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The room temperature aerosol deposition method is especially promising for the rapid deposition of ceramic thick films, making it interesting for functional components in energy, mobility, and telecommunications applications. Despite this, a number of challenges remain, such as an enhanced electrical conductivity and internal residual stresses in as-deposited films. In this work, a novel technique that integrates a sacrificial water-soluble buffer layer was used to fabricate freestanding ceramic thick films, which allows for direct observation of the film without influence of the substrate or prior thermal treatment. Here, the temperature-dependent chemical and structural relaxation phenomena in freestanding BaTiO3 films were directly investigated by characterizing the thermal expansion properties and temperature-dependent crystal structure as a function of oxygen partial pressure, where a clear nonlinear, hysteretic contraction was observed during heating, which is understood to be influenced by lattice defects. As such, aliovalent doping and atmosphere-dependent annealing experiments were used to demonstrate the influence of local chemical redistribution and oxygen vacancies on the thermal expansion, leading to insight into the origin of the high room temperature conductivity of as-deposited films as well as greater insight into the influence of the induced chemical, structural, and microstructural changes in room temperature deposited functional ceramic thick films. Graphical abstract

The benefits of the multiphase convergence strategy to design ferroelectric ceramics for piezoelectric energy harvesting applications over a broad temperature range.

Ferroelectrics have become indispensable electroceramic materials in modern electronic applications. While point-defect engineering is a common tool to modify the properties of ferroelectrics, dislocations have not been widely considered, although they were previously shown to alter electrical properties in other oxides. Here, we study the room temperature uniaxial deformation of the perovskite ferroelectric single crystalline KNbO3 in 010 p c and 101 p c orientations. We demonstrate a large plastic deformation in the range of 5%. Dislocation and domain structure were investigated across different length scales using optical microscopy, electron channeling contrast imaging, and transmission electron microscopy. Planar arrangement of dislocations in slip bands was observed, while the predominant appearance of edge dislocations indicates a dominant dislocation motion by the kink-pair mechanism. Increased dislocation density resulted in decreased ferroelectric domain size from 1.8 μm to 0.5 μm after deformation. Piezoresponse force microscopy highlights the effect of dislocations on domain nucleation and their mobility.

Controlling the growth of complex relaxor ferroelectric thin films and understanding the relationship between biaxial strain-structural domain characteristics are desirable for designing materials with a high electromechanical response. For this purpose, epitaxial thin films free of extended defects and secondary phases are urgently needed. Here, we used optimized growth parameters and target compositions to obtain epitaxial (40-45 nm) 0.67Pb(Mg1/3Nb2/3)O3-0.33PbTiO3/(20 nm) SrRuO3 (PMN-33PT/SRO) heterostructures using pulsed-laser deposition (PLD) on singly terminated SrTiO3 (STO) and ReScO3 (RSO) substrates with Re = Dy, Tb, Gd, Sm, and Nd. In situ reflection high-energy electron diffraction (RHEED) and high-resolution X-ray diffraction (HR-XRD) analysis confirmed high-quality and single-phase thin films with smooth 2D surfaces. High-resolution scanning transmission electron microscopy (HR-STEM) revealed sharp interfaces and homogeneous strain further confirming the epitaxial cube-on-cube growth mode of the PMN-33PT/SRO heterostructures. The combined XRD reciprocal space maps (RSMs) and piezoresponse force microscopy (PFM) analysis revealed that the domain structure of the PMN-33PT heterostructures is sensitive to the applied compressive strain. From the RSM patterns, an evolution from a butterfly-shaped diffraction pattern for mildly strained PMN-33PT layers, which is evidence of stabilization of relaxor domains, to disc-shaped diffraction patterns for high compressive strains with a highly distorted tetragonal structure, is observed. The PFM amplitude and phase of the PMN-33PT thin films confirmed the relaxor-like for a strain state below ∼1.13%, while for higher compressive strain (∼1.9%) the irregularly shaped and poled ferroelectric domains were observed. Interestingly, the PFM phase hysteresis loops of the PMN-33PT heterostructures grown on the SSO substrates (strain state of ∼0.8%) exhibited an enhanced coercive field which is about two times larger than that of the thin films grown on GSO and NSO substrates. The obtained results show that epitaxial strain engineering could serve as an effective approach for tailoring and enhancing the functional properties in relaxor ferroelectrics.

In this report, the influence of cobalt doping and annealing atmosphere on the electrical conductivity and polarization switching of BiFeO3 (BFO) ceramics was studied. Electrical conductivity as well as hardening behavior has been found to increase with introduction of acceptor C o F e ' sites. BFO ceramics doped with Co exhibit p-type conductivity, dominated by Fe4+ defects, which can be successfully reduced during high-temperature annealing in N2. However, indications of local reduction were found, presumably on domain walls and grain boundaries. A mechanism of hardening is proposed, which assumes two types of pinning centers: i) V B i ' ' ' and F e F e • related and ii) C o F e ' and V O • • related, most probably bound into complexes, which are shown to play the key role in the hardening behavior and hysteresis loop pinching and biasing. The results of this study could further promote designing local and bulk conductivity and hardening properties of BFO-based materials.

Bi0.88Gd0.12FeO3 multiferroics are of interest for next-generation electronics and are shown with a remnant magnetization 0.2 emu·g−1, coercive field 8 kOe, Curie temperature 370 °C and magnetization of 0.7 emu·g−1 at magnetic fields 30 kOe. Scanning probe microscopy confirmed the intrinsic multiferroicity in the perovskite phase with coexistence of ferroelectric/ferroelastic and ferromagnetic domain structures. Strong magnetic hysteresis was produced by thermal cycling to 1000 °C due to degeneration of the perovskite phase into iron oxide inclusions, highlighting the importance of processing, thermal history and thermodynamic stability for minimizing the amount of parasitic magnetic secondary phases. This is an open access article distributed under the terms of the Creative Commons CC-BY license, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

The effects of strontium doping (0-2mol%) on structure, microstructure and functional properties of potassium sodium niobate (KNN) thin films deposited on Pt(111)/TiOy/SiO2/Si substrates were investigated. Incorporation of Sr up to 1mol% into the KNN crystal lattice hindered the grain growth, vertical roughness and contributed to the fine-grained and dense thin film microstructure with monoclinic crystal syngony. This effectively reduced leakage current and improved ferroelectric characteristics. Higher doping content (2mol%) led to the formation of secondary phases and complete deterioration of functional properties. Stabilization of 1mol% Sr-doped KNN solution with diethanolamine resulted in the film with dielectric constant and losses of 394 and 0.018 at 100 kHz, respectively, leakage current of 3.8 • 10−8 A/cm2 at 100 kV/cm and well saturated ferroelectric hysteresis with Pr of 6.8 μC/cm2 and low Ec of 85 kV/cm. Benefiting from improved leakage current characteristics at high electric fields and less defect structure, the film showed maximal local piezoelectric coefficient, d33 ∼ 110 pm/V determined by piezo-response force microscopy (PFM), ability to reach fully saturated local hysteresis under low switching DC voltage of 15 V, and good ferroelectric domain mobility proven by successful in-situ poling of chosen area using PFM lithography.

Interactions between grain boundaries and domain walls were extensively studied in ferroelectric films and bicrystals. This knowledge, however, has not been transferred to polycrystalline ceramics, in which the grain size represents a powerful tool to tailor the electromechanical and dielectric response. Here, we relate changes in dielectric and electromechanical properties of a bulk polycrystalline Pb(Zr0.7Ti0.3)O3 to domain wall interactions with grain boundaries. Samples with grain sizes in the range of 3.9–10.4 μm were prepared and their microstructure, crystal structure, and dielectric/electromechanical properties were investigated. A decreasing grain size was accompanied by a reduction in large-signal electromechanical properties and an increase in small-signal relative permittivity. High-energy diffraction analysis revealed increasing microstrains upon decreasing the grain size, while piezoresponse force microscopy indicated an increased local coercive voltage near grain boundaries. The changes in properties were thus related to strained material volume close to the grain boundaries exhibiting reduced domain wall dynamics.

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Ferroelectric Bi4Ti3O12 nanoparticles can be hydrothermally synthesized in two distinct morphologies, i.e., nanoplatelets and nanowires. The nanowires exhibit a new layered crystal structure that has not been described before.

We show how sintering in different atmospheres affects the structural, microstructural, and functional properties of ~30 μm thick films of K0.5Na0.5NbO3 (KNN) modified with 0.38 mol% K5.4Cu1.3Ta10O29 and 1 mol% CuO. The films were screen printed on platinized alumina substrates and sintered at 1100 °C in oxygen or in air with or without the packing powder (PP). The films have a preferential crystallographic orientation of the monoclinic perovskite phase in the [100] and [−101] directions. Sintering in the presence of PP contributes to obtaining phase-pure films, which is not the case for the films sintered without any PP notwithstanding the sintering atmosphere. The latter group is characterized by a slightly finer grain size, from 0.1 μm to ~2 μm, and lower porosity, ~6% compared with ~13%. Using piezoresponse force microscopy (PFM) and electron backscatter diffraction (EBSD) analysis of oxygen-sintered films, we found that the perovskite grains are composed of multiple domains which are preferentially oriented. Thick films sintered in oxygen exhibit a piezoelectric d33 coefficient of 64 pm/V and an effective thickness coupling coefficient kt of 43%, as well as very low mechanical losses of less than 0.5%, making them promising candidates for lead-free piezoelectric energy harvesting applications.

A systematic study of (1−x)Pb(Fe0.5Nb0.5)O3–xBiFeO3 (x = 0–0.5) was performed by combining dielectric and electromechanical measurements with structural and microstructural characterization in order to investigate the strengthening of the relaxor properties when adding BiFeO3 into Pb(Fe0.5Nb0.5)O3 and forming a solid solution. Pb(Fe0.5Nb0.5)O3 crystalizes in monoclinic symmetry exhibiting ferroelectric-like polarization versus electric field (P–E) hysteresis loop and sub-micron-sized ferroelectric domains. Adding BiFeO3 to Pb(Fe0.5Nb0.5)O3 favors a pseudocubic phase and a gradual strengthening of the relaxor behavior of the prepared ceramics. This is indicated by a broadening of the peak in temperature-dependent permittivity, narrowing of P–E hysteresis loops and decreasing size of ferroelectric domains resulting in polar nanodomains for x = 0.20 composition. The relaxor behavior was additionally confirmed by Vogel–Fulcher analysis. For the x ≥ 0.30 compositions, broad high-temperature anomalies are observed in dielectric permittivity versus temperature measurements in addition to the frequency-dispersive peak located close to room temperature. These samples also exhibit pinched P–E hysteresis loops. The observed pinching is most probably related to the reorganization of polar nanoregions under the electric field as shown by synchrotron X-ray diffraction measurements as well as by piezo-response force microscopy analysis, while in part affected by the presence of charged point defects and anti-ferroelectric order, as indicated from rapid cooling experiments and high-resolution transmission electron microscopy, respectively.

For the first time, we demonstrated successful post-synthesis incorporation of metal dopants at elevated temperature into a host structure of Sn2P2S6, known as the grandfather of dichalcogenide ferroelectrics with a formula M2P2X6 (M = metal and X = chalcogen). With the example of Cu, we show that the integration of dopant atoms into the bulk of an already grown crystal could be easily tuned up to 0.5 at% affecting the structural, optical, vibrational, electrical, and ferroelectric properties. Thermally diffused copper atoms in Sn2P2S6 bulk are in the metallic state, inducing a multiaxial expansion of the Sn2P2S6 unit cell for 2–3.4%. The energy reduction between indirect and direct optical transitions was observed, combined by small hardening for acoustic and soft optical vibrational modes originating in the partial substitution of Sn by Cu in the Sn2P2S6 crystal lattice. Similar to hydrostatic pressure, the structurally bonded copper initiates a small downward shift in the critical temperature Tc. The presence of copper has a substantial impact on the shape smearing of the ferroelectric domains as well as on the behaviour of the dielectric permittivity. The real part of the dielectric constant e′ reaches its maximal value at intermediate concentrations of Cu 0% < x < 0.5%, showing an ∼20% increase with respect to the parent structure. The incorporated metal atoms provoke a monotonous expansion of the ferroelectric P–E loops along the increased dopant content direction. An increase in the electrical conductivity at higher Cu concentration reveals a trend for inducing a metal-like behaviour.

The search for new single-phase multicaloric materials, combining electrocaloric and magnetocaloric effects, is just at its beginning. Since the highest caloric effects are obtained near ferroic phase transitions, multiferroics with room-temperature ferroic anomalies are promising candidates for multicaloric cooling. In this work, such materials were prepared by tailoring the temperature of the ferroic anomalies by introducing BiFeO3, a material possessing high-temperature ferroic phase transitions, into the multicaloric Pb(Fe0.5Nb0.5)O3 to form a solid solution. A series of (1−x)Pb(Fe0.5Nb0.5)O3–xBiFeO3 (x = 0–0.5) were prepared. Among them, 0.8Pb(Fe0.5Nb0.5)O3–0.2BiFeO3 exhibits both dielectric permittivity and magnetic susceptibility anomalies at room temperature and is therefore one of the first such single-phase materials. However, at higher temperatures the material exhibits excessive Joule heating that critically degrades the electrocaloric cooling effect, while the antiferromagnetic nature of the material results in a low magnetocaloric response. Because of that, the multicaloric properties of 0.8Pb(Fe0.5Nb0.5)O3–0.2BiFeO3 were further improved by doping the material with Mn and Gd ions. This results in a composition with negligible Joule heating up to 75 °C and with room-temperature electrocaloric effect of more than 1 °C, and a high magnetocaloric effect of ∼3 °C at cryogenic temperatures. Furthermore, this material also exhibits the highest room-temperature magnetocaloric effect (∼8 × 10−3 °C) among all already known Pb(Fe0.5Nb0.5)O3-based multicalorics.

In this work the preparation of a protective insulating alumina coating on magnetocaloric gadolinium elements was investigated. In order to prepare a dense ceramic coating at room temperature the aerosol deposition technique was used. The study reveals that the powder morphology and particle size are important parameters that influence the deposition efficiency, powder packing and consequently also the density and functional properties of the alumina coating. The optimal powder pre-deposition treatment includes heating the powder to 1150 °C, followed by milling. The deposition of this powder resulted in the preparation of dense alumina coatings with a low specific electrical conductivity of 6.4∙10 − 14 Ω −1 m −1 .

Designing multicaloric single-phase materials with combined electro- and magnetocaloric effects is still at its initial stage and presents a number of challenges. One of the main challenges encountered so far is to reduce the excessive electrical conductivity, which leads to the appearance of Joule heating that might completely degrade the electrocaloric response. In this work, multicaloric Pb(Fe0.5Nb0.5)O3 material was successfully prepared exhibiting pronounced electrocaloric effect above room temperature and maximum magnetocaloric effect at cryogenic temperature. The conductivity was suppressed by controlling the sintering temperature. The ceramic sintered at 1000 °C exhibits maximum electrocaloric effective cooling of 0.88 °C at 28 °C and maximum magnetocaloric effect of 0.14 °C at −271 °C. The caloric properties can be further improved by doping Pb(Fe0.5Nb0.5)O3 with manganese. In comparison to the undoped sample, Pb(Fe0.5Nb0.5)O3 doped with 0.5 mol% of manganese exhibits three times higher maxima of electrocaloric effective cooling (2.47 °C at 80 °C) and magnetocaloric temperature change (0.44 °C at −271 °C).

A novel technique for the rapid room‐temperature deposition of porous ceramic, glass, or metal thick films using the aerosol deposition (AD) method is presented. The process is based on the co‐deposition of the desired film material and a second water‐soluble constituent, resulting in a ceramic‐ceramic composite. Following the subsequent removal of water‐soluble end member, a network of pores is retained. To demonstrate the process, porous BaTiO3 thick films were fabricated through co‐deposition with NaCl. Microstructural images show the clear development of a porous structure, which was found to enhance the dielectric properties over dense thick films, possibly related to the lower extent of internal residual stress. This simple but highly effective porous structure fabrication can be applied to any film and substrate material stable in water and is promising for the application of AD‐processed films in gas sensors, solid oxide fuel cells, and humidity sensors.

Sodium niobate thin films doped with manganese (NN), and NN films modified with 5 or 10 mol % calcium zirconate (CZ) on platinized silicon substrates were prepared by chemical solution deposition. The 250-nm-thick films crystallize in a perovskite phase with fine, equiaxed grains. The NN films exhibit well-shaped ferroelectric loops with a remanent polarization and coercive field of ∼10 μC/cm2 and ∼100 kV/cm, respectively. The modification with CZ strongly influences the ferroelectric response of the films: the remanent polarization progressively decreases to around 2.5 μC/cm2. The absence of an anti-ferroelectric response, which has previously been confirmed in bulk NN-CZ ceramics, is attributed to the nanoscale microstructure and residual thermal stresses. All the studied films exhibit a piezoelectric response with the highest piezoelectric d33 coefficient of 35 pm/V at 300 kV/cm bias field for the NN modified films with 5 mol % CZ, making them candidates for lead-free piezoelectric thin-film applications.

Interest in the piezoelectric and ferroelectric properties of micro- and nanomaterials is increasing due to the advances being made in nanotechnology. However, there are only a few techniques that can detect functional properties at the nanoscale, and one of them is piezo-response force microscopy (PFM). So far, this technique has been mainly used to study surface properties of piezoelectric films. In this investigation, we develop a procedure to study films in the cross section by PFM and to investigate the relaxor-ferroelectric domain structure of pristine, screen-printed, and aerosol-deposited 0.65Pb(Mg1/3Nb2/3)O3–0.35PbTiO3 films in the cross section. Due to the different preparation methods used for two films, the grain size and, thus, the relaxor-ferroelectric domain structures differ. Micron-scale domains are observed in the screen-printed films, while sub micrometer-scale domains are found in the aerosol-deposited films. However, no change in the ferroelectric domain structures was observed across the thicknesses of the films.

The preparation of metal–ceramic layered composites remains a challenge due to the incompatibilities of the materials at the high temperatures of the co-firing process. For densification, the ceramic thick-film materials must be subjected to high-temperature annealing (usually above 900 °C), which can increase the production costs and limit the use of substrate or co-sintering materials with a low oxidation resistance and a low melting point, such as metals. To overcome these problems, the feasibility of preparing dense, defect-free, metal–ceramic multilayers with a room-temperature-based method should be investigated. In this study, we have shown that the preparation of ceramic–metal Al2O3/Al/Al2O3/Gd multilayers using aerosol deposition (AD) is feasible and represents a simple, reliable and cost-effective approach to substrate functionalisation and protection. Scanning electron microscopy of the multilayers showed that all the layers have a dense, defect-free microstructure and good intra-layer connectivity. The top Al2O3 dielectric layer provides excellent electrical resistance (i.e., 7.7 × 1012 Ω∙m), which is required for reliable electric field applications.

The electrocaloric effect (ECE), i.e., the conversion of the electric into the thermal energy has recently become of great importance for development of a new generation of cooling technologies. Here, we explore utilization of [Pb(Mg1∕3Nb2∕3)O3]0.9[PbTiO3]0.1 (PMN-10PT) relaxor ceramics as active elements of the heat regenerator in an ECE cooling device. We show that the PMN-10PT relaxor ceramic exhibits a relatively large electrocaloric change of temperature ΔTEC > 1 K at room temperature. The experimental testing of the cooling device demonstrates the efficient regeneration and establishment of the temperature span between the hot and the cold sides of the regenerator, exceeding several times the ΔTEC within a single PMN-10PT ceramic plate.

Despite the importance of $({\mathrm{Na}}_{1/2}{\mathrm{Bi}}_{1/2})\mathrm{Ti}{\mathrm{O}}_{3}$ as an end member in lead-free ferroelectrics and as an oxide ion conductor, the relaxor/ferroelectric nature remains unclear. In order to understand the relaxor-like behavior, frequency-dependent macroscopic mechanical measurements of polycrystalline $({\mathrm{Na}}_{1/2}{\mathrm{Bi}}_{1/2})\mathrm{Ti}{\mathrm{O}}_{3}$ were performed as a function of poling state, revealing the role of a potential field-induced long-range ferroelectric order on the nonlinear hysteretic stress-strain behavior. The mechanical measurements showed an increase in remanent strain and decrease in coercive stress with electrical poling, consistent with previous studies of relaxors. Electrical poling and mechanical texturing were found to influence the frequency dispersion of the relative permittivity, highlighting the potentially relaxor-like response. Further, the relative permittivity showed a directional dependence with respect to the previously applied electrical and mechanical fields. These data are discussed in conjunction with ex situ stress- and electric-field-dependent piezoresponse force microscopy measurements that revealed a clear ferroelectric domain switching through the application of a sufficiently high electric field, but no change of the domain configuration for uniaxial compressive stresses up to \ensuremath{-}750 MPa. The in situ stress-dependent crystal structure, which was characterized using synchrotron x-ray diffraction, however, indicates stress-induced ferroelastic domain switching as the primary hysteretic process.

Controlling the growth of complex relaxor ferroelectric thin films and understanding the relationship between biaxial strain-structural domain characteristics are desirable for designing materials with a high electromechanical response. For this purpose, epitaxial thin films free of extended defects and secondary phases are urgently needed. Here, we used optimized growth parameters and target compositions to obtain epitaxial (40-45 nm) 0.67Pb(Mg

Macroscopic polarity and its dynamic response to external electric fields and temperature in the nominally ergodic relaxor phase of pristine lead magnesium niobate crystals and ceramics, Pb(Mg1/3Nb2/3)O3 (PMN), were investigated. Dynamic pyroelectric measurements provide evidence for persistent macroscopic polarity of the samples. Annealing experiments below and above Burns temperature of polarized samples relate this polarity to the presence of polar nano entities and their dynamics. The dc electric field strength required for macroscopic polarization reversal is similar to the amplitude of the ac field where dynamic nonlinear dielectric permittivity reaches maximum. Consequently, the aforementioned maximum is related to the reorientation of polar nano entities. The results question the existence of an ergodic state in PMN below Burns temperature., Comment: 14 pages main text, 5 pages supplementary information

Electro-mechanical interactions between charged point defects and domain walls play a key role in the functional properties of bulk and thin-film ferroelectrics. While for perovskites the macroscopic implications of the ordering degree of defects on domain-wall pinning have been reported, atomistic details of these mechanisms remain unclear. Here, based on atomic and nanoscale analyses, we propose a pinning mechanism associated with conductive domain walls in BiFeO3, whose origin lies in the dynamic coupling of the p-type defects gathered in the domain-wall regions with domain-wall displacements under applied electric field. Moreover, we confirm that the degree of defect ordering at the walls, which affect the domain-wall conductivity, can be tuned by the cooling rate used during the annealing, allowing us to determine how this ordering affects the atomic structure of the walls. The results are useful in the design of the domain-wall architecture and dynamics for emerging nanoelectronic and bulk applications. Defects play an important role in the pinning of domain walls (DW) in ferroelectric materials but the underlying mechanism is still elusive. Here, the authors report on the dynamic interaction between electronic defects and DWs in BiFeO3 resulting not only in pinning but also affecting the DW conductivity.

ABO 3 -type perovskite crystallites with symmetrical crystal structures do not show a tendency to grow in the shape of rods and plates, which are of great scientific interest due to their anisotropic physical properties. A topochemical transformation is one of the most convenient approaches for the preparation of such defined-shape perovskite particles, the functional properties of which can be additionally tailored by the formation of solid solutions. In this study a one-step topochemical conversion reaction from a Bi 4 Ti 3 O 12 template to A-site-substituted complex Ba 1-x Sr x TiO 3 perovskite microplates was investigated in order to understand the mechanism and to determine the compositional, structural and morphological correlations between the template and the final plate-like particles. Based on our finding that Sr incorporates in a 2.7-times larger amount than expected from the initial Ba/Sr ratio (0 1-x Sr x TiO 3 solid-solution composition could be prepared using this topochemical transformation. The tetragonal distortion of the Ba 1-x Sr x TiO 3 plates, expressed as the c/a ratio, was found to decrease linearly from 1.0092 (x = 0) to 1.0037 (x = 0.23), while the compositions with higher x were cubic (c/a=1). According to a piezo-response force microscope (PFM) examination, Ba 1-x Sr x TiO 3 plates with 0 ≤x ≤ 0.175 showed ferroelectric and piezoelectric characteristics. The temperature of the ferroelectric-to-paraelectric phase transition, as determined by differential scanning calorimetry (DSC), linearly decreased from 124 °C (x = 0) to 88 °C (x = 0.11). XRD examinations revealed a strong (001) preferential orientation for the plates (0 ≤ x ≤ 0.11) and the typical (001)/(100) peak splitting indicated the presence of c - and a -domains. The successful preparation and design of Ba 1-x Sr x TiO 3 plates increase the potential of this topochemical transformation for the preparation of plates with a variety of solid-solution compositions and controlled characteristics.

Growth of Pb(Mg 1/3 Nb 2/3 )O 3 –33PbTiO 3 thin films by pulsed-laser deposition directly on non-conductive SrTiO 3 substrates for d 33 -mode energy harvesters (EHs) was studied, as they offer a higher figure-of-merit than d 31 -mode EHs. It was found that a high defect density, present in the film grown at 0.13 mbar, is manifested in the form of splitting of the (00 l ) peaks in X-ray diffraction, which was avoided by raising the process pressure to 0.27 mbar. Nevertheless, both films grow in a combined 2D and 3D manner, and form out-of-phase boundaries (OPBs) with a PbO rock-salt structure between the as-grown islands. It was found that the overall composition of the sample with optimized structural and functional properties was Pb 1.07 Mg 0.19 Nb 0.44 Ti 0.32 O 3 , which is close to stoichiometric. The surplus of Pb is compensated by the formation of OPBs and Mg deficit maintains macroscopic electroneutrality. In-plane and out-of-plane relative permittivities of 1900 and 980, respectively, imply macroscopic out-of-plane polarization.

The vast majority of studies on field-induced changes in (1–x)Pb(Mg1/3Nb2/3)O3–xPbTiO3 (PMN–xPT) materials at the morphotropic phase boundary (MPB) have been performed on single crystals, while the more complex responses in polycrystalline materials have not yet been resolved. By using combined microscopy and diffraction techniques, this study aims to determine the structural changes induced by application of an electric field to two representative MPB compositions of the PMN–xPT family, namely, PMN–30PT with the initial Cm and Pm coexisting phases, and PMN–35PT with the P4mm and Pm phases. Both ceramic compositions are characterized by a hierarchical domain structure with domains present at different length-scales. Based on the applied field measurements, major contributing effects in both compositions are outlined and discussed with respect to the processes related to the monoclinic phase and the adaptive phase theory. It is shown that the highly mobile domain walls are largely involved, along with the field-induced polarization rotation in the monoclinic PMN–30PT, and a phase transition to a mainly tetragonal structure in PMN–35PT. These multiscale results elucidate important aspects of field-induced changes in PMN–xPT materials, contributing to the understanding of the complex electrical and electromechanical response of relaxor ferroelectrics.

Purpose The purpose of this study is to design, fabricate and investigate low-temperature co-fired ceramic (LTCC) structures with integrated microfluidic elements. Special attention is paid to the study of fluid properties of micro-channels and microvalves, which are important constitutive parts of both, microfluidic systems and individual microfluidic devices. Design/methodology/approach Several test patterns of fluid channels with different geometry and different types of valves were designed and realized in LTCC technology. All test structures were tested under the flow of two fluids (liquids): water and isopropyl alcohol. Flow rates at different applied pressure were measured and hydrodynamic resistance and diode effect were calculated. Findings The investigation of the channels showed that viscosity of fluidic media has significant influence on the hydrodynamic resistance in channels with rectangular cross-section, while this effect is small on channels with square cross-section. The viscosity also has a decisive influence on the diode effect of different shape of valves, and therefore, it is important in the selection of the valve in practical applications. Research limitations/implications In this work, the investigation of hydrodynamic resistance of channels and diode effect of passive valves is limited on selected geometry and only on two fluidic media and two applied pressures. All these and some other parameters have a significant influence on fluidic properties, but this will be the topic of the next research work, which will be supported by numerical modelling. Practical implications The presented results are useful in the future designing process of LTCC-based microfluidic devices and systems. Originality/value Microfluidic in the LTCC structures is an unconventional use of this technology. Therefore, the fluid properties are relatively unsearched. On the other hand, the global use of microfluidic devices and systems is growing rapidly in various applications. They are mostly made by polymer materials, however, in more demanding applications; ceramic is a useful alternative.

The integration of functional ceramics with metals remains challenging due to the thermally activated processes and the incompatibilities that arise during the high-temperature ceramic sintering process. In order to overcome this, low-temperature processing methods can be employed. In this work, dense 0.9Pb(Mg1/3Nb2/3)O3–0.1PbTiO3 thick films were deposited on low-cost, stainless-steel substrates at room temperature using an aerosol-deposition method. The key material parameters for a successful aerosol deposition of the powder were identified and used in the process, which resulted in homogeneous 15-µm-thick films. The as-deposited films can withstand electric fields of 900 kV⋅cm−1 and exhibit promising room-temperature energy-storage properties: the recoverable energy density reaches 7.0 J⋅cm−3 with an energy-storage efficiency of ∼70%. A post-deposition stress relaxation by annealing at 500°C further improves the recoverable energy density, leading to 9.8 J⋅cm−3 at 900 kV⋅cm−1 with an energy-storage efficiency of ∼80%. The energy-storage performance exhibits excellent temperature stability up to 200°C and an electric-field cycling stability up to 16 million cycles. The low-temperature integration of energy-storage-efficient thick films onto stainless steel opens up possibilities for numerous new, pulsed-power and power-conditioning electronic applications.

The conditions for the topochemical transformation of variously sized Bi4Ti3O12 template plates into BaTiO3 particles were studied in order to control their morphology, crystal structure, and preferential orientation. In the transformation from sub-200 nm- and μm-sized template plates in the presence of surplus BaCO3 (Bi4Ti3O12/BaCO3 = 1:10), the final BaTiO3 particles retained a memory of the precursor size when the conversion reaction in the molten salt (NaCl/KCl) occurred at 660 and 900 °C, respectively. In both cases the side length of the template was well preserved, while the thicknesses of the final BaTiO3 plates were larger compared to those of the templates. The morphology of the BaTiO3 particles formed from micrometer-sized Bi4Ti3O12 plates at 660 °C did not closely resemble the template shape because of the exfoliation and disintegration processes. Through the transformation of sub-200 nm Bi4Ti3O12 plates at 900 °C the formed BaTiO3 particles grew by Ostwald ripening, and thus also the shape of...

Pb(Fe 1/2 Nb 1/2 )O 3 powders have been prepared via different synthesis routes: conventional solid state, molten salt, combustion, hydrothermal and mechanochemical activation assisted syntheses. The homogenized powders were pressed into pellets, sintered at 1000 °C in an oxygen atmosphere and characterized. The ceramic samples prepared by mechanochemical activation assisted synthesis exhibited the best functional properties. These ceramics were highly dense, with no secondary phases exhibiting sharp ferroelectric hysteresis loops with the remanent polarization 28.1μC/cm2and coercive field 3.1 kV/cm. In all other samples, the dielectric permittivity, dielectric losses versus temperature and polarization versus electric field measurements reveal enhanced electrical conductivity.

A complex domain structure with variations in the morphology is observed at ambient temperature in monoclinic Pb(Fe1/2Nb1/2)O3. Using electron microscopy and piezoresponse force microscopy, it is possible to reveal micrometre-sized wedge, lamellar-like, and irregularly shaped domains. By increasing the temperature, the domain structure persists up to 80 &deg, C, and then starts to disappear at around 100 &deg, C due to the proximity of the ferroelectric&ndash, paraelectric phase transition, in agreement with macroscopic dielectric measurements. In order to understand to what degree domain switching can occur in the ceramic, the mobility of the domain walls was studied at ambient temperature. The in situ poling experiment performed using piezoresponse force microscopy resulted in an almost perfectly poled area, providing evidence that all types of domains can be easily switched. By poling half an area with 20 V and the other half with &minus, 20 V, two domains separated by a straight domain wall were created, indicating that Pb(Fe1/2Nb1/2)O3 is a promising material for domain-wall engineering.

Na1/2Bi1/2TiO3‐based relaxor ferroelectrics are extensively investigated for use in transduction applications because of their relatively large electromechanical properties. Integration of these materials into devices, however, requires better temperature stability in addition to electromechanical properties. This work demonstrates a novel approach to enhance the temperature stability of the long‐range ferroelectric order as well as to enhance electromechanical properties in a non‐ergodic relaxor 0.93(Na1/2Bi1/2)TiO3‐0.07BaTiO3 (NBT‐7BT) without changing the chemical composition through, for example, chemical substitutions or second phase particles. The approach involves the room temperature deposition of copper electrodes directly on the relaxor ceramic substrate using the aerosol deposition (AD) method. The collision of solid‐state particles with the substrate surface during AD results in large impact and residual stresses, inherent to the AD process, which are shown with piezo‐response force microscopy to induce long‐range ferroelectric domain ordering in non‐ergodic relaxor NBT‐7BT. Using Raman spectroscopy, the magnitude and depth profile of the stress‐induced transformation are determined. It is demonstrated that deposition‐induced stresses significantly increase the temperature stability of the electromechanical properties, where long‐range ferroelectric ordering is observed up to 150 °C, which is approximately 41 °C higher than NBT‐7BT samples without the AD processed electrode. Moreover, the AD treatment also facilitates ferroelectric domain switching at a lower electric field, enabling maximum polarization at a relatively lower field and an enhancement in the piezoelectric response. It is shown that the deposition‐induced stress is responsible for such an enhancement. Importantly, this impact‐stress‐driven tailoring of electromechanical properties can potentially be utilized for other functional ceramic materials as well, where internal residual stress can result in enhanced functional properties.

Electrocaloric (EC) cooling elements in the form of multilayers (MLs) were prepared. The elements consist of five layers of the relaxor-ferroelectric 0.9Pb(Mg 1/3 Nb 2/3 )O 3 –0.1PbTiO 3 , about 60 μm thick, with internal platinum electrodes and exhibiting a dense, uniform microstructure with a grain size of 1.7 μm. The largest temperature change Δ T EC of 2.26 K was achieved at an electric field ( E ) of 100 kV cm −1 and at 105 °C, measured by a high-resolution calorimeter. These results agree well with the indirect measurements. The EC coefficient, Δ T EC /Δ E, obtained for the MLs, is similar to the value obtained for bulk ceramics of the same composition. The Δ T EC values above 2 K over a broad temperature range from 75 to 105 °C make the ML elements suitable candidates for EC cooling devices at significantly lower voltages than bulk ceramic plates with comparable dimensions and mass.

Mobile charged defects, accumulated in the domain-wall region to screen polarization charges, have been proposed as the origin of the electrical conductivity at domain walls in ferroelectric materials. Despite theoretical and experimental efforts, this scenario has not been directly confirmed, leaving a gap in the understanding of the intriguing electrical properties of domain walls. Here, we provide atomic-scale chemical and structural analyses showing the accumulation of charged defects at domain walls in BiFeO3. The defects were identified as Fe4+ cations and bismuth vacancies, revealing p-type hopping conduction at domain walls caused by the presence of electron holes associated with Fe4+. In agreement with the p-type behaviour, we further show that the local domain-wall conductivity can be tailored by controlling the atmosphere during high-temperature annealing. This work has possible implications for engineering local conductivity in ferroelectrics and for devices based on domain walls.