Entropy engineering has recently emerged as a promising strategy for enhancing the performance of energy-storage ceramics. In this work, four high-entropy compositions with equimolar ratios were designed, and their single-phase formation behavior was analyzed by combining formation-energy calculations with lattice-distortion evaluation. A potential quasi-linear high-entropy additive, (Na0.2La0.2Ba0.2Sr0.2Ca0.2)TiO3, was thereby identified. Experimental results reveal that this composition delivers a high recoverable energy-storage density (Wrec) of 3.83 J cm−3 and an ultrahigh efficiency (η) of 94.4% under an electric field of 430 kV cm−1, confirming its effectiveness as a high-entropy energy-storage modifier. This study integrates experimental characterization with computational analysis to preliminarily assess the phase stability of high-entropy perovskite ceramics, offering theoretical guidance for future material design and compositional optimization.

Optical means instead of electric fields may offer a new pathway for low-power and wireless control of magnetism, holding great potential to design next-generation memory and spintronic devices. Artificial multiferroic materials have shown remarkable suitability as platforms towards the optical control of magnetic properties. However, the practical use of magnetic modulation should be both stable and reversible and, particularly, it should occur at room temperature. Here we show an unprecedented reversible modulation of magnetism using low-intensity visible-light in Fe75Al25/BaTiO3 heterostructures, at room temperature. This is enabled by the existence of highly oriented charged domain walls arranged in arrays of alternating in-plane and out-of-plane ferroelectric domains with stripe morphology. Light actuation yields a net anisotropic stress caused by ferroelectric domain switching, which leads to a 90-degree reorientation of the magnetic easy axis. Significant changes in the coercivity and squareness ratio of the hysteresis loops can be light-modulated, encouraging the development of novel low energy-consumption wireless magneto-optical devices.

Low-consumption ceramics processing routes are expected to replace conventional ones due to environmental concerns. In this context, flash sintering is garnering interest because it allows dense ceramics to be obtained in just a few minutes and at relatively low temperatures. This is particularly interesting for sintering alkaline-based compounds due to the easy volatilization of these elements. In this work, current-controlled flash sintering is used to obtain potassium-sodium niobate (KNN)-based piezoceramics with refined microstructure and suitable stoichiometry, leading to improved functional properties. KNN-based materials are currently outstanding lead-free piezoceramics, with their properties highly sensitive to the proper construction of the polymorphic phase boundary, as in the case of the first promising composition (K0.44Na0.52Li0.04)(Nb0.86Ta0.10Sb0.04)O3. Results of this work show that sintering parameters may determine the polymorphic behavior of this system, thereby evincing flash sintering allows polymorphic phase boundary to be fine-tuned. It is demonstrated that the convergence of microstructure refinement and compositional control holds the potential for enhancing properties through a proper electric current control during flash sintering.

The concept of multiphysics, where materials respond to diverse external stimuli, such as magnetic fields, electric fields, light irradiation, stress, heat, and chemical reactions, plays a fundamental role in the development of innovative devices. Nanomanufacturing, especially in low-dimensional systems, enhances the synergistic interactions taking place on the nanoscale. Light-matter interaction, rather than electric fields, holds great promise for achieving low-power, wireless control over magnetism, solving two major technological problems: the feasibility of electrical contacts at smaller scales and the undesired heating of the devices. Here, we shed light on the remarkable reversible modulation of magnetism using visible light in epitaxial Fe3O4/BaTiO3 heterostructure. This achievement is underpinned by the convergence of two distinct mechanisms. First, the magnetoelastic effect, triggered by ferroelectric domain switching, induces a proportional change in coercivity and remanence upon laser illumination. Second, light-matter interaction induces charged ferroelectric domain walls' electrostatic decompensations, acting intimately on the magnetization of the epitaxial Fe3O4 film by magnetoelectric coupling. Crucially, our experimental results vividly illustrate the capability to manipulate magnetic properties using visible light. This concomitant mechanism provides a promising avenue for low-intensity visible-light manipulation of magnetism, offering potential applications in multiferroic devices.

Abstract Ba0.85Ca0.15Zr0.1Ti0.9O3 (BCZT) stands out among lead‐free ferroelectric oxides under consideration to replace state‐of‐the‐art high‐sensitivity piezoelectric Pb(Zr,Ti)O3, for a range of energy conversion ceramic technologies. However, the best performances have been reported for very coarse‐grained materials, and attempts to refine microstructure below 10 µm grain size consistently result in significant property degradation. Here a comprehensive study of the grain size effects on the properties of BCZT across the micron scale is reported, down to the verge of the submicron one. Results show a distinctive early evolution of properties for grain sizes between 1 and 5 µm. For the larger sizes in this range, an opposite effect is found for the piezoelectric charge coefficient and electric field‐induced strain with respect to the very coarse‐grained material, while very good overall performance is maintained. For the lower sizes, relaxor features appear, yet materials can still be poled indicating their ferroelectric nature. This strongly resembles size effects in the Pb(Mg1/3Nb2/3)O3‐PbTiO3 system, driven by the slowing down of the relaxor to ferroelectric transition with size reduction, though kinetics seem to slow down across much larger grain sizes for BCZT. Concomitant changes in the polymorphic phase coexistence are described and discussed by synchrotron X‐ray diffraction.

Photostrictive materials have a growing interest because of their great potential as light-driven actuators, among other optomechanical applications. In this context, the optical control of macroscopic strain in ferroelectrics has recently attracted remarkable attention as an effective alternative to the conventional electric control of strain. Here, a clear correlation between optical absorption and light-induced strain in polycrystalline BaTiO3 is shown. Specifically, the grain size and the sample thickness dependence of optical absorption when the material is irradiated with energy photons lower than the band gap evidence that light absorption at charged domain walls is the core of the observed photo-response in ferroelectrics. The photoinduced electronic reconstruction phenomenon is proposed as the primary physical mechanism for light absorption at charged domain walls. Results open a new pathway to designing ferroelectric-based devices with new functionalities like thickness gradient-based photo-controlled nanoactuators.

Flash sintering is a novel sintering technique that allows high-density ceramics to be obtained at low temperatures and using short dwell times, thus providing an energy-efficient alternative to conventional sintering. The microstructure of flash-sintered samples can be fine-tuned by a proper control of electrical parameters such as current density, electric field, and current profile, yielding significant improvements of functional properties. The starting powder should also be carefully selected since better sintering results are reported for smaller green grain sizes. However, this work evidences time evolution of electrical properties of flash-sintered BaTiO3 ceramics from submicron powders. The results reveal that these transformations greatly depend on powder grain size and can be further adjusted with an adequate selection of electric power profiles. This work provides new insights into ongoing phenomena during field-assisted sintering, such as grain growth and defect formation dynamics. Although the results focus on BaTiO3, it offers a new pathway to tailor the microstructure of flash-sintered ceramics, which may be extended to other electronic materials. Flash sintering experiments on different-sized BTO powders are performed, and the influence of the conditions over the achieved microstructures and functional properties is shown. For smaller powder sizes a time instability of properties is revealed.

Due to environmental concerns, extensive research has been carried out to develop high-performance lead-free piezoceramics capable of replacing commercial lead-based materials. The lead-free (Ba0.7Ca0.3)TiO3−Ba(Zr0.2Ti0.8)O3 system has emerged as a candidate for room temperature transducer applications because a high piezoelectric charge coefficient is achieved in this system for compositions at the morphotropic phase boundary. However, conventional ceramic processing of these eco-friendly piezoceramics demands high energy consumption because long-lasting, high-temperature heat treatments are needed, which often lead to microstructural degradation that compromises the material reliability. Field-assisted flash sintering has started to be explored since the application of an adequate electric field was shown to significantly reduce the sintering time and temperature, thereby controlling grain growth. In this work, Ba0.85Ca0.15Zr0.1Ti0.9O3 ceramics are obtained by current-controlled flash sintering of mechanosynthesized nanopowders. Exhaustive control of the sintering parameters allows tailoring of the microstructure, which allows dense fine-grained flash-sintered ceramics exhibiting a high electric field-induced strain response to be obtained.

Light-induced ferroelectric domain wall motion turns out to be a promising phenomenon to develop new photocontrolled devices. However, the physical origin of this light-matter coupling when material is irradiated with visible light remains unclear. Here, a phenomenological model predicting the motion of charged domain walls (CDWs) is developed. The photoinduced electronic reconstruction mechanism is proposed as the primary absorption mechanism, leading to a linear dependence for the polarization perturbation with the light intensity. Domain wall motion is then driven by the energetic difference between domains in a CDW array, such that the macroscopic polarization can be easily tuned.

Flash sintering is arousing growing interest because high-density ceramics can be obtained at lower temperatures and shorter dwell times than conventional sintering. However, not only temperature and dwell times should be controlled during flash sintering but also parameters such as the electric field and electric current should be considered. Controlling all the parameters during the processing allows comprehensive control of the microstructure and, consequently, functional properties can be improved. In this work, it is evidenced that an exhaustive control of the flash electric current is a crucial factor for tailoring the microstructure of BaTiO3 ceramics. The results reveal that the most suitable way to control the sintering process is by using non-linear current profiles because better densification and improved grain growth is achieved. Although the results focus on BaTiO3, this work offers a new pathway to tailor the microstructure of flash sintered ceramics, which may be extended to other materials.

The fragility parameter is one of the most important material constants that is extensively used in glass science, playing a central role in the enhancement of understanding the glass formation process of disordered systems. Although fragility has been widely used, this concept has never been precisely defined and evaluated in relaxor ferroelectrics. Here, we have filled up this scientific gap. Based on a generalized Vogel–Fulcher–Tammann equation, the fragility parameter is introduced for relaxor ferroelectrics. The new formulation has been quantitatively assessed by combining dielectric spectroscopy and pyroelectric measurements on canonical relaxors. A clear correlation between the fragility and a new local structural heterogeneity-related order parameter elucidates new information about the ferroelectric order of relaxor ferroelectrics. This may open a new pathway to disentangle relaxation phenomena in other relaxor ferroics.

The use of photonic concepts to achieve nanoactuation based on light triggering requires complex architectures to obtain the desired effect. In this context, the recent discovery of reversible optical control of the domain configuration in ferroelectrics offers a light-ferroic interplay that can be easily controlled. To date, however, the optical control of ferroelectric domains has been explored in single crystals, although polycrystals are technologically more desirable because they can be manufactured in a scalable and reproducible fashion. Here we report experimental evidence for a large photostrain response in polycrystalline BaTiO3 that is comparable to their electrostrain values. Domains engineering is performed through grain size control, thereby evidencing that charged domain walls appear to be the functional interfaces for the light-driven domain switching. The findings shed light on the design of high-performance photoactuators based on ferroelectric ceramics, providing a feasible alternative to conventional voltage-driven nanoactuators.

An efficient long-term storage of cryogenic propellants is a challenge for future space exploration missions. The vapour bubbles formed as a result of boil-off in the tank walls can generate foam structures, which could be hazardous in different operations in orbit. A recently proposed approach to control the dynamics of bubbles is based on the generation of an acoustic field by means of a piezoelectric transducer. This technology needs to be validated at cryogenic temperatures in order to be applicable in space. In this perspective, different piezoelectric elements and matching layer materials have been tested at cryogenic temperatures to assess their performance at such environmental conditions. We consider the use of soft PZT piezoceramics coupled with an epoxy resin as the matching layer. Experimental data reveal that epoxy resin-based acoustic matching layers exhibit a linear increase in the transmittance of the acoustic amplitude at cryogenic conditions. The peak-to-peak amplitude increases as temperature decreases up to a factor of 1.6. This result opens the possibility of generating and transmitting acoustic waves at cryogenic temperatures, which could be used in the recently proposed technology to control the dynamics of vapour bubbles in cryogenic fuel tanks.

Dielectric and piezoelectric responses of slightly textured, lead barium niobate ceramics are studied. The designed morphotropic phase boundary composition ( Pb 0.63 Ba 0.37 Nb 2 O 6) shows considerable nonlinear dielectric and piezoelectric responses. While these nonlinear behaviors lead to significant instabilities of the functional properties, interesting features are revealed as a consequence of the texturing effect in the composition studied. An improved dielectric performance and a lower nonlinear piezoelectric response are observed when the electric field is applied to the sample in the forging direction. The results are quantitatively discussed in the framework of the Preisach and Rayleigh models. In this context, a decrease in the nonlinear response can be associated with a lower grain size related to the texture. The results of this work show that texturing is an effective route for controlling the undesirable nonlinear behavior of piezoceramics with tetragonal tungsten bronze structure.

Ultrasonic transducer design is focused to maximize performance in specific applications, usually leading to complex design and expensive construction and assembly. With the aim to overcome this drawback, a general-purpose immersion ultrasonic transducer for pulsed regime applications has been developed. The design of each element of the transducer is described in this paper, wherein materials and geometries for each part have been recommended. A simple theoretical model has been proposed in order to predict the form of the received electric signal in the target transducer. The model is based on the assumption that the piezoelectric element acts as an underdamped oscillator, forced by the acoustic field coming from the propagation medium. Excellent agreement between the experimental measurements and the analytical model is achieved. Electrical impedance measurements reveal negligible differences between the resonance frequency of the active element and that of the assembled transducer. The designed devices have been characterized in water using two identical transducers placed face to face with changeable orientation. The experimental results show a highly linear response and the generation of a collimated acoustic field. The effects of the thickness of the matching layer on the transmission coefficient have been also studied, resulting in a smooth decrease in the received amplitude, which may significantly lower large-scale production costs.

Finding a feasible principle for a future generation of nanooptomechanical systems is a matter of intensive research, because it may provide new device prospects for optoelectronics and nanomanipulation techniques. Here we show that the strain of a ferroelectric crystal can be manipulated to achieve macroscopic, stable, and reproducible dimensional changes using illumination with photon energy below the material bandgap. The photoresponse can be activated without direct light incidence on the actuation area, because the cooperative nature of the phenomenon extends the photoinduced strain to the whole material. These results may be useful for developing the next generation of high-efficiency photocontrolled ferroelectric devices.

Relaxor ferroelectrics are characterized by a broadened and dispersive permittivity peak in their temperature-dependent dielectric spectra. Although several models have been proposed to explain the nature of these materials, understanding their relaxation dynamics still remains open and requires additional theoretical and experimental explanations. Particularly, a precise determination of the freezing temperature still remains controversial because the influence of dynamic ruptures at temperatures approaching the freezing states (dynamic crossovers) has never evaluated before. In this paper, a model-free approach for describing the super-Arrhenius behaviour in glassy systems is validated for relaxor ferroelectrics. As a result, a predicted dynamic change at a specific temperature (crossover temperature) is evidenced by a derivative-based representation of the relaxation time data. The Stickel function is suggested as a more straightforward but model-dependent method for obtaining the dynamic crossover temperature. Furthermore, the divergence (freezing) temperature is obtained on the basis of the Gruneisen-style activation energy temperature index without assuming any model equation for parameterizing the relaxation data. The influence of the dynamic change occurrences on the freezing temperature determination is also considered, showing that the dynamic crossover temperature determination is a key factor for a proper finding of the freezing temperature in relaxor ferroelectrics.

Relaxor ferroelectrics (RF) are outstanding materials owing to their extraordinary dielectric, electromechanical, and electro-optical properties. Although their massive applications, they remain to be one of the most puzzling solid-state materials because understanding their structural local order and relaxation dynamics is being a long-term challenge in materials science. The so-called Vogel-Fulcher-Tamman (VFT) relation has been extensively used to parameterize the relaxation dynamics in RF, although no microscopic description has been firmly established for such empirical relation. Here, we show that VFT equation is not always a proper approach for describing the dielectric relaxation in RF. Based on the Adam-Gibbs model and the Grüneisen temperature index, a more general equation to disentangle the relaxation kinetic is proposed. This approach allows to a new formulation for the configurational entropy leading to a local structural heterogeneity related order parameter for RF. A new pathway to disentangle relaxation phenomena in other relaxor ferroics could have opened.

Grain-size effect on functional properties of piezoceramics is nowadays an important topic due to the potential applications of these materials at the submicron scale. In this context, we explore the effect of the grain size reduction on the functional properties stability of piezoceramics. Submicron- and micro-structured Pb(Zr,Ti)O-3 based materials are taken as model samples to carry out this study. Rayleigh analysis is used to quantitatively evaluate the domain wall contribution. The results show that the stability of properties depends strongly on grain size. Specifically, the nonlinear response decreases significantly when the grain size is reduced to the submicron scale. This behavior can be explained by taking into account that a grain size reduction involves a grain boundary increment, which may clamp domain walls. The results suggest that grain size engineering may be an effective alternative to the widely used compositional engineering in order to control the undesirable nonlinear behavior in piezoceramics.

The (Ba,Ca)(Zr,Ti)O3 ceramic system has received special attention in recent years because it may lead to promising lead-free piezoceramics. However, the stability of the functional properties of these materials is an important issue that requires greater attention. In this work, the (Ba0.85Ca0.15)(Zr0.1Ti0.9)O3 compound (BCZT) is taken as a reference material for evaluating the variation of the functional properties when an external stimulus (e.g., electric field or dynamical stress) is applied, which may constitute an important drawback of piezoceramics. The results show that BCZT exhibits a huge nonlinear behavior, which notably limits this lead-free material for transfer to applications. The instabilities manifest at considerably low amplitudes of the applied electric field or dynamical stress due to a large extrinsic contribution from the irreversible motion of domain walls. Understanding and controlling the physical phenomena related to the domain wall motion presents a fundamental challenge for achieving an effective enhancement of the functional property stability of this system.