Pole Mechanism Research Articles

Ferroelectric domain engineering with femtosecond pulses of different wavelengths.

Direct femtosecond laser writing of ferroelectric domain structures has been an indispensable technique for engineering the second-order optical nonlinearity of materials in three dimensions. It utilizes localized thermoelectric field motivated by nonlinear absorption at the position of laser focus to manipulate domains. However, the impact of laser wavelengths, which is pivotal in nonlinear absorption, on the inverted domains is still sketchy. Herein, the light-induced ferroelectric domain inversion is experimentally studied. It is shown that the domain inversions can be achieved over a broad spectral range, but the optical threshold for domain inversion varies dramatically with the laser wavelength, which can be explained by considering the physical mechanism of femtosecond laser poling and nonlinear absorption properties of the crystal. Meanwhile, the effects of other laser processing parameters are also experimentally investigated. Our findings are useful to guide the fabrication of high-performance optical and electronic devices based on ferroelectric domains.

Exotic role of poling protocol on augmentation of magnetoelectricity in BCZT/CNZF layered composites

Here, we report exotic role of electrical poling of layered BCZT-CNZF bulk composite for a sustainable advancement of magnetoelectric (ME) technology. Practically, it seems quite difficult to access full potential of ME composites due to their weak ME coupling performances. Using a standard poling protocols, we successfully deployed coupling performance of laminated ME composite, comprises of ferroelectric (FE) layer of BCZT and a ferrite layer of CNZF. However, the ME coupling constant of laminated composite is optimized by lowering volume fraction of FE component to strengthen the mechanical strain in piezoelectric layer, while fixing the thickness of the magnetostrictive ferrite layer. Here, we employed systematic zero field cooled (ZFC) and field cooled (FC) electrical poling protocol on morphotropic phase boundary (MPB) based BCZT composition, well-appreciated for it’s remarkable electromechanical activity. We report a record augmentation in magnetoelectric coupling as a consequence of prudent field cooled poling mechanism. On the basis of our findings, we emphasize that the degree of magnetoelectricity may be significantly improved for miniaturization of efficient devices via proper execution of poling technique.

Enhanced tensile properties and intersecting nanotwins formation mechanism of Ti44Al48Nb8 alloy via electromagnetic levitation processing

Combining the electromagnetic levitation (EML) method with materials processing techniques (pressure die-casting and copper mold solidification), bulk Ti44Al48Nb8 alloy samples with different shapes were prepared, and their microstructure evolution, tensile properties and deformation behavior were systematically investigated. Assisted with a double aberration corrected transmission electron microscope (TEM) and molecular dynamics (MD) simulation, three types of intersecting nanotwins were observed and the formation mechanism of step-like and intersecting nanotwins under both tensile loading and at highly undercooled state were discussed. For the 35 g cone-shaped Ti44Al48Nb8 sample by EML, the microstructure consists of lamellar α2-Ti3Al+γ-TiAl matrix, Nb-rich and Al-rich region, showing a typical peritectic morphology. The average grain size has been significantly reduced after levitation die-casting and copper mold casting, due to the relatively high cooling rate and external stress. The rapidly solidified microstructure of a 0.6 g sample undercooled at 61 K has the similar microstructure with large samples. With the increase of bulk undercooling at 300 K, elemental segregation has been effectively inhibited and the intersecting nanotwins were formed, which shows a unique hierarchical structure. The samples processed by copper-mold casting have good tensile properties, which can be attributed to the refined microstructure, the generation of dislocation and stacking faults, and the formation of intersecting nanotwins. Based on the results of MD simulation and atomic-scale quasi-in-situ TEM observation, the analogous dissociation of dislocation dominated by pole mechanism occurs, resulting in the formation of 1/6<112> Shockley partial dislocation, 1/6<110> stair-rod dislocation and 1/3<111> Frank partial dislocation. When samples were highly undercooled, the generated internal stress can facilitate twinning at a much lower stress level, which can be beneficial for the formation of nanotwins at undercooled state.

High-performance and high-thermally stable PSN-PZT piezoelectric ceramics achieved by high-temperature poling

• A universal and practical method of high-temperature poling is put up forward. • Great comprehensive properties are obtained: d 33 = 562 pC/N and T C = 350 °C. • The mechanism of high-temperature poling is clarified. • High-temperature poling remarkably promote temperature stability of properties. High piezoelectric properties and superior thermal stability are both important indicators of piezoelectric ceramics serving at high temperature. However, since these properties are usually mutually exclusive, high performance and superior thermal stability are hard to achieve simultaneously. Here we report that a high piezoelectricity ( d 33 ∼ 562 pC/N) and superior thermal stability (the variation is within 7% from 20 to 330 °C) were both achieved in 0.4 mol% ZnO-doped 0.02Pb(Sb 1/2 Nb 1/2 )-0.51PbZrO 3 –0.47PbTiO 3 by high-temperature poling. Compared with traditional poling method, high-temperature poling method forms a small-sized and highly oriented domain structure, which can effectively improve the piezoelectric and dielectric properties of piezoelectric ceramics. At the same time, the enhanced pinning effect of defect ions and stabilized domain structure due to high-temperature poling also contribute to the superior temperature stability of the piezoelectric and dielectric properties. This work provides an effective method for designing piezoelectric materials with high performance and good temperature stability for high temperature sensor applications.

Newer insights into the discrimination of pole mechanisms of twinning in a face-centered cubic high-Mn steel

Mechanism of deformation twinning during tensile straining of an Fe-0.013C-29Mn-2.4Al steel is reported. Transmission electron microscopy examinations revealed that twinning occurred through a modified pole mechanism proposed by Niewczas and Saada. In this mechanism, twinning Shockley partial dislocations and their stacking faults are formed through interaction among the prismatic dislocations with Frank partials of the Frank dipoles. The activation of the observed pole mechanism was explained through the length of the sessile Frank partials.

Non-Invasive Visualization of Ferroelectric Domain Structures on the Non-Polar y-Surface of KTiOPO4 via Raman Imaging

Potassium titanyl phosphate (KTP) is a nonlinear optical material with applications in high-power frequency conversion or quasi-phase matching in submicron period domain grids. A prerequisite for these applications is a precise control and understanding of the poling mechanisms to enable the fabrication of high-grade domain grids. In contrast to the widely used material lithium niobate, the domain growth in KTP is less studied, because many standard methods, such as selective etching or polarization microscopy, provides less insight or are not applicable on non-polar surfaces, respectively. In this work, we present results of confocal Raman-spectroscopy of the ferroelectric domain structure in KTP. This analytical method allows for the visualization of domain grids of the non-polar KTP y-face and therefore more insight into the domain-growth and -structure in KTP, which can be used for improved domain fabrication.

Second‐Order Optical Response in Electrically Polarized Sodo‐Niobate Amorphous Thin Films: Particularity of Multilayer Systems

Herein, our attention is focused on the second‐order optical properties of thermally poled sodo‐niobate amorphous thin films through an original methodology that combines both macroscopic and microscopic second harmonic generation techniques. By probing the geometry and the magnitude of the second‐order nonlinear (SONL) optical response at different scales, a key aspect of thin film's poling mechanisms compared with bulk glasses is demonstrated that lies in the appearance of a charge accumulation at the film/substrate interface and that is described by the Maxwell–Wagner effect. A way to minimize this effect is then proven by promoting an induced built‐in static field in the plane of the film using a microstructured electrode. A SONL optical susceptibility as high as 29 pm V−1 is measured and its geometry and location are controlled at the micrometer scale; it constitutes an improvement of at least one order of magnitude compared with other poled amorphous inorganic materials and is comparable with that of lithium niobate single crystal.

Estimation of second harmonic generation intensity-noise in random periodically poled lithium niobate

Periodically poled lithium niobate (PPLN) predominantly has a random duty-cycle error (RDE), latent in them by virtue of poling mechanism. This error needs to be quantitatively predicted to abstain from parasitic harmonic generation. In this paper, we have calculated the influence of the RDEs degenerate noise in second-harmonic generation (SHG) consisting of PPLN. Here, we propose a method for calculating the random domain-wall distribution statistics by the SHG. We explored the equivalence between the statistics of random domain distribution by SHG and far-field diffraction pattern method.

The role of dielectric breakdown in the electro-thermal poling of D263T glass

Electro-thermal poling of a technical glass containing mobile Na+ and K+ ions is investigated in an experiment. Ex-situ analysis of the concentration profiles by means of ToF-SIMS demonstrates the formation of two zones; a zone depleted of both Na+ and K+ ions and a zone where K+ has been enriched above the bulk concentration. Theoretical analysis by means of Monte Carlo calculations are capable of rationalizing these profiles. The key to the mechanism of poling is the transient dielectric breakdown of the material leading to ejection of electrons into the anode and depletion of cations towards the cathode leaving an electroneutral zone behind.

Enhancement of pyroelectric catalysis of ferroelectric BaTiO3 crystal: The action mechanism of electric poling

In this work, the commercial BaTiO3 crystal was cut into the same wafers along (101) crystal plane. These wafers were poled under various poling fields to study the effect of electric poling on the pyroelectric catalysis performance during the process of dye decomposition. Under 140 cold-hot (28 - 60 °C) cycles, the dye decomposition ratio using the unpoled BaTiO3 catalyst is close to 0, whereas it reaches ~ 56% using the BaTiO3 poled under a poling field of ~5.00 kV/mm. The poling treatment shows a great influence on the pyroelectric catalysis since it directly affects the number of charges generated on the surface of BaTiO3 crystal under the external temperature variation excitation. The generation of these middle product hydroxyl radicals further proves the reaction mechanism of the pyroelectric catalysis. The good catalysis and recyclability performance suggests the poled BaTiO3 pyroelectric crystal is an potential material in dye wastewater remediation through utilizing room-temperature thermal energy.

Thermal poling induced second-order optical nonlinearity in phosphosilicate glass thin films

ABSTRACTA phosphosilicate glass (PSG) nonlinear film is prepared on a fused silica plate using plasma- enhanced chemical vapour deposition (PECVD) and thermal poling. Under all poling conditions, the second-harmonic generation (SHG) signals of the PSG thin-film samples are stronger than those of pristine fused silica. The poling mechanism can be well explained qualitatively by the electric-field induced second-harmonic generation (EFISH) and dipole reorientation models. The hindering effect of the film-glass interface is also observed. Besides, the threshold poling temperature (To), poling voltage (Vo) and poling duration (to) of the PSG thin-film samples are all smaller than those of pristine fused silica, which may be ascribed to less dense PSG films. The nonlinear profile of the PSG thin-film sample is distributed in the whole film and the partial glass substrate on the anodic side of the sample. The second-order nonlinear susceptibility (χ(2)) is around 0.58 and 0.32 pm/V, respectively.

In Situ Neutron Diffraction Studies on Poling of the Hard PZT Ceramic PIC181

The poling of hard Lead Zirconate Titanate (PZT) materials is a complex process requiring optimisation of the poling parameters time, temperature, and electric field magnitude. A unique method is presented to monitor the poling process in operando on the unit cell level with neutron diffraction through the analysis of changes in reflection patterns. Diffraction analysis after poling reveals the lattice and domain contributions using poling strain as a measure. This allows for the evaluation of induced dipole alignment and process efficiency. It gives insight into the role of domain wall motions in hard PZT ceramics and how they are affected by poling parameters. Additionally, a poled sample is cycled bipolar and analyzed. It shows a strongly asymmetric strain hysteresis with major contributions from domain wall motions in the tetragonal phase. Macroscopically measured hysteresis loops verify the findings from diffraction. The present work contributes to improving poling results, efficiency and saving energy. The diffraction analysis allows a novel investigation method of the poling mechanisms and provides extensive results that give new insights into the material behavior. With a fundamental research method, this work reveals unprecedented details that can be directly applied to the specific application field of poling technology.

Effect of sodium addition and thermal annealing on second-order optical nonlinearity in thermally poled amorphous Ta2O5 thin films

We demonstrate second-order optical nonlinearity (SON) induced in amorphous tantalum pentoxide (Ta2O5) films by thermal poling. The effects of sodium addition and thermal annealing on the efficiency and stability of second harmonic generation (SHG) have been investigated. Maker fringe analysis has been used to quantify the poling-induced SON. χ(2) of 0.46 ± 0.02 pm/V and 0.34 ± 0.02 pm/V was achieved for sodium-containing and pure Ta2O5 films, respectively. Both the strength and the temporal stability of the induced nonlinearity are discussed with respect to the poling mechanisms and measured electrical conductivity. The lower density of uncombined charges of the Ta2O5 thin films is believed to play a role in the strength of SHG signal, and the rate of SHG decay decreases with thermal annealing.

Deformation and annealing behaviour of dual phase TWIP steel from the perspective of residual stress, faults, microstructures and mechanical properties

The present study aims to examine the deformation and annealing behaviour of Fe–0.07C–20Mn–2.6Si–1.6Al TWIP steel in the viewpoint of microstructural characterisation, fault analysis, triaxial residual stress measurement and mechanism of twin formation. 50% cold deformation results in improvement of hardness and tensile strength (428 HV and 1419 MPa, respectively), whereas annealing at 900 °C of the same leads to improvement in ductility (61%) with the decrease in strength (873 MPa). The residual stress is maximum and compressive in nature in deformed sample which has been diminishing after annealing. Hot rolled and hot rolled-solution treated samples develop dual phase microstructure along with annealing twins, whereas fine nano twins and high dislocation density with dual phase microstructure are apparent after 50% cold deformation. The presence of Shockley partial dislocation, overlapping of stacking faults, Lomer-Cottrell lock, intrinsic and extrinsic stacking faults affect the mechanical properties as obstacles of dislocation movements or assisting twin formation. Goss and Brass components of texture are dominating after rolling, whereas annealing results in weakening of rolling texture components. The nucleation mechanism of twin has been consistent with the pole mechanism along with the deviation process. Hence the present work amplifies the present understanding of deformation and annealing behaviour on low carbon dual phase TWIP steel from different characterisation perspectives.

Investigation of nanoscale twinning in an advanced high manganese twinning-induced plasticity steel

A twinning induced plasticity (TWIP) steel, developed for automotive applications, was characterized down to the nanoscale to investigate the nature of the strengthening mechanisms. Both tensile-deformed and non-deformed materials were studied by light optical microscopy, X-ray diffraction, electron backscatter diffraction, and transmission electron microscopy. The investigated TWIP steel showed extensive twinning upon deformation. With high-resolution transmission electron microscopy, nano-twins as small as 3 nm in width were observed, and large-angle convergent-beam electron diffraction identified the pole mechanism as one of the twinning mechanisms in this TWIP steel. This study emphasizes that a thoughtful combination of techniques is necessary to fully capture the microstructure of this TWIP steel and explain the origin of superior mechanical properties compared to other TWIP steel grades.

Enhanced piezoelectricity in plastically deformed nearly amorphous Bi12TiO20-BaTiO3 nanocomposites

Bulk Bi12TiO20-BaTiO3 (BTO-BT) nanocomposites are fabricated through the high-temperature interfacial reaction between nanometer-sized BaTiO3 particles and melting Bi12TiO20. Although the obtained BTO-BT nanocomposites are nearly amorphous and display very weak ferroelectricity, they exhibit relatively strong piezoelectricity without undergoing the electrical poling process. The volume fraction of crystalline Bi12TiO20 is reduced to less than 10%, and the piezoelectric constant d33 is enhanced to 13 pC/N. Only the presence of the macroscopic polar amorphous phases can explain this unusual thermal stable piezoelectricity. Combining the results from X-ray diffraction, Raman spectroscopy, and thermal annealing, it can be confirmed that the formation of macroscopic polar amorphous phases is closely related to the inhomogeneous plastic deformation of the amorphous Bi12TiO20 during the sintering process. These results highlight the key role of plastically deformed amorphous Bi12TiO20 in the Bi12TiO20-based polar composites, and the temperature gradient driven coupling between the plastic strain gradient and polarization in amorphous phases is the main poling mechanism for this special type of bulk polar material.

Optical fiber poling by induction: analysis by 2D numerical modeling.

Since their first demonstration some 25 years ago, thermally poled silica fibers have been used to realize device functions such as electro-optic modulation, switching, polarization-entangled photons, and optical frequency conversion with a number of advantages over bulk free-space components. We have recently developed an innovative induction poling technique that could allow for the development of complex microstructured fiber geometries for highly efficient χ(2)-based device applications. To systematically implement these more advanced poled fiber designs, we report here the development of comprehensive numerical models of the induction poling mechanism itself via two-dimensional (2D) simulations of ion migration and space-charge region formation using finite element analysis.

Amorphous phases and composition dependence of piezoelectricity in BaTiO3–Bi2O3 polar amorphous ceramics

Composite ceramics with the nominal formula BaTiO3–xBi2O3 (x=0.15, 0.2, 0.25, 0.5, 0.667 and (1) were sintered under a small thermal gradient. After sintering, the monoclinic α Bi2O3 changed into cubic Bi12TiO20 and a very small amount of rhombohedral Bi8.11Ba0.89O13.05 in the x=0.2–1 samples; both direct and converse piezoelectric effects were observed for these samples without undergoing the electrical poling process. Because these composites do not contain obviously oriented grains and their piezoelectricity does not depend on ferroelectricity, temperature gradient-driven plastic flexoelectricity of the grain boundary amorphous phases may be the main poling mechanism. In this study, the largest value of the d33 piezoelectric constant of approximately 12pC/N was found in the x=0.667 sample; this sample also exhibits the highest amorphous content. The depoling temperature of this type of polar material is determined solely by the melting temperature of Bi12TiO20, favoring the potential use of these composites as piezoelectric materials for high-temperature applications.

Effect of poling on nanodomains and nanoscale structure in A-site disordered lead-free piezoelectric Na0.5Bi0.5TiO3–BaTiO3

This paper establishes the nanoscale poling mechanism operating in A-site disordered lead-free piezoelectric ceramics. Nanoscale domain maps and quantitative structural changes were obtained by deploying high-resolution transmission electron microscopy, dielectric spectroscopy, Raman spectroscopy and neutron scattering. Based on these results a microscopic model is proposed that provides insight into the E-field induced structural transformation. The stripe-like nanodomains in the unpoled system transformed into lamellar tetragonal domains with a reduced degree of displacement disorder during poling. It is proposed that the synergic effect of change in octahedral tilt disorder and cation displacement disorder leads to this transformation under an E-field. The criterion for achieving superior functional response includes stabilization of the long range order and reduction in the tilt disorder through compositional adjustments. Understanding of the poling mechanism in lead-free piezoelectric materials has been mostly limited to the behavior of domains under an applied field. However, this work provides an in-depth understanding of the changes in the local structure along with domain morphology under an applied field.

Correlation of macroscopic and structural properties in Piezoceramics

Piezoelectric ceramics exhibit the remarkable property to couple elastic strain and polarization under the influence of an applied electric field. Among the various types of ferroelectric devices only actuators rely on high electric fields to generate high strains and forces. Prominent examples for actuators are multilayer stack actuators used for nanopositioning or in modern combustion engines for automobiles to control injection cycles. Despite extensive studies and elaborated measurement techniques, the correlation between macroscopic strain and structural response is still not fully understood. Most of the relevant systems found up to now are compositions close to phase boundaries linking highly correlated phases. This results in major challenges for structural analyses due to overlapping reflections. Apart from the well-known field induced structural responses such as domain switching and the piezoelectric effect we recently identified field induced phase transitions in different systems as an additional poling mechanism [1,2]. In this contribution we present a structural analysis of in situ powder diffraction data that is capable of resolving all three involved poling mechanisms within only one experiment. The key to obtain enough information for such an analysis is a combination of high resolution and a broad Q-range, together with different sample orientations. This can be done with either X-ray or Neutron powder diffraction. The results not only separately reveal the contributions of each poling mechanism to the macroscopic strain, but also different behaviours of the individual phases. Several studies on lead containing as well as lead free systems showed significant changes while crossing the phase boundaries. Additionally, the calculation of the elastic strain perfectly matches the macroscopic observations, confirming the accuracy of the applied models.