Domain Switching Research Articles

Enhanced domain switching contributing to large strain response in (Bi0.5Na0.5)TiO3–SrTiO3 lead-free thin films

The acquisition of lead-free piezoelectric films with large strain is the key factor in promoting micro-actuator development. A lead-free compound, Bi0.5Na0.5TiO3, exhibits extensive potential in achieving a large strain response and a high inverse piezoelectric coefficient. In this work, (1-x)Bi0.5Na0.5TiO3-xSrTiO3 (BNT-100xST, x = 0.1, 0.2, 0.25) solid solution thin films have been prepared using the chemical solution deposition method. The dielectric nonlinearity and ferroelectric properties of BNT-ST thin films have been systematically studied to investigate the domain wall motion in the films. The most significant domain wall motion was obtained in BNT-20STST thin film, in which film a large strain of 0.89 % was obtained. In addition, the relation between structure and properties as a function of temperature was studied by the temperature-dependent dielectric properties and Raman spectra analysis.

Phase‐Field Study of Nanocavity‐Assisted Mechanical Switching in PbTiO3 Thin Films

AbstractFerroelectric thin films hold significant promise in various nanoelectronic applications, demanding precise control over their domain structures. While electrical field‐driven polarization switching is currently employed, it often leads to undesirable side effects. In contrast, mechanical switching offers a voltage‐free alternative but faces challenges in thicker films. Recent breakthroughs have demonstrated stable mechanical switching in films up to 200 nm thick, attributed to the presence of nanocavities. These nanoscale voids are believed to facilitate domain transitions, serving as essential pinning centers. In this study, mechanical domain switching in thick ferroelectric films is investigated using phase‐field modeling, with a specific focus on evaluating the influence of nanocavities on domain stability. The effects of cavity parameters (size, depth, and dielectric properties) on mechanical switching stability under various applied pressures are systematically examined. The findings reveal the intricate interplay between these factors and outline the conditions for stable mechanical switching. Furthermore, phase‐field simulations are employed to showcase the energetic mechanisms governing nanocavity‐assisted mechanical switching, while also highlighting the pivotal role of these defects as pinning centers. This investigation elucidates the nanocavity‐assisted mechanical control of polarization and the potential for optimizing thin film design through nanocavity engineering, thus enabling mechanical switching across substantial film thicknesses.

Regulation of domain wall motion in PZT-based ceramics through the introduction of local stress fields

At present, a big challenge exists yet in the piezoelectric ceramic material that high piezoelectric performance and low losses (large Qm and low tanδ) are difficult to achieve concurrently due to the effects of domain switching and domain wall motion on electromechanical properties. In this work, by introducing secondary-phase particles (SnO2 particles) into the hard PZT matrix, we successfully build local stress fields in the ceramic. These local stress fields not only pin the domain and domain wall but also diminish the domain size and increase the domain wall density. The former is in favor of reducing the losses, while the latter is beneficial to promoting the piezoelectric properties. Thus, the optimized piezoelectric properties and losses in the ceramic can be obtained simultaneously. The results show that in the PZT/0.3 wt%SnO2 composite, the mechanical quality factor reaches 2800 and the dielectric loss is only 0.4 %, which are superior to the hard PZT matrix. Meanwhile, the composite ceramic has a high piezoelectric constant of 390 pC/N. These excellent properties will push the development of next-generation high-power electromechanical devices.

Domain-modified engineering for low-power resistive switching in ferroelectric diodes

Neuromorphic devices based on ferroelectric resistive switching (RS) effects are promising to simulate the information recognition and memory of the human brain. However, the high power of RS elements in crossbar arrays is still an issue, limiting the neuromorphic applications. Here, we propose a domain-modified engineering for low-power RS in ferroelectric diodes by locally introducing relaxor ferroelectric units to lower domain switching barriers. A low-power RS of ∼ 70 μW, with large OFF/ON resistance ratio and high endurance, is achieved in Au/0.8BaTiO3-0.1Ba0.7Sr0.3TiO3-0.1BaTi0.7Zr0.3O3/Pt diodes, which is about 48.5% lower than that in Au/BaTiO3/Pt diodes. The interaction between macrodomains is depressed by domain modification engineering, lowering domain switching barriers, thereby operating voltage and power are significantly modulated. Meanwhile, good nonvolatility is obtained since the remanent polarization is partially maintained by the initial macrodomains and its decrease is slowed down by the relaxor units. This work provides a strategy to lower RS power by domain modification engineering for developing memristors and neuromorphic computing devices.

Effects of interfacial buffering layer on imprint and domain switching dynamics in Pb(Zr,Ti)O3 thin-film heterostructures

Interfacial engineering is important for ferroelectric thin-film heterostructures because of the modulation of boundary conditions of the spontaneous polarizations and their switching behaviors, which are essential for ferroelectric electronics. In this work, we study the effects of interfacial buffering layer, 5-nm-thick SrTiO3 (STO), on the imprint and domain switching of epitaxial Pt/Pb(Zr,Ti)O3/SrRuO3 (SRO) thin-film heterostructures and capacitors. By buffering the ultrathin SrTiO3 layer at the Pb(Zr,Ti)O3 surface, the imprint effect can be dramatically alleviated as observed in the piezoresponse force microscopy (PFM)-measured domain structures and polarization–electric field hysteresis loops in thin-film capacitors. However, when the SrTiO3 layer is buffered at the Pb(Zr,Ti)O3/SrRuO3 interface, the imprint effect is slightly increased. These phenomena are explained based on the band alignments among the Pt and SrRuO3 electrodes and the Pb(Zr,Ti)O3 layer associated with the existence of oxygen vacancies in the SrTiO3 layer. With the reduction of imprint effect, the domain switching dynamics are also improved in the SrTiO3-buffered Pb(Zr,Ti)O3 capacitor, in which the switching activation field is decreased by about 45.3% in comparison with that of the pristine capacitor. These results facilitate the design and optimization of ferroelectric devices with the improvements in domain configurations, switching behaviors and band alignments.

Multiple factors of regulation for transient negative capacitance in PbZr(1−x)Ti(x)O3 ferroelectric thin films

The negative capacitance (NC) of ferroelectric (FE) materials can effectively break the ‘Boltzmann tyranny’ and drive the continuation scaling of Moore’s law. In this work, to find a novel way for amplifying the transient NC, a series network of external resistors and PbZr(1−x)Ti(x)O3 (PZT) FE capacitors was constructed. Uniform modeling and simulation were performed using Kirchhoff’s current law, electrostatics equations, and Landau–Khalatnikov equations. The derived results revealed that the mismatch of switching rate between free charge and polarization during FE domain switching is responsible for the transient NC generation. Some interesting results were obtained for the regulation of the transient NC by various factors such as the strain between the FE film and substrate, the viscosity coefficient, the ratio of Ti components, the external resistance magnitude, and the operating temperature. This work provides considerable insight into the control of FE transient NC, and offers guidance for obtaining larger and longer transient NC in the widely used PZT thin films.

In situ study on enhanced plastic deformability of Lanthanum-doped Bismuth ferrite processed by flash sintering

BiFeO3 is a promising multiferroic material for versatile device applications due to its co-existence of magnetic (i.e., antiferromagnetic) and ferroelectric ordering at room temperature. While its functional properties have been extensively investigated, the exploration of its mechanical behavior was limited mostly to the thin-film form of BiFeO3. In this work, we conducted in situ micropillar compression experiments to investigate the deformation behavior of La-doped BiFeO3 (La-BFO) samples processed by both conventional and flash sintering methods. The conventionally sintered La-BFO exhibited limited deformability at room temperature and 450 °C. In contrast, the deformability of the flash-sintered La-BFO specimens was substantially improved by nearly 100% at both testing temperatures. Detailed post-mortem studies suggest that preexisting dislocations and wide anti-phase boundaries introduced during flash sintering can toughen flash-sintered La-BFO by easing dislocation migration and ferroelastic domain switching. This study provides a fresh perspective to design an advanced multifunctional system with improved mechanical properties.

The composition / field-induced octahedral tilt, domain switch and improved piezoelectric properties in BF-BT ceramics across phase transition

To clarify the structural mechanism of high piezoelectric activity of (1-x)BiFeO3-xBaTiO3 ((1-x)BF-xBT) solid solution, the evolution of phase structure and domain configuration and their effects on piezoelectric properties were studied...

Ultra-large electromechanical deformation in lead-free piezoceramics at reduced thickness.

Lead-free piezoceramics with large controllable deformations are highly desirable for numerous energy converter applications ranging from consumer electronics to medical microrobots. Although several new classes of high-performance ferroelectrics have been discovered, a universal strategy to enable various piezoceramics to realize large electromechanical deformations is still lacking. Herein, by gradually reducing the thickness from 0.5 mm to 0.1 mm, we discover that a large nominal electrostrain of ∼11.49% can be achieved in thin 0.937(Bi0.5Na0.5)TiO3-0.063BaTiO3 (BNT-BT) ceramics with highly asymmetric strain-electric field curves. Further analyses of the polarization switching process reveal that the boosted strain curves originate from the bending deformation driven by asymmetric ferroelastic switching in the surface layers. Based on this, one monolayer BNT-BT was designed to realize digital displacement actuation and a scanning mirror application with a maximum mirror deflection angle of 44.38°. Moreover, the surface effect-induced bending deformation can be extended to other piezoceramics, accompanied by derived shape retention effects. These discoveries raise the possibility of utilizing thickness engineering to design large-displacement actuators and may accelerate the development of high-performance lead-free piezoceramics.

Achieving High Piezoelectric Performance across a Wide Composition Range in Tetragonal (Bi,Na)TiO3-BaTiO3 Films for Micro-electromechanical Systems.

Tetragonal (1-x)(Bi,Na)TiO3-xBaTiO3 films exhibit enhanced piezoelectric properties due to domain switching over a wide composition range. These properties were observed over a significantly wider composition range than the morphotropic phase boundary (MPB), which typically has a limited composition range of 1-2%. The polarization axis was found to be along the in-plane direction for the tetragonal composition range x = 0.06-1.0, attributed to the tensile thermal strain from the substrate during cooling after the film formation. A "two-step increase" in remanent polarization against an applied maximum electric field was observed at the high-field region due to the domain switching, and a very high piezoelectric response (effective d33 value, denoted as d33,f) over 220 pm/V was achieved for a wide composition range of x = 0.2-0.5 with high tetragonality, exceeding previously reported values for bulk ceramics. Moreover, a transverse piezoelectric coefficient, e31,f, of 19 C/m2 measured using a cantilever structure was obtained for a composition range of at least 10 atom % (for both x = 0.2 and 0.3). This value is the highest reported for Pb-free piezoelectric thin films and is comparable to the best data for Pb-based thin films. Reversible domain switching eliminates the need for conventional MPB compositions, allowing an improvement in the piezoelectric properties over a wider composition range. This strategy could provide a guideline for the development of environmentally acceptable lead-free piezoelectric films with composition-insensitive piezoelectric performance to replace Pb-based materials with MPB composition, such as PZT.

Improving high-field strain and temperature stability on KNN-based ceramics sintered in reducing atmosphere via defect engineering

High-field strain and its temperature stability of (1–x) K0.48Na0.52Nb0.96Ta0.04O3-xBaZrO3+8%MnO+3%ZrO2 (in mole, KNNT-xBZ+8Mn) ceramics sintered in reducing atmosphere are improved simultaneously via defect design in A and B site. There is a conducting type transition from n-type to p-type at x = 0.07. The BaZrO3 dopant not only induces the increase of defects (ZrNb′, BaNa·, BaK·) concentration, but also results in the increase of defect (MnNb‴) concentration, because more Mn ions as +2 oxidation state in ceramics is triggered by BaZrO3 doping modification. Defect dipoles (MnNb′′′−Vo··, ZrNb′-Vo··, BaNa·-VNa′, BaK·-VK′) in poled and aged ceramics enhance the reversibility of the non–180° domains switching, which increases the high-field strain of KNNT-xBZ+8Mn ceramics. The reversibility of non–180° domain switching can be preserved to high temperature due to stable defect dipoles (BaNa·-VNa′, BaK·-VK′) in A-site. The KNNT-xBZ+8Mn ceramics at x = 0.07 show the largest high-field strain coefficient (543 pm/V@20 kV/cm) and the highest temperature stability (125 °C). The KNNT-xBZ+8Mn ceramic is a lead-free material with great potential to be applied in the fabrication of multilayer ceramic actuators with Ni inner electrodes in the future.

Magnetic-Field-Assisted Electric-Field-Induced Domain Switching of a Magnetic Single Domain in a Multiferroic/Magnetoelectric Ni Nanochevron/[Pb(Mg1/3Nb2/3)O3]0.68-[PbTiO3]0.32 (PMN-PT) Layered Structure.

We report the magnetic-field-assisted electric-field-controlled domain switching of a magnetic single domain in a multiferroic/magnetoelectric Ni nanochevrons/[Pb(Mg1/3Nb2/3)O3]0.68-[PbTiO3]0.32 (PMN-PT) layered structure. Initially, a magnetic field was applied in the transverse direction across single-domain Ni nanochevrons to transform each of them into a two-domain state. Subsequently, an electric field was applied to the layered structure, exerting the converse magnetoelectric effect to transform/release the two-domain Ni nanochevrons into one of two possible single-domain states. Finally, the experimental results showed that approximately 50% of the single-domain Ni nanochevrons were switched permanently after applying our approach (i.e., the magnetization direction was permanently rotated by 180 degrees). These results mark important advancements for future nanoelectromagnetic systems.

Electric field tuning of multistate and nonvolatile resistance variation in amorphous Fe75Si25/PMN-0.3PT (0 0 1) heterostructures

The multistate resistance states in the amorphous Fe75Si25/0.7Pb(Mg1/3Nb2/3)O3-0.3PbTiO3 (PMN − 0.3PT) (001) heterostructure were modulated by electric fields (E). Based on the in-plane nonvolatile stress changes associated with ferroelectric domain switching in PMN-0.3PT, the widening and narrowing of surface gaps, and the fact that magnetism generally tracks the strain variation in amorphous Fe75Si25 films, the distinct four-state and nonvolatile resistance tuning near the coercive E-field are observed. Then, combining the converse magnetoelectric coupling and magnetoresistive effect, we quantify the coaction effect and equivalence relation between the E-field and magnetic fields (H) on the resistance modification. Meanwhile, another four-state resistance is obtained under the coaction of the E-fields and H-fields. All eight resistive states exhibit excellent E-field switchable behavior and stability performance at room temperature. These results provide a promising approach for exploring and designing multistate and multifield controlled spintronic memory devices.

Acoustic sensor based on a PVDF-TrFE/BTO composite structure with improved ferroelectric and piezoelectric properties

Ferroelectric composite structures of poly (vinylidene fluoride-co-trifluoroethylene)/ barium titanate (PVDF-TrFE/BTO) were prepared using a solvent casting method and altered using electrical and mechanical modes to improve their ferroelectric characteristics. The PFM and P-E loop analytic studies validated the enhanced ferroelectric and piezoelectric capabilities of the modified composite structures following mechanical stretching and electrical poling. The stretched and poled samples (PT-BT-s-p) were able to achieve a maximum saturated polarization of 5.98 µC/cm2 with suitable saturation loops and domain switching points. The presence of ferroelectric domains was further confirmed by the PFM amplitude and PFM phase graphs of the PT-BT-s-p composite structures. Furthermore, the suggested composite structure achieved a maximum piezoelectric coefficient (d33) value of 11 pC/N. Finally, a lab-scale experiment with a sound wave sensing application was performed and seen with superior outcomes with varying waveforms, amplitudes, and frequencies, making it a promising contender for future sensory devices.

Effects of phase transition on the dynamic discharge energy density of antiferroelectric ceramics

AbstractAntiferroelectrics (AFEs) are widely used for energy storage capacitors. At present, there are two methods to evaluate the energy density of AFE: the recoverable energy density Wre calculated by the low‐frequency P–E loop and the dynamic discharge energy density Wdis calculated by the fast discharge current. It has been widely observed that the value of Wdis is lower than Wre but less attention was paid to how to increase Wdis. Compared with Wre, the value of Wdis is closer to the energy density of AFE pulse capacitors in practical applications. In this work, the effects of phase transition properties on the dynamic discharge energy density were studied from the aspect of domain switching mobility. Compositions with P–E loop varying from “square” to “slant” were fabricated. It was found that in AFEs with “square” P–E loops, the recoverable energy density Wre was remarkably higher than Wdis. By modifying the P–E loops to long slim, the value of Wdis tended to be close to Wre, resulting in higher dynamic discharge energy efficiency. This indicates that by adjusting the P–E loop, higher Wdis can be achieved in AFE with lower Wre. The AFEs with long slim P–E loops also have faster discharge speeds, leading to higher power density. The outstanding fast discharge performance of AFEs with long slim P–E loops originated from their faster domain mobility and less viscous force during domain switching. This work provides a new approach to designing the AFEs energy storage materials by tuning their dynamic phase‐transition properties and domain mobility.

Exploring Multi‐Bit Logic In‐Memory with Memristive HfO2‐Based Ferroelectric Tunnel Junctions

AbstractThe increasing demand for data movement and energy consumption in physically separate von Neumann architectures, where the processor and memory are distinct entities, highlights the severity of the memory‐wall problem. Thus, memristor‐based logic‐in‐memory (LiM) has garnered significant interest as it is a paradigm that enables both logic and memory functionalities to be performed within a single device. Ferroelectric tunnel junctions (FTJs) have the advantages of low energy consumption and high scalability; thus, they are particularly appropriate for use as analog memristors in LiMs. Precise and accurate programming of the analog resistance states in FTJs is essential to achieve an efficient memristor‐based LiM design. However, existing switching models for FTJs cannot completely consider the ferroelectric domain switching, which challenges multi‐bit LiM operations. This particularly applies in cases involving updates from one intermediate resistance state (IRS) to another IRS, such as transitioning from State 01 to 10 in 2‐bit LiM. In this study, a novel phenomenon associated with domain switching is observed in the IRS of an HZO FTJ device and applied it to an LiM implementation. These findings can contribute to the operational accuracy and update rules of not only FTJ‐based LiMs but also other FTJ applications, such as crossbar arrays.

Observation of Micro-Scale Domain Structure Evolution under Electric Bias in Relaxor-Based PIN-PMN-PT Single Crystals

Relaxor ferroelectrics play a vital role as functional components in electromechanical devices. The observation of micro-scale domain structure evolution under electric bias in relaxor ferroelectrics has posed challenges due to their complex domain morphology characterized by small-sized domains. The present study aims to investigate the dielectric diffusion–relaxation characteristics, domain structure, and domain switching evolution under electric bias in high-performance single crystals of Pb(In1/2Nb1/2)O3-Pb(Mg1/3Nb2/3)O3-33PbTiO3. The findings reveal the presence of strip-like domain patterns that interlock irregular small-sized nanodomains in PIN-PMN-33PT single crystals. Furthermore, the sample undergoes three distinct stages under electric bias, including the nucleation of new domains, the gradual forward expansion of domains, and the lateral expansion of domains. These observations provide valuable insights for understanding and exploring domain engineering techniques in relaxor ferroelectrics.

Synaptic devices based on organic ferroelectric memtransistor with arithmetic calculating and logic functions

The bionic features offered by memory device are being actively explored. However, two-terminal memristors exhibit variability and limited capacity due to their inherent single presynaptic input scheme. Compared with the two-terminal memristor, the memtransistor can realize the modulation of conductive channel through the synergistic effect of gate, which enables the multifunctional modulation. Here, based on Schottky barrier tuning at metal-semiconductor interfaces by means of ferroelectric domain switching, a programmable memtransistor with arithmetic calculating and logic function is realized. Memtransistor with drain and gate adjustable non-volatile memory function effectively simulates the plasticity of biological synapses. Moreover, four arithmetical operations: addition, subtraction, multiplication and division are carried out by using the synaptic device. At the same time, the logic gate functions of “XOR” and “XNOR” were implemented based on ferroelectric memtransistor. This result will be helpful to further promote the development of memory computing for synaptic devices.

Ultrahigh strain in PZ-PT-BNT piezoelectric ceramic

Low strain limits the further application of Pb(Zr,Ti)O3 (PZT) piezoelectric ceramics in actuators. Herein, a ternary piezoelectric ceramic xPbTiO3-(0.95-x)PbZrO3-0.05(Bi0.5Na0.5)TiO3 (xPT-PZ-BNT) is proposed and prepared by solid-state method to improve the strain characteristics. Results indicate that a biased electric field is intentionally constructed by defects arising from the incorporation of BNT into PZ-PT ceramic, which promotes non-180° domains to restore to initial states, thereby contributing to the increase in strain. Moreover, the electric domain configuration is efficiently modified by adjusting the component proportion in xPT-PZ-BNT ceramics, in which the 0.42 PT-PZ-BNT presents short and broad domains with fast response to external electric field. Rayleigh analysis indicates that the strain contributed by domain switching is dominant in PT-PZ-BNT ceramics under a high electric field. Consequently, a large strain of 0.4% is achieved in 0.42 PT-PZ-BNT ceramic with the variation less than 10% in the temperature range of 25∼175 °C. This study not only deeply analyzes the effect of domain configuration on the strain for PZT piezoelectric ceramics, but also demonstrates an effective approach to increase the strain through constructing internal biased electric field and regulating domain configuration.

A Homochiral Fulgide Organic Ferroelectric Crystal with Photoinduced Molecular Orbital Breaking

AbstractThermally triggered spatial symmetry breaking in traditional ferroelectrics has been extensively studied for manipulation of the ferroelectricity. However, photoinduced molecular orbital breaking, which is promising for optical control of ferroelectric polarization, has been rarely explored. Herein, for the first time, we synthesized a homochiral fulgide organic ferroelectric crystal (E)‐(R)‐3‐methyl‐3‐cyclohexylidene‐4‐(diphenylmethylene)dihydro‐2,5‐furandione (1), which exhibits both ferroelectricity and photoisomerization. Significantly, 1 shows a photoinduced reversible change in its molecular orbitals from the 3 π molecular orbitals in the open‐ring isomer to 2 π and 1 σ molecular orbitals in the closed‐ring isomer, which enables reversible ferroelectric domain switching by optical manipulation. To our knowledge, this is the first report revealing the manipulation of ferroelectric polarization in homochiral ferroelectric crystal by photoinduced breaking of molecular orbitals. This finding sheds light on the exploration of molecular orbital breaking in ferroelectrics for optical manipulation of ferroelectricity.