Search Results (108)

Misfit strain between the substrate and the superlattice plays a critical role in determining the domain configurations and ferroelectric properties of superlattice heterostructures. This implies that a proper substrate material can be selected to design and tailor the domain structure and the properties of the superlattice. However, the influence of the substrate-induced strain on domain structures and polarization switching processes under different substrates is difficult to observe experimentally. In this study, we employ the phase-field method to explore the effects of different substrates on the domain patterns and switching properties of superlattice heterostructures. A phase diagram mapping substrate lattice parameters against the electric field was constructed for ferroelectric (SrTiO₃)₈/(BaTiO₃)₈ superlattice thin films. Néel-type skyrmion structures were observed under an applied electric field and could be stabilized upon field removal. Two distinct switching modes were also identified, depending on the substrate. Additionally, we observed that misfit strain-induced hysteresis linearization enhances both recoverable energy density and energy storage efficiency, suggesting that superlattice heterostructures hold promise for energy storage applications. Our findings provide new insights into the switching mechanisms of superlattice structures and pave the way for designing next-generation functional nanoelectronic devices. Full article

The formation and growth of isolated domains during local switching by a biased tip of a scanning probe microscope in a (100) cut of a bismuth titanate Bi₄Ti₃O₁₂ single crystal were studied experimentally. The as-grown domain structure consists of two domain types: a-type (out-of-plane) and b-type (in-plane). Local switching of the a-type domain area leads to anisotropic growth of a hexagonal a-type domain (a-a switching) with 180° walls. The dependence of the domain size on the pulse duration during domain growth along the b-axis was considered in terms of the anisotropic current-limited domain wall motion. Local switching of the b-type domain area leads to formation of a hexagonal a-type domain (b-a switching) with 90° walls increasing in size linearly with the applied voltage. The dependence of the domain size on the pulse duration was measured over a wide range of humidities. The increase in the domain size at moderate humidity is attributed to the effect of the water meniscus. The decrease in the domain size at high humidity is attributed to backswitching under the action of the residual depolarization field, facilitated by a conductive water layer on the side surfaces of the sample. The obtained results provide useful insights into the domain kinetics of ferroelectrics with C₂ symmetry and can pave the way for the development of domain engineering techniques. The obtained results establish a direct relationship between local switching kinetics, crystallographic anisotropy, and environmental conditions. This provides the scientific community with a new framework for understanding domain wall motion in multiaxial ferroelectrics, which is essential for the development of stable and reliable domain-engineered devices. Full article

Piezo-enhanced photocatalysis is progressively considered an eco-friendly technology for contaminant removal, harvesting not only solar energy but also mechanical vibrations found in nature. Multiferroic materials present a coupled effect of various properties and can potentially increase the applicability of this process. In this study, Cr- doped bismuth ferrite thin film was deposited on SrTiO₃ substrate by HiPIMS, and its photo-, piezo-, and piezo-photocatalytic efficiencies in Rhodamine B (RhB) degradation were analyzed. The highest removal percentage was found under the simultaneous exposure of visible light and mechanical vibrations, reaching 86.2% after 180 min. The calculated efficiencies for photo- and piezocatalysis were 12.2% and 83.7%, respectively. The rate constant (k) for piezo-photocatalysis was 16.1 times higher than that found during photocatalytic experiments. To assess the contribution of each reactive species to the decomposition process, different reagents were added to the Rhodamine B contaminated solution. The results revealed that when p-benzoquinone was used, the degradation efficiency declined significantly from 86.2% to 37.6%, suggesting that superoxide radicals (O₂^•−) play a key role in decomposing RhB molecules. The structural, chemical, optical, and ferroelectric changes caused by the catalytic processes were analyzed and linked to the proposed degradation mechanisms. The poor photocatalytic efficiency was linked to an improper band structure and an improper polarization orientation of the ferroelectric domains in the as-deposited film. The degradation mechanisms in piezo-photocatalysis were driven partly by the band bending caused by mechanical vibrations and partly by the reorientation of the induced polarization of the domains in the unstrained film. Full article

The efficient and accurate description of gradient energy anisotropy remains a significant challenge in the phase-field modeling of ferroelectric/antiferroelectric (FE/AFE) composite systems. To address this limitation, we have developed a perturbation model for solving anisotropic gradient energy based on Fourier spectral methods. Through a Fourier-space perturbation scheme, we achieve the ability to treat the full anisotropic gradient energy tensor with spatial variations, overcoming limitations of previous constant-coefficient or isotropic approximations. The application of this model to FE/AFE composites demonstrates exceptional robustness and convergence efficiency. Numerical results indicate that the proposed perturbation scheme can accurately reproduce antiferroelectric phase diagrams and AFE-FE phase transition pathways under varying gradient energy parameters. Furthermore, the algorithm exhibits superior scalability, allowing for a seamless extension to three-dimensional (3D) simulation domains. This capability facilitates the visualization of complex nanodomain structures and reveals the intricate 3D evolution mechanisms of polarization textures. Full article

Lead-free transparent ferroelectric ceramics with integrated opto-electro-mechanical functionalities are pivotal for next-generation multifunctional devices. In this study, K_0.48Na_0.52NbO₃-xLa₂O₃ (KNN-xLa, x = 0.005 − 0.04) ceramics were fabricated via a conventional solid-state route to investigate the La³⁺-induced multiscale structural evolution and its modulation of optical and electrical properties. La³⁺ substitution drives a critical structural transition from an anisotropic orthorhombic phase (Amm2) to a high-symmetry pseudocubic-like tetragonal phase (P4mm) for x ≥ 0.025, characterized by minimal lattice distortion (c/a = 1.0052). This enhanced structural isotropy, coupled with submicron grain refinement (<1 μm) driven by ${\mathrm{V}}_{\mathrm{A}}^{\prime }$-mediated solute drag, effectively suppresses light scattering. Consequently, a high-transparency plateau (T₇₈₀ ≈ 53–58%, T₁₇₀₀ ≈ 70–72%) is achieved for 0.025 ≤ x ≤ 0.035. Simultaneously, the system undergoes a crossover from normal ferroelectric (FE) to relaxor (RF) state, governed by an FE–RF boundary at x = 0.015. While x = 0.005 exhibits robust piezoelectricity (d₃₃ ≈ 92 pC/N), the x = 0.015 composition facilitates a transitional polar state with large strain (0.179%) and high polarization (P_m ≈ 33.3 μC/cm², P_r ≈ 15.8 μC/cm²). Piezoresponse force microscopy (PFM) confirms the domain evolution from lamellar macro-domains to speckle-like polar nanoregions (PNRs), elucidating the intrinsic trade-off between optical transparency and piezoelectricity. This work underscores La³⁺ as a potent structural modifier for tailoring phase boundaries and defect chemistry, providing a cost-effective framework for developing high-performance transparent electromechanical materials. Full article

Hexagonal rare-earth manganites, as prototypical improper ferroelectrics in which structural distortions give rise to ferroelectricity, exhibit unique physical phenomena that are absent in conventional proper ferroelectrics. Owing to their Z₂ × Z₃ topologically protected ferroelectric domain structure, characterized by the convergence of six domains at vortex core, hexagonal manganites can host charged domain walls exhibiting multiple distinct conductive states and unconventional physical effects such as the half-wave rectification effect within a single bulk single crystal, opening up promising avenues for the practical applications. Moreover, as an excellent experimental platform for verifying the Kibble–Zurek mechanism, hexagonal manganites not only possess a broad application potential but also embody rich and fundamental physical insights. Given a series of recent advances in this field, it is essential to systematically summarize and discuss the key findings, current progress, and future research perspectives concerning the hexagonal manganite system. In this review, the origin of ferroelectricity in hexagonal manganites are first clarified, followed by a discussion of the formation and transformation mechanisms of unique ferroelectric domain structures, as well as the intrinsic mechanical properties. Subsequently, the manipulation of topological defects are compared, including electric fields, thermal treatment, oxygen vacancies, and stress–strain fields. Building upon these discussions, the distinct physical effects observed in hexagonal manganites are comprehensively summarized, such as domain wall conductance, dielectric and ferroelectric properties, and thermal conductivity. Finally, based on a detailed summary of the major achievements, the unresolved issues that warrant further investigation are highlighted, thereby offering guidance for future research directions and providing valuable insights for the broader study of ferroelectric materials. Full article

One-dimensional (1D) multiferroic composite nanofibers are known to exhibit enhanced magnetoelectric (ME) coupling compared to their thin-film and bulk counterparts with similar compositions. While measuring their local ME coupling at the nanoscale is essential for understanding multiferroic interactions, it remains challenging due to their complex structure. In this work, multiferroic Pb(Zr_0.52Ti_0.48)O₃-CoFe₂O₄ (PZT-CFO) Janus-type nanofibers were synthesized by electrospinning. This unique structure is expected to provide a more compact and continuous interface between the ferroelectric and ferromagnetic phases compared to core–shell configurations. X-ray diffraction confirmed the coexistence of the perovskite PZT and spinel CFO phases without detectable impurities. The Janus configuration was directly verified by scanning electron microscopy and Kelvin probe force microscopy, which revealed a distinct surface potential contrast between the two halves of a single nanofiber. Magnetic hysteresis loops demonstrated the macroscopic ferromagnetic behavior of the nanofiber assembly. Local magnetoelectric coupling was probed using piezoresponse force microscopy under an applied magnetic field. An enhancement of the intrinsic piezoresponse from 15 pm to 19 pm. was observed upon applying an 8000 Oe magnetic field, providing direct evidence of strain-mediated ME coupling at the nanoscale. Although no ferroelectric domain switching was observed, likely due to the substrate clamping effect, the observed piezoresponse modulation confirms the functional ME interaction. These findings suggest that the Janus nanofibers hold promise for applications in one-dimensional multiferroic devices. Full article

The phase transitions and switching dynamics of topological polar textures in hafnium oxide (HfO₂)-based cylindrical-shell ferroelectrics are studied using a three-dimensional (3D) phase field model based on the self-consistent solution of the time-dependent Ginzburg–Landau model and Poisson equation. The comprehensive interplays of bulk free energy, gradient energy, depolarization energy, and elastic energy are taken into account. When a cylindrical ferroelectric device is biased under the in-plane radial electric field, there is a size-controlled phase transition between the ferroelectric (FE), antiferroelectric (AFE), and paraelectric (PE) phases, depending on ferroelectric film thickness and cylindrical shell radius. For in-plane polarization textures at the equilibriums, the FE phase has a Néel-like texture with a center-type four-quad domain, the AFE phase has a monodomain texture, and the PE phase has a Bloch-like texture with a vortex four-quad domain. These polarization domain textures are resultant from energy competition and topologically protected by the geometrical confinement. The polarization dynamics from polar states towards equilibriums are analyzed considering the separated contributions of x- and y-components of polarizations that are driven by x-y in-plane electric fields. The emergent topological domains and phase transitions provide guidelines for geometrical engineering of a novel nano-structured ferroelectric device that is different from the planar one, offering new possibilities for multi-functional high-density ferroelectric memory. Full article

Multilayer heterostructures of [(BiFeO₃)_m/(SrTiO₃)_n]_p were synthesized on ITO-coated quartz substrates via pulsed laser deposition, with varying thickness ratios (r = n/m) and periodicities (p = 1–3). Structural, electrical, and piezoelectric properties were systematically investigated using X-ray diffraction, AFM, and PFM. The BiFeO₃ layers crystallized in a distorted rhombohedral phase (R3c), free of secondary phases. Compared to single-layer BiFeO₃ films, the multilayers exhibited markedly lower leakage current densities and enhanced piezoelectric response. Electrical conduction transitioned from space-charge-limited current at low fields (E < 100 kV/cm) to Fowler–Nordheim tunneling at high fields (E > 100 kV/cm). Optimal performance was achieved for r = 0.30, p = 1, with minimal leakage (J = 8.64 A/cm² at E = 400 kV/cm) and a peak piezoelectric coefficient (d₃₃ = 55.55 pm/V). The lowest coercive field (Ec = 238 kV/cm) occurred in the configuration r = 0.45, p = 3. Saturated hysteresis loops confirmed stable ferroelectric domains. These findings demonstrate that manipulating layer geometry in [(BiFeO₃)_m/(SrTiO₃)_n]_p stacks significantly enhances functional properties, offering a viable path toward efficient, lead-free piezoelectric nanodevices. Full article

The design and adjustable properties of nanoporous materials are important for current and future technological applications, research, and development. In addition, nanoporous ferroelectric materials have the potential to achieve competitive ferroelectric, dielectric, and piezoelectric characteristics. In this work, using the phase-field model, we found that the shape of pores in barium titanite ceramics governs the formation of the ferroelectric domain structure and the switching hysteresis loop. A remanent polarization-coercive field (P_r-E_c) diagram is introduced to denote the shape of the hysteresis loops. We performed a fundamental study in understanding how the domain structures affect the properties of domain-engineered porous ferroelectrics. Simulation results show that the hysteresis loop of porous ferroelectrics can be designed by controlling the shape/orientation of the ellipse-shaped pores. Numerical simulations also verify that the dielectric/piezoelectric properties can be improved with artificially designed porous structures. These phase-field results may be useful in the development of highly performing lead-free ferroelectric/piezoelectric materials. Full article

This work presents an innovative hydrothermal approach for fabricating flexible piezoelectric PZT thin films on 20 μm titanium foil substrates using TiO₂ and SrTiO₃ (STO) interlayers. Three heterostructures (Ti/PZT, Ti/TiO₂/PZT, and Ti/TiO₂/STO/PZT) were synthesized to enable low-temperature growth and improve ferroelectric performance for advanced flexible MEMS. Characterizations including XRD, PFM, and P–E loop analysis evaluated crystallinity, piezoelectric coefficient d₃₃, and polarization behavior. The results demonstrate that the multilayered Ti/TiO₂/STO/PZT structure significantly enhances performance. XRD confirmed the STO buffer layer effectively reduces lattice mismatch with PZT to ~0.76%, promoting stable morphotropic phase boundary (MPB) composition formation. This optimized film exhibited superior piezoelectric and ferroelectric properties, with a high d₃₃ of 113.42 pm/V, representing an ~8.65% increase over unbuffered Ti/PZT samples, and displayed more uniform domain behavior in PFM imaging. Impedance spectroscopy showed the lowest minimum impedance of 8.96 Ω at 10.19 MHz, indicating strong electromechanical coupling. Furthermore, I–V measurements demonstrated significantly suppressed leakage currents in the STO-buffered samples, with current levels ranging from 10⁻¹² A to 10⁻⁹ A over ±3 V. This structure also showed excellent fatigue endurance through one million electrical cycles, confirming its mechanical and electrical stability. These findings highlight the potential of this hydrothermally engineered flexible heterostructure for high-performance actuators and sensors in advanced MEMS applications. Full article

This paper considers the uniaxial orientation effect on the structure and piezoelectric properties of vinylidene fluoride-tetrafluoroethylene copolymer ferroelectric films. The films were exposed to uniaxial orientation stretching in a temperature range from 20 °C to 60 °C; then, they were contact polarized under normal conditions. The temperature dependence of the electric strength was determined. The longitudinal piezoelectric coefficient d₃₃ values were measured by the quasi-static Berlincourt method. The piezoresponse force microscopy (PFM) method was used to investigate the film domain structure before and after polarization, and the local piezoelectric coefficient values were also calculated. Phase composition was studied using differential scanning calorimetry and infrared spectroscopy with the Fourier transform. It was found that uniaxial orientation stretching contributed to an increase in the piezoelectric coefficient d₃₃ from 5 pC/N to 16–20 pC/N. The results obtained indicate the importance of the amorphous phase contribution to the formation of the piezoelectric properties in polymeric materials. Full article

Various types of strain, as well as chemical pressure induced by dopants, can effectively tailor the performance of perovskite thin films, including their optical, electrical or photoelectrochemical properties. The control of these functional properties through such engineering techniques is key to fulfilling the application-specific requirements of ferroelectric devices in various fields. Numerous models and experimental data have been published on this subject, especially on ferrite-based ferroelectric materials. Within this paper, the mechanisms of tuning ferroelectric intrinsic properties, such as polarization and ferroelectric domain configurations, through epitaxial strain and doping, as well as the role of these techniques in influencing functional properties such as dielectric and photoelectrochemical ones, are presented. This review examines the significant improvements in dielectric properties and photoelectrochemical efficiency achieved by the strategical control of key functionalities including dielectric losses, domain structures, charge separation and surface reactions in strained/doped ferroelectric thin films, highlighting the advancements and research progress made in this field in recent years. Full article

The excellent temperature stability and high saturation polarization of Bi_0.5Na_0.5TiO₃ (BNT) make it a promising candidate for energy storage capacitors. However, its disadvantages, such as low breakdown strength, high remnant polarization, and a complex sintering process, limit its further development. To address this, (1 − x) Bi_0.5Na_0.5TiO₃−x Sr(Mg_1/3Nb_2/3)O₃ ceramics were fabricated, where ion doping was employed to modify the domain structure, reduce the grain size, and improve the energy storage performance. With the increase in dopant concentration, the evolution from long-range-ordered ferroelectric micro-domains into short-range-ordered randomly oriented polar nanoregions (PNRs) was revealed, as demonstrated by XRD and Raman spectroscopy. This resulted in a diffuse phase transition peak and a significant reduction in remnant polarization. However, the saturation polarization also decreased. Finally, the optimal energy storage performance was achieved at a medium dopant concentration (x = 0.10), accompanied by reduced grain size and a dense microstructure. This composition exhibited a discharged energy density of 1.64 J/cm³ at a low electric field of 150 kV/cm, representing a notable improvement over pure BNT, which showed a highly lossy P-E loop and a discharged energy density of only 0.14 J/cm³ at the same electric field. Full article

This work explores the deposition of hexagonal (h-) LuMnO₃ thin films in the P6₃cm phase and investigates the conditions under which the synergy of ferroelectric and photoactive properties, can be achieved to confirm the potential of this material for applications in the development of next-generation photovoltaic devices. Single-phase h-LuMnO₃ was successfully deposited on different substrates, and the thermal stability of the material was confirmed by Micro-Raman spectroscopy analysis from 77 to 850 K, revealing the suitable ferro- to para-electric transition near 760 K. Optical measurements confirm the relatively narrow band gap at 1.5 eV, which corresponds to the h-LuMnO₃ system. The presence of domain structures and the signature of hysteresis loops consistent with ferroelectric behaviour were confirmed by piezoresponse force microscopy. In addition, light-dependent photocurrent measurements revealed the photoactive sensitivity of the material. Full article