Field-induced Changes Research Articles

Synergistic contributions of the poling field-induced changes in local structure on the piezoelectric properties of modified BaTiO3 system

Abstract Local structural heterogeneity is a key factor in improving the piezoelectric properties of non-centrosymmetric piezoelectric systems. This work investigates electric field-induced structural and microstructural changes at localized and average scales to elucidate the structure-property correlations that enhance piezoelectric performance in Sn-doped BaTiO3 systems exhibiting coexisting phase boundaries. Despite showing field-induced structural phase transformation, the sample displays variations in piezocoefficient values with the nature of phase boundary compositions. Raman spectroscopy measurements reveal that the TiO6/SnO6 octahedra near the tetragonal-orthorhombic phase boundary exhibit significantly greater poling field-induced structural heterogeneities in local structure compared to those near the orthorhombic-cubic phase boundary. X-ray absorption spectroscopic results on Ti and Sn K-edge in unpoled and poled samples reveal that the dipolar contribution responsible for the piezoelectricity originates from field-induced distortion associated with both TiO6 and SnO6 octahedra. Near the vicinity of the tetragonal-orthorhombic phase boundary, both the TiO6 and SnO6 contributions are cumulative and exhibit better piezoelectricity. On the other hand, at the orthorhombic-cubic phase boundary, the dipolar contributions from these octahedra are counterintuitive, resulting in a reduction of piezoelectricity. These results could provide a pathway to design materials with an enhanced piezoelectric response by considering various phase boundary aspects before applying a poling field prior to making them piezoactive.

Electric fields imbue enzyme reactivity by aligning active site fragment orbitals

It is broadly recognized that intramolecular electric fields, produced by the protein scaffold and acting on the active site, facilitate enzymatic catalysis. This field effect can be described by several theoretical models, each of which is intuitive to varying degrees. In this contribution, we show that a fundamental effect of electric fields is to generate electrostatic potentials that facilitate the energetic alignment of reactant frontier orbitals. We apply this model to demystify the impact of electric fields on high-valent iron-oxo heme proteins: catalases, peroxidases, and peroxygenases/monooxygenases. Specifically, we show that this model easily accounts for the observed field-induced changes to the spin distribution within peroxidase active sites and explains the transition between epoxidation and hydroxylation pathways seen in Cytochrome P450 active site models. Thus, for the intuitive interpretation of the chemical effect of the field, the strategy involves analyzing the response of the orbitals of active site fragments, and their energetic alignment. We note that the energy difference between fragment orbitals involved in charge redistribution acts as a measure for the chemical hardness/softness of the reactive complex. This measure, and its sensitivity to electric fields, offers a single parameter model from which to quantitatively assess the effects of electric fields on reactivity and selectivity. Thus, the model provides an additional perspective to describe electrostatic preorganization and offers ways for its manipulation.

Evaluating the Ability of External Electric Fields to Accelerate Reactions in Solution.

This study investigates the catalytic effects of external electric fields (EEFs) on two reactions in solution: the Menshutkin reaction and the Chapman rearrangement. Utilizing a scanning tunneling microscope-based break-junction (STM-BJ) setup and monitoring reaction rates through high-performance liquid chromatography connected to a UV detector (HPLC-UV) and ultraperformance liquid chromatography coupled with quadrupole time-of-flight mass spectrometry (UPLC-q-ToF-MS), we observed no rate enhancement for either reaction under ambient conditions. Density functional theory (DFT) calculations indicate that electric field-induced changes in reactant orientation and the minimization of activation energy are crucial factors in determining the efficacy of EEF-driven catalysis. Our findings suggest that the current experimental setups and field strengths are insufficient to catalyze these reactions, underscoring the importance of these criteria in assessing the reaction candidates.

Modulating allergenicity of prawn tropomyosin (penaeus chinensis) via pulsed electric field-induced conformational changes

The effect of electric field intensities (EFIs, 5–20 kV/cm) and treatment times (0.5–2 h) on allergenicity and spatial conformation of prawn tropomyosin was evaluated. The results demonstrated that the IgG and IgE binding capacity of tropomyosin maximally increased by 24.34 % and 29.16 % respectively, followed by a subsequent decrease after 20 kV/cm treatment for 1 h. Interestingly, 5–10 kV/cm treatments significantly decreased the α-helix content (P < 0.05) and fluorescence intensity, while 20 kV/cm treatment promoted extensive spiralization, resulting in a tightly packed structure. The increased flexibility further exposed the hydrolysis sites and strengthened the gastrointestinal digestibility of tropomyosin. Additionally, molecular dynamic simulation indicated that extended EFIs increased structural flexibility and depolymerized the tropomyosin dimers through destroying intermolecular hydrogen bonds (formed within arginine and glutamate), which allowed tropomyosin to be easily recognized by IgG/IgE. Whereas, decrease of solvent-accessibility surface area (SASA), hydrophobic surface area induced conformation folded and caused epitopes masked.

AC electric field-induced changes in viscosity of aqueous ceramic suspensions and tuning of freeze-cast microstructure and compressive strength

A systematic parametric study was conducted on alternating current (AC) electric field-assisted freeze-casting to enable a comprehensive understanding of tuning freeze-cast microstructure and compressive strength and provide insights into the role of AC field. A novel finding was that the AC field increased the viscosity of aqueous ceramic suspensions, where the viscosity increase was dependent on the ceramic loading of suspensions, dispersant concentration, and field duration. Viscosity increased with field duration for a fixed solid loading and dispersant concentration. It was suggested that AC field-induced dielectrophoretic (DEP) forces decreased interparticle distances and increased interparticle interactions in ceramic suspensions, hence viscosity. It was revealed that the increase in viscosity of ceramic suspensions due to the AC field could be reversed. It was demonstrated that simple magnetic stirring of the suspensions previously subjected to an AC field (which increased viscosity) reduced viscosity to the level of the as-prepared suspensions. For materials fabrication, an AC electric field was applied to aqueous ceramic suspensions for the desired duration, then turned OFF, followed by freeze-casting, which remarkably influenced freeze-cast sintered microstructure. The impact of the field on microstructure increased with solid loading, dispersant concentration, and field duration, and microstructure changes were associated with viscosity of suspensions prior to freeze-casting. With increasing viscosity, freeze-cast microstructure became increasingly dendritic, i.e., bridge density increased. A positive correlation was observed between bridge density and compressive strength for all the materials. Depending on the solid loading, dispersant concentration, and field duration, about 5- to 8-fold increase in strength was achieved.

Relative profile measurements in 1.5T MR-linacs: investigation of central axis deviations

Objective. In 1.5 T MR-linacs, the absorbed dose central axis (CAX) deviates from the beam's CAX due to inherent profile asymmetry. In addition, a measured CAX deviation may be biased due to potential lateral (to the beam) effective point of measurement (EPOML) shifts of the detector employed. By investigating CAX deviations, the scope of this study is to determine a set ofEPOMLshifts for profile measurements in 1.5 T MR-linacs.Approach. The Semiflex 3D ion chamber and microDiamond detector (PTW, Germany) were considered in the experimental study while three more detectors were included in the Monte Carlo (MC) study. CAX deviations in the crossline and inline profiles were calculated based on inflection points of the 10×10 cm2field, at five centers. In MC simulations, the experimental setup was reproduced. A small water voxel was simulated to calculate CAX deviation without the impact of the detector-specificEPOMLshift.Main results. All measurements were consistent among the five centers. MC-based and experimental measurements were in agreement within uncertainties. Placing the microDiamond in the vertical orientation does not appear to affect the detector'sEPOML, which is on its central longitudinal axis. For the Semiflex 3D in the crossline direction, the CAX deviation was 2.3 mm, i.e. 1 mm larger than the ones measured using the microDiamond and simulated considering the ideal water detector. Thus, anEPOMLshift of 1 mm is recommended for crossline profile measurements under both Semiflex 3D orientations. For the inline profile, anEPOMLshift of -0.5 mm was determined only for the parallel configuration. In the MC study, CAX deviations were found detector- and orientation-dependent. The dead volume is responsible for theEPOMLshift only in the inline profile and under the parallel orientation.Significance. This work contributes to data availability on the correction or mitigation of the magnetic field-induced changes in the detectors' response.

Investigation of the effect of martensitic phase transition temperature and Curie temperature difference on magnetic and magnetocaloric properties under low magnetic field on Si-doped Ni-Mn-In Heusler alloys

This study examines the impact of substituting Si for Mn on the structural, magnetic, and magnetocaloric properties of Ni43Mn46−x Si x In11 (x = 0.3 and 0.6) alloys. To this end, a range of analytical techniques are employed, including scanning electron microscopy (SEM), room temperature x-ray powder diffraction (XRD), and magnetization measurements. Above the martensitic transition temperature, the Ni43Mn46−x Si x In11 alloys exhibit cubic L2 1 (space group FM-3M). Below this temperature they adopt a tetragonal L1 0 (space group I4/mmm). The martensitic transition temperature decreased when Si is substituted for Mn. The magnetic field-induced entropy change is calculated from magnetic field-dependent magnetization measurements using Maxwell’s equations. The maximum magnetic field-induced entropy changes for Ni43.16Mn45.56Si0.29In11 and Ni43.51Mn44.82Si0.59In11 alloys are calculated 8.20 J kg−1K−1 and 3.15 J kg−1 K−1, respectively, in the vicinity of the magnetostructural phase transition for a magnetic field change of 18 kOe. It is demonstrated that the temperature differential between the high-temperature austenite phase's Curie point (T C ) and the mean martensitic transformation temperature (T M ), namely (T M -T C ), influences the martensitic transition temperatures and, consequently, on the magnetic field-induced entropy change (ΔS M ).

Non-equilibrium transport in polymer mixed ionic-electronic conductors at ultrahigh charge densities.

Conducting polymers are mixed ionic-electronic conductors that are emerging candidates for neuromorphic computing, bioelectronics and thermoelectrics. However, fundamental aspects of their many-body correlated electron-ion transport physics remain poorly understood. Here we show that in p-type organic electrochemical transistors it is possible to remove all of the electrons from the valence band and even access deeper bands without degradation. By adding a second, field-effect gate electrode, additional electrons or holes can be injected at set doping states. Under conditions where the counterions are unable to equilibrate in response to field-induced changes in the electronic carrier density, we observe surprising, non-equilibrium transport signatures that provide unique insights into the interaction-driven formation of a frozen, soft Coulomb gap in the density of states. Our work identifies new strategies for substantially enhancing the transport properties of conducting polymers by exploiting non-equilibrium states in the coupled system of electronic charges and counterions.

Electric field-induced volume change in pyro-vanadate-phosphates: Toward an alternative actuator architecture

We discovered large electric-field-induced strain in pyro-vanadate-phosphate Cu2−xZnxV1.8P0.2O7. Distinct from conventionally used piezoelectric materials including lead-zirconate-titanate, this material expands almost isotropically at room temperature when an electric field is applied. This volume change, exceeding 1000 ppm under the field of E = 3900 V/cm, is of the largest class induced by an electric field. The strain is phenomenologically interpreted as electrostriction because it is symmetric about E = 0 and because it obeys a higher term than E-linear such as E squared. The present x-ray diffraction experiments suggest that the applied electric field distorts the crystal lattice, although there is no structural phase transition. This material performs a volume-change-driven actuator function that is distinct from the strain-driven counterpart of piezoelectric materials. The discovery of actuator functionality in a material system with a non-perovskite structure, unlike the actuator materials developed to date, is a major breakthrough for future actuator engineering.

Unlocking guanine’s potential: Unveiling electronic transitions and nanoelectronic applications through electric field modulation

Guanines, key players in DNA and RNA, exist as dynamic keto and enol forms, influencing reactivity and potential applications. This study explores the impact of external electric fields on these forms using computational methods in gas and solvent (water) phases. Analyzing the energy gap, dipole moment, enthalpy, and Gibbs free energy revealed distinct responses. The keto form showed a significant decrease in the energy gap in the presence of an electric field, particularly in water, indicating enhanced reactivity. Conversely, the enol form exhibited a stabilizing effect with increasing electric field strength. Thermodynamic properties highlighted solvent-dependent interactions and electric field-induced changes in electron density distribution. The study further investigated guanine’s potential for nanoelectronics by calculating I-V curves, revealing promising characteristics, especially for the keto form in the aqueous phase. Additionally, the analysis of solvation and cohesive energies provided insights into solute–solvent interactions and intrinsic molecular stability. Overall, this research contributes to understanding how guanine responds to electric fields, paving the way for novel guanine-based materials with potential applications in nanoelectronics.

Strong influence of magnetic field and non-uniform stress on elastic modulus and transition temperatures of twinned Ni–Fe(Co)–Ga alloy

The magnetization value and electric resistivity of the single-crystalline sample of Ni50Fe19Co4Ga27 shape memory alloy were measured. The elastic modulus was determined by the Dynamic Mechanical Analysis (DMA). The characteristic temperatures of martensitic transformation (MT) of the alloy were estimated from the temperature dependences of magnetization, electric resistivity and elastic modulus. A significant disparity between MT temperatures resulting from DMA and those estimated from magnetic and resistivity measurements was discovered. It was argued that the discrepancy is caused by the non-uniform mechanical stressing of twinned single crystal by the DMA analyzer. Moreover, the DMA measurements revealed a significant decrease of the elastic modulus of twinned martensite under the applied magnetic field of 1.5 kOe. To explain this effect, the temperature-dependent Young’s modulus of twinned crystal lattice was computed. The computations showed that the experimentally observed field-induced change of the elastic modulus is caused by the stress-assisted detwinning of the crystal lattice by the applied magnetic field.

Extreme magnetoresistance at high-mobility oxide heterointerfaces with dynamic defect tunability

Magnetic field-induced changes in the electrical resistance of materials reveal insights into the fundamental properties governing their electronic and magnetic behavior. Various classes of magnetoresistance have been realized, including giant, colossal, and extraordinary magnetoresistance, each with distinct physical origins. In recent years, extreme magnetoresistance (XMR) has been observed in topological and non-topological materials displaying a non-saturating magnetoresistance reaching 103−108% in magnetic fields up to 60 T. XMR is often intimately linked to a gapless band structure with steep bands and charge compensation. Here, we show that a linear XMR of 80,000% at 15 T and 2 K emerges at the high-mobility interface between the large band-gap oxides γ-Al2O3 and SrTiO3. Despite the chemically and electronically very dissimilar environment, the temperature/field phase diagrams of γ-Al2O3/SrTiO3 bear a striking resemblance to XMR semimetals. By comparing magnetotransport, microscopic current imaging, and momentum-resolved band structures, we conclude that the XMR in γ-Al2O3/SrTiO3 is not strongly linked to the band structure, but arises from weak disorder enforcing a squeezed guiding center motion of electrons. We also present a dynamic XMR self-enhancement through an autonomous redistribution of quasi-mobile oxygen vacancies. Our findings shed new light on XMR and introduce tunability using dynamic defect engineering.

Electric field-induced changes in photoluminescence and Raman spectra of MoS2 on PVA-coated conductive substrate with nematic liquid crystals: a combined numerical and experimental study

Electric field-induced changes in photoluminescence and Raman spectra of MoS2 on PVA-coated conductive substrate with nematic liquid crystals: a combined numerical and experimental study

Magnetocaloric effect at the reorientation of the magnetization in ferromagnetic multilayers with perpendicular anisotropy

We investigate the magnetocaloric effect obtained by the rotation of a magnetic field applied to an exchange-coupled multilayer system composed of two different ferromagnetic (FM) materials. We specifically consider a system in which the two FMs have perpendicular uniaxial anisotropy axes and utilize conditions which yield a reorientation of the total magnetization when compensation between the anisotropies of the two layers occurs. We calculate the consequent entropy change associated with the “artificial” reorientation. By using known parameters from MnBi and Co we predict an entropy change of Δs=0.34 J kg−1 K−1 for perfect coupling. Lastly, we study the behavior of the multilayer under a rotating magnetic field via a micromagnetic model. When the layer thicknesses are of the order of the local domain wall width, the magnetic field-induced entropy change can be obtained with magnetic fields one order of magnitude lower than in the uncoupled case.

In-situ electric field-tailored exchange bias in the manganite/ferroelectric multiferroic heterostructures

The application of electric field-induced magnetic structure changes has significantly advanced nonvolatile data storage with ultralow energy consumption, as well as spintronics and quantum computing processes. In artificial perovskite oxide multiferroic structures composed of ferromagnetic and ferroelectric layers, the evolution of magnetic phases and ferroelectric domains often contribute to the magnetoelectric coupling. To fully understand the mechanisms behind electric field-induced changes in magnetic structures and enable the miniaturization of magnetoelectric devices, it is crucial to achieve local ferroelectric domain-triggered ferromagnetic evolution. In this study, we have fabricated La0.7Ca0.3MnO3/Pb(Zr0.52Ti0.48)O3 (LCMO/PZT) heterostructures, where the magnetic phase separation of LCMO and the ferroelectric domain of PZT can be modulated by substrates and piezoelectric force microscopy, respectively. Our experiments demonstrate that by switching the polarization states of PZT, we can observe electric field control of the magnetic exchange bias effect through changes in the phase separation of the LCMO layer. These results contribute to the development of magnetoelectric devices with enhanced properties and offer valuable insights for future design strategies.

Temperature- and magnetic field-induced magnetic structural changes in the Fe3Si/FeSi2 superlattice

Artificial lattices with semiconductor spacers are expected to exhibit changes in their magnetic structure owing to the control of their electronic states. The temperature (T) and magnetic-field (H ext) dependence of the in-plane magnetic structure of an [Fe3Si/FeSi2]20 superlattice with a nonmagnetic and semiconducting FeSi2 spacer layer is investigated using magnetization and polarized neutron reflectivity measurements. When H ext = 5 mT, nearly collinear antiferromagnetic (AF) structures are observed from 4 to 298 K. When H ext = 1 T, field-induced fan-like, noncollinear AF structures showing ferromagnetic components along H ext and transverse AF components are observed at low T.

Electrical Chain Rearrangement: What Happens When Polymers in Brushes Have a Charge Gradient?

Under the influence of electric fields, the chains in polyelectrolyte brushes can stretch and collapse, which changes the structure of the brush. Copolymer brushes with charged and uncharged monomers display a similar behavior. For pure polyelectrolyte and random copolymer brushes, the field-induced structure changes only the density of the brush and not its local composition, while the latter could be affected if charges are distributed inhomogeneously along the polymer backbone. Therefore, we systematically study the switching behavior of gradient polyelectrolyte brushes in electric fields for different solvent qualities, grafting densities, and charges per chain via coarse-grained molecular dynamics simulations. Similar to random copolymers and pure polyelectrolytes, these brushes show a mixed-phase transition: intermediate states between fully stretched and collapsed are characterized by a bimodal chain-end distribution. Additionally, we find that the total charge of the brush plays a key role in the critical field required for a complete transition. Finally, we find that gradient polyelectrolyte brushes are charge-enriched at the brush-solvent interface under stretched conditions and charge-depleted under collapsed conditions, allowing for control over the local composition and thus the surface charge of the brush due to the inhomogeneous charge along the grafted chains.

Magnetostructural Transformation and Magnetocaloric Properties of (Ni37.5Co12.5Mn35Ti15)100−xBx (x = 0.0 and 0.4) Melt-Spun Ribbons

The effect of B-doping on the martensitic transformation (MT), microstructure, room temperature (RT) crystal structure, and magnetocaloric properties of a typical all-d-metal Ni37.5Co12.5Mn35Ti15 quaternary alloy was studied by synthesizing melt-spun ribbon samples of nominal composition (Ni37.5Co12.5Mn35Ti15)100−xBx with x = 0.0 and 0.4. For B-free samples, SEM images show a grain-oriented microstructure formed by the columnar in shape-elongated grains with their major axis oriented along the thermal gradient during solidification. By contrast, the B-doped samples show smaller grains whose orientation tends to be perpendicular to the contact surface with the copper wheel. For all samples, austenite (AST) and martensite (MST) phases exhibited a cubic B2-type and 5M monoclinic crystal structure, respectively. The martensitic transition temperature (TM) and the Curie temperature of the austenite phase (TCA) were reduced from 295 K to 253 K and 333 K to 276 K, respectively, with the addition of B. The effect of thermal annealing for different times (from 30 min to 4 h) at 1073 K was studied. Thermal annealing increases the martensitic transformation temperature, whereas TCA remains unchanged. The maximum magnetic field-induced entropy changes |ΔST|max for B-doped samples were around 4.5 J kg−1 K−1 and 4.7 J kg−1 K−1 for as-solidified and annealed samples (1073 K–4 h), respectively, compared to that found for the undoped samples (i.e., ΔST = 16 J kg−1 K−1). However, the entropy reduction is accompanied by an increase in the full width at half-maximum of the ΔST(T) curve.

Microwave Field-Induced Changes in Raman Modes and Magnetic Force Images of Antiferromagnetic NiO Films

Effective control of domain walls or magnetic textures in antiferromagnets promises to enable robust, fast, and nonvolatile memories. The lack of net magnetic moment in antiferromagnets implies the need for creative ways to achieve such a manipulation. We conducted a study to investigate changes in magnetic force microscopy (MFM) imaging and in the magnon-related mode in Raman spectroscopy of virgin NiO films under a microwave pump. After MFM and Raman studies were conducted, a combined action of broadband microwave (0.01–20 GHz, power scanned from −20 to 5 dBm) and magnetic field (up to 3 kOe) were applied to virgin epitaxial (111) NiO and (100) NiO films grown on (0001) Al2O3 and (100) MgO substrates, following which the MFM and Raman studies were repeated. We observed a suppression of the magnon-related Raman mode subsequent to the microwave exposure. Based on MFM imaging, this effect appeared to be caused by the suppression of large antiferromagnetic domain walls due to the possible excitation of antiferromagnetic spin oscillations localized within the antiferromagnetic domain walls.

Experimental characterization of four ionization chamber types in magnetic fields including intra-type variation

Background and purposeFor dosimetry in magnetic resonance (MR) guided radiotherapy, assessing the magnetic field correction factors of air-vented ionization chambers is crucial. Novel MR-optimized chambers reduce MR-imaging artefacts, enhancing their quality assurance utility. This study aimed to characterize two new MR-optimized ionization chambers with sensitive volumes of 0.07 and 0.016cm3 regarding magnetic field correction factors and intra-type variation and compare them to their conventional counterparts. Material and methodsFive chambers of each type were evaluated in a water phantom, using a clinical linear accelerator and an electromagnet, as well as a 1.5 T MR-linac system. The magnetic field correction factor kB→,Q, addressing the change of response caused by a magnetic field, was assessed together with its intra-type variation. MR-optimized and conventional chambers were compared using a Mann-Whitney U-Test. ResultsConsidering 1.5 T and a perpendicular chamber orientation, we observed significant differences in the magnetic field-induced change in chamber reading between the two 0.016cm3 chamber versions (p = 0.03). For a 7MV beam, MR-optimized chambers (0.016/0.07 cm3) showed kB→,Q values of 1.0426(66) and 1.0463(44), compared to 1.0319(53) and 1.0480(41) of their conventional counterparts. In anti-parallel orientation, kB→,Q was 1.0012(69) and 0.9863(49) for the MR-optimized chambers. The average intra-type variation of kB→,Q over all chamber types was 0.3%. ConclusionMagnetic field correction factors were successfully determined for four ionization chamber types, including two new MR-optimized versions, allowing their use in MR-linac absolute dosimetry. Evaluation of the intra-type variation enabled the assessment of their contribution to the uncertainty of tabulated kB→,Q.