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Este trabajo explora la relación entre pobreza multidimensional e informalidad laboral contextualizándolas en la economía popular Argentina, la cual concentra a más de cuatro millones de trabajadores/as. En América Latina y, particularmente, en Argentina se han implementado un gran número de políticas para fomentar la formalización de trabajos populares como estrategia de desarrollo social. Esta monografía cuestiona cómo afecta la formalización del trabajo informal independiente de los barrios populares a la pobreza y sus dimensiones, considerando que su mera existencia constituye una violación a los derechos humanos inherentes a toda persona. Teniendo en cuenta el marco teórico de mercados informales multisegmentados y en base a una revisión sistemática exploratoria de la literatura internacional y el Registro Nacional de Trabajadores/as de la Economía Popular, utilizo un método mixto para indagar y comprender las posibles consecuencias de la inserción laboral de trabajadores/as individuales de barrios populares a su situación de pobreza. Combino esta base teórica con un análisis sobre la política de Monotributo Social en Argentina desde sus comienzos en 2004 hasta el 2020, con el fin de formular recomendaciones que permitan mejorar las políticas de inserción laboral en clave de derechos humanos que contemplen la complejidad del entramado social y popular.

The implementation of nano-engineered composite oxides opens up the way towards the development of a novel class of functional materials with enhanced electrochemical properties. Here we report on the realization of vertically aligned nanocomposites of lanthanum strontium manganite and doped ceria with straight applicability as functional layers in high-temperature energy conversion devices. By a detailed analysis using complementary state-of-the-art techniques, which include atom-probe tomography combined with oxygen isotopic exchange, we assess the local structural and electrochemical functionalities and we allow direct observation of local fast oxygen diffusion pathways. The resulting ordered mesostructure, which is characterized by a coherent, dense array of vertical interfaces, shows high electrochemically activity and suppressed dopant segregation. The latter is ascribed to spontaneous cationic intermixing enabling lattice stabilization, according to density functional theory calculations. This work highlights the relevance of local disorder and long-range arrangements for functional oxides nano-engineering and introduces an advanced method for the local analysis of mass transport phenomena., J.S. acknowledges the support of ICN2 (funded by the CERCA programme/Generalitat de Catalunya and by the Severo Ochoa programme SEV-2017-0706) for the XRD measurements. M.A. acknowledges the support from the Feodor Lynen Research Fellowship Program of the Alexander von Humboldt Foundation and the Isaac Newton Trust, 17.25(a). M.A. and J.D. acknowledge the support from the EPSRC Centre of Advanced Materials for Integrated Energy Systems (CAM-IES) under EP/P007767/1. J.D. also acknowledge support from EPSRC grants EP/N004272/1, EP/T012218/1, the Royal Academy of Engineering- CIET1819_24, ERC POC grant 779444, Portapower. X.W. and H.W. acknowledge the funding support from the U.S. National Science Foundation for the TEM effort at Purdue University (DMR-1565822 and DMR-2016453). This project has received funding from the European Union’s Horizon 2020 research and innovation program under grant agreement No 824072 (HARVESTORE), No 681146 (ULTRASOFC) and No 101017709 (EPISTORE) and was supported by an STSM Grant from the COST Action MP1308: Towards Oxide-Based Electronics (TO-BE), supported by COST (European Cooperation in Science and Technology).

The implementation of nano-engineered composite oxides opens up the way towards the development ofa novel class of superior energy materials. Vertically aligned nanocomposites are characterized by acoherent, dense array of vertical interfaces, which allows for the extension of local effects to the wholevolume of the material. Here, we use such a unique architecture to fabricate highly electrochemicallyactive nanocomposites of lanthanum strontium manganite and doped ceria with unprecedented stabilityand straight applicability as functional layers in solid state energy devices. Direct evidence of synergisticlocal effects for enhancing the electrochemical performance, stemming from the highly ordered phasealternation, is given here for the first time using atom-probe tomography combined with oxygen isotopicexchange. Interface-induced cationic substitution, enabling lattice stabilization, is presented as the originof the observed long-term stability. These findings reveal a novel route for materials nano-engineeringbased on the coexistence between local disorder and long-range arrangement.

Journal of synchrotron radiation 28(1), 146-157 (2021). doi:10.1107/S1600577520013223, For high-resolution powder diffraction in material science, high photon energies are necessary, especially for in situ and in operando experiments. For this purpose, a multi-analyser detector (MAD) was developed for the high-energy beamline P02.1 at PETRA III of the Deutsches Elektronen-Synchrotron (DESY). In order to be able to adjust the detector for the high photon energies of 60 keV, an individually adjustable analyser–crystal setup was designed. The adjustment is performed via piezo stepper motors for each of the ten channels. The detector shows a low and flat background as well as a high signal-to-noise ratio. A range of standard materials were measured for characterizing the performance. Two exemplary experiments were performed to demonstrate the potential for sophisticated structural analysis with the MAD: (i) the structure of a complex material based on strontium niobate titanate and strontium niobate zirconate was determined and (ii) an in situ stroboscopy experiment with an applied electric field on a highly absorbing piezoceramic was performed. These experiments demonstrate the capabilities of the new MAD, which advances the frontiers of the structural characterization of materials., Published by Wiley-Blackwell, [S.l.]

Taiwan and Vietnam have taken successful measures to combat the spread of COVID-19 at the early stages. Many authors attributed the successful policies to the lessons learned by these countries during the severe acute respiratory syndrome (SARS) pandemic in 2002.(Ohara, 2004) This manuscript provides a summary of recent early-stage policies that were successful in mitigating the spread and creating resilience against the negative consequences of COVID-19 in Taiwan and Vietnam. Crucially, these policies go beyond and complement social isolation. As social isolation is expected to have a negative socio-economic impact on the population and adherence is likely to decrease with time(Armitage and Nellums, 2020; Weems et al., 2020), it is important to consider a broad range of policies to promote a steady control of the COVID-19 spread. Initially, we provide a brief introduction to some general concepts related to COVID-19. Thereafter, we introduce a concise review of policies and their dates relative to the first detection case in Taiwan and Vietnam as well as doing a comparative analysis.

According to the United Nations (UN), 41% of the world’s population is under the age of 24 (United Nations Population Division). Despite being a considerably large group, the youth has been commonly underrepresented in decision-making in the public and private sectors. To combat this situation, the UN launched the Youth 2030 strategy in 2018 thereby recognizing the need to empower the youth to reach their full potential (Youth 2030: The UN Youth Strategy). In this contribution, we provide a brief description of some of the recent transnational youth networks (TYNs) and their features in order to discuss the role of such networks to empower the youth. We propose here that such networks constitute a novel and powerful form of public diplomacy (PD) because of their experiential educational aspects that they develop in their members. Moreover, these networks also offer a rather unique opportunity of building interpersonal relationships among global prominent individuals thereby influencing the international agenda. We further discuss how such networks can advance substantially the UN Sustainable Development Goals (SDGs) agenda (Sustainable Development Goals).

Any dielectric material under a strain gradient presents flexoelectricity. Here, we synthesized 0.75 sodium bismuth titanate −0.25 strontium titanate (NBT-25ST) core–shell nanoparticles via a solid-state chemical reaction directly inside a transmission electron microscope (TEM) and observed domain-like nanoregions (DLNRs) up to an extreme temperature of 800 °C. We attribute this abnormal phenomenon to a chemically induced lattice strain gradient present in the core–shell nanoparticle. The strain gradient was generated by controlling the diffusion of strontium cations. By combining electrical biasing and temperature-dependent in situ TEM with phase field simulations, we analyzed the resulting strain gradient and local polarization distribution within a single nanoparticle. The analysis confirms that a local symmetry breaking, occurring due to a strain gradient (i.e. flexoelectricity), accounts for switchable polarization beyond the conventional temperature range of existing polar materials. We demonstrate that polar nanomaterials can be obtained through flexoelectricity at extreme temperature by tuning the cation diffusion., The limited number of materials with a switchable electrical polarization available for applications can be increased by exploiting the flexoelectric effect. Here, switchable polarization in nanoparticles induced by an elemental distribution dependent strain gradient up to 800 °C is demonstrated.

In this work, the relationship between the structural mechanisms and macroscopic electrical properties of the Nb-modified 0.96(Bi0.5Na0.84K0.16TiO3)–0.04SrTiO3 (BNKT–ST) system were elucidated by using temperature dependent and in situ synchrotron X-ray diffraction (XRD) techniques. For the composition x = 0.0175, a large-signal piezoelectric coefficient (Smax/Emax = d33*) of 735 pm V−1 at 6 kV mm−1 was observed at room temperature. Interestingly, at a higher temperature of 110 °C, the sample still showed a large d33* of 570 pm V−1. Furthermore, the temperature-invariant electrostrictive coefficient for this sample was found to be 0.0285 m4 C−2 over the temperature range of 25–170 °C. Moreover, the energy density for x = 0.030 sample was ∼1.0 J cm−3 with an energy storage efficiency of ˃70% in the temperature range of 25–135 °C. These results suggest that the synthesized Nb-modified BNKT–ST system is promising for the design of ceramic actuators as well as capacitor applications.

The electric field–temperature phase diagrams of three bismuth sodium titanate-based relaxor ferroelectrics are reported, namely 0.94(Na1/2Bi1/2TiO3)–0.06(BaTiO3), 0.80(Na1/2Bi1/2TiO3)–0.20(K1/2Bi1/2TiO3) and 0.75(Na1/2Bi1/2TiO3)–0.25(SrTiO3). Relaxor behavior is demonstrated by temperature-dependent dielectric permittivity measurements in the unpoled and poled states, as well as by the field-induced phase transition into a ferroelectric phase from the relaxor phase. From temperature-dependent thermometry measurements, we identified the threshold electric field to induce the ferroelectric phase and obtained the released latent heat of the phase transition. We determined the nonergodic and ergodic relaxor phase temperature range based on the absence or presence of reversibility of the relaxor to ferroelectric transition. For all three compositions, the electric field–temperature phase diagram was constructed and a critical point was identified. The constructed electric field–temperature phase diagrams are useful to find optimum operational ranges of ferroelectrics and relaxors for electromechanical and electrocaloric applications.

Point defects largely determine the properties of functional oxides. So far, limited knowledge exists on the impact of cation vacancies on electroceramics, especially in (Na1/2Bi1/2)TiO3 (NBT)-based materials. Here, we report on the drastic effect of A-site non-stoichiometry on the cation diffusion and functional properties in the representative ferroelectric (Na1/2Bi1/2)TiO3–SrTiO3 (NBT–ST). Experiments on NBT/ST bilayers and NBT–ST with Bi non-stoichiometry reveal that Sr2+-diffusion is enhanced by up to six orders of magnitude along the grain boundaries in Bi-deficient material as compared to Bi-excess material with values of grain boundary diffusion ∼10−8 cm2 s−1 and ∼10−13 cm2 s−1 in the bulk. This also means a nine orders of magnitude higher diffusion coefficient compared to reports from other Sr-diffusion coefficients in ceramics. Bi-excess leads to the formation of a material with a core–shell microstructure. This results in 38% higher strain and one order of magnitude lower remanent polarization. In contrast, Bi-deficiency leads to a ceramic with a grain size six times larger than in the Bi-excess material and homogeneous distribution of compounds. Thus, the work sheds light on the rich opportunities that A-site stoichiometry offers to tailor NBT-based materials microstructure, transport properties, and electromechanical properties.

© 2017 The American Ceramic Society Surface chemistry and topo-physical properties determine the interactions of biomaterials with their physiological environment. Ferroelectrics hold great promise as the next generation of scaffolds for tissue repair since they feature tunable surface electrical charges, piezoelectricity, and sensing capabilities. We investigate the topography, wettability, chemical stability, and cytotoxicity in salient ferroelectric systems such as (1−x) (Na1/2Bi1/2)TiO3–xBaTiO3, (1−x)Ba(Zr0.2Ti0.8)O3−x(Ba0.7Ca0.3)TiO3, and Pb(Zr,Ti)O3 to test their suitability as biomaterials. The lead-free ferroelectrics promote in vitro cell viability and proliferation to a considerably high extent. 0.94 mol % (Na1/2Bi1/2)TiO3–0.06 mol% BaTiO3 showed the greatest potential leading to a cell viability of (149 ± 30)% and DNA synthesis of (299 ± 85)% in comparison to the reference. Lead leaching from Pb(Zr,Ti)O3 negatively affected the cultured cells. Wettability and chemical stability are key factors that determine the cytotoxicity of ferroelectrics. These variables have to be considered in the design of novel electroactive scaffolds based on ferroelectric ceramics.

Dielectric relaxation in ABO3 perovskite oxides can result from many different charge carrier-related phenomena. Despite a strong understanding of dielectric relaxations, a detailed investigation of the relationship between the content of oxygen vacancies (VO) and dielectric relaxation has not been performed in perovskite oxide films. In this work, we report a systematic investigation of the influence of the VO concentration on the dielectric relaxation of Eu0.5Ba0.5TiO3-δ epitaxial thin films. Nuclear resonance backscattering spectrometry was used to directly measure the oxygen concentration in Eu0.5Ba0.5TiO3-δ films. We found that dipolar defects created by VO interact with the off-centered Ti ions, which results in the dielectric relaxation in Eu0.5Ba0.5TiO3-δ films. Activation energy gradually increases with the increasing content of VO. The present work significantly extends our understanding of relaxation properties in oxide films.

Mixed ionic electronic conductors (MIEC) are pivotal materials in a number of electrochemical devices that are relevant for clean energy technologies and industrial chemical processes. In this report progress, an overview of the recent strategies to tune surfaces and interfaces of MIEC fluorite and perovskite oxides for solid oxide fuel cells and microsolid oxide fuel cells electrodes is provided. Most of the works presented focus on salient strategies to improve the oxygen reduction reaction (ORR) and the fuel oxidation reaction kinetics. Herein insights on the current understanding of heterointerfaces in epitaxial thin films and vertically aligned nanocomposites for ORR kinetics is provided. A selection of oxide materials having potential for thin-film anode application is also presented. Further, recent salient results in grain boundary engineering and ex-solution as well as strain engineering and photoactivation for the development of advanced electrodes is discussed.

Canonical relaxors exhibit an electric-field-induced phase transition between a macroscopically nonpolar and polar phase that can be tuned from being stable at low temperature to being reversible at high temperature. The reversibility of this phase change determines the electromechanical performance and large strains can be achieved if the polar phase is intrinsically unstable. This paper is on the thermal depolarization characteristics of a BNT-BT-based multiphase relaxor ceramic observed through the transition temperature from field-induced polar to nonpolar state. It is shown that the progress of detexturization strongly depends on the crystallographic phase. In the more susceptible phase, it becomes significant about 40 °C below the macroscopically observed transition temperature. Additionally, the surface domain structure vanishes at lower temperatures than expected from both dielectric and structural measurements. The development of strong interfacial stresses aiding depolarization, and a mismatch in chemical pressure between surface and bulk, are discussed as the origins for the observed effects. Tailoring of interfacial stresses through chemical adaption of crystallographic phase fractions opens up a pathway to optimize the strain performance of actuator materials and can become a useful tool to stabilize metastable crystallographic phases as well as for property tuning in piezotronics, Mott insulators and multiferroics. Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI.

Compositional engineering with a focus on structural phase transitions has been considered as the most important approach for enhancement of the functional properties of ferroelectric materials due to the critical fluctuation of physical properties. Of special interest are electric-field-induced phase transitions, which can terminate in a liquid–vapor-type critical point with a strong enhancement of functional properties. Whereas the critical point in liquid–vapor space considers changes in temperature and pressure, the critical point in this study is placed in electric field–temperature diagrams. In single crystals, temperature and electric field of a critical point are sharply defined and therefore not appealing for practical applications. However, in ceramics, it is demonstrated that the orientational dependence of the critical point leads to a broadened temperature and electric field range. The presence of a diffuse critical point in ceramics provides a conceptually novel approach for the enhancement of functional properties, such as piezoelectric and electrocaloric (EC) responses, as validated here on the example of the 0.75Bi1/2Na1/2TiO3-0.25SrTiO3 lead-free relaxor ferroelectric ceramics. The realization of a broad criticality range will further facilitate the development of the piezoelectric and EC materials and provide an alternative concept to manipulate the functional properties by application of an electric field.

In this paper, we report on studies of the electrocaloric (EC) effect in lead-free (1−x)Ba(Zr0.2Ti0.8)O3–x(Ba0.7Ca0.3)TiO3 ceramics with compositions range between 0.32 ≤ x ≤ 0.45. The EC effect was measured directly using a modified differential scanning calorimeter. The maximum EC temperature change, ΔTdirect = 0.33 K under an electric field of 2 kV/mm, was observed for the composition with x = 0.32 at ~63°C. We found that the EC effect peaks not only around the Curie temperature but also at the transition between the ferroelectric phases with different symmetries. A strong discrepancy observed between the results of the direct measurements and indirect estimations points out that using Maxwell's equations is invalid for the thermodynamic nonequilibrium conditions that accompany only partial (incomplete) poling of ceramics. We also observe a nonlinearity of the EC effect above the Curie temperature and in the temperature range corresponding to the tetragonal ferroelectric phase.

The influence of B-site disorder on the dielectric, microstructural, and structural characteristics of unpoled, lead-free (Bi1/2Na1/2)TiO3-0.06Ba(ZrxTi1-x)O3 piezoelectric ceramics with x = 0.02, 0.10, and 0.15 was investigated. The low and medium doping level introduced a stabilization of polar nanoregions reflected in the shift of the dispersive permittivity anomalies to higher temperatures and the development of lamellar rhombohedral domains embedded in the prevalent tetragonal nanodomain matrix. For higher Zr level, the regions of lamellar domains remain, but the dielectric characteristics indicate a reduction in the previous stabilization effect. This behavior is rationalized by a reduction in the correlation length due to the increasing amount of nonpolar sample volume with increasing Zr addition.

The Bi1/2Na1/2TiO3-based materials exhibit the largest electric-field-induced strains among lead-free piezoceramics and are considered as promising candidates for actuation applications. A typical representative of this group is (1-x)Bi1/2Na1/2TiO3-xSrTiO3, where its excellent electromechanical properties were recently related to the existence of a core–shell microstructure. Although the latter was also reported in other Bi1/2Na1/2TiO3-based ceramics, the formation mechanism remains unknown. In the present work we therefore first investigated the solid-state reaction occurring during calcination using simultaneous thermogravimetric analysis, X-ray diffraction, scanning and transmission electron microscopy. The reaction occurred in two steps, whereby the cores and shells had different formation reaction temperatures, which resulted in a metastable heterogeneous microstructure. Furthermore, a series of sintered samples with different relative densities, grain sizes, and core densities was prepared. Modifications of these microstructural parameters resulted in variation of the maximal strain by 17% and in the electric-field required to trigger the phase transitions by 38%.

BaTiO3-based lead-free piezoelectric materials have long been known as “a mediocre class of piezoelectric materials.” However, they have seen significant renewed interest in recent years ever since the discovery of high piezoelectricity in Ba(Zr, Ti)O3-(Ba, Ca)TiO3 as well as the related Ba(Sn, Ti)O3-(Ba, Ca)TiO3 and Ba(Hf, Ti)O3-(Ba, Ca)TiO3 systems. The unexpectedly high piezoelectricity in this class of BaTiO3 (BT)-based materials is still not well understood and has stimulated significant research activity. We present a concise discussion of the notions leading to high piezoelectricity in BaTiO3-based systems. In particular, the possible role of a multiphase-coexisting point is highlighted. © 2018. This is the authors’ accepted and refereed manuscript to the article.

The design of core–shell materials affords additional degrees of freedom to tailor functional properties as compared to solid solution counterparts. Although to date most of the work in core–shell materials has focused on dielectrics, piezoelectric core–shell ceramics may gain similar interest. Generalities of core–shell functional ceramics features are addressed in this work. A model system, Bi1/2Na1/2TiO3–SrTiO3, is introduced to discuss structure–property relationships. We demonstrate that this system features a core–shell microstructure for the composition corresponding to 25 at.% Sr. The material is studied by means of macroscopic functional properties and in situ structural characterization techniques at different length scales, such as X-ray diffraction, transmission electron microscopy, and Raman spectroscopy. The evolution of the core–shell with field and temperature determines its functional properties. The high strain of the system, ~0.3% at 4 kV/mm, is due to an electric-field-induced phase transition of the core and shell. Upon field removal the core remains in a poled state, whereas the shell is characterized by a reversible transformation. The reversibility of the phase transition of shells and associated switching are key features in the observed giant strain. Dielectric anomalies are found to be related to changes in oxygen octahedral tilting angles within the core and shell.

The temperature-dependent crack growth resistance behavior of the lead-free (1 − x)Ba(Zr0.2Ti0.8)O3–x(Ba0.7Ca0.3)TiO3 (x = 0.385) ceramic was characterized using compact-tension specimens from 25 °C to 60 °C. The observed plateau fracture toughness at 25 °C was found to be approximately 37% lower than commercial Pb(Zr,Ti)O3. At elevated temperature, the maximum fracture toughness displayed a decrease, which was found to be related to the temperature-dependent elastic and ferroelastic properties. Mechanical measurements are presented that demonstrate decreasing effective switching strain, coercive stress and Young’s modulus with increasing temperature.

The effect of 1 at% Fe- and FeNb-doping on the temperature and stress stability of the electromechanical properties of (Ba 1− x Ca x )(Zr y Ti 1− y )O 3 (BCZT) was investigated. For the composition (Ba 0.89 Ca 0.11 )(Zr 0.135 Ti 0.865 )O 3 with rhombohedral symmetry, doping reduces the Curie point and the temperature stability of the large-signal electromechanical properties significantly. The large-signal piezoelectric coefficient d 33 * at room temperature was reduced to 500 pm/V compared to 700 pm/V in the undoped composition at 1 kV/mm. The electrostrain, however, was found to be less sensitive to mechanical prestresses, showing a plateau up to stresses of 80 MPa in both doped compositions. These effects were attributed to a reduction of the domain wall mobility due to a smaller grain size, charged defect dipoles and the proximity of the room-temperature measurements to the reduced ferroelectric-paraelectric phase transition temperature. The study reveals that the exceptionally large strains observed in BCZT rely on the instabilities around the polymorphic phase transition in the system. Aliovalent doping changes this sensitive system and reduces the electrostrain considerably.

© 2017 The American Ceramic Society The lead-free (1−x)Ba(Zr0.2Ti0.8)O3-x(Ba0.7Ca0.3)TiO3 system is considered as promising candidate for the replacement of lead-based piezoceramics in actuation applications, during which electric fatigue is a major concern. This issue was addressed in this work, where the unipolar fatigue resistance of three (1−x)Ba(Zr0.2Ti0.8)O3-x(Ba0.7Ca0.3)TiO3 compositions with different crystallographic structures (rhombohedral, orthorhombic, and tetragonal) was evaluated. Strain asymmetry and development of an internal bias field were observed in all compositions. The decrease in the remanent polarization and the large signal piezoelectric coefficient after 107 unipolar cycles was found to lie between 6%-12% and 2%-13%, respectively. The most pronounced fatigue was observed for the orthorhombic composition, which has the largest extrinsic contribution to strain. On the other hand, the best fatigue resistance was observed for the tetragonal composition, which has a predominantly intrinsic strain response. The correlation of fatigue resistance with strain mechanism was corroborated with determination of the Rayleigh parameters and changes in the domain morphology after cycling as confirmed by piezoresponse force microscopy.

The Ba(Zr0.2Ti0.8)O3–x(Ba0.7Ca0.3)TiO3 system was synthesized in a wide compositional range in order to study the relationship between its phase diagram and electromechanical properties. Phase transitions were marked using peaks in temperature-dependent permittivity, providing up to three transitions from the rhombohedral phase to an orthorhombic, tetragonal and finally cubic phase, which meet in a region that is termed the phase convergence region in this work. In situ small and large signal electromechanical properties were studied as a function of temperature with specific emphasis on these transitions. A small signal piezoelectric coefficient, d33, presents maximized values at the transition from the orthorhombic to the tetragonal phase, while a large signal piezoelectric coefficient, d 33 ∗ , does so at both rhombohedral to orthorhombic and to tetragonal phase transitions. Maximum polarization Pmax was the only quantity determined that had a clear maximum at the phase convergence region.

The dielectric and electromechanical properties of 0.75Bi1/2Na1/2TiO3–0.25 SrTiO3 (25ST) as a function of temperature and frequency were studied. It is shown that the 25ST is a relaxor ferroelectric as evidenced by the temperature-dependent dielectric relaxations with an incipient piezoelectricity featured by the presence of a reversible electric-field-induced phase transformation at room temperature. The transition occurs on a broad electric field strength range depending on field amplitude and frequency. It is also accompanied by a huge strain that is attributed to repetitive poling and depoling originating due to the reversibility of the phase transition. The 25ST makes an attractive lead-free candidate for stack actuators as it presents a high normalized d33* of ~600 pm/V at a low electric field of 4 kV/mm for frequencies ranging from 0.1 up to 100 Hz.

This article details the influence of zirconium doping on the piezoelectric properties and relaxor characteristics of 94(Bi1/2Na1/2)TiO3–6Ba(ZrxTi1−x)O3 (BNT–6BZT) bulk ceramics. Neutron diffraction measurements of BNT–6BZT doped with 0%–15% Zr revealed an electric-field-induced transition of the average crystal structure from pseudo-cubic to rhombohedral/tetragonal symmetries across the entire compositional range. The addition of Zr up to 10% stabilizes this transition, resulting in saturated polarization hysteresis loops with a maximum polarization of 40 μC/cm2 at 5.5 kV/mm, while corresponding strain hysteresis measurements yield a maximum strain of 0.3%. With further Zr addition, the ferroelectric order is progressively destabilized and typical relaxor characteristics such as double peaks in the current density loops are observed. In the strain hysteresis, this destabilization leads to an increase of the maximum strain by 0.05%. These changes to the physical behavior caused by Zr addition are consistent with a reduction of the transition temperature TF-R, above which the field-induced transformation from the relaxor to ferroelectric state becomes reversible.

Lead-free relaxor ferroelectrics that feature a core-shell microstructure provide an excellent electromechanical response. They even have the potential to replace the environmentally hazardous lead-zirconia-titanate (PZT) in large strain actuation applications. Although the dielectric properties of core-shell ceramics have been extensively investigated, their piezoelectric properties are not yet well understood. To unravel the interfacial core-shell interaction, we studied the relaxation behaviour of field-induced ferroelectric domains in 0.75Bi1/2Na1/2TiO3-0.25SrTiO3 (BNT-25ST), as a typical core-shell bulk material, using a piezoresponse force microscope. We found that after poling, lateral domains emerged at the core-shell interface and propagated to the shell region. Phase field simulations showed that the increased electrical potential beneath the core is responsible for the in-plane domain evolution. Our results imply that the field-induced domains act as pivotal points at the coherent heterophase core-shell interface, reinforcing the phase transition in the non-polar shell and thus promoting the giant strain.

The most widely used ferroelectric material in actuator applications is PZT due to superior electromechanical properties. This solid solution is formed by combining the PbTiO3 and PbZrO3 binary system. The phase diagram of the PbTiO3–PbZrO3 binary system is introduced in Fig. 3.1

Ferroelectric materials have been traditionally designed around phase boundaries to enhance electromechanical properties. The enhancement has been attributed to several fundamental reasons and remains an open research area.

Figure 5.1 introduces the XRD patterns of BZT-BCT calcined powders at 1300 °C. All diffractograms can be ascribed to a perovskite structure with secondary phases marked with *. Indexing throughout this work was performed based on a primitive cubic prototype, with pc denoting pseudocubic Miller indices.

Coupling of order parameters provides a means to tune functionality in advanced materials including multiferroics, superconductors, and ionic conductors. We demonstrate that the response of a frustrated ferroelectric state leads to coupling between order parameters under electric field depending on grain orientation. The strain of grains oriented along a specific crystallographic direction, ⟨h00⟩, is caused by converse piezoelectricity originating from a ferrodistortive tetragonal phase. For ⟨hhh⟩ oriented grains, the strain results from converse piezoelectricity and rotostriction, as indicated by an antiferrodistortive instability that promotes octahedral tilting in a rhombohedral phase. Both strain mechanisms combined lead to a colossal local strain of (2.4 ± 0.1) % and indicate coupling between oxygen octahedral tilting and polarization, here termed “rotopolarization”. These findings were confirmed with electromechanical experiments, in situ neutron diffraction, and in situ transmission electron microscopy in 0.75Bi1/2Na1/2TiO3-0.25SrTiO3. This work demonstrates that polar and non-polar instabilities can cooperate to provide colossal functional responses This work is licensed under a Creative Commons Attribution 4.0 International License. The images or other third party material in this article are included in the article’s Creative Commons license, unless indicated otherwise in the credit line; if the material is not included under the Creative Commons license, users will need to obtain permission from the license holder to reproduce the material. To view a copy of this license, visit http://creativecommons.org/licenses/by/4.0

Materials in two composition regimes, Bi1/2Na1/2TiO3–BaTiO3–CaZrO3 (BNT–BT–CZ) and Bi1/2Na1/2TiO3–BaTiO3–K0.5Na0.5NbO3–CaZrO3 (BNT–BT–KNN–CZ), were synthesized via the mixed oxide route and their structural, dielectric and electrical properties were investigated. CZ was identified to render the two local maxima in permittivity more diffused. This resulted in temperature-insensitive relative permittivity spectra with average values from ∼470 up to ∼2300 and operational windows of at least ∼400 °C with less than 15% of variation in the temperature range from −100 up to above 500 °C. Moreover, loss factors are below ∼10% and RC constants range from ∼0.03 s up to ∼4 s at 300 °C. The materials of current investigation are highly attractive for developing capacitors of wide temperature usage.

In response to the current environmental regulations against the use of lead in daily electronic devices, a number of investigations have been performed worldwide in search for alternative piezoelectric ceramics that can replace the market-dominating lead-based ones, representatively Pb(Zr x Ti1-x )O3 (PZT)-based solid solutions. Selected systems of potential importance such as chemically modified and/or crystallographically textured (K, Na)NbO3 and (Bi1/2Na1/2)TiO3-based solid solutions have been developed. Nevertheless, only few achievements have so far been introduced to the marketplace. A recent discovery has greatly extended our tool box for material design by furnishing (Bi1/2Na1/2)TiO3-based ceramics with a reversible phase transition between an ergodic relaxor state and a ferroelectric with the application of electric field. This paired the piezoelectric effect with a strain-generating phase transition and extended opportunities for actuator applications in a completely new manner. In this contribution, we will present the status and perspectives of this new class of actuator ceramics, aiming at covering a wide spectrum of topics, i.e., from fundamentals to practice.

Applications ranging from microphones to AFM transducers exploit the interplay between mechanical stress and electric field arising from structural transitions in certain perovskite oxides. The classic material contains lead, however, and efficient, environmentally friendly alternatives have long been sought. The authors use a challenging technique to visualize the real-time microstructural evolution of a lead-free ferroelectric system, and the multidomain states and transitions they find are expected to inform the search for additional systems, as well as the applications that will rely on them.

The macroscopic electromechanical behavior of lead-free bilayer composites was characterized at room temperature. One layer consisted of a nonergodic relaxor, (Bi1/2Na1/2)TiO3–7BaTiO3, with an electric-field-induced longrange ferroelectric order, whereas the other is understood to be an ergodic relaxor [(Bi1/2Na1/2)TiO3–25SrTiO3] that undergoes a reversible electric-field-induced macroscopic nonpolar-to-polar transition. Microstructural evidence of a bilayer with low diffusion between the two components is also demonstrated. By taking advantage of the different macroscopic strain– and polarization–electric-field responses of the two constituents, internal mechanical and electrical fields can be developed that enhance the unipolar strain over that expected by a rule of mixtures approximation, thereby improving the properties needed for application of such materials to actuator systems. It is possible through further tailoring of the volume fractions and macroscopic properties of the constituents to optimize the electromechanical properties of multilayer lead-free ferroelectrics.

The diffusionless pseudobinary phase diagram, monodomain properties, and free energy of $(1\ensuremath{-}x)\mathrm{Ba}(\mathrm{Z}{\mathrm{r}}_{0.2}\mathrm{T}{\mathrm{i}}_{0.8}){\mathrm{O}}_{3}\text{\ensuremath{-}}x(\mathrm{B}{\mathrm{a}}_{0.7}\mathrm{C}{\mathrm{a}}_{0.3})\mathrm{Ti}{\mathrm{O}}_{3}$ are computed for comparison with experimental results. Specifically, the variation of the spontaneous polarization, anisotropy energy, and free energy with respect to temperature, composition, and polarization direction are discussed relative to the results of resonant piezoelectric measurements performed over a wide compositional range as a function of temperature. The phase angle, relative permittivity, piezoelectric and coupling coefficients, and elastic compliances were used to investigate relations between the computed and measured pseudobinary phase diagrams and the measured piezoelectric and elastic properties. It was found that ${d}_{33}$ values along the orthorhombic to tetragonal phase boundary are $\ensuremath{\sim}30%$ higher than those both along the rhombohedral to orthorhombic phase boundary and in the region where phases converge. It is shown that the reduction in anisotropy energy in these regions of the phase diagram is by itself insufficient to explain the measured properties. The highest small signal piezoelectric activity is found along the orthorhombic to tetragonal phase boundary due to a combination of reduced anisotropy energy, high remanent/spontaneous polarization, and increased elastic softening. The combined computed and experimental results are used to demonstrate that the interdependent behavior of these properties should be considered in the design of engineered piezoelectric ceramics.

International audience; Strong electrocaloric effect in lead-free 0.65Ba(Zr 0.2 Ti 0.8)O 3-0.35(Ba 0.7 Ca 0.3)TiO 3 ceramics obtained by direct measurements Solid solutions of (1 À x)Ba(Zr 0.2 Ti 0.8)O 3-x(Ba 0.7 Ca 0.3)TiO 3 promise to exhibit a large electrocaloric effect (ECE), because their Curie temperature and a multiphase coexistence region lie near room temperature. We report on direct measurements of the electrocaloric effect in bulk ceramics 0.65Ba(Zr 0.2 Ti 0.8)O 3-0.35(Ba 0.7 Ca 0.3)TiO 3 using a modified differential scanning calorimeter. The adiabatic temperature change reaches a value of DT EC ¼ 0.33 K at $65 C under an electric field of 20 kV/cm. It remains sizeable in a broad temperature interval above this temperature. Direct measurements of the ECE proved that the temperature change exceeds the indirect estimates derived from Maxwell relations by about $50%. The discrepancy is attributed to the relaxor character of this material. V C 2015 AIP Publishing LLC. [http://dx.doi.org/10.1063/1.4907774] During the last several years, an increased interest has been paid to the electrocaloric effect (ECE) in ferroelectric materials as a route to develop small, effective, low cost, and environmentally friendly solid-state refrigerators. 1,2 The ECE is defined as an adiabatic and reversible temperature change of a dielectric material when an electric field is applied or removed. 3 If the exchange of heat with the environment is enabled, it defines the change of entropy as a function of the applied electric field under isothermal conditions. 4,5 Since Mischenko et al. reported on the giant electro-caloric effect in PbZr 0.95 Ti 0.05 O 3 thin films in 2006, 6 the ECE has been reported for many different ferroelectric materials such as thick and thin films, 7–10 polymers, 11,12 bulk ceramics, 13,14 and single crystals. 15,16 In general, the ECE peaks are a few degrees above the ferroelectric-paraelectric phase transition. 1 The largest values have been achieved for thin films, 10 where much higher electric fields can be applied than to bulk materials. However, for application, the heating/ cooling capacity is the key factor. Hence, bulk materials, which have large enough heating/cooling capacity, are better suitable for mid-and large-scale cooling applications. 1 To compare the ECE in different materials, the ratio between induced temperature change and applied field, DT EC /DE, called the electrocaloric strength, has been introduced.

We present a critical review that encompasses the fundamentals and state-of-the-art knowledge of barium titanate-based piezoelectrics. First, the essential crystallography, thermodynamic relations, and concepts necessary to understand piezoelectricity and ferroelectricity in barium titanate are discussed. Strategies to optimize piezoelectric properties through microstructure control and chemical modification are also introduced. Thereafter, we systematically review the synthesis, microstructure, and phase diagrams of barium titanate-based piezoelectrics and provide a detailed compilation of their functional and mechanical properties. The most salient materials treated include the (Ba,Ca)(Zr,Ti)O3, (Ba,Ca)(Sn,Ti)O3, and (Ba,Ca)(Hf,Ti)O3 solid solution systems. The technological relevance of barium titanate-based piezoelectrics is also discussed and some potential market indicators are outlined. Finally, perspectives on productive lines of future research and promising areas for the applications of these ma...

The temperature at which the electric field induced long-range ordered ferroelectric state undergoes transition into the short-range ordered relaxor state, TF-R, is commonly defined by the onset of strong dispersion of the dielectric permittivity. However, this combined macroscopic property and structural investigation of the polarization reversal process in the prototypical lead-free relaxor 0.94(Bi1/2Na1/2)TiO3-0.06Ba(Zr0.02Ti0.98)O3 reveals that an applied electric field can trigger depolarization and onset of relaxor-like behavior well below TF-R. The polarization reversal process can as such be described as a combination of (1) ferroelectric domain switching and (2) a reversible phase transition between two polar ferroelectric states mediated by a non-polar relaxor state. Furthermore, the threshold fields of the second, mediated polarization reversal mechanism depend strongly on temperature. These results are concomitant with a continuous ferroelectric to relaxortransition occurring over a broad temperature range, during which mixed behavior is observed. The nature of polarization reversal can be illustrated in electric-field-temperature (E-T) diagrams showing the electric field amplitudes associated with different polarization reversal processes. Such diagrams are useful tools for identifying the best operational temperature regimes for a given composition in actuator applications.

The method of thermally stimulated depolarization currents (TSDC) and polarization switching experiments over a large field, time, and temperature regime are used to refine the controversial phase diagram of Ba(Zr0.2Ti0.8)O3−x(Ba0.7Ca0.3)TiO3 and comprehend its relation to ferroelectric and piezoelectric properties. TSDC results suggest the existence of three ferroelectric phases for the composition range of 0.30 ≤ x ≤ 0.60, which can be assigned to the rhombohedral (R), presumably orthorhombic (O), and tetragonal (T) symmetries. Spontaneous polarization is maximal all over the entire intermediate phase region, where the activation barrier for polarization switching is small, not just at R-O or O-T boundaries as might be deduced from previous observations.

Contributions to the piezoelectric response of (1 − x)Ba(Zr0.2Ti0.8)O3-x(Ba0.7Ca0.3)TiO3 ceramics are quantified by small signal measurements made as functions of bias field and temperature. The highest fraction of intrinsic contributions is observed far from phase boundaries, of extrinsic contributions around phase boundaries, and of irreversible switching in the orthorhombic phase. The largest piezoelectric response, d33 = 475 ± 85 pC/N, is found near the orthorhombic to tetragonal phase boundary due to both reversible and irreversible switching. A peak in reversible switching above the Curie temperature for all compositions suggests a line of critical points associated with first order phase transitions, indicating that concurrence of triple and tricritical points in the zero-field phase diagram is not the responsible mechanism of enhanced piezoelectricity.