Ferroelectric Domain Configurations Research Articles

Frustrated Magnetism and Ferroelectricity in a Dy3+-Based Triangular Lattice

Triangular lattice magnets have attracted extensive research interest because they are potential hosts for geometrically frustrated magnetism and strong quantum fluctuations. Here, utilizing a laser floating zone technique, we report the first-time successful growth of a DyInO3 sizable crystal, which contains Dy3+-based triangular layers. The fine-tuning of Indium stoichiometry was found to be the key factor in the stabilization of the desired hexagonal phase. The X-ray diffraction study of the crystal structure reveals a non-centrosymmetric P63mc space group. Switchable polarization, i.e., ferroelectricity, and ferroelectric domain configuration are experimentally demonstrated at room temperature. Anisotropic magnetic and thermodynamic measurements unveil antiferromagnetic interactions, the absence of long-range ordering down to 0.1 K, and a possible doublet ground state, indicating a strongly frustrated magnetism. Our findings suggest that the DyInO3 crystal is an excellent platform for studying emergent phenomena and their interplay with coherent topological defects in the quantum realm.

What lies beneath? Investigations of atomic force microscopy-based nano-machining to reveal sub-surface ferroelectric domain configurations in ultrathin films

Multiferroic materials, encompassing simultaneous ferroelectric and ferromagnetic polarization states, are enticing multi-state materials for memory scaling beyond existing technologies. Aurivillius phase B6TFMO (Bi6TixFeyMnzO18) is a unique room temperature multiferroic material that could ideally be suited to future production of revolutionary memory devices. As miniaturization of electronic devices continues, it is crucial to characterize ferroelectric domain configurations at very small (sub-10 nm) thickness. Direct liquid injection chemical vapor deposition allows for frontier development of ultrathin films at fundamental (close to unit cell) dimensions. However, layer-by-layer growth of ultrathin complex oxides is subject to the formation of surface contaminants and 2D islands and pits, which can obscure visualization of domain patterns using piezoresponse force microscopy (PFM). Herein, we apply force from a sufficiently stiff diamond cantilever while scanning over ultrathin films to perform atomic force microscopy (AFM)-based nano-machining of the surface layers. Subsequent lateral PFM imaging of sub-surface layers uncovers 45° orientated striped twin domains, entirely distinct from the randomly configured piezoresponse observed for the pristine film surface. Furthermore, our investigations indicate that these sub-surface domain structures persist along the in-plane directions throughout the film depth down to thicknesses of less than half of an Aurivillius phase unit cell (˂ 2.5 nm). Thus, AFM-based nano-machining in conjunction with PFM allows demonstration of stable in-plane ferroelectric domains at thicknesses lower than previously determined for multiferroic B6TFMO. These findings demonstrate the technological potential of Aurivillius phase B6TFMO for future miniaturized memory storage devices. Next-generation devices based on ultrathin multiferroic tunnel junctions are projected.

Multifunctionality of Li2 SrNb2 O7 : Memristivity, Tunable Rectification, Ferroelasticity, and Ferroelectricity.

Layered Li2 SrNb2 O7 , an inorganic oxide in its bulk single-crystalline form, is experimentally demonstrated to exhibit multiple structural facets such as ferroelasticity, ferroelectricity, and antiferroelectricity. The transition from a room temperature (RT) centrosymmetric structure to a low-temperature out-of-plane ferroelectric and in-plane antiferroelectric structure and the low-temperature (LT) ferroelectric domain configuration are unveiled in TEM, piezoresponse force microscopy, and polarization loop studies. Li2 SrNb2 O7 also exhibits highly tunable ferroelasticity and excellent Li+ in-plane conduction, which leads to a giant in-plane memristor behavior and an in-plane electronic conductivity increase by three orders of magnitude by electric poling at room RT). The accumulation of Li+ vacancies at the crystal-electrode interface is visualized using insitu optical microscopy. The Li-ionic biased state shows a clear in-plane rectification effect combined with a significant relaxation upon time at RT. Relaxation can be fully suppressed at LTs such as 200K, and utilizing an electric field cooling, a stable rectification can be achieved at 200K. The results shed light on the selective control of multifunctionalities such as ferroelasticity, ferroelectricity, and ionic-migration-mediated effects (a memristor effect and rectification) in a single-phase bulk material utilizing, for example, different directions, temperatures, frequencies, and magnitudes of electric field.

Unveiling the Synergistic Effect of Ferroelectric Polarization and Domain Configuration for Reversible Zinc Metal Anodes.

The tendency of zinc (Zn) anodes to form uncontrolled Zn electrodeposits and the occurrence of side‐reactions at Zn‐electrolyte interfaces are a fundamental barrier hampering broad applications of aqueous rechargeable Zn‐based batteries. Herein, a ferroelectric domain‐mediated strategy is proposed to manipulate the Zn plating behavior and achieve controllable Zn growth orientation by coating Zn foil with a ferroelectric tetragonal KTN (t‐KTN) layer. The ferroelectric domain of t‐KTN single crystals exhibits periodic distribution of upward and downward polarizations, corresponding to alternating positively and negatively charged surfaces. The charged ferroelectric surfaces can manipulate the transfer kinetics of Zn ions and the concentration distribution of anions via the interplay between ferroelectric dipoles and adsorbed ions. With the synergistic effect of the ferroelectric polarization and domain configurations, the well‐aligned interlamellar arrays composed of electrodeposited Zn are formed in the initial deposition process, which enable selective deposition within interlamellar arrays and eliminate the dendrite growth during the following plating process. As a result, the t‐KTN layer‐modified Zn anode enables reversible Zn plating/stripping with low voltage hysteresis for over 1200 h at 1 mA cm−2 in symmetric cells, and the assembled full cell exhibits a significantly enhanced cycling stability of over 5500 cycles at 5 A g−1.

High Piezoelectric Performance in Pb(Ni1/3Nb2/3)O3-Pb(Sc1/2Nb1/2)O3-PbTiO3 Ternary System Featuring Small Structural Distortion and Heterogeneous Domain Configuration.

Ternary/polynary perovskite solid solutions based on binary systems are well-known for their high piezoelectric performance. In this work, a series of Pb(Ni1/3Nb2/3)O3-Pb(Sc1/2Nb1/2)O3-PbTiO3 compositions with the particularly high piezoelectric coefficient of d33* > 1000 pm/V and d33 > 700 pC/N have been developed. The optimal performance was achieved in the 0.52PNN-0.14PSN-0.34PT composition (d33* = 1120 pm/V, d33 = 804 pC/N, and Tm = 109 °C). The high piezoelectric performance of this system is reported and is superior to those of most lead-based ternary/polynary ceramics. By a combination of in situ high-energy synchrotron diffraction with transmission electron microscopy (TEM), the origin of the high piezoelectric response has been unambiguously revealed. Upon application of an external electric field, synchrotron diffraction profiles show no splitting but prominent shifting, indicating that the large intrinsic lattice strain arising from the reduced crystal anisotropy and facilitated polarization variation is associated with the high piezoelectric response. Furthermore, microscopic studies by TEM highlight a heterogeneous ferroelectric domain configuration generated by a small local structural distortion, which is also beneficial for the high piezoelectric performance in the proposed ternary piezoelectric systems. The design process of ternary perovskite solid solutions with a wide morphotropic phase boundary region and small structural distortion may be enlightening for the exploration of other high-performance polynary piezoelectrics.

Surface structure and quenching effects in BiFeO3‐BaTiO3 ceramics

AbstractThe structure and properties of Mn‐doped 0.67BiFeO3‐0.33BaTiO3 ceramics are systematically investigated with respect to the effects of annealing prior to rapid cooling by quenching in air. Air‐quenching induces a change in crystal structure from pseudo‐cubic to rhombohedral, with higher quenching temperatures leading to an increased rhombohedral distortion. These structural changes are correlated with the appearance of more well‐defined ferroelectric domain configurations. It is shown that the surface preparation procedures for XRD measurements can induce significant changes in the peak profiles, indicating differences in crystal structure between the surface and bulk regions. Frequency dispersion in the temperature‐dependent relative permittivity for the as‐sintered sample is significantly reduced after quenching, accompanied by enhancement of the Curie point and improved temperature‐stability of piezoelectric properties. It is proposed that the formation of defect clusters by A‐site cation diffusion during cooling is circumvented by quenching, leading to the observed modification of structural distortion and ferroelectric properties.

Asymmetric Character of the Ferroelectric Phase Transition and Charged Domain Walls in a Hybrid Improper Ferroelectric

AbstractIn improper ferroelectrics, the spontaneous ordering is typically driven by a structural distortion or a magnetic spin alignment. The induced electric polarization is only a secondary effect. This dependence is a rich source for unusual phenomena and ferroelectric domain configurations for proper, polarization‐driven ferroelectrics. This study focuses on the polar domain structure and the hysteretic behavior at the ferroelectric phase transition in Ca3Mn1.9Ti0.1O7 as a representative of the recently discovered hybrid improper ferroelectric class of multiferroics. Combining optical second harmonic generation and Raman spectroscopy gives access to the spontaneous structural distortion and the resulting improper electric polarization. This study shows that hybrid improper ferroelectrics contrast proper and improper ferroelectrics in several ways. Most intriguingly, adjacent ferroelectric domains favor head‐to‐head and tail‐to‐tail domain walls over charge‐neutral configurations. Furthermore, the phase transition occurs in an asymmetric fashion. The regime of phase coexistence of the nonpolar and polar phases shows a clear and abrupt upper temperature limit. In contrast, the coexistence toward low temperatures is best described as a fade‐out process, where 100‐nm‐sized islands of the nonpolar phase expand deep into the polar phase.

Direct observations of changes in ferroelectric domain configurations around the indentation and ahead of the crack front in soft-doped PZT

The indentation response of polycrystalline soft doped-lead Zirconate Titanate (PZT) with varying ferroelectric domain configurations is investigated using nano and micro indentation. The as-poled (AP) PZT samples are selectively annealed at below and above the Curie temperature, Tc, to obtain different ferroelectric domain configurations. In the fully depoled state (with completely random ferroelectric domain configurations), PZT exhibit higher hardness, H (∼ 40%) as compared to AP PZT (where ferroelectric domains are highly ordered). Severe cracking is observed at the imprint corners at high indentation loads and ferroelectric domain configurations are visualized in the vicinity and ahead of the indentation crack using piezoresponse force microscopy. The ferroelectric domains remain fully plastic in the regions from where the crack has propagated and just ahead of the crack, while farther from the indentation crack, they are elastic. The indentation fracture toughness, KICi values computed from the cracks emanated from imprint corners indicate that ferroelectric domain configurations also influence toughening behavior of PZT. The results are rationalized using remnant strain, εr and converse piezocharge coefficient, d33* measured around the indentation crack. This work highlights the new pathways to tailor strength and toughness of PZTs.

Tailoring nanomechanical properties of hard and soft PZT piezoceramics via domain engineering by selective annealing

The nanomechanical properties of polycrystalline “hard” and “soft” lead zirconate titanate (PZT) (abbreviated as PZT-H and PZT-S, respectively) are measured on samples having different ferroelectric domain configurations. The ferroelectric domain configurations are varied by selectively annealing the as poled samples below and above the curie temperature, Tc. The ferroelectric domain configurations characterized using piezoresponse force microscopy reveal that the degree of randomization of ferroelectric domains increases with increasing annealing temperature. Nanoindentation experiments reveal that the above Tc annealed samples exhibit the highest hardness, H among all the samples. All the samples, exhibit strong indentation size effect where H decreases with increasing in indentation load. The possible reasons for enhancement in Hin annealed samples is attributed to the differences in ferroelectric domain configurations, defect dipoles, and oxygen vacancies. The results provide insights about designing piezoelectric materials with good combination of mechanical and piezoelectric properties.

Direct Observations of Changes in Ferroelectric Domain Configurations Around the Indentation and Ahead of the Crack Front

The indentation response of polycrystalline lead zirconate titanate (PZT) with varying ferroelastic domain configurations is investigated using nano and micro indentation. In the fully depoled state (with completely random domain configurations), PZT exhibit higher hardness, H as compared to poled PZT. Severe cracking is observed at the imprint corners at high indentation loads and the ferro-elastic domain configurations are visualized in the vicinity and ahead of the crack using piezoresponse force microscopy. The domains remain fully plastic in the regions from where the crack has propagated and just ahead of the crack while farther from the crack their remain elastic. The results are rationalized using remanent strain, e r results highlight the toughening mechanisms in the as poled PZTs. and converse piezocharge coefficient, d *33 measured around microcrack. The results highlight the toughening mechanisms in the as poled PZTs.

Identification of the consequences of Pb-O chemical bond modification, Pb lone pair and Pb volatilization on the intrinsic and extrinsic physical properties of Ba1-xPbxTiO3 (x ≤ 0–0.5)

In classical ferroelectric BaTiO3, inclusion of Pb at A-site, forms a unique system in terms of improvement in the physical properties and for investigation of several interesting aspects associated with the physical chemistry and materials science. Manipulation of ferroelectric instability with high tetragonality arises due to Pb-O bond which exhibits strong covalent nature along with the presence of the stereochemically active lone pair of Pb (i.e. 6s2). In contrast, Ba-O chemical bond is ionic in nature. In the present work, Pb is progressively substituted with Ba, to observe the intrinsic effects on the physical properties such as tetragonality, phase transition temperature, vibrational modes, piezoelectric coefficient, ferroelectric domain configuration etc. Phase transition temperature significantly increases with substitution of Pb, which is a manifestation of the effect of chemical bond modification. Sintering temperature effects both intrinsic as well as extrinsic contributions to the physical properties of the system.

Understanding Microscopic Operating Mechanisms of a van der Waals Planar Ferroelectric Memristor

AbstractFerroelectric memristors represent a promising new generation of devices that have a wide range of applications in memory, digital information processing, and neuromorphic computing. Recently, van der Waals ferroelectric In2Se3 with unique interlinked out‐of‐plane and in‐plane polarizations has enabled multidirectional resistance switching, providing unprecedented flexibility in planar and vertical device integrations. However, the operating mechanisms of these devices have remained unclear. Here, through the demonstration of van der Waals In2Se3‐based planar ferroelectric memristors with the device resistance continuously tunable over three orders of magnitude, and by correlating device resistance states, ferroelectric domain configurations, and surface electric potential, the studies reveal that the resistive switching is controlled by the multidomain formations and the associated energy barriers between domains, as opposed to the commonly assumed Schottky barrier modulations at the metal‐ferroelectric interface. The findings reveal new device physics through elucidating the microscopic operating mechanisms of this new generation of devices, and provide a critical guide for future device development and integration efforts.

Achieving single domain in rhombohedral and tetragonal Mn‐doped Pb(In1/2Nb1/2)‐Pb(Mg1/3Nb2/3)‐PbTiO3 crystals for infrared detecting applications

AbstractThe [111]‐oriented rhombohedral Mn‐doped 0.15Pb(In1/2Nb1/2)‐0.55Pb(Mg1/3Nb2/3)O3‐0.30PbTiO3 (Mn:PIMNT(15/55/30)) crystal and the [001]‐oriented tetragonal Mn‐doped 0.29Pb(In1/2Nb1/2)‐0.29Pb(Mg1/3Nb2/3)O3‐0.42PbTiO3 (Mn:PIMNT(29/29/42)) crystal were poled under different conditions. The pyroelectric performance of the two crystals as a function of poling temperature, as well as the relationship with ferroelectric domain configuration and phase structure was investigated systematically. The pyroelectric properties of the two crystals enhance with rising the poling temperature, which can be attributed to the improvement of the single state. And for the rhombohedral Mn:PIMNT(15/55/30) crystal locating near morphotropic phase boundary (MPB), the increase of tetragonal phase induces the deterioration of pyroelectric properties. Due to more residual tetragonal phase, the pyroelectric coefficient of the Mn:PIMNT(15/55/30) crystal poled at 150°C is lower than that poled at 100°C. In general, both the crystals poled above TC achieve nearly single state, exhibiting the best pyroelectric properties with relatively high Curie temperature (TC), where P = 9.71 × 10−4 C m−2 K−1, Fi = 3.88 × 10−10 m V−1, Fv = 0.068 m2 C−1 and Fd = 29.7 × 10−5 Pa−1/2 for the rhombohedral Mn:PIMNT(15/55/30) crystal (TC = 171°C) and P = 6.78 × 10−4 C m−2 K−1, Fi = 2.71 ×10−10 mV−1, Fv = 0.1 m2 C−1, Fd = 23.54 × 10−5 Pa−1/2 for the tetragonal Mn:PIMNT(29/29/42) single crystal (TC = 251°C), meeting the stable operation of infrared detector at relatively high environmental temperatures.

Manipulating topological transformations of polar structures through real-time observation of the dynamic polarization evolution

Topological structures based on controllable ferroelectric or ferromagnetic domain configurations offer the opportunity to develop microelectronic devices such as high-density memories. Despite the increasing experimental and theoretical insights into various domain structures (such as polar spirals, polar wave, polar vortex) over the past decade, manipulating the topological transformations of polar structures and comprehensively understanding its underlying mechanism remains lacking. By conducting an in-situ non-contact bias technique, here we systematically investigate the real-time topological transformations of polar structures in PbTiO3/SrTiO3 multilayers at an atomic level. The procedure of vortex pair splitting and the transformation from polar vortex to polar wave and out-of-plane polarization are observed step by step. Furthermore, the redistribution of charge in various topological structures has been demonstrated under an external bias. This provides new insights for the symbiosis of polar and charge and offers an opportunity for a new generation of microelectronic devices.

Ferroelectric Domain Walls in PbTiO3 Are Effective Regulators of Heat Flow at Room Temperature.

Achieving efficient spatial modulation of phonon transmission is an essential step on the path to phononic circuits using "phonon currents". With their intrinsic and reconfigurable interfaces, domain walls (DWs), ferroelectrics are alluring candidates to be harnessed as dynamic heat modulators. This paper reports the thermal conductivity of single-crystal PbTiO3 thin films over a wide variety of epitaxial-strain-engineered ferroelectric domain configurations. The phonon transport is proved to be strongly affected by the density and type of DWs, achieving a 61% reduction of the room-temperature thermal conductivity compared to the single-domain scenario. The thermal resistance across the ferroelectric DWs is obtained, revealing a very high value (≈5.0 × 10-9 K m2 W-1), comparable to grain boundaries in oxides, explaining the strong modulation of the thermal conductivity in PbTiO3. This low thermal conductance of the DWs is ascribed to the structural mismatch and polarization gradient found between the different types of domains in the PbTiO3 films, resulting in a structural inhomogeneity that extends several unit cells around the DWs. These findings demonstrate the potential of ferroelectric DWs as efficient regulators of heat flow in one single material, overcoming the complexity of multilayers systems and the uncontrolled distribution of grain boundaries, paving the way for applications in phononics.

Dielectric switching studies of polyvinylidene fluoride thin films with dominant planar ferroelectric domain configuration for flexible electronic devices

Electrical switching characteristics of the polymer chains of polyvinylidene fluoride (PVDF) thin films with dominant planar domain configuration were investigated in this work. PVDF a semi-crystalline piezoelectric polymer is known to undergo structural transformation when subjected to electric field. In this study, the I-V characteristics of PVDF was analyzed by varying the delay time from 0.1 to 0.001 seconds in order to understand the response of switching behavior; a promising attribute that governs the operational speed of the device. A hysteretic behavior in the I-V characteristics was observed at different drive voltages. The ferroelectric polarization domains responds at different voltages and give rise to polarization switching currents. In addition to this, at relatively larger voltages (> 10 V) the amorphous intermediate regions of PVDF is expected to undergo an amorphous to crystalline transformation. Hence, the switching characteristics of the ferroelectric domains in the form of switching currents and the dipolar re-orientation arising due to the amorphous to crystalline transformation by rotation of polymer chains are captured at different voltages. Furthermore, a longer delay time (0.1 seconds) is employed to capture the current arising from a reversible amorphous to crystalline transformation. The dielectric relaxation time for the rotation of polymer chains in PVDF was inferred from independent studies and observed to be between 100 to 500 μS.

Flexural fracture mechanisms and fatigue behaviors of Bi4Ti3O12-based high-temperature piezoceramics sintered at different temperatures

In this paper, a series of Aurivillius phase Bi4Ti2.95W0.05O12.05 + 0.2 wt% Cr2O3 (ab. BTWC) ceramics were prepared by a solid-reaction process and sintered at different temperatures (1050 ℃~1150 ℃), their microstructures, fracture mechanisms and fatigue behaviors were investigated under three-point-bending mode. The results show that the grain size of BTWC ceramics increases with increasing the sintering temperature. The typical transgranular mode dominates the fracture behavior of the samples sintered at lower temperatures, while the intergranular fracture can be also observed in the samples sintered at higher temperatures. Besides, the storage modulus (E’) and mechanical loss (tanmδ) of BTWC ceramics have a subtle variation with the increase of sintering temperature. In addition, the high-temperature environment could not only decrease the fracture toughness and bending strength of ceramics but also change their fracture mode. On the other hand, the bending strength also decreases with the decrease of loading rates, which could be attributed to the slow crack growth referring to the dynamic fatigue behavior of brittle materials. The slow crack growth parameter (n) of BTWC ceramics shows a downtrend with increasing their sintering temperature, indicating that those high temperature sintering samples possess a higher susceptibility when subjected to the long-term stress corrosion. Furthermore, the sample sintered at 1125 ℃ exhibits an excellent fatigue resistance when subjected to the cyclic stress. The corresponding fatigue mechanism is not only related to the ferroelectric domain configuration but also involved with the pores or impurities.

Bi-ferroic memristive properties of multiferroic tunnel junctions

The giant tunnelling electroresistance (TER) and memristive behaviours of ferroelectric tunnel junctions make them promising candidates for future information storage technology. Using conducting ferromagnetic layers as electrodes results in multiferroic tunnel junctions (MFTJs) which show spin dependent transport. The tunnelling magnetoresistance (TMR) of such structures can be reversibly controlled by electric pulsing owing to ferroelectric polarisation-dependent spin polarisation at the ferroelectric/ferromagnetic interface. Here, we show multilevel electric control of both TMR and TER of MFTJs, which indicates the bi-ferroic or magneto-electric memristive properties. This effect is realised by manipulating the ferroelectric domain configuration via non-volatile partial ferroelectric switching obtained by applying low voltage pulses to the junction. Through electrically modulating the ratio between up- and down-polarised ferroelectric domains, a broad range of TMR (between ∼3% and ∼30%) and TER (∼1000%) values can be achieved. The multilevel control of TMR and TER using the electric pulse tunable ferroelectric domain configuration suggests a viable way to obtain multiple state memory.

An optical method for characterizing domain wall motions and ferroelectric hysteresis in tetragonal Mn:Fe:KTN co-doped crystals

An optical method is proposed to extract the displacement vector of domain wall (DW) sidewise motion from ferroelectric domain configuration pattern on a tetragonal Mn:Fe:KTN crystal. The ferroelectric domain configuration evolution under an external electric field is observed in situ using optical microscope imaging system, and the relative displacement of DW sideways motion between two adjacent electric fields is extracted. By the combination of the new domain length vector extracted, the ferroelectric domain displacement vector as a function of field strength can be obtained; what is more, the hysteresis loop can be achieved during field cycling. The method provides an access to directly manipulating DW motion and exploring the properties of ferroelectric materials from ferroelectric domain configuration pattern.

Ferroelectric Heterostructures for Synapse Devices

Ferroelectric polarization related charge conduction have shown intriguing properties of ferroelectric heterostructure devices, such as ferroelectric tunnel junction, switchable diode, and ferroelectric memristor. Recently, ferroelectric heterostructure has been proposed for synapse device exhibiting a high on/off ratio, low power consumption and short process time. In ferroelectric-based synapse devices, gradual electroresistive modulation is associated with change of ferroelectric domain configuration, providing the controllability of the electric conductance for the effective operation of synapse devices. In this work, we demonstrated a ferroelectric-field-effect transistor based synapse devices with channel layer of metal to semiconducting transition (MST) oxide. Ferroelectric polarization switching can modulate the amount of applied energy to MST oxide phase transition and channel conductance at the same time. Our ferroelectric heterostructure with analog-like electroresistive modulation is highly desirable for realizing a efficient synapse device.