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Conformable electronics are regarded as the next generation of personal healthcare monitoring and remote diagnosis devices. In recent years, piezoelectric-based conformable ultrasound electronics (cUSE) have been intensively studied due to their unique capabilities, including nonradiative monitoring, soft tissue imaging, deep signal decoding, wireless power transfer, portability, and compatibility. This review provides a comprehensive understanding of cUSE for use in biomedical and healthcare monitoring systems and a summary of their recent advancements. Following an introduction to the fundamentals of piezoelectrics and ultrasound transducers, the critical parameters for transducer design are discussed. Next, five types of cUSE with their advantages and limitations are highlighted, and the fabrication of cUSE using advanced technologies is discussed. In addition, the working function, acoustic performance, and accomplishments in various applications are thoroughly summarized. It is noted that application considerations must be given to the tradeoffs between material selection, manufacturing processes, acoustic performance, mechanical integrity, and the entire integrated system. Finally, current challenges and directions for the development of cUSE are highlighted, and research flow is provided as the roadmap for future research. In conclusion, these advances in the fields of piezoelectric materials, ultrasound transducers, and conformable electronics spark an emerging era of biomedicine and personal healthcare., (© 2023 The Authors. Advanced Materials published by Wiley-VCH GmbH.)

In this study, 2.0 mol% CuO-added 0.96(K0.5Na0.5)(Nb1−zSbz)O3–0.04(Bi0.5Ag0.5)ZrO3 [CKN(N1−zSz)–BAZ] piezoceramics (0.0 ≤ z ≤ 0.08) were densified at 980 °C without the secondary phase. The crystal structure of the CKN(N1−zSz)–BAZ piezoceramics changed from the tetragonal–orthorhombic structure to the tetragonal–orthorhombic–pseudocubic structure with increasing z. The CKN(N1−zSz)–BAZ piezoceramics (0.0 ≤ z ≤ 0.07) were well textured at 980 °C along the [001] direction, without holes, when 3.0 mol% Na(Nb0.9Sb0.1)O3 (NNS) templates were used. However, the specimens textured using NaNbO3 (NN) templates exhibited holes owing to the dissolution of the NN templates. Moreover, the elastic modulus and hardness of the specimen (z = 0.05) textured using the NNS template were larger than those of the specimen (z = 0.05) textured using the NN template, possibly because of the absence of holes. The [001]-textured CKN(N1−zSz)–BAZ piezoceramics exhibited a reduced dielectric constant and enhanced piezoelectric properties. Particularly, the [001]-textured CKN(N0.95S0.05)–BAZ piezoceramic provides large d33 (610 pC N−1), kp (0.68) and d33 × g33 (30 × 10−12 m2 N−1) values. A cantilever-shaped piezoelectric energy harvester was fabricated using the [001]-textured CKN(N0.95S0.05)–BAZ ceramic, which showed a large output power of 1.6 mW at the resonance frequency, indicating that this piezoceramic is a good candidate for a piezoelectric energy harvester. [ABSTRACT FROM AUTHOR]

Intrinsic SrTiO3 is a quantum paraelectric, but moderately Bi-doped SrTiO3 exhibits dielectric frequency dispersion similar to relaxor ferroelectrics. In this paper, detailed electron microscopic studies of the microstructures of Bi-doped SrTiO3 samples were presented. It was found that the Sr sites were replaced by off-central Bi, resulting in tensile strain in the strontium titanate (STO) lattice. In the Bi-doped SrTiO3 samples, the valence of titanium mainly showed the Ti 4 + characteristic. According to the dielectric behavior and microstructure analysis, the polar nanoregions (PNRs) composed of strained SrTiO3 nanoclusters should be responsible for the ferroelectric relaxor behavior in samples with moderate Bi content. [ABSTRACT FROM AUTHOR]

The effect of doping on the chemical and physical properties of semiconductors, alloys, ferroelectrics, glasses, and other substances has been a classic topic in materials science for centuries. Strontium titanate, SrTiO3, is an archetypal perovskite of interest for both fundamental science as quantum paraelectric and numerous outstanding physical properties and applications, including dielectrics, tunable microwave and photovoltaic devices, superconductors, thermoelectrics, potential multiferroics. Its chemical doping with transition metals leads to new functionalities, but intrinsic mechanisms of structural responses, activated by impurities, have not been systematically investigated. Herein, we present the results of a comparative study of the crystal structure, vibrational spectra, and dielectric properties of SrTiO3:M (M = Mn, Ni, and Fe, 2 at%) single crystals. It is shown that impurities constitute a different tendency to off-centering and the formation of dipoles: Mn and Fe atoms are shifted from the center of the oxygen octahedron, while Ni atoms remain on-centered. As a result, small chemical doping has a dramatic effect on the dielectric response through various structural mechanisms, including the pseudo Jahn–Teller effect, the first-order Jahn–Teller effect, and defect-induced distortion. These findings open up fundamentally new possibilities for the practical solution of a difficult problem: controlling the dielectric responses of quantum paraelectrics by choosing the type of chemical additive. [ABSTRACT FROM AUTHOR]

High-performance relaxor ferroelectrics for energy-storage capacitors have attracted enormous attention, but the difficulty in simultaneously enhancing energy density (Wrec) and efficiency (η) largely hinders their development. Herein, we introduce an effective strategy to collaboratively improve Wrec and η values in NaNbO3-based lead-free relaxor ferroelectric (FE) ceramics through enhancing the antiferrodistortion of the FE superlattice, realizing an excellent comprehensive energy-storage performance of Wrec ∼ 8.5 J cm−3 and η ∼ 90%. Both the local FE orthorhombic supercells with a significantly enhanced antiferrodistortive degree and the formation of highly concentrated stripe-like polar nanodomains should be responsible for the markedly delayed polarization saturation, the suppressed polarization hysteresis and the maintained maximum polarization. These structural features also ensure outstanding temperature-insensitive charge–discharge properties of high-power density ∼343 ± 6% MW cm−3, high discharge energy density ∼4.3 ± 10% J cm−3 and ultra-short discharge time <30 ns at 0–150 °C, demonstrating great application potential in next-generation advanced pulse power capacitors. As a result, enhancing antiferrodistortion should be a valuable way to develop novel high-performance relaxor ferroelectric capacitors. [ABSTRACT FROM AUTHOR]

Previously, we scrutinized the dielectric spectra of a binary glass former made by a low-molecular high-Tg component 2-(m-tertbutylphenyl)-2′-tertbutyl-9,9′-spirobi[9H]fluorene (m-TPTS; Tg = 350 K) and low-Tg tripropyl phosphate (TPP; Tg = 134 K) [Körber et al., Phys. Chem. Chem. Phys. 23, 7200 (2021)]. Here, we analyze nuclear magnetic resonance (NMR) spectra and stimulated echo decays of deuterated m-TPTS-d4 (2H) and TPP (31P) and attempt to understand the dielectric spectra in terms of component specific dynamics. The high-Tg component (α1) shows relaxation similar to that of neat systems, yet with some broadening upon mixing. This correlates with high-frequency broadening of the dielectric spectra. The low-Tg component (α2) exhibits highly stretched relaxations and strong dynamic heterogeneities indicated by "two-phase" spectra, reflecting varying fractions of fast and slow liquid-like reorienting molecules. Missing for the high-Tg component, such two-phase spectra are identified down to wTPP = 0.04, indicating that isotropic reorientation prevails in the rigid high-Tg matrix stretching from close to T g T P P to T g 1 w T P P . This correlates with low-frequency broadening of the dielectric spectra. Two Tg values are defined: T g 1 ( w T P P ) displays a plasticizer effect, whereas T g 2 ( w T P P ) passes through a maximum, signaling extreme separation of the component dynamics at low wTPP. We suggest understanding the latter counter-intuitive feature by referring to a crossover from "single glass" to "double glass" scenario revealed by recent MD simulations. Analyses reveal that a second population of TPP molecules exists, which is associated with the dynamics of the high-Tg component. However, the fractions are lower than suggested by the dielectric spectra. We discuss this discrepancy considering the role of collective dynamics probed by dielectric but not by NMR spectroscopy. [ABSTRACT FROM AUTHOR]

0.88Pb(Zr0.52Ti0.48)O3 - 0.12Pb(Mn1/3Sb2/3)O3 - 0,02 at%E piezoelectric ceramics, with E = Pr3+ were synthesized by using a conventional method, namely a solid state reaction technique. X-ray diffraction (XRD) and Scanning Electron Microscopy (SEM) were employed for the structural and microstructural investigations. Piezoelectric methods were used for the dielectric and piezoelectric properties determination. The results of XRD show a perovskite structure and XRD patterns, indexing on a tetragonal cell structure, was carried out for the most common phases. The SEM micrographs of the sintered compositions reveal a homogenous structure with a sharp or rounded grain boundary. The modified PZT ceramic presents still superior piezoelectric properties. Based on the results obtained, one can conclude that the analysed piezoelectric ceramics are useful for device applications. [ABSTRACT FROM AUTHOR]

A detailed analysis of photoluminescence of Eu-doped Na0.5Bi0.5TiO3 (NBT) is performed using it as a tool for describing the local structure of NBT. The obtained results reveal the low symmetry of the Eu3+ local environment in NBT, as indicated by the observed maximal number of sublevels of the 5D0→7F1 and the 5D0→7F2 luminescence transitions, clearly observed at low temperatures. Approximation of the luminescence spectra by Gaussian peaks provides valuable information about the shift of the involved levels upon change of the excitation wavelength. Variation in the strength of the crystal field in Eu-doped NBT is evaluated. Temperature dependence of the luminescence above room temperature is analyzed for the poled and the unpoled states of the material. The results obtained for Eu-doped NBT are compared with the results for Er-doped NBT reported previously. [ABSTRACT FROM AUTHOR]

The ferroelectric, ferroelastic, and dielectric properties as well as the crystal structure were investigated for polycrystalline donor doped lead zirconate titanate (PZT) with grain sizes ranging from 0.25 to 5 μm, which were prepared using a novel zirconium titanium hydrate precursor (ZTH) with a specific surface area of 310 m2/g. Piezoforce microscopy was used to investigate the change in the domain structure, revealing a change in the domain configuration from a complex 3D structure to a simple lamellar domain formation at a 1 μm grain size that corresponded to a rapidly increasing internal mechanical stress observed with in situ synchrotron x-ray experiments. The correlation between the change in domain configuration, increasing internal stresses, effects of poling on the crystal structure, and the macroscopic ferroelectric and ferroelastic properties are discussed in detail, allowing a deeper understanding of size effects in polycrystalline donor doped PZT ceramics. [ABSTRACT FROM AUTHOR]

Relaxation spectra of molecular glass formers devoid of secondary relaxation maxima, as measured by dielectric spectroscopy (DS), nuclear magnetic resonance (NMR) relaxometry, photon correlation spectroscopy (PCS), and Fabry–Perot interferometry, are quantitatively compared in terms of the Kohlrausch stretching parameter βK. For a reliable estimate of βK, the excess wing contribution has to be included in the spectral analysis. The relaxation stretching probed by PCS and NMR varies only weakly among the liquids (βK = 0.58 ± 0.06). It is similar to that found in DS, provided that the liquid is sufficiently nonpolar (relaxation strength Δ ε ≲ 6). For larger strengths, larger β K D S (narrowed relaxation spectra) are found when compared to those reported from NMR and PCS. Frequency–temperature superposition (FTS) holds for PCS and NMR. This is demonstrated by data scaling and, for the few glass formers for which results are available, by the equivalence of the susceptibilities χ P C S ″ ω τ ∝ χ N M R ″ τ ∝ χ N M R ″ ω , i.e., measuring at a constant frequency is equivalent to measuring at a constant temperature or constant correlation time. In this context, a plot of the spin–lattice relaxation rate R1(T) as a function of the spin–spin relaxation rate R2(T) is suggested to reveal the stretching parameter without the need to perform frequency-dependent investigations. Dielectrically, we identify a trend of increasing deviations from FTS with increasing Δε. Depending on the technique and glass former, the relative relaxation strength of the excess wing varies, whereas its exponent appears to be method independent for a given substance. For polar liquids, we discuss possible reasons for the discrepancy between the results from PCS and NMR as compared to those from DS. [ABSTRACT FROM AUTHOR]

The character of extrinsic contributions to the dielectric and pyroelectric properties of Pb0.99[(Zr0.52Ti0.48)0.98Nb0.02]O3 (PZT) films on Ni foil and Si wafers was explored using Rayleigh analysis, third harmonic phase angle, and Preisach analysis from 15 K to 296 K. The temperature dependence of the domain structure, domain wall mobility, and domain switching influenced the intrinsic, extrinsic, and secondary contributions to the pyroelectric coefficients. This, in turn, produced markedly different room temperature pyroelectric coefficients of ∼250 μC/m2 K and ∼100 μC/m2 K, respectively, for films on Ni and Si. At room temperature, the dielectric irreversible Rayleigh parameter αray was 15.5 ± 0.1 and 28.4 ± 1.6 cm/kV for PZT on Si and Ni, respectively. The higher αray value for the Ni sample suggests more domain wall motion at room temperature, which was attributed to the lower stiffness on the Ni foil compared to the ∼500 μm thick Si substrate. Below 200 K, αray for the PZT Si sample exceeds that of the Ni/PZT sample. This is believed to arise from differences in the energy landscape of pinning centers for the domain wall motion. It is proposed that the residual stresses not only set the preferred domain structures but also the barrier heights for domain wall motion and domain switching. [ABSTRACT FROM AUTHOR]

Ultrafast decays of the intrinsic phonon modes within 260–790 cm−1 range of frequencies, which are symmetry forbidden in the first-order Raman scattering in bulk SrTiO3 crystal, have been traced using time-resolved coherent Raman technique. The effective phonon decay times are within 0.86–1.38 ps and yield corresponding linewidths of 7.7–12.3 cm−1 for optical lattice vibrations. Symmetry breakage mechanisms related to free charged carriers resulting from vacancies do not appear to play a major role. [ABSTRACT FROM AUTHOR]

Atmospheric water adsorbed by porous materials may significantly change its electrodynamic response in a wide frequency range. Mechanical and chemical stabilities of silicon dioxide along with a proven manufacturing method of porous SiO2 samples made it convenient for studying the effects of moisture adsorption on various parameters of the porous media. We report the dielectric properties of SiO2-based nanoporous glass in the frequency range of 20 Hz–400 THz at ambient atmospheric conditions and at a low residual pressure of ≤1 mbar. We observed a significant low-frequency dispersion of the complex dielectric permittivity and enhancement of dielectric loss for the porous sample exposed to the ambient moisture. In the terahertz range, the change in dielectric response is smaller and correlates with the moisture saturation of the sample. [ABSTRACT FROM AUTHOR]

This work presents the results of study of the behavior of longitudinal (LA), quasilongitudinal (QLA), and transverse (TA) acoustic phonons in single crystals of Na1/2Bi1/2TiO3 (NBT) within a temperature range from 110 K to 850 K. Measurements were carried out by means of Brillouin light scattering on phonons with a wave vector qph || [100], qph || [010], and qph || [110], regarding the cubic phase of NBT. Temperature dependences of sound velocity, attenuation, and intensity of LA, QLA, and TA phonons have been plotted. Anomalies in the behavior of sound velocity and attenuation of LA phonons in the vicinity of antiferrodistortive structural phase transition from the cubic to the tetragonal phases have been found. It is shown that broad anomalies in the sound velocity and attenuation of acoustic phonons typical to diffuse phase transition are not connected directly with the anomaly in the dielectric permittivity of the crystal. Elastic C11 and C44 modules in the cubic phase of NBT have been defined. [ABSTRACT FROM AUTHOR]

Oxygen vacancies in reduced SrTiO 3 are investigated by Raman spectroscopy and dynamic elastic modulus measurements. The anelastic spectrum is used to evaluate the amount and state of the O vacancies, which result to be almost completely paired and otherwise aggregated at a concentration of 0.5 mol. %, with only 1/6 of them isolated at room temperature. Raman spectra recorded as a function of temperature in as-grown and reduced samples are examined regarding the different processes which can contribute to them. Chemometric analysis is used to highlight the specific influence of oxygen vacancies on the Raman spectra. It is shown that oxygen vacancies induce a relaxation of selection rules leading to the activation of first-order lines even in the cubic phase. Furthermore, regions around oxygen vacancies are demonstrated to be responsible for the asymmetric broadening of Raman lines. [ABSTRACT FROM AUTHOR]

As a mechanical analog of ferroelectricity and ferromagnetism, ferroelasticity has made outstanding contributions in the fields of energy conversion, information processing, and mechanical switching. However, research on 2D ferroelasticity is lacking so far, and it is still a challenge to synthesize 2D perovskite ferroelastics. Here, we successfully constructed three 2D organic–inorganic hybrid ferroelastics: (PEA)2CdCl4 [PEA = phenethylamium cation, 1], (3-FPEA)2CdCl4 [3-FPEA = 3-fluorophenethylamium cation, 2] and (4-FPEA)2CdCl4 [4-FPEA = 4-fluorophenethylamium cation, 3]. These compounds undergo a structural phase transition between 379–385 K, exhibit temperature-triggered ferroelasticity, and possess a dielectric transition. The structural analysis of temperature-variable single crystals indicates that the reason for the phase transition of the ferroelastics is the order–disorder transition of cations and distortion of the anion framework. This research provides new options for a new generation of 2D perovskite ferroelastics. [ABSTRACT FROM AUTHOR]

High strain piezoceramics are required for various sensor and actuator applications such as opening and closing of valves in fuel injector systems, for controlled flow of fuel in automobiles, applications for micro-propulsion in satellites, and other engineering applications. The precision control of fuel flow in automobiles is necessary for fuel efficiency and pollution control. In this article, lead free piezo systems having higher strain are reviewed with a focus on origin/mechanisms of high strain behavior with critical comments and future directions. Lead zirconate titanate (PZT) delivers linear but low strain of ~0.15% of total length due to the piezoelectric effect. However, lead free piezoceramic material systems such as bismuth sodium titanate (BNT), potassium sodium niobate (KNN), barium zirconate titanate (BZT) etc. deliver high but non-linear strains, as high as 0.79% due to electrostriction. [ABSTRACT FROM AUTHOR]

While doping is widely used for tuning physical properties of perovskites in experiments, it remains a challenge to exactly know how doping achieves the desired effects. Here, we propose an empirical and computationally tractable model to understand the effects of doping with Fe-doped BaTiO3 as an example. This model assumes that the lattice sites occupied by a Fe ion and its nearest six neighbors lose their ability to polarize, giving rise to a small cluster of defective dipoles. Employing this model in Monte Carlo simulations, many important features such as reduced polarization and the convergence of phase transition temperatures, which have been observed experimentally in acceptor doped systems, are successfully obtained. Based on microscopic information of dipole configurations, we provide insights into the driving forces behind doping effects and propose that active dipoles, which exist in proximity to the defective dipoles, can account for experimentally observed phenomena. Close attention to these dipoles is necessary to understand and predict doping effects. [ABSTRACT FROM AUTHOR]

Having reviewed the previous studies on Mn-doped SrTiO3 materials, we found that Mn2+ and/or Mn4+ ions are usually present in the SrTiO3 host lattice and lead to paramagnetic, spin-glass, or ferromagnetic (FM) behavior. Mn2+ can occupy at both octahedral (Ti) and dodecahedral (Sr) sites, while Mn4+ only occupies the Ti site. To get more insight into this material system, we have prepared polycrystalline SrTi1-xMnxO3 (x = 0–0.10) samples by solid-state reactions. The results obtained from analyzing the powder X-ray diffraction patterns, and Raman scattering, X-ray absorption, and electron-spin-resonance spectra indicate an incorporation of Mn2+ and Mn3+ ions into the SrTiO3 host lattice. Isolated Mn2+ ions are dominant in the samples with x ≤ 0.02 and can occupy both Ti and Sr sites, leading to two sets of the hyperfine sextet lines. An increase in the Mn content with x > 0.02 enhances the Mn3+ concentration and stimulates the formation of a minor tetragonal phase besides the main cubic phase of SrTiO3. This enhances the Lorentzian-shaped broad background line of dipolar and magnetic interactions between Mn ions. Besides the resonant signals of isolated Mn2+ ions and dipolar/magnetic interactions between Mn ions, there is also the resonant signal associated with intrinsic defects. We believe that intrinsic defects together with the Mn doping at suitable concentrations (x > 0.02) are an important pivot for tailoring room-temperature FM order in SrTi1-xMnxO3 ceramics. [ABSTRACT FROM AUTHOR]

Lead free relaxor ferroelectrics have attracted continuing interest due to their outstanding and eco-friendly properties. In this paper, dielectric relaxation behavior of the 0.6BaTiO3-0.4Bi(Mg1/2Ti1/2)O3 ceramic (BT-40BMT), which is a typical lead free relaxor ferroelectric, is theoretically and experimentally investigated. At first, the observed dielectric relaxation was quantitatively characterized by a statistical model, indicating that the minority co-related polar nano regions (PNRs) dominate the total polarization. Kinetics of the PNRs were subsequently studied by micro-Raman measurements performed at various temperatures. Here, the relaxation of written domains formed by the piezoresponse force microscopy (PFM) tip-bias induced electric field was also studied, which describes the polarization retention performance of BT-40BMT. The absence of ferroelectric signal contribution in local switching was also confirmed by the contact mode Kelvin PFM technique, indicating the lack of local ferroelectricity. Moreover, the temperature insensitive energy storage property from 293K to 443K was obtained. High voltage pulsed discharge behavior was also investigated by using the pulsed current. A power density of 7.9 x 108W/kg is obtained under a pulsed voltage of 50 kV. Combined with the fast discharge time, the 0.6BaTiO3-0.4Bi(Mg1/2Ti1/2)O3 ceramic is considered as a candidate material for high voltage pulse power applications. [ABSTRACT FROM AUTHOR]

Lead free relaxor ferroelectrics have attracted continuing interest due to their outstanding and eco-friendly properties. In this paper, dielectric relaxation behavior of the 0.6BaTiO3-0.4Bi(Mg1/2Ti1/2)O3 ceramic (BT-40BMT), which is a typical lead free relaxor ferroelectric, is theoretically and experimentally investigated. At first, the observed dielectric relaxation was quantitatively characterized by a statistical model, indicating that the minority co-related polar nano regions (PNRs) dominate the total polarization. Kinetics of the PNRs were subsequently studied by micro-Raman measurements performed at various temperatures. Here, the relaxation of written domains formed by the piezoresponse force microscopy (PFM) tip-bias induced electric field was also studied, which describes the polarization retention performance of BT-40BMT. The absence of ferroelectric signal contribution in local switching was also confirmed by the contact mode Kelvin PFM technique, indicating the lack of local ferroelectricity. Moreover, the temperature insensitive energy storage property from 293 K to 443 K was obtained. High voltage pulsed discharge behavior was also investigated by using the pulsed current. A power density of 7.9 × 108 W/kg is obtained under a pulsed voltage of 50 kV. Combined with the fast discharge time, the 0.6BaTiO3-0.4Bi(Mg1/2Ti1/2)O3 ceramic is considered as a candidate material for high voltage pulse power applications. [ABSTRACT FROM AUTHOR]

Arrangement of 90-degree domain walls in the domain structure of the ⟨ 111 ⟩ pc -oriented single crystal plates of BaTiO3 was intentionally modified by combinations of in-plane and out-of-plane steady state electric poling at ambient temperature. It is shown that the annealed, in-plane, and out-of-plane poled samples exhibit markedly different dielectric properties at low temperatures. The difference in low-temperature permittivity behavior is enhanced by the out-of-plane fast-decayed bipolar electric pulse treatment, but the efficiency of this enhancement is strongly dependent on the initial domain structure. The absence of a clear signature of the pulse treatment in optical observations of the domain structure suggests that it might involve mostly changes in the 180-degree domain wall subsystem. [ABSTRACT FROM AUTHOR]

While the unique geometrical frustration of pyrochlore Yb2Ti2O7 has attracted attention, the dielectric and other properties of this pyrochlore beyond frustrated magnetism are not well understood. Here, we report on the fascinating low-temperature dielectric relaxation of Yb2-xBaxTi2O7-δ (x = 0–0.20) and demonstrate that this phenomenon is related to structural distortion. A-site Ba substitution, which increases the density of point defects and introduces a different atomic radius, enhances the chemical disorder and structural distortion. As a result, the increases in oxygen vacancies and nonmagnetic Ba2+ and Yb2+ ions dilute the ferromagnetic Yb3+–Yb3+ interactions, as indicated by the decrease in effective magnetic moment. On the other hand, the distorted octahedra facilitate the hopping of Yb ions, and the random distribution of Ba2+ ions at the Yb3+ sites gives rise to additional random fields, leading to significantly increased dielectric relaxation. The room-temperature dielectric constant is improved to ∼170, twice that of pristine Yb2Ti2O7. This work provides a comprehensive view of the structural, magnetic, and dielectric properties of Yb2Ti2O7 and lays the foundation for additional research into pyrochlore compounds. [ABSTRACT FROM AUTHOR]

Molecular ferroelastics have received particular attention for potential applications in mechanical switches, shape memory, energy conversion, information processing, and solar cells, by taking advantages of their low‐cost, light‐weight, easy preparation, and mechanical flexibility. The unique structures of organic–inorganic hybrid perovskites have been considered to be a design platform for symmetry‐breaking‐associated order–disorder in lattice, thereby possessing great potential for ferroelastic phase transition. Herein, we review the research progress of organic–inorganic hybrid perovskite ferroelastics in recent years, focusing on the crystal structures, dimensions, phase transitions and ferroelastic properties. In view of the few reports on molecular‐based hybrid ferroelastics, we look forward to the structural design strategies of molecular ferroelastic materials, as well as the opportunities and challenges faced by molecular‐based hybrid ferroelastic materials in the future. This review will have positive guiding significance for the synthesis and future exploration of organic–inorganic hybrid molecular ferroelastics. [ABSTRACT FROM AUTHOR]

Structural distortions such as cation off-centering are frustrated in the pyrochlore structure due to the triangular arrangement of cations on the pyrochlore lattice. This geometric constraint inhibits a transition from a paraelectric to a ferroelectric phase in the majority of pyrochlore oxide materials. Few pyrochlore materials can overcome this frustration and exhibit polar crystal structures, and unraveling the origin of such leads to the understanding of polarity in complex materials. Herein we hypothesize that frustration on the pyrochlore lattice can be relieved through A-site doping with rare earth cations that do not possess stereochemically active lone pairs. To assess if frustration is relieved, we have analyzed cation off-centering in various Bi2−xRExTi2O7 (RE = Y, Ho) pyrochlores through neutron and X-ray total scattering. Motivated by known distortions from the pyrochlore literature, we present our findings that most samples show local distortions similar to the β-cristobalite structure. We additionally comment on the complexity of factors that play a role in the structural behavior, including cation size, bond valence, electronic structure, and magnetoelectric interactions. We posit that the addition of magnetic cations on the pyrochlore lattice may play a role in an extension of the real-space correlation length of electric dipoles in the Bi-Ho series, and offer considerations for driving long-range polarity on the pyrochlore lattice. [ABSTRACT FROM AUTHOR]

The domain structures of (LixNa1-x)NbO3 (x=0, 0.05, 0.10, and 0.13) epitaxial films on SrRuO3/ (001) SrTiO3 substrates were studied by laser scanning microscopy and reciprocal space mapping. The stripe domains with in-plane antiferroelectric polarization of an orthorhombic P phase were observed at x=0. At x=0.05 and 0.10, the crystal phase was changed to an orthorhombic Q phase and the domain structure was changed to a mixture of stripe domains with in-plane ferroelectric polarization and thick line-like domains with out-of-plane ferroelectric polarization. At x=0.13, the line-like domain pattern was altered to a leaf-like domain pattern and out-of-plane ferroelectric polarization of a rhombohedral N phase was induced in the stripe domains. After an electric field was applied along an out-of-plane direction, some of the stripe domains with the in-plane polarization of the P phase at x=0 and those with the in-plane polarization of the Q phase at x=0.05 were switched to domains with out-of-plane polarization of the Q phase. On the other hand, stripe domains with out-of-plane ferroelectric polarization of the N phase were formed in the line-like and stripe domains of the Q phase at x=0.10. At x=0.13, most domains changed to stripe domains of the N phase. The relationship between the domains and the remanent polarization was discussed. [ABSTRACT FROM AUTHOR]

Electrical characterizations of Nb2O5 doped 0.65BiFeO3-0.35BaTiO3 (0.65BF-0.35BT) ceramic were carried out over broad temperature and frequency ranges through dielectric spectroscopy, impedance spectroscopy, and ac conductivity measurements. The dielectric constant and loss tangent are drastically reduced with introducing Nb2O5 into the 0.65BF-0.35BT system. Two dielectric anomalies are detected in the temperature regions of 100°C = T = 280°C and 350°C = T = 480°C, and the Curie temperature (TC) was confirmed in higher temperature region. A dielectric relaxation with large dielectric constants was detected near the TC. This dielectric relaxation becomes even stronger with the gradual increase in the Nb2O5 content. Impedance spectroscopy results clearly show the contributions of grains and grain boundaries in the frequency range of 100Hz = f = 1MHz, and the relaxation processes for grains and grain boundaries are non-Debye-type. The grain boundaries are more resistive than that of the grains, revealing the inhomogeneity in samples. The experimental results are well fitted based on a Maxwell-Wagner (MW) interfacial polarization model below 100kHz, and the MW interfacial polarization effect becomes more and more obvious with the increase in the Nb2O5 content. The increase in dielectric constant is possibly related to space charge polarization, which is caused by charges accumulated at the interface between the grain and grain boundaries. Frequency dependence of the ac conductivity confirms the MW interfacial polarization effect below 100kHz. [ABSTRACT FROM AUTHOR]

Achieving high energy storage density (ESD), energy storage efficiency (η) and exceptional stability is deemed the foremost challenge for the application of lead-free dielectric energy storage materials. Relaxor ferroelectric (REF) ceramics are one of the most promising candidate materials for energy storage materials by virtue of their low remnant polarization, hysteresis, and high permittivity. Here, we demonstrated that excellent energy storage properties (high recoverable energy storage density Wrec of 5.23 J cm−3 and 5.47 J cm−3 with high η of 89.7% and 90.6%) are achieved in Hf-modified (0.7Ba0.55Sr0.45–0.3Bi0.5Na0.5)TiO3 (BSBNT) relaxor ferroelectric ceramics. Analysis of a first order reversal curve (FORC) and piezoresponse force microscopy (PFM) indicate that the incorporation of Hf can effectively inhibit the polarization nonlinearity and reduce the size of polar nanoregions, resulting in improved energy density and efficiency. Additionally, the introduction of Hf greatly enhances the breakdown strength by improving the electric insulation, suppressing the electronic transition and boosting the bandgap. For practice application, the (0.7Ba0.55Sr0.45–0.3Bi0.5Na0.5)(Ti0.85Hf0.15)O3 ceramics also show excellent temperature (−95 to 125 °C) and frequency (1–1000 Hz) stability at 250 kV cm−1. Meanwhile, the energy storage properties (ESPs) of ceramics can maintain stability even after 106 hysteresis cycles. This work provides a feasible approach that can be employed to develop high-performance lead-free capacitors in high-power electronics and pulse power systems. [ABSTRACT FROM AUTHOR]

The comparative analysis of the dielectric properties of bismuth-containing pyrochlores with different manifestation of atomic order/disorder was carried out. We examined the dielectric properties (including behavior in electric fields) of two pyrochlore compounds: BZN (presumably a composition close to Bi 1. 5 Zn 0. 5 Nb 1. 5 O 6. 5) ceramics with chemical disorder in both A and B cation sublattices and Bi2Ti2O7 single crystal with fully chemical ordered structure. The fundamental differences between the dielectric properties of the BZN ceramics and Bi2Ti2O7 single crystal were shown. In particular, in the dielectric relaxation behavior (which cannot be described via Arrhenius law in the Bi2Ti2 O 7) or in the influence of the electric fields on the dielectric permittivity (splitting of the field-cooled and zero-field-cooled behaviors was observed for Bi2Ti2O7 below estimated freezing temperature). The results of this study highlights the special role of Bi2Ti2O7 as a candidate material for studying aspects of geometric frustration related with pyrochlore structure in non-magnetic medium and specifies the future directions of research. [ABSTRACT FROM AUTHOR]

Over the past two decades, lead-free piezoceramics have been developed aiming to replace toxic lead-bearing lead zirconate titanate (PZT). A large number of lead-free piezo systems were explored during this period as evidenced from the huge number of publications. At this juncture, it was felt necessary to publish a review article focusing on material systems and processes delivering high d33 in order to give direction to future research for its further improvement equivalent to or higher than the d33 level delivered by PZT. The important lead-free piezo systems under consideration are: modified barium titanates such as barium calcium titanate zirconate (BCTZ), barium calcium tin titanate (BCSnT), barium calcium hafnium titanate (BCHfT), and potassium sodium niobate (KNN). In this article, an effort has been made to review the high piezoelectric properties achieved on the above lead-free piezo systems explaining the reasons and mechanisms behind high piezo properties and possible future directions of the research for further enhancement of properties. [ABSTRACT FROM AUTHOR]

Piezoelectric nanogenerators (PENG) collect energy from the environment and biomechanical movements and convert this mechanical energy into electrical energy. They have become an attractive alternative to traditional rechargeable batteries for providing electrical power low energy portable devices. As PENGs became the center of attention in robots, wearable devices, medical equipment, and many other fields, the development of piezoelectric materials has become mandatory. This review reviews the basic information, structure, properties, and preparation methods of Barium Titanate, one of the most important PENGs, its development in recent years, and the progress towards high energy generation. [ABSTRACT FROM AUTHOR]

HgTe plates have been grown by vapor phase epitaxy on (111) SrTiO3 substrates with a preferred orientation in the (111) crystalline direction, as indicated by x-ray diffraction. Examination of the plates using the micro-Raman mapping shows that the HgTe plates exhibit unusual strain patterns: the Raman peaks from the transverse-optical and longitudinal-optical phonons for the thicker (central) parts of the HgTe plates are at the same frequency as that of the bulk HgTe, while the Raman peaks for the thinner parts of the HgTe plates, which surround the thicker parts and can hardly be seen in a scanning electron microscope, are significantly larger in frequency. The full width at half maximum is smaller in the thinner areas than in the thicker parts. Theoretical analysis shows that the HgTe plates on SrTiO3 substrates suffer from compressive stress, and this may be sufficient to induce the three-dimensional topological insulator behavior in HgTe. [ABSTRACT FROM AUTHOR]

We report for the first time the microwave characterization of 0.92(Bi0.5Na0.5)TiO3-0.08BaTiO3 (BNT-BT0.08) ferroelectric thin films fabricated by the sol-gel method and integrated in both planar and out-of-plane tunable capacitors for agile high-frequency applications and particularly on the WiFi frequency band from 2.4 GHz to 2.49 GHz. The permittivity and loss tangent of the realized BNT-BT0.08 layers have been first measured by a resonant cavity method working at 12.5 GHz. Then, we integrated the ferroelectric material in planar inter-digitated capacitors (IDC) and in out-of-plane metal-insulator-metal (MIM) devices and investigated their specific properties (dielectric tunability and losses) on the whole 100 MHz-15 GHz frequency domain. The 3D finite-elements electromagnetic simulations of the IDC capacitances are fitting very well with their measured responses and confirm the dielectric properties determined with the cavity method. While IDCs are not exhibiting an optimal tunability, the MIM capacitor devices with optimized Ir/MgO(100) bottom electrodes demonstrate a high dielectric tunability, of 30% at 2.45 GHz under applied voltages as low as 10 V, and it is reaching 50% under 20V voltage bias at the same frequency. These highfrequency properties of the MIM devices integrating the BNT-BT0.08 films, combining a high tunability under low applied voltages indicate a wide integration potential for tunable devices in the microwave domain and particularly at 2.45 GHz, corresponding to the widely used industrial, scientific, and medical frequency band. [ABSTRACT FROM AUTHOR]

Using first-principles calculations, we show that a specific chemical ordering of Na and Bi in Na0.5Bi0.5TiO3 is responsible for the co-existence of its ferroelectric phases with rhombohedral R3c and monoclinic Cc structures, which are relevant to its morphotropic phase boundary and large piezoelectric response. We identify the signatures of chemical ordering in the calculated phonon spectra and establish the prevalence of A-type ordering through comparison with experiment. We uncover a mechanism of the observed electric field induced Cc to lower energy R3c structural transformation promoted by a hybrid soft mode involving a combination of TiO6 rotations and a polar component. [ABSTRACT FROM AUTHOR]

BaTiO3 appears in cubic and hexagonal variants, both of which are centrosymmetric. Samples of cubic BaTiO3 are known to exhibit breaking of the centric symmetry locally and globally. It has been proposed that the local symmetry breaking originates in polar regions, the precursors of the ferroelectric phase. Origins of the macroscopic symmetry breaking, which are not well understood, have been previously tentatively correlated with inhomogeneities in the samples, such as strain gradients that may align or redistribute objects such as charged point defects or polar regions making material macroscopically polar. No such data are available for BaTiO3 with hexagonal symmetry. We compare dielectric, elastic, and pyroelectric properties of the two materials in polycrystalline form. In contrast to cubic BaTiO3, hexagonal BaTiO3 does not exhibit macroscopic pyroelectric response at room temperature. This is consistent with apparent absence of polar regions in the hexagonal material, and the fact that in hexagonal BaTiO3, strain rather than polarization is the order parameter for the phase transition into ferroelectric-ferroelastic phase. The thermally stimulated currents measured in hexagonal and cubic BaTiO3, however, show that both materials exhibit noncentric macroscopic symmetry. This result supports the idea that extrinsic factors, such as strain gradients, which are apparently common for both materials, may break the macroscopic symmetry, which may then lead to alignment and redistribution of polar regions or charged defects. [ABSTRACT FROM AUTHOR]

Here, we reported a high unipolar strain and large piezoelectricity in new (1-x)K0.45Na0.55Nb0.96 Sb0.04O3-xBi0.5Na0.5HfO3 ceramics. The rhombohedral-tetragonal (R-T) phase boundary was constructed in the ceramics with 0.0333 value of ~419 pC/N. More importantly, a high unipolar strain of ~0.31% was observed due to the multiphase coexistence. In addition, the piezoelectricity of the ceramics could be effectively enhanced if their compositions are located at the phase boundaries region, where a very low electric field of ~1.2 kV/mm can readily rotate the R/T domains. We also noticed that the deviation from phase boundary induced by applying an external electric field results in the deterioration of piezoelectricity after the "second-poling" method. We believe that as a potassium-sodium-niobate based material, the ceramics developed in this work may find practical applications in lead-free piezoelectric devices such as actuators and fuel injectors in the future owing to the significant enhancement in their piezoelectricity as well as strain. [ABSTRACT FROM AUTHOR]

Eu+3 was incorporated into the lattice of a lead-free ferroelectric Na1/2Bi1/2TiO3 (NBT) as per the nominal formula Na0.5Bi0.5-xEuxTiO3. This system was investigated with regard to the Eu+3 photoluminescence (PL) and structural behaviour as a function of composition and electric field. Electric field was found to irreversibly change the features in the PL spectra and also in the x-ray diffraction patterns below the critical composition x=0.025. Detailed analysis revealed that below the critical composition, electric field irreversibly suppresses the structural heterogeneity inherent of the host matrix NBT and brings about a long range ferroelectric state with rhombohedral (R3c) distortion. It is shown that the structural disorder on the nano-scale opens a new channel for radiative transition which manifests as a new emission line branching off from the main 5D0→7F0 line along with a concomitant change in the relative intensity of the other crystal field induced Stark lines with different J values. The study suggests that Euþ3 luminescence can be used to probe the relative degree of field induced structural ordering in relaxor ferroelectrics and also in high performance piezoelectric alloys where electric field couples very strongly with the lattice and structural degrees of freedom. [ABSTRACT FROM AUTHOR]

Optical properties and structural variations of Na0.5Bi0.5TiO3-7%BaTiO3 (NBT-7%BT) single crystal have been studied by temperature-dependent optical ellipsometry and Raman spectroscopy from 4.2 to 300 K. The second derivative of the complex dielectric functions reveals two interband transitions (Ecp1 and Ecp2) located at about 3.49 and 4.25 eV, respectively. Depending on the temperature evolution of electronic transitions, structural variations appear near 60, 150, and 240 K, respectively. These anomalies are also well illustrated from the low-frequency phonon modes involving vibrations of Bi. The low-temperature structural variations of NBT-7%BT crystal can be associated with instability of the crystalline lattice driven by off-centered Bi ions, followed by the variations of polarizability of the unit cells. [ABSTRACT FROM AUTHOR]

The morphotropic phase boundary composition Bi1/2Na1/2TiO3-20 mol. % Bi1/2Na1/2TiO3 was chosen as initial material to do selective A-site aliovalent doping replacing Na and K by 1 at. % La, respectively. The materials were studied macroscopically by measuring dielectric and electromechanical properties. The Na-replaced material has a lower freezing temperature Tfr, lower remanent polarization and remanent strain, and thus a higher degree of ergodicity than the K-replaced material. These results are contrasted with local poling experiments and hysteresis loops obtained from piezoresponse force microscopy. The faster relaxation of the tip-induced local polarization and the lower remanent state in bias-on and -off loops confirm the higher degree of ergodicity of the Na-replaced material. The difference in functional properties is attributed to small variations in chemical pressure achieved through selective doping. Raman results support this working hypothesis. [ABSTRACT FROM AUTHOR]

Residual ferroelectricity is observed in barium strontium titanate ceramics over 30 °C above the global phase transition temperature, in the same temperature range in which anomalously large flexoelectric coefficients are reported. The application of a strain gradient leads to strain gradientinduced poling or flexoelectric poling. This was observed by the development of a remanent polarization in flexoelectric measurements, an induced d33 piezoelectric response even after the strain gradient was removed, and the production of an internal bias of 9 kV m-1. It is concluded that residual ferroelectric response considerably enhances the observed flexoelectric response. [ABSTRACT FROM AUTHOR]

To realize the enhancement in piezoelectric activities, the composition-induced phase boundaries in (1-y)(K0.40Na0.60)0.985 Li0.015(Nb1-xSbx)O3-yBi0.5Na0.5ZrO3 lead-free ceramics were designed and fabricated by the conventional solid-state method. We presented the evolutions of their phase structure, microstructure, and electrical properties with the change of Sb5+ and Bi0.5Na0.5ZrO3 contents. A rhombohedral-tetragonal phase boundary was successfully built in the composition region of 0.04 ⩽ x ⩽ 0.09 ( y = 0.025) and 0.025 ⩽ y ⩽ 0.035 ( x = 0.06), and then the desirable piezoelectric coefficients and bipolar strains (e.g., d33∼390 pC/N, kp∼0.45, Smax∼0.2%, and TC∼250 °C) were simultaneously induced. We think that this may provide a direction of designing high-performance (K,Na)NbO3-based ceramics. [ABSTRACT FROM AUTHOR]

Sheet molding compounds (SMC) are ready‐to‐mold thermoset composite materials reinforced with discontinuous fibers, usually compression molded. Finite element (FE) based compression molding tools can be employed to optimize this process; FE tools require to define material models using raw material data measured through different characterization techniques. In this study, the cure kinetics of an epoxy‐based carbon fiber SMC has been characterized by means of differential scanning calorimetry (DSC) and moving die rheometer (MDR) techniques. Based on these datasets, Claxton‐Liska and Kamal‐Souror models have been set and the compression molding of a validation plate was performed, both experimentally and virtually. The results indicate that, even if both characterization techniques are valid for SMC curing characterization, MDR technique enables the characterization of the material at real molding temperatures and the model based on MDR leads to more accurate results. [ABSTRACT FROM AUTHOR]

The crystal structure and lattice dynamics of quantum paraelectric BaxSr1−xTiO3 (x = 0, 0.01, 0.02) solid solutions are studied using X‐ray diffraction (XRD), Raman and terahertz‐infrared (THz‐IR) spectroscopies in a temperature range of 4–300 K. XRD and Raman spectroscopy reveal the cubic‐to‐tetragonal nonpolar structural phase transition at about 100 K. At the same time, Raman spectra manifest the presence of polar modes, TO2 and TO4, normally prohibited in paraelectric phase. Emergence of these modes indicates the appearance of the polar nanoregions in a broad temperature range. The modes become more intensive at low temperatures, and temperature dependence of their intensities on cooling reveals the kink‐like change of the slope from flat to steep, indicating on activation of polar nanoregions. The transmission THz‐IR spectra show that squared frequency of the polar TO1 soft mode, responsible for ferroelectric transition, follows Cochran's behavior at high temperatures. However, at low temperatures, it doesn't vanish at extrapolated Curie temperature but saturates, demonstrating the plateau feature below 20 K. This behavior, coherent with known saturation of the dielectric constant, indicates that transition to ferroelectric phase in BaxSr1−xTiO3 is suppressed by quantum fluctuations and the system stays in quantum paraelectric state at very low temperatures. [ABSTRACT FROM AUTHOR]

Perovskite-structured Dy-doped BZT–BCNT system has been investigated with variation of Dy doping through the solid-state reaction method. X-ray diffraction (XRD) and microscopic studies confirm the results in the rhombohedral stoichiometry without any secondary phases and uniform grain growth, respectively. Tolerance factor and electronegativity also confirm the presence of Dy doping in BZT–BCNT ceramic system with a stable rhombohedral crystallinity forming vacancy sites for oxygen ions. Optimum piezoelectric (PE) properties in non-Pb PE ceramic systems obtained due to trivalent donor Dy doping at A-site and pentavalent donor Nb at B-site are possible members for actuator and energy harvesters. Dielectric and PE studies signifying the rhombohedral perovskite behavior of this lead-free ceramic system confess that the proposed investigation could yield further potential PE sensors and actuator applicative futuristic studies. [ABSTRACT FROM AUTHOR]

This study examines the ferroelectric, pyroelectric, and dielectric properties of La-doped bismuth sodium titanate ceramics B i 0.5 N a 0.5 1 − x L a x T i O 3 (BNLT), using amounts of 0–6.7 at. % La. The precursor powders used to make dense BNLT ceramics were obtained via the sol–gel method using the acetic acid route. All samples were calcined at 700 °C for 1 h and sintered at 1150 °C for 30 min in an encapsulated crucible to avoid Na and Bi volatilization yielding relative densities equal to or higher than 94%. The obtained x-ray diffraction patterns, typical of the perovskite structure, confirm the incorporation of lanthanum into the lattice, which evolved from a rhombohedral phase to a mixture of rhombohedral and cubic structures at higher concentrations. The thermogravimetry and differential scanning calorimetry results indicate that the crystallization of precursor powders of BNT takes place between 500 and 700 °C. In addition, the scanning electron microscopy micrographs reveal a decrease in grain size from 4.5 to 0.5 µm with increasing La content. The ferroelectric hysteresis curves show that the best ferroelectric properties were obtained for BNT 1.3% La, where the obtained values of remnant polarization and coercive field were Pr = 29 µC/cm2 and Ec = 39 kV/cm, respectively. At this concentration, the pyroelectric response shows a higher value, four times higher than the pyroelectric signal of pure BNT. [ABSTRACT FROM AUTHOR]

A combination of impedance spectroscopy, time-of-flight secondary ion mass spectrometry and literature data are used to show that, (i) the bulk oxide ion conductivity of A-site, alkaline earth-doped BiFeO3 (BF) is independent of the ionic radius of the alkaline earth ion (Ca, Sr, Ba) and, (ii) despite very different A-site environments in (Na1/2Bi1/2)TiO3 and BF, similar high levels and optimisation of bulk oxide ion conductivity in these Bi-based tilted perovskites is achieved at modest acceptor doping levels of ∼1–10%. These results clearly demonstrate that optimisation of oxide ion conductivity in these materials requires concepts beyond a simple crystallochemical approach based on matching the ionic radii of acceptor dopant and host lattice ions. [ABSTRACT FROM AUTHOR]

The relationship between phase boundary and energy storage properties in x mol% Fe-doped Ba(Zr0.04Ti0.96)O3 (BZT4-xFe) ceramics was studied. The BZT4-xFe (x = 0 ~ 2) ceramics were fabricated via a conventional solid-state reaction method. The average grain size (ξ) is reduced from ~ 1.63 to ~ 1.23 μm with increasing Fe-doping content. X-ray diffraction (XRD) reveals that orthorhombic (O) and tetragonal (T) phases coexist at x = 0 ~ 0.8 and a mixing of O and cubic (C) phases was observed at x = 1 ~ 2. A slush polar state with the coexistence of O and T phases appeared near the O-T transition temperature (TO−T) in BZT4-xFe (x = 0 ~ 0.8) ceramics. A critical behavior can be observed in the BZT4-xFe ceramics. The O-T phase boundary with the slush polar state can increase the energy storage density Wrec in BZT4-xFe ceramics. The energy storage properties of BZT4-0.4Fe ceramics exhibit a good temperature, frequency, and fatigue stability. [ABSTRACT FROM AUTHOR]

Potassium sodium niobate, (K1−xNaxNbO3, KNN), is often discussed in the realm of lead-free piezoelectrics due to the widespread restrictions on the use of hazardous lead in electronics. However, as PbZr1−xTixO3 (PZT) is by far the best performing piezoelectric for sensors, actuators and other industry applications, it is somewhat difficult to envision a lead-free alternative. KNN does offer other benefits over archetypical piezoelectrics, such as biocompatibility and easily tunable phase transition temperatures, which will soon be utilized in new device applications. In this review, we will discuss KNN thin films and the techniques used to synthesize them. We will discuss how properties are tailored through additivities and review future applications in which KNN thin films are leading the way. We will also consider the environmental impact of this material, and finally the role which chemists can play in developing KNN thin films in the near future. [ABSTRACT FROM AUTHOR]