image showed the surface morphology and ferroelectric domain structure in YCrO 3 thin films respectively. [ABSTRACT FROM AUTHOR]

We report the ferroelectric properties of the epitaxial BiFeO 3 (BFO) thin films grown on Nb-doped SrTiO 3 substrates. The (001) and (111) BFO thin films were grown epitaxially on a single-crystalline (100) and (111) Nb-doped SrTiO 3 substrate by pulse laser deposition, respectively. The (111) BFO film gave higher remnant polarization in the ferroelectric hysteresis loop than that of the (001) film. The (001) and (111) BFO films revealed striped and mosaic ferroelectric domain structures, respectively. The ferroelectric domain size vs. film thickness was in accordance with the scaling law of Landau, Lifshitz and Kittel. The domains of the (001) BFO film were larger than those of the (111) BFO film. This is because the (111) BFO film has a relatively large remnant polarization, even though the (111) film has a lower domain wall energy. [ABSTRACT FROM AUTHOR]

We report an experimental study of the domain structure of ferroelectric YMnO3 and YMn0.9Fe0.1O3 using polycrystalline samples prepared by direct hydrothermal crystallisation at 240 °C, well below their structural phase transition temperatures. Powder X-ray diffraction shows the expected P63cm space group for both samples with an increase in a and a small decrease in c with Fe incorporation, consistent with an adjustment of MnO5 tilting, while XANES spectra at the Mn and Fe K edges show the oxidation state of both metals are maintained at +3 in the doped sample. High resolution TEM shows that curved stripe, annular and vortex domains can all be observed in the YMnO3 crystals, proving that the structural phase transition is not the only driving force for the occurrence of the annular and vortex domains. Furthermore, the absence of the annular and vortex domains in YMn0.9Fe0.1O3 indicates that the tilting state of MnO5 bipyramids plays an important role in the domain formation. Atomic resolution STEM images confirm that the ferroelectric domain walls correspond to structural antiphase boundaries similar to the crystals made via high temperature solid-state reactions. [ABSTRACT FROM AUTHOR]

Epitaxial CaBi 2 Nb 2 O 9 (CBNO) thin films were deposited on Nb-doped SrTiO 3 substrates. The CBNO thin films as a lead-free ferroelectric material exhibit a good ferroelectric property with the remanent polarization of 10.6 μC/cm 2 . In the fatigue resistance test, the CBNO thin films have no degradation in polarization up to 1×10 12 switching cycles, which is applicable for non-volatile ferroelectric random access memories (FeRAMs). Furthermore, piezoresponse force microscopy study (PFM) reveals that the CBNO thin films have larger ferroelectric domain structures than those of PbTiO 3 thin films. From the Landau, Lifshiftz, and Kittel׳s scaling law, it is inferred that the domain wall energy of CBNO thin films is probably very similar to that of the PbTiO 3 thin films. [ABSTRACT FROM AUTHOR]

Piezoresponse force microscopy (PFM) was employed to investigate ferroelectric domain structures and their dynamic behavior of lead magnesium niobate–lead titanate [Pb(Mg 1/3 Nb 2/3 )O 3 – x PbTiO 3 (PMN–PT)] transparent ceramics under an tip-bias-induced electric field. A remarkable effect of fluctuation of PT content on the domain configurations and domain dynamic response in PMN–PT transparent ferroelectric ceramics were found by PFM. Comparing with PMN–10%PT and PMN–20%PT, the reversed polarization of macrodomain area in PMN–35%PT and PMN–25%PT exhibits a relatively higher response behavior and better polarization retention performance under the PFM tip-bias-induced electric field, which correspond to their unique macroscopic electro-optic properties. [ABSTRACT FROM AUTHOR]

We investigated ferroelectric characteristics of BiFeO 3 (BFO) thin films on SrRuO 3 (SRO)/yttria-stabilized zirconia (YSZ)/glass substrates grown by pulsed laser deposition. YSZ buffer layers were employed to grow highly crystallized BFO thin films as well as SRO bottom electrodes on glass substrates. The BFO thin films exhibited good ferroelectric properties with a remanent polarization of 2 P r = 59.6 μC/cm 2 and fast switching behavior within about 125 ns. Piezoelectric force microscopy (PFM) study revealed that the BFO thin films have much smaller mosaic ferroelectric domain patterns than epitaxial BFO thin films on Nb:SrTiO 3 substrates. Presumably these small domain widths which originated from smaller domain energy give rise to the faster electrical switching behavior in comparison with the epitaxial BFO thin films on Nb:SrTiO 3 substrates. [ABSTRACT FROM AUTHOR]

Angle-resolved piezoresponse force microscopy (AR-PFM) was used in conjunction with electron backscatter diffraction (EBSD) to study ferroelectric domain structure in polycrystalline nearmorphotropic lead zirconate titanate (PZT). We introduce the details of AR-PFM including experimental method, the process to generate AR-PFM maps, and the interpretation of AR-PFM map, using domain patterns observed in bulk PZT. The spatial distortion caused by scanner creep and nonlinearity in scanning probe microscopy was corrected through image registration, taking advantage of the features present in topography images. Domain structures were mapped using AR-PFM data, and the maps consistently show alternating piezoresponse axes in a lamellar pattern of non-180° domain structure. Comparison of AR-PFM and EBSD data showed a discrepancy between the direction of lateral surface displacement and the in-plane polarization direction. Additionally, using suitable domain patterns, AR-PFM enabled discrimination between the tetragonal and rhombohedral phases at the sub-grain scale. [ABSTRACT FROM AUTHOR]

The recent discoveries of both chemical-driven and strain-driven morphotropic phase boundaries (Mobs) in BiFeO3(BFO) thin films have opened up new horizons in developing high-performance lead-free piezoelectrics. An attempt to bridge these two MPBs is made by doping La into highly strained BFO thin films with the coexistence of tetragonal-like and rhombohedral-like phases. The structural, morphological, and ferroelectric properties of such films are investigated. It is observed that La doping changes the energy landscape between the tetragonal-like and the rhombohedral-like polymorphs due to the chemical pressure imposed by the La substitution. Polar instability is found upon increasing La doping for the in-plane polarization component, which correlates with the vanishing of in-plane ferroelectric domain structures. The transition sequence of the in-plane ferroelectric polarization resembles that previously reported for the bulklike rhombohedral phase of BFO under continuous La doping, indicating the universality of the chemical-alloying effect on the ferroelectric order. [ABSTRACT FROM AUTHOR]

The 180° ferroelectric domain walls (FDWs) have long been regarded as purely Ising type in ferroelectrics, but recent theoretical works suggested that they can also have Néel- and/or Bloch-like rotations. Using a combination of first-principles calculations with phase-field simulations, we studied the 180° FDWs on different crystallographic planes in prototypical ferroelectric perovskite BaTiO3. The polarization profiles of 180° FDWs on (100) and (410) planes revealed that the (100)- and (410)-FDWs both exhibit Néel-like character besides their intrinsic Ising character, while the (410)-FDW also simultaneously shows a Bloch-like oblique of ∼6 nm, as a consequence of the deviation of polarization gradient from the high symmetry direction. Due to the existence of the Néel-like component of polarization, 180° FDWs in BaTiO3 exhibit a multilayer charge redistribution and thus may strongly trap charged defects. [ABSTRACT FROM AUTHOR]

Ferroelectric domains are engineered in lithium niobate crystals by scanning strongly absorbed UV laser light across the crystal surface. Focused UV laser light can not only write, but also erase previously written domains on the non-polar faces of lithium niobate, which allows tailoring of domain patterns. Such domain pattern was generated and afterward investigated by piezoresponse force microscopy and hydrofluoric acid etching. It was found that domains with dimensions down to 2 μm can be engineered, which was ∼30 % of the focus beam diameter (7 μm) used for writing the domains. Additionally, it was found that an unique domain depth profile can be formed, which is inclined to the crystallographic axes and can be described as 'half-crescent-shaped'. [ABSTRACT FROM AUTHOR]

Thin films of NaNbO3 have been grown under anisotropic tensile strain on orthorhombic (110) DyScO3 (DSO) substrates. Ferroelectric domain formation starts at about 6 nm film thickness and a periodic one‐dimensional pattern of type a1/a2/a1/a2 is formed with exclusive in‐plane electric polarization and individual domains aligned along the [001]DSO direction. With the onset of plastic strain relaxation at about 27 nm film thickness the one‐dimensional domain pattern transforms into a two‐dimensional array with domains aligned also along the $[1\bar 10]_{\rm DSO} $ direction and an additional out‐of‐plane component of the electrical polarization. With increasing film thickness the pseudocubic NaNbO3 unit cells exhibit an in‐plane monoclinic distortion which is very small for thin films and approaches the bulk value of 0.67° at film thicknesses larger than 130 nm. (© 2014 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) Part of Focus Issue on “Functional Oxides” (Eds.: T. Frauenheim, J. M. Knaup, P. Broqvist, S. Ramanathan) The ferroelectric domain structure in strained NaNbO3 thin films grown on DyScO3 substrate is investigated. Structural properties of the domains and direction of the polarization vector vary with film thickness and are connected to the onset of plastic strain relaxation. [ABSTRACT FROM AUTHOR]

Perfect (111)-oriented Pb(ZrTi)O (PZT) thin films were grown on cobalt ferrite buffered Pt(111)/Ti/SiO/Si substrate by pulsed laser deposition method using various targets with different Zr/Ti ratios ranging from 30/70 to 70/30. The results of X-ray diffraction analyses indicated that the composition of morphotropic phase boundary in the present PZT films is same as the bulk PZT (Zr/Ti = 52/48). The effect of Zr/Ti ratio of the PZT films was investigated by the ferroelectric domain structure and the piezoelectric characteristics of the films by piezoresponse force microscopy, as well as polarization measurement. The results revealed that the present tetragonal PZT film has a higher ferroelectric domain switching than rhombohedral one and the film with composition of Zr/Ti = 52/48 showed relatively high value of squareness of P-E loop and E as well as high piezoresponse. [ABSTRACT FROM AUTHOR]

Using conductive and piezoforce microscopy, we reveal a complex picture of electronic transport at weakly conductive 109° domain walls in bismuth ferrite films. Even once initial ferroelectric stripe domains are changed/erased, persistent conductive paths signal the original domain wall position. The conduction at such domain wall "footprints" is activated by domain movement and decays rapidly with time, but can be re-activated by opposite polarity voltage. The observed phenomena represent true leakage conduction rather than merely displacement currents. We propose a scenario of hopping transport in combination with thermionic injection over interfacial barriers controlled by the ferroelectric polarization. [ABSTRACT FROM AUTHOR]

We investigate magnetic domain wall (MDW) dynamics induced by applied electric fields in ferromagnetic-ferroelectric thin-film heterostructures. In contrast to conventional driving mechanisms where MDW motion is induced directly by magnetic fields or electric currents, MDW motion arises here as a result of strong pinning of MDWs onto ferroelectric domain walls (FDWs) via local strain coupling. By performing extensive micromagnetic simulations, we find several dynamical regimes, including instabilities such as spin wave emission and complex transformations of the MDW structure. In all cases, the time-averaged MDW velocity equals that of the FDW, indicating the absence of Walker breakdown. [ABSTRACT FROM AUTHOR]

We present a simple technique for fabricating quasi-periodic bulk sub-μm ferroelectric domain gratings in Rb-doped KTiOPO4 (RKTP) based on self-organized ferroelectric domain formation. One-dimensional ferroelectric domain structures, with an average periodicity of 650 ± 200 nm and extending throughout 1 mm thick crystals, are obtained by etching and subsequent electric field poling using planar electrodes. The sub-μm structures in RKTP were used to demonstrate 5th order non-collinear quasi-phase matched backward second harmonic generation. [ABSTRACT FROM AUTHOR]

The motion of ferroelectric domain walls (DWs) is critical for various applications of ferroelectric materials. One important question that is of interest both scientifically and technologically, is whether the ferroelectric DW has significant inertial response. To address this problem, we performed canonical ensemble molecular dynamics simulations of 180° and 90° DWs under applied electric fields. Examination of the evolution of the polarization and local structure of DWs reveals that they stop moving immediately after the removal of electric field. Thus, our computational study shows that ferroelectric DWs do not have significant intrinsic inertial response. [ABSTRACT FROM AUTHOR]

Ferroelectric domain structure evolution induced by an external electric 1eld was investigated by means of nematic liquid crystal (NLC) method in two strontium-barium niobate single crystals of nominal composition: Sr0.70Ba0.30Nb2O6 (SBN:70 -- relaxor) and Sr0.26Ba0.74Nb2O6 (SBN:26 -- ferroelectric). Our results provide evidence that the broad phase transition and frequency dispersion that are exhibited in SBN:70 crystal have a strong link to the con1guration of ferroelectric microdomains. The large leakage current revealed in SBN:26 may compensate internal charges acting as pinning centers for domain walls, which gives rise to a less restricted domain growth similar to that observed in classical ferroelectrics. Microscale studies of a switching process in conjunction with electrical measurements allowed us to establish a relationship between local properties of the domain dynamics and macroscopic response i.e., polarization hysteresis loop and dielectric properties. [ABSTRACT FROM AUTHOR]

The domain structure and its relation with the microstructure were studied in BST glass-ceramics with different concentration of AlF3additive using several microscopic methods. It was shown that the increase of the AlF3concentration led to larger grain size and smaller fraction of the glass regions. The piezoelectric force microscopy (PFM) domain contrast appeared after electric field poling. Larger PFM signal and higher fraction of the polarized grains were obtained for higher AlF3concentration. The grain aggregates polarized almost in one direction were revealed. Essential dependence of the domain structure of glass-ceramics on its microstructure was confirmed. [ABSTRACT FROM AUTHOR]

The theoretical model of the ferroelectric domain wall motion has been developed. It is demonstrated that for a proper phenomenon description it is necessary to consider the thermoelectroelasticity gradient terms. It is shown that in the linear approximation the general solution of three-dimensional problem in transversely isotropic thermoelectroelastic media can be obtained by means of five newly introduced harmonic potential functions. As an example of the proposed model applicability, the electroelastic field induced by a sphere (SPM tip) located near a plane boundary of two half-spaces is considered and described. [ABSTRACT FROM AUTHOR]

Domain switching in the vicinity of a crack tip is known as one of the major aspects of local nonlinear behavior of ferroelectrics, and it plays an important role in the fracture behavior. In the present paper, a fracture model based on a phase field continuum and a damage variable is presented to study the fracture behavior of ferroelectrics and its interaction with the domain structures. In this model the energy of fracture is regularized by the damage variable. When the damage variable equals one, it represents undamaged material. In this case, the energy reduces to the phase field potential with the spontaneous polarization being an order parameter, and the system of equations becomes the same as that of a conventional phase field continuum. When the damage variable becomes zero, it represents a crack region, and the potential becomes the energy density stored in the crack medium. The evolution of the damage variable is governed by a Ginzburg-Landau type equation. In this way, the fracture model can simulate the fracture behavior such as crack growth, kinking and formation, with no a priori assumption on fracture criteria and predefined crack paths. The model is implemented in a 2D Finite Element Method in combination with implicit time integration and non-linear Newton iteration. As example, the fracture model is used to simulate the fracture of an edge crack in a ferroelectric single crystal under mechanical mode-I loading. In the simulation crack propagation, kinking and formation are observed. In particular, the results show the interaction between the domain structure evolution and the crack propagation. [ABSTRACT FROM AUTHOR]

• Large piezoelectric coefficient. • Island-like regions in bismuth ferrite oxide compound. • The micrometric size islands are polycrystalline. • Island formation reduces the substrate clamping effect. • Polarization fatigue on ferroelectric island-like regions. We investigate the piezoelectric and ferroelectric properties in island-like ferroelectric regions of bismuth ferrite oxide films. Samples were synthesized by the simultaneous laser ablation of bismuth, and iron oxide targets. Bismuth content in the deposited films was controlled with the plasma density (N p) that is produced during the ablation of the Bi target. A change in the N pBi alters the Bi incorporation into the films. Relatively homogeneous films deposited at N pBi of 11 × 1012 cm−3 with an effective piezoelectric coefficient (d eff) of ~15 pm/V served as the starting point. A reduction of N pBi at 2 × 1012 cm−3 produced films with almost null piezoelectrical response but at 4 × 1012 cm−3 caused the formation of island-like ferroelectric regions with large d eff values that spans from 70 to 108 pm/V. The island-like regions presented upright hysteretic phase-switching loops with low coercive voltages and squareness values close to unity. The resulting large d eff values were attributed to the reduction of the substrate-clamping effect, the (001)-textured BiFeO 3 structure, and the coexistence of secondary phases with the main BiFeO 3 phase. The mechanisms for polarization switching and the electromechanical response of the island-like regions are discussed. Finally, some preliminary results of ferroelectric fatigue experiments in island-like regions are presented. [ABSTRACT FROM AUTHOR]

A novel confocal second harmonic generation (SHG) interference microscope with a transmission optical system is devised. This microscope is a kind of SHG tomography which provides us 3-dimensional images of heterogeneous structures in polar materials in non-destructive way. We apply successfully this microscope to observations of periodically poled domain structures in quasi-phase matching devices. [ABSTRACT FROM AUTHOR]

The crystallographic features of the ferroelectric domain structures in (Sr1-xBax)Bi2Ta2O9 single crystals have been examined by transmission electron microscopy. The unique 90° domain structures were found in these single crystals. In SrBi2Ta2O9 with x = 0, particularly the majority domains with the ±[110]t polarization vectors in the tetragonal notation are divided by the minority ones with the ±[1 &1macr; 0]t vectors, which were observed as a curved-line contrast in dark field images. [ABSTRACT FROM AUTHOR]

The crystallographic features of the ferroelectric domain structures in (Sr1-xBax)Bi2Ta2O9 single crystals have been examined by transmission electron microscopy. The unique 90° domain structures were found in these single crystals. In SrBi2Ta2O9 with x = 0, particularly the majority domains with the ±[110]t polarization vectors in the tetragonal notation are divided by the minority ones with the ±[1 &1macr; 0]t vectors, which were observed as a curved-line contrast in dark field images. [ABSTRACT FROM AUTHOR]

The stability and evolution of ferroelectric domain structures in thin films are studied. Elastic solutions are derived for both elastically anisotropic and isotropic thin films with arbitrary domain structures, subject to the mixed stress-free and constraint boundary conditions. These solutions are employed in a three-dimensional phase-field model to investigate simultaneously the effect of substrate constraint and temperature on the volume fractions of domain variants, domain-wall orientations, surface topology, domain shapes, and their temporal evolution for a cubic-to-tetragonal ferroelectric phase transition. A specific example of a [001] orientated film heteroepitaxially grown on a [001] cubic substrate is considered. It is shown that the shapes of a-domains with tetragonal axes parallel to the film surface are significantly different from those of c-domains with tetragonal axes perpendicular to the film surface. For the substrate constraints and temperatures under which both a- and c-domains coexist, both types of a-domains are present with their tetragonal axes perpendicular to each other, and the domain wall orientations deviate from the 45 orientation generally assumed in thermodynamic analyses. It is demonstrated that a substrate constraint results in sequential nucleation and growth of different tetragonal domains during a ferroelectric phase transition. [ABSTRACT FROM AUTHOR]

To form tetragonally strained PbTiO 3 (PTO) thin films, PTO thin films were deposited on single-crystal Rh substrates using pulsed laser deposition (PLD). Reducing the PLD deposition rate could further increase the tetragonal strain of the PTO thin films, improve the crystallinity due to the layer-by-layer growth of the films, and improve their ferroelectric and piezoelectric properties. From the time-dependent ferroelectric switching current curves of the PTO capacitors, it was confirmed that the switching speed of the ferroelectric polarization increases as the crystallinity of the thin film improves. In particular, it was confirmed that the band gap could be increased due to the tetragonal strains formed by the lattice misfit between PTO and Rh, which supports the good leakage current characteristics of the PTO films with relatively large tetragonal strains. • The tetragonally strained PbTiO 3 thin films on Rh substrates showed improved ferroelectric and piezoelectric properties. • The crystallinity of the PbTiO 3 thin films have been improved due to layer-by-layer growth mode. • The band gap of the PbTiO 3 is increased by the tetragonally strained. • Ferroelectricity and leakage current characteristics improve as the band gap of PbTiO 3 increases. [ABSTRACT FROM AUTHOR]