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Lead-free piezoelectric actuators emerge as promising substitutes for their lead-containing counterparts to address environmental concerns. However, they often confront a trade-off between low driving electric fields and high electro-strain. Herein, a novel strategy to boost electro-strain under low electric fields is proposed by doping high-electronegativity B-site atoms into perovskite potassium sodium niobate-based ceramics. Our findings reveal that high-electronegativity B-site atoms elevate the covalency of B-O bonding, softening the short-range repulsion and introducing local multiphase coexistence. This leads to more nanoscale domain structures and lower coercive field, thereby enabling large strains to be produced at lower electric fields. Notably, a substantial 0.2 % bipolar electro-strain and 0.1 % unipolar electro-strain under 10 kV cm-1 is achieved in Sr, Sb co-doped potassium sodium niobate ceramics, with a broad working frequency and temperature range, as well as excellent fatigue resistance. This study unveils innovative insights into designing lead-free piezoelectric ceramics with remarkable electro-strain performance and low driving electric field, promising a significant advancement in lead-free piezoelectric materials science and piezoelectric actuators. [Display omitted] [ABSTRACT FROM AUTHOR]

Pseudobinary Gd 5 (Si,Ge) 4 compounds show a giant magnetocaloric effect due to an intriguing structure-magnetism interplay. Here, we report a high resolution transmission electron microscopic study of microstructure in a melt-grown compound of Gd 5 Si 1.5 Ge 2.5. Electron diffraction showed that mesoscopic microstructure of the compound consists of crystals of a monoclinic structure and two kinds of orthorhombic structure. However, atomic-level imaging revealed a coexistence of mosaic-like nanodomains of these structures in each crystal. The nanodomains have twin-like interfaces along the b axis of the crystal but have semicoherent interfaces along a perpendicular axis due to stacking faults. Such a nanoscale structural heterogeneity is due to covalent bond-controlled phase separation at elevated temperatures. This finding offers insights into phase relations and abnormal magnetic behavior of Gd 5 (Si,Ge) 4 compounds and points out a route of synthesizing bulk nanocomposites via nanoscale phase separation. Image, graphical abstract [ABSTRACT FROM AUTHOR]

Strain glass transition attracts increasing attention in ferroelastic alloys in the context that martensitic transformation serves as the dominant mechanism for shape memory alloys. However, observing the coexistence of strain glass transition and martensitic transformation has not been reported. In this work, we introduce the strain glass transition by doping element to form highly nickel-rich Ni 55 Ti 45 at.% alloys and in the meantime attain the characteristics of martensitic transformation in the alloys. We confirm the existence of strain glass transition by 1) no exothermic/endothermic peaks in heat flow curves, 2) two deviations in electric resistivity curves, 3) two frequency-dependent dips of storage modulus, and 4) successive formation and constrained growth of nanodomains over a wide temperature range. We observe the martensitic transformation characterized by 1) two pronounced exothermic peaks upon cooling and one endothermic peak upon heating in heat flow curves, 2) thermal hysteresis in electric resistivity curves, and 3) macroscopic martensitic twins in transmission electron microscopy images. With these two phase transformations, the quasilinear superelasticity, high strength, and large elastocaloric Δ T ad of up to 9.7 K are achieved. By designing the strain maps and microstructural evolution pathways, we have provided a temperature-composition transformation path diagram to offer mechanistic insights and tuning strategies for the development of advanced alloys. [Display omitted] [ABSTRACT FROM AUTHOR]

Abstract X-ray diffraction (XRD) reciprocal space mapping (RSM) was used to investigate how nanograted electrodes affect the nanodomain distribution and average crystal structure in near-surface regions of poled Pb(Mg 1/3 Nb 2/3)O 3 -30%PbTiO 3 (PMN-30PT) single crystals. The RSM scans revealed a transverse broadening along the (H00) direction, which was quite different from that of either the rhombohedral (R) or monoclinic A (M A) phase. This broadening provides evidence of a non-uniform distribution of tilt angles between neighboring nanodomains, induced by a gradient in the applied electric field (E). Investigations of the front and back surfaces of the crystals revealed significant differences in the RSM scans. Gradients in the domain distribution and apparent symmetry may extend throughout the crystal thickness. The data evidence changes in the nanodomain distribution that results in adaptations of the average symmetry. Graphical abstract Image 1 [ABSTRACT FROM AUTHOR]

The vast majority of studies on field-induced changes in (1– x )Pb(Mg 1/3 Nb 2/3 )O 3 – x PbTiO 3 (PMN– x PT) 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– x PT family, namely, PMN–30PT with the initial Cm and Pm coexisting phases, and PMN–35PT with the P 4mm 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– x PT materials, contributing to the understanding of the complex electrical and electromechanical response of relaxor ferroelectrics. [ABSTRACT FROM AUTHOR]

The domain structure, dielectric, and piezoelectric properties of 0.7 Pb(Mg 1/3 Nb 2/3 )O 3 -0.3PbTiO 3 (PMN-PT) single crystals with nanocomposite electrode, which includes MnO x semiconductor nanogratings and a Ti/Au conductive layer, were studied in this paper. These artificial MnO x nanogratings can alter the electric field distribution and then enhance the domain density. PMN-PT crystals with Ti/Au-MnO x nanocomposite electrodes showed high piezoelectric constant of 2250 p.m./V and dielectric constant of 5400 at 1 kHz, respectively. Compared to ones with conventional planar electrodes, the piezoelectric and dielectric constants of the samples with nanocomposite electrodes were increased 36.7% and 38.3%, respectively. Piezoresponse force microscopy (PFM) images revealed the domain pattern near the electrode/single crystal interface. A linear domain structure induced by the MnO x nanocomposite electrode was found in the samples with thickness less than 200 μm. Time-of-flight secondary ion mass spectrometry (TOF-SIMS) results showed the diffusion of Mn about 300 nm in depth in PMNPT crystal after heat treatment during MnO x nanocomposite electrode. It is believed that the localized high electric fields induced by fringe effects caused by the nanocomposite electrode can enhance nucleation of new domains, and that diffusion from the patterned Mn layer may also lead to an enhancement in domain wall mobility. Our findings open up a new domain engineering technique for tailoring the dielectric and piezoelectric properties of PMN-PT single crystals. [ABSTRACT FROM AUTHOR]

The mechanisms behind the high piezoelectricity of (K,Na)NbO 3 -based lead-free ceramics were investigated, including electric field-induced phase transitions and composition-driven nanodomains. The construction of a rhombohedral-tetragonal (R-T) phase boundary, confirmed using several advanced techniques, allowed a large piezoelectric constant ( d 33 ) of 450 ± 5 pC/N to be obtained in (1- x )K 0.4 Na 0.6 Nb 0.945 Sb 0.055 O 3 - x Bi 0.5 Na 0.5 (Hf 1- y Sn y )O 3 (0 ≤ x ≤ 0.06 and 0 ≤ y ≤ 0.5) ceramics possessing an ultralow Δ U T-R of 7.4 meV. More importantly, the existence of an intermediate phase, i.e., the electric-induced phase (EIP), bridging the rhombohedral R [ P s //(111)] and tetragonal T [ P s //(001)] phases during the polarization rotation was demonstrated. Striped nanodomains (∼40 nm) that easily responded to external stimulation were also observed in the ceramics with an R-T phase. Thus, the enhanced piezoelectric properties originated from EIP and the striped nanodomains. [ABSTRACT FROM AUTHOR]

Large magnetostriction with low saturation magnetic field was recently reported in Fe-Pd ferromagnetic strain glass alloys. Such behaviour is highly desirable for miniaturized sensor and actuator applications. The origin of high performance magnetostriction in Fe-Pd ferromagnetic strain glass is suggested to stem from its martensitic nanodomains. However, the atomic formation mechanism underlying these nanodomains and their associated local crystal symmetry breaking have not been well revealed. Moreover, accumulating experimental results indicate that the nano-structure can lead to a small saturation field but cannot guarantee large magnetostriction. Consequently, the necessary conditions for low field triggered large magnetostriction of Fe-Pd ferromagnetic strain glass alloys still remain unclear. In this paper, the chemistry, structure and transformation properties of the Fe 98- x Cu 2 Pd x (x = 28.5 ∼ 31) system are systematically explored to discover the origin of the high performance magnetostriction of ferromagnetic strain glass alloys. We found that the structure of ferromagnetic strain glass consists of local chemical order. This leads to tetragonal martensitic nanodomains with the local crystal symmetry breaking. The local chemical order also induces strong local phonon softening and a low modulus during the strain glass transition. Further investigation shows that the combination of martensitic nanodomains and low modulus are the necessary conditions to achieve both large magnetostriction and a low saturation field, because they can result in small energy barriers for the rotation of nanodomains. These findings provide an effective guideline to design high performance magnetostrictive materials and devices. [Display omitted] [ABSTRACT FROM AUTHOR]

Characteristics of the strain glass transition exhibited in as-quenched and 250 °C 1–5 h aged Ti 48.7 Ni 51.3 SMA were studied by various tests/measurements. The results of frequency-dependent storage modulus vs. temperature measurement, the temperature-dependent resistivity, thermal conductivity, and specific heat tests demonstrated the signature and characteristics of the strain glass transition exhibited in as-quenched and 250 °C early-aged Ti 48.7 Ni 51.3 SMA. The plate-/disk-like morphology and spatially heterogeneous distribution of the real Ni-rich nanodomains in as-quenched and 250 °C 1–5 h aged specimens were quantitatively characterized using small-angle X-ray scattering (SAXS) technique. The formative origin of the real nanodomains and the relationship between the real nanodomains and the strain nanodomains are proposed accordingly. Experimental results indicated R-like phase and Ti 3 Ni 4 -like precipitates co-existing in the strain glass of 250 °C early-aged specimens, and they also demonstrated the growth behavior of the real nanodomains exhibited in specimens during thermal aging. It was also found that increasing the aging time can elevate the T g from ∼−60 °C to ∼−20 °C, which indicates the tunable characteristic of T g for as-quenched Ti 48.7 Ni 51.3 SMA. [ABSTRACT FROM AUTHOR]

We show that in layered oxides that are employed as cathodes in lithium-ion batteries, the cation layers can order on different {111} NaCl planes within a single particle, which makes the lithium layer discontinuous across a particle. The findings challenge previous assertions that lithium undergoes 2-D diffusion in layered oxides and the data provide new insights into the decrease in rate capabilities for some layered oxides. Therefore, it is critically important to understand how these discontinuities form and how the loss of 2-D diffusion impacts the overall performance of the layered oxide cathode materials. Employing X-ray diffraction (XRD) and aberration-corrected scanning transmission electron microscopy (STEM), we find that as the material transitions from a disordered to an ordered state, it forms four orientation variants corresponding to the four {111} NaCl planes. This transition is not intrinsic to all layered oxides and appears to be more strongly affected by nickel. Furthermore, with energy dispersive spectroscopy (EDS), we show that there is an increase in the nickel concentration at the interface between each orientation variant. This reduces the rate of lithium diffusion, negatively affects the rate capability, and could be contributing to the overall capacity fade. [ABSTRACT FROM AUTHOR]

Phase boundary engineering (PBE) has remarkably enhanced the piezoelectric properties of potassium sodium niobate {(K, Na)NbO 3 , KNN} piezoceramics, yet the physical mechanisms need to be further understood. Here we outline a new physical phenomenon to describe piezoelectricity enhancement in KNN-based ceramics with PBE. We propose that the enhancement is due to the multi-phase coexistence featured with strong relaxation behavior. The strong relaxation behavior was unambiguously revealed by cryogenic experiments and originated from the polar nanoregions (PNRs) exhibiting a scale of 2.1 nm and a weak tetragonality (c/a = 1.0040). in situ temperature-dependent experiments uncovered the thermal evolution of the ferroelectric matrix and PNRs in both unpoled and poled samples, the first report in KNN-based ceramics. Our experiments combined with phenomenological theory revealed that ultra-fine nanodomains, PNRs, and easy polarization rotation together promote macro dielectric and piezoelectric properties in the relaxation-featured multi-phase coexistence. This work reveals the physical mechanism from different levels (e.g., local-mesoscopic-macroscopic), thus providing a new systematic understanding of the observed enhancement of piezoelectricity. Proposing a new physical mechanism, relaxor-featured multi-phase coexistence, to explain piezoelectricity enhancement in potassium sodium niobate-based ceramics. [Display omitted] [ABSTRACT FROM AUTHOR]

The strain glass transition has been found in many ferroelastic systems, but the microstructural nature of strain glass is still unclear. Here, two-dimensional second and fourth order moment invariants as well as image entropy are used to evaluate the presence of a strain-glass state in simulated microstructure images of a doped ferroelastic system. Four different microstructural states are identified, depending on the doping concentration of point defects and the temperature. The martensitic state is characterized by a broad moment invariant distribution peaking near the invariants for the circle, whereas systems that display the strain glass transition produce distinctly different distributions. The image entropy is found to increase with increasing defect concentration; above the critical defect concentration of 0.1, image entropy becomes nearly linearly dependent on temperature. The image analysis approach is capable of characterizing the range of strain domain shapes that occur in the different microstructural states of a doped ferroelastic system. [ABSTRACT FROM AUTHOR]

We report a first-principles density functional theory study on the interaction of interstitial O atoms in body-centered cubic β -Ti 3 Nb alloy, the lattice distortion induced by O and its effect on the β to α ″ transformation. Our calculations demonstrate strong repulsion between O atoms in general, but also reveal a weak attraction at an O–O separation of around 5.63 Å ( 3 a ), which corresponds to a Ti 6 Nb 2 O structure. At low concentration (Ti 96 Nb 32 O), O induces a local α ″-like structure in β -Ti 3 Nb lattice, albeit to the extent of the nearest- and next-nearest neighbors, and exerts either a remarkable (6–8 meV atom −1 ) or a negligible (0–1 meV atom −1 ) energy barrier to the β to α ″ transformation, dependent on the orientation of its elastic dipole with respect to the external stress. At high concentration (Ti 6 Nb 2 O), interstitial O atoms give rise to the shuffling of neighboring {1 1 0} planes along the 〈 1 1 ¯ 0 〉 direction and generate a semi- α ″ structure, which is believed to be the nanodomain structure observed in experiment by Miyazaki and co-workers. In both cases, O brings up suppression effect on the β to α ″ transformation. [ABSTRACT FROM AUTHOR]

Two main explanations exist for the deformation mechanisms in Ti–Nb-based gum metals, i.e. the formation of reversible nanodisturbance and reversible stress-induced martensitic transformation. In this work, we used the in situ synchrotron-based high-energy X-ray diffuse-scattering technique to reveal the existence of a specific deformation mechanism, i.e. deformation-induced spatially confined martensitic transformations, in Ti–24Nb–4Zr–8Sn–0.10O single crystals with cubic β parent phase, which explains well some anomalous mechanical properties of the alloy such as low elastic modulus and nonlinear superelasticity. Two kinds of nanosized martensites with different crystal structures were found during uniaxial tensile loading along the [1 1 0] β axis at room temperature and 190 K, respectively. The detailed changes in the martensitic phase transformation characteristics and the transformation kinetics were experimentally observed at different temperatures. The domain switch from non-modulated martensite to a modulated one occurred at 190 K, with its physical origin attributed to the heterogeneity of local phonon softening depending on temperature and inhomogeneous composition in the parent phase. An in-depth understanding of the formation of stress-induced spatially confined nanosized martensites with a large gradient in chemical composition may benefit designs of high-strength and high-ductility alloys. [ABSTRACT FROM AUTHOR]

Abstract: The microstructure and thermal expansion behavior of a Ti–23Nb–2Zr–0.7Ta–1.2O alloy (Gum metal) were investigated. A systematic diffraction pattern analysis using transmission electron microscopy revealed that a -type transverse lattice modulation is present in the Ti–23Nb–2Zr–0.7Ta–1.2O alloy. Martensite-like nanodomains corresponding to -type lattice modulations were observed in dark-field micrographs. Six variants of lattice modulation were confirmed to be distributed equivalently in the β phase in the annealed condition. Cold rolling resulted in preferential growth of a nanodomain variant which is most suited to releasing the applied stress although the long-range martensitic transformation was prevented by the local stress of the domain structure caused by oxygen atoms. It is suggested that the very small thermal expansion coefficient in the as-rolled specimen is caused by the preferential growth of the nanodomain variant due to residual stress. [Copyright &y& Elsevier]

Abstract: The microstructure and martensitic transformation behavior of (Ti–23Nb)–1.0O (at.%) alloy have been closely and systematically investigated by transmission electron microscopy (TEM). Diffuse streaks along the directions with intensity maxima at 1/2 positions between basal spots are observed in selected area diffraction patterns obtained from the β phase. The streaks correspond to six variants of transverse lattice modulation caused by randomly distributed oxygen atoms and their local strain fields. Nanosized modulated domains (nanodomains) in the β phase are confirmed in dark field micrographs. These nanodomains act as local barriers to martensitic transformation, thereby suppressing long-range martensitic transformation in the (Ti–23Nb)–1.0O alloy. We suggest a new mechanism for superelasticity in oxygen-containing β-Ti–Nb alloys based on the results of in situ X-ray diffraction measurements and in situ TEM observations. [Copyright &y& Elsevier]

Piezoelectric energy harvesting is a promising means to realize self-powered microelectronic devices. However, the low power density severely restricts its development. The key challenge lies in manipulating ferroic domain structure in order to overcome thermodynamic constraints (high piezoelectric constant d together with high dielectric constant ε) of piezoelectric materials, and obtain a high figure of merit for energy harvesting (transduction coefficient = d 2 /ε). Here, we propose a new strategy to decouple between ε and d , and thus enhance the salient figure of merit for polycrystalline ceramics by manipulating the intragranular structure. We fabricated high-quality ferroelectric/metal (Ba 0.85 Ca 0.15 Ti 0.9 Zr 0.1 O 3 /Ag, BCTZ/Ag) lead-free piezocomposites with intragranular structure, in which the electrostrictive coefficient (Q) is substantially enhanced, leading to stable piezoelectric coefficient. Meanwhile, the non-ferroelectric metal Ag phase distributed in BCTZ ferroelectric grains results in the sharp drop of dielectric constant. The transduction coefficient, current density and power density of BCTZ/0.03Ag sample are up to 10000 × 10−15 m2/N, 1.04 μ A/mm2 and 3.62 μ W/mm3, outperforming state-of-the-art lead-free piezoelectric ceramics. This work provides a new paradigm for the design of high-performance lead-free piezoelectric energy harvesting materials. [Display omitted] [ABSTRACT FROM AUTHOR]

Abstract: The observations of the pseudo-periodical chessboard (CB) microstructure in metal and ceramic solid solutions indicate that this is a general phenomenon. We propose a theory and three-dimensional (3-D) computational modeling explaining the origin of the CB microstructure in the cubic→tetragonal decomposition. The 3-D modeling demonstrates that the formation of two-phase CB structures is contingent on the formation of a compositionally stabilized precursor state with the tweed structure that is spontaneously formed at the initial stage of the transformation. The modeling has shown that this tweed structure is a distribution of spatially correlated tetragonal nanodomains whose spatial arrangement has the CB topological features. This precursor tweed structure serves as a template for the precipitation of the equilibrium cubic phase. The CB-like tweed template channels the microstructure evolution towards the two-phase CB structure whose complex and detailed 3-D geometry is in excellent agreement with electron microscopic observations. The thermodynamic analysis and obtained evolution sequences allow us to formulate the necessary thermodynamic, structural and kinetic conditions for the CB structure formation. Reasons for its relative stability are discussed. It is also shown that the coherency between the cubic and tetragonal phases comprising the CB structure produces the stress-induced tetragonality of the cubic phase, orthorhombicity of the tetragonal phase, and rotations of cubic phase rods. These effects should diminish and disappear upon lifting of coherency. [Copyright &y& Elsevier]

The increase of the domain shape dimensionality from one-dimensional (1D) to two-dimensional (2D) representing creation of the magnetic bubbles by application of the uniform magnetic field to the stripe domain structure is a well-known effect used for the magnetic memory. The analogy between ferromagnetic and ferroelectric domains stimulates a search of a similar effect in ferroelectrics. Here, we present the discovered 1D to 2D transformation of the domain shape under the action of pyroelectric field appeared in lithium niobate crystal as a result of irradiation by IR laser pulses. The imaging at the surface reveals the transformation of the stripe domains appeared after the first pulse into the regular arrays of isolated circular domains after the second pulse, whereas the imaging in the bulk reveals the transformation of the comb-like domain to array of isolated conical domains. The process was considered in terms of the kinetic approach. The mechanism of the comb-like domain formation by continuous tooth generation during domain elongation is proposed. The 1D to 2D transformation is attributed to the domain splitting due to the backward motion of the charged domain wall. The proposed mechanisms are confirmed by computer simulation of the temporal dependence of the pyroelectric field excess over the threshold value. [Display omitted] [ABSTRACT FROM AUTHOR]