Some Properties of Ferroelectric and Ferromagnetic Compounds Rmno3
Properties of ferroelectric and ferromagnetic compounds of manganite with rare earths
FERROELECTRICS↗
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Ferroelectric bolometer for space research.
Solid solution dielectric mode ferroelectric bolometer compared with other thermal detectors for space applications
BOLOMETER↗
180 deg domain formation in ferroelectrics with shorted electrodes.
180 degree domain formation in ferroelectric crystals unaffected by presence of shorted electrodes due to surface layer properties differing from bulk
MAGNETIC DOMAIN↗
Controlled Nucleation and Stabilization of Ferroelectric Domain Wall Patterns in Epitaxial (110) Bismuth Ferrite Heterostructures
Ferroelectric domain walls, topological entities separating domains of uniform polarization, are promising candidates as active elements for nanoscale memories. In such applications, controlled nucleation and stabilization of domain walls are critical. In this work, using in situ transmission electron microscopy and phase-field simulations, a controlled nucleation of vertically oriented 109° domain walls in (110)-oriented BiFeO 3 (BFO) thin films is reported. In the switching experiment, reversed domains that are nucleated preferentially at the nanoscale edges of the “crest and sag” pattern-like electrode under external bias subsequently grow into a stable stripe configuration. In addition, when triangular pockets (with an in-plane polarization component) are present, these domain walls are pinned to form stable flux-closure domains. Phase field simulations show that i) field enhancement at the edges of the electrode causes site-specific domain nucleation, and ii) the local electrostatics at the domain walls drives the formation of flux closure domains, thus stabilizing the striped pattern, irrespective of the initial configuration. The results demonstrate how flux closure pinning can be exploited in conjunction with electrode patterning and substrate orientation to achieve a desired topological defect configuration. These insights constitute critical advancements in exploiting domain walls in next generation ferroelectronic devices.
75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
Precipitation Hardening in Ferroelectric Ceramics
Domain wall motion in ferroics, similar to dislocation motion in metals, can be tuned by well-concepted microstructural elements. In demanding high-power applications of piezoelectric materials, the domain wall motion is considered as a lossy hysteretic mechanism that should be restricted. Current applications for so-called hard piezoelectrics are abundant and hinge on the use of an acceptor-doping scheme. However, this mechanism features severe limitations due to enhanced mobility of oxygen vacancies at moderate temperatures. By analogy with metal technology, the authors present here a new solution for electroceramics, where precipitates are utilized to pin domain walls and improve piezoelectric properties. Through a sequence of sintering, nucleation, and precipitate growth, intragranular precipitates leading to a fine domain structure are developed as shown by transmission electron microscopy, piezoresponse force microscopy, and phase-field simulation. This structure impedes the domain wall motion as elucidated by electromechanical characterization. As a result, the mechanical quality factor is increased by ≈50% and the hysteresis in electrostrain is suppressed considerably. This is even achieved with slightly increased piezoelectric coefficient and electromechanical coupling factor. This novel process can be smoothly implemented in industrial production processes and is accessible to simple laboratory experimentation for microstructure optimization and implementation in various ferroelectric systems.
36 MATERIALS SCIENCE↗
Nonresonant Raman Control of Ferroelectric Polarization
Important advances is recently made in the search for materials with complex multi-phase landscapes that host photoinduced metastable collective states with exotic functionalities. In almost all cases so far, the desired phases are accessed by exploiting light–matter interactions via the imaginary part of the dielectric function through above-bandgap or resonant mode excitation. Nonresonant Raman excitation of coherent modes is experimentally observed and proposed for dynamic material control, but the resulting atomic excursion is limited to perturbative levels. Here, in this study, this challenge is overcome by employing nonresonant ultrashort pulses with low photon energies well below the bandgap. Using mid-infrared pulses, ferroelectric reversal is induced in lithium niobate, and the large-amplitude mode displacements are characterized through femtosecond stimulated Raman scattering and second harmonic generation. This approach, validated by first-principle calculations, defines a novel method for synthesizing hidden phases with unique functional properties and manipulating complex energy landscapes at reduced energy consumption and ultrafast speeds.
Shi, Jiaojian [Stanford Univ., CA (United States);↗
Electronic Transport and Ferroelectric Switching in Ion-Bombarded, Defect-Engineered BiFeO 3 Thin Films
Despite continued interest in the multiferroic BiFeO 3 for a diverse range of applications, use of this material is limited by its poor electrical leakage. This work demonstrates some of the most resistive BiFeO 3 thin films reported to date via defect engineering achieved via high-energy ion bombardment. High leakage in as-grown BiFeO 3 thin films is shown to be due to the presence of moderately shallow isolated trap states, which form during growth. Ion bombardment is shown to be an effective way to reduce this free carrier transport (by up to ≈4 orders of magnitude) by trapping the charge carriers in bombardment-induced, deep-lying defect complexes and clusters. The ion bombardment is also found to give rise to an increased resistance to switching as a result of an increase in defect concentration. This study demonstrates a systematic ion-dose-dependent increase in the coercivity, extension of the defect-related creep regime, increase in the pinning activation energy, decrease in the switching speed, and broadening of the field distribution of switching. Ultimately, the use of such defect-engineering routes to control materials will require identification of an optimum range of ion dosage to achieve maximum enhancement in resistivity with minimum impact on ferroelectric switching.
36 MATERIALS SCIENCE↗
Exploring Physics of Ferroelectric Domain Walls in Real Time: Deep Learning Enabled Scanning Probe Microscopy
The functionality of ferroelastic domain walls in ferroelectric materials is explored in real-time via the in situ implementation of computer vision algorithms in scanning probe microscopy (SPM) experiment. The robust deep convolutional neural network (DCNN) is implemented based on a deep residual learning framework (Res) and holistically nested edge detection (Hed), and ensembled to minimize the out-of-distribution drift effects. The DCNN is implemented for real-time operations on SPM, converting the data stream into the semantically segmented image of domain walls and the corresponding uncertainty. Further the pre-defined experimental workflows perform piezoresponse spectroscopy measurement on thus discovered domain walls, and alternating high- and low-polarization dynamic (out-of-plane) ferroelastic domain walls in a PbTiO 3 (PTO) thin film and high polarization dynamic (out-of-plane) at short ferroelastic walls (compared with long ferroelastic walls) in a lead zirconate titanate (PZT) thin film is reported. This work establishes the framework for real-time DCNN analysis of data streams in scanning probe and other microscopies and highlights the role of out-of-distribution effects and strategies to ameliorate them in real time analytics.
36 MATERIALS SCIENCE↗
Transient Terahertz Oscillations During Photoinduced Polarization Topology Reconfiguration in Ferroelectric Superlattices
Terahertz resonances embedded in crystalline heterostructures could close a spectral gap between conventional electronics and photonics while opening new windows on non-equilibrium lattice dynamics. We show that femtosecond optical screening of the depolarization field in epitaxial PbTiO3/SrTiO3 superlattices launches a collective polar mode that oscillates near 1 THz and coherently spans the entire mini-Brillouin zone. Wave-vector-resolved pump–probe X-ray diffraction resolves a nearly dispersion-less oscillation at 0.87 THz and 0.94 THz at the zone boundary and zone center, respectively, persisting for ~2.5 ps, corresponding to a weakly damped resonance. Dynamical phase-field simulations reveal the origin of the mode to mesoscopic rotation of closure-domain textures during the photo-excited transition from an unscreened to a screened electrostatic state. Varying the PbTiO3 and SrTiO3 ratio tunes the mode frequency continuously from 0.9 to 1.4 THz, providing a quantitative design rule for frequency-selectable THz oscillators in ferroelectric heterostructures. By coupling nanoscale polarization reconfiguration to long-wavelength coherent dynamics, this work establishes depolarization-field engineering to topology-driven THz functionality and expanding the landscape of collective lattice dynamics.
Sri Gyan, Deepankar [Univ. of Wisconsin, Madison, ↗
Domain imaging in ferroelectric thin films via channeling-contrast backscattered electron microscopy
We report that ferroelastic domain walls provide opportunities for deterministically controlling mechanical, optical, electrical, and thermal energy. Domain wall characterization in micro- and nanoscale systems, where their spacing may be of the order of 100 nm or less is presently limited to only a few techniques, such as piezoresponse force microscopy and transmission electron microscopy. These respective techniques cannot, however, independently characterize domain polarization orientation and domain wall motion in technologically relevant capacitor structures or in a non-destructive manner, thus presenting a limitation of their utility. In this work, we show how backscatter scanning electron microscopy utilizing channeling contrast yield can image the ferroelastic domain structure of ferroelectric films with domain wall spacing as narrow as 10 nm.
47 OTHER INSTRUMENTATION↗
Weak Ferroelectricity and Leakage Current Behavior of Multiferroic CoCr{sub 2}O{sub 4} Nanomaterials
Multiferroic CoCr{sub 2}O{sub 4} is synthesized by low-temperature sol-gel auto combustion technique. High energy synchrotron x-ray diffraction pattern confirms the single-phase cubic structure with space group Fd3m. Average crystallite size (17.91 nm) and negative micro-strain (9.86 × 10{sup −4}) are estimated by Williamson–Hall (W-H) plot. FTIR confirms the formation of spinel metal oxide-based cobalt chromites. The strong decrease in ε′ and tan δ at higher frequency can be interpreted by Maxwell-Wagner-type interfacial polarization. Weak ferroelectricity is mainly attributed to the partial reversal of polarization. J-E characteristic reveals the Ohmic (I–V) and Child’s square law (I–V{sup 2}) behavior observed in CoCr{sub 2}O{sub 4} nanomaterials with slope value ~ 1.04 and ~ 1.6, respectively. The conduction process for the leakage current density is interpreted using the space-charge limited current (SCLC) mechanism.
77 NANOSCIENCE AND NANOTECHNOLOGY↗
Correlating hidden local structural distortion with antiferroelectric-ferroelectric transition in PbZrO 3 -based perovskites
Externally stimulated antiferroelectric-ferroelectric (AFE-FE) transition makes AFE materials attractive for many applications ranging from energy storage to sensing. This transition-mediated macroscopic electrical characteristics have been extensively investigated, yet the underlying structural evolution remains poorly understood. Herein, we study the local- and long-range structural evolutions in the Nb-doped Pb(Zr,Sn,Ti)O 3 perovskites by in-situ X-ray total scattering and diffraction, which show three different types of AFE-FE transitions. The evolution of long-range structure from diffraction and local structure identified by atomic pair distribution function (PDF) are consistent well with the phase transition behavior indicated by macroscopic polarization/strain measurements, while discrepancies exist. Interestingly, frequently employed long-range structure picture that the uniform AFE pseudo-tetragonal to FE rhombohedral transformation is insufficient to understand the distinct composition-dependent AFE-FE transition behaviours. Instead, the reversibility of this transition correlates with the chemically sensitive local atomic displacements revealed by newly developed in-situ PDF. The critical electric field of transition is associated with the local structural differences between the AFE and FE state. The macroscopic electrostrains can be well estimated by the phase transition associated lattice strain and domain alignment from in-situ synchrotron XRD data, while the local strains calculated from in-situ PDFs are found to be much lower. Finally, these results provide a fresh insight into the AFE-FE transition, and advance the understanding of structure-property relationships in AFE materials.
36 MATERIALS SCIENCE↗
Single Crystal Growth of Relaxor Ferroelectric Ba 2 PrFeNb 4 O 15 by the Optical Floating Zone Method
Uniaxial tungsten bronzes have received increasing interest because of their potential application as lead-free ferroelectrics as well as their flexibility-via chemical substitution. Here we demonstrate growth of single crystals of one such material, Ba 2 PrFeNb 4 O 15 , which possesses the tetragonal tungsten bronze structure, by the optical floating zone method. The challenge of this growth is to control the stability of the molten zone which allows the growth to persist for a long enough time to achieve large volume single crystals. Our work reveals that the use of a slight overpressure of air allows the molten zone to be maintained up to 7 h at a traveling speed of 4 mm/h. The obtained crystals were studied using high-resolution single crystal scattering, powder X-ray diffraction, and dielectric measurements. We find that Ba 2 PrFeNb 4 O 15 possesses a rather complex average structure with a monoclinic symmetry in a P 112/ m space group and unit cell parameters of a = 12.49188(8) Å, b = 12.49232(8) Å, c = 3.92863(1) Å, and γ = 90.056 °, with an additional incommensurate superstructural modulation superimposed. The temperature dependence of dielectric properties has been investigated by comparing as-grown, O 2 -annealed, and Ar-annealed samples. A broad relaxation dielectric peak is observed around 150 K for the O 2 -annealed sample, indicating a typical relaxor behavior below 150 K. A larger dielectric permittivity (ε' ≈ 1300) than those of corresponding ceramics (up to ε' ≈ 200) is found in the oxygen annealed crystals. In conclusion, we suggest that as-grown single crystals are oxygen deficient and that the oxygen vacancies can be eliminated by an oxygen annealing treatment.
36 MATERIALS SCIENCE↗
Predictive Design of Hybrid Improper Ferroelectric Double Perovskite Oxides
The computational design of suitable multiferroic double perovskite oxides requires finding materials that exhibit sizable polarization, magnetization, and coupling between them. Oxides with the chemical formula of AA'BB'O 6 with building blocks of ABO 3 single perovskite oxides in centrosymmetric Pnma symmetry are strong candidates that have been reported to satisfy such criteria. The system lowers to noncentrosymmetric, polar P2 1 symmetry if A/A' layered and B/B' rocksalt cation orderings are imposed. A detailed compositional search over a variety of chemical spaces followed by evaluating their polarization may lead to the identification of more of these compounds with ferroelectric ordering. The standard density functional theory practices to estimate polarization within the Berry phase formalism require the systems to be perfectly insulating. The number of compounds that can be evaluated using this method is therefore limited. In this work, we introduce a predictive learning strategy based on importance sampling to build a series of machine learning models using results from first-principles simulations to predict polarization and the corresponding switching barrier. The geometry-driven features related to charge states and cationic radii play key roles in predicting the switching barrier with complementary contributions from the key structural mode-based order parameters. These modes become important to draw reasonable predictions of polarization components from machine learning models. In conclusion, our predictive models identify candidates with high polarizations and low switching barriers from a pool of double perovskite oxides, suitable for future investigation for their potential applications in spintronic devices.
36 MATERIALS SCIENCE↗
Structural Correlation to Piezoelectric and Ferroelectric Mechanisms in Rhombohedral Pb(Zr,Ti)O 3 Ceramics by in-Situ Synchrotron Diffraction
Here, the evidence of fundamental lattice strain and domain switching contribution to the piezoelectric and ferroelectric responses of ceramics has been well studied, while the contribution from crystal structure variation has been rarely reported in terms of the existence of intergranular stress/strain and crystallographic texture. In the present study, the detailed electric field induced structure evolution in rhombohedral PbZr 0.55 Ti 0.45 O 3 (PZT55) has been investigated by in-situ high-energy synchrotron diffraction. The phase of PZT55 is stable in the rhombohedral one against bipolar electrical loading. It is interesting to find that both spontaneous polarization and unit cell volume exhibit a butterfly shape in response to electric field. Direct evidence has revealed that the lattice strain and volume expansion show similar variation tendency to the piezoelectric response in the rhombohedral PZT55. The macro-polarization of PZT55 derives from the combination of domain switching and spontaneous polarization change.
36 MATERIALS SCIENCE↗
Relaxor Ferroelectric-Like Spatiotemporal Memory in Field-Driven Lipid Bilayers
Lipid membranes are often regarded as passive barriers, yet their nonlinear dielectric response remains poorly understood. Using all-atom molecular dynamics, we show that fully hydrated dipalmitoylphosphatidylcholine bilayers exhibit relaxor ferroelectric-like behavior under time-dependent electric fields. Unlike crystalline relaxors, which are bipolar and display little remanent polarization, lipid bilayers exhibit a unipolar polarization response: even an alternating current field produces persistent, asymmetric polarization. Furthermore, the underlying free-energy landscape contains two distinct minima, a nonpolarized state and a unipolarly polarized state, between which stochastic thermally activated transitions occur. Directionally resolved Van Hove analysis reveals pronounced anisotropy arising from out-of-plane electric dipole alignment, interleaflet coupling, and lateral polarization domains. Each field cycle nucleates polarization at distinct sites and monitors their relaxation, marking a crossover from thermal fluctuations to field-sustained polarization. Remarkably, these polarized domains persist after field removal, generating long-lived, spatially coherent dipolar patterns that encode nanoscale polarization memory. Potassium chloride amplifies these effects via dielectric screening and a modified hydration structure, enhancing electric dipole flexibility and cooperativity. Together, these results establish protein-free bilayers as nonlinear, history-dependent dielectrics capable of sustaining field-tunable electromechanical coupling, providing an emergent physical foundation for nanoscale information storage and memory phenomena reminiscent of short- and long-term plasticity in soft neuromorphic systems.
Insulators↗
Controlling the Magneto-Optical Response in Ultrathin Films of EuO 1– x via Interface Engineering with Ferroelectric BaTi 2 O 5
Utilizing pulsed laser deposition, a film of EuO 1–x was deposited onto a Si(001) substrate with MgO buffer and compared to the same heterostructure with an additional BaTi 2 O 5 thin film on top of the EuO 1–x surface. X-ray diffraction (XRD) indicates the films crystallize into a preferred EuO(111) orientation; it also reveals the clear presence of EuSi 2 , which suggests Si or Eu diffuses across the MgO buffer layer. EuO 1–x films exhibit a ferromagnetic (FM) signature and temperature-dependent exchange bias, indicated by MOKE measurements, suggesting the presence of a magnetic order well above the EuO Curie temperature with possible origins in charge carrier density near the interface. In comparison, an antiferromagnetic character persists well above the EuO Curie temperature of 69 K and the enhanced Curie temperature of 150 K for BaTi 2 O 5 films grown on the EuO 1–x films. Furthermore, the antiferromagnetic behavior is not seen in thicker EuO 1–x thin films when integrated with other ferroelectric (FE) phases of the BaO–TiO 2 system, suggesting an origin in the perturbed charge population at the BaTi 2 O 5 /EuO 1–x interface.
36 MATERIALS SCIENCE↗
Switchable electric polarization and ferroelectric domains in a metal-organic-framework
Multiferroics and magnetoelectrics with coexisting and coupled multiple ferroic orders are materials promising new technological advances. While most studies have focused on single-phase or heterostructures of inorganic materials, a new class of materials called metal–organic frameworks (MOFs) has been recently proposed as candidate materials demonstrating interesting new routes for multiferroism and magnetoelectric coupling. Herein, we report on the origin of multiferroicity of (CH 3 ) 2 NH 2 Mn(HCOO) 3 via direct observation of ferroelectric domains using second-harmonic generation techniques. For the first time, we observe how these domains are organized (sized in micrometer range), and how they are mutually affected by applied electric and magnetic fields. Lastly, calculations provide an estimate of the electric polarization and give insights into its microscopic origin.
75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗