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The integration of dissimilar materials in heterostructures has long been a cornerstone of modern materials science - seminal examples are the two-dimensional (2D) materials and van der Waals heterostructures. Recently, new methods have been developed, which enable the realization of ultra-thin freestanding oxide films approaching the 2D limit. Oxides offer new degrees of freedom, due to the strong electronic interactions, especially the 3d orbitals, which give rise to rich exotic phases. Inspired by this progress, we have developed a new platform for assembling ultra-thin freestanding oxide thin films with different materials and orientations into artificial stacks with heterointerfaces. We show that the oxide stacks can be tailored by controlling the stacking sequences as well as the twist angle between the constituent layers with atomically sharp interfaces, leading to distinct moiré patterns in the transmission electron micrographs of the full stacks. Stacking and twisting has been recognized as a key degree of structural freedom in 2D materials but until now has never been realized for oxide materials. Our approach opens unexplored avenues for fabricating artificial 3D oxide stacking structure with freestanding membranes across a broad range of complex oxide crystal structures with functionalities not available in conventional 2D materials. This article is protected by copyright. All rights reserved.

Cerium oxide (ceria, CeO2) is one of the most promising mixed ionic and electronic conducting materials. Previous atomistic analysis has widely covered the effects of substitution on oxygen vacancy migration. However, an in-depth analysis of the role of cation substitution beyond trivalent cations has rarely been explored. Here, we investigate soluble monovalent (Li+, Na+, K+, Rb+), divalent (Fe2+, Co2+, Mn2+, Mg2+, Ni2+, Zn2+, Cd2+, Ca2+, Sr2+, Ba2+), trivalent (Al3+, Fe3+, Sc3+, In3+, Lu3+, Yb3+, Y3+, Er3+, Gd3+, Eu3+, Nd3+, Pr3+, La3+) and tetravalent (Si4+, Ge4+, Ti4+, Sn4+, Hf4+, Zr4+) cation substituents. By combining classical simulations and quantum mechanical calculations, we provide an insight into defect association energies between substituent cations and oxygen vacancies as well as their effects on the diffusion mechanisms. Our simulations indicate that oxygen ionic diffusivity of subvalent cation-substituted systems follows the order Gd3+Ca2+Na+. With the same charge, a larger size mismatch with the Ce4+ cation yields a lower oxygen ionic diffusivity, i.e., Na+K+, Ca2+Ni2+, Gd3+Al3+. Based on these trends, we identify species that could tune the oxygen ionic diffusivity: we estimate that the optimum oxygen vacancy concentration for achieving fast oxygen ionic transport is ≈2.5% for GdxCe1-xO2-x/2, CaxCe1-xO2-x and NaxCe1-xO2-3x/2 at 800 K. Remarkably, such a concentration is not constant and shifts gradually to higher values as the temperature is increased. We find that co-substitutions can enhance the impact of the single substitutions beyond that expected by their simple addition. Furthermore, we identify preferential oxygen ion migration pathways, which illustrate the electro-steric effects of substituent cations in determining the energy barrier of oxygen ion migration. Such fundamental insights into the factors that govern the oxygen diffusion coefficient and migration energy would enable design criteria to be defined for tuning the ionic properties of the material, e.g., by co-substitutions.

Electrostriction is a property of dielectric materials whereby an applied electric field induces a mechanical deformation proportional to the square of that field. The magnitude of the effect is usually minuscule (–19 m2 V–2 for simple oxides). However, symmetry-breaking phenomena at the interfaces can offer an efficient strategy for the design of new properties. Here we report an engineered electrostrictive effect via the epitaxial deposition of alternating layers of Gd2O3-doped CeO2 and Er2O3-stabilized δ-Bi2O3 with atomically controlled interfaces on NdGaO3 substrates. The value of the electrostriction coefficient achieved is 2.38 × 10–14 m2 V–2, exceeding the best known relaxor ferroelectrics by three orders of magnitude. Our theoretical calculations indicate that this greatly enhanced electrostriction arises from coherent strain imparted by interfacial lattice discontinuity. These artificial heterostructures open a new avenue for the design and manipulation of electrostrictive materials and devices for nano/micro actuation and cutting-edge sensors.

In this review paper, recent progress in the fabrication, transfer, and fundamental physical properties of freestanding oxide perovskite thin films is discussed. First, the main strategies for the synthesis and transfer of freestanding perovskite thin films are analyzed. In this initial section, particular attention is devoted to the use of water-soluble (Ca,Sr,Ba)3Al2O6 thin films as sacrificial layers, one of the most promising techniques for the fabrication of perovskite membranes. The main functionalities that have been observed in freestanding perovskite thin films are then reviewed. In doing so, the authors begin by describing the emergence of new phenomena in ultrathin perovskite membranes when released from the substrate. They then move on to a summary of the functional properties that are observed in freestanding perovskite membranes under the application of strain. Indeed, freestanding thin films offer the unique possibility to actively control the strain state far beyond what can be observed with traditional methods, allowing the investigation of the profound interplay between structural and electronic properties in oxides. Overall, this review highlights the potential of oxide-based freestanding thin films to become the preferred platform for the study of novel functionalities in perovskite oxide materials.

The phase transition process of pure and 0.5 at% Fe-doped 0.95(Na1/2Bi1/2)TiO3–0.05BaTiO3 (NBBT5) single crystals under in-situ electric-field was investigated using the Raman spectroscopy. The pure NBBT5 exhibited R3c (a−a−a− octahedral tilting) symmetry when subjected to an external electric field (E) up to 70 kV/cm. While after the Fe-doping, the crystal underwent a transition from P4bm (a0a0c+ octahedral tilting) to P4mm (a0a0c0 octahedral tilting) phase under E of 30–40 kV/cm. The results indicated that the octahedral tilting in the Fe-NBBT5 was substantially suppressed by the electric field, which was suggested to contribute to the enhanced piezoelectric response compared to the pure one.

An ion-conducting crystal possessing non-cubic crystal symmetry and a non-dilute composition will in general display a multiplicity of different migration paths and different site energies for the mobile ions. Predicting the macroscopic rate of ion transport, and in particular, identifying substituent cations that optimise this rate, is therefore challenging. In this study, molecular dynamics simulations employing pair potentials were used to calculate the oxygen tracer diffusion coefficient as a function of temperature in various substituted systems based on the rhombohedral perovskite oxide bismuth ferrite, BiFeO3. Substituent cations that maximise (or minimise) are identified. The results also reveal the limits of the standard crystal-chemical approach to maximising by matching the size of the substituent cation to that of the host's. The implications for the use of BiFeO3 as a high-performance oxide-ion conductor or as a multiferroic medium are discussed.

A nanolaminated structure that is predominated by nanoscale lamellar boundaries with misorientations

Oxygen defective ceria, e.g. Gd-doped ceria, shows giant electromechanical properties related to a complex local rearrangement of its lattice. Although they are not entirely identified, the electroactive mechanisms arise from cations and oxygen vacancies (VO) pairs (Ce-VO), and the local structural elastic distortion in their surroundings. Here, we study the geometry and behaviour of Ce-Vo pairs in a grain boundaries-free bulk Ce0.9Gd0.1O1.95 single crystal under an AC electric field of ca. 11 kV/cm. The analysis was carried out through X-ray absorption spectroscopy (XAS) techniques at Ce L-III edge. Using Density Functional Theory (DFT) calculations, we investigated the effects of the strain on states' density and orbitals at the valence band edge. Our research indicates that the electrostriction increases at low temperatures. The electromechanical strain has a structural nature and can rise of one order of magnitude, i.e., from 5·10-4 at room temperature to 5·10-3 at -193 °C, due to an increase in the population of the electrically active pairs. At a constant VO concentration, the material can thus configure heterogeneous pairs and elastic nanodomains that are either mechanically responsive or not.

$(\mathrm{N}{\mathrm{a}}_{1/2}\mathrm{B}{\mathrm{i}}_{1/2})\mathrm{Ti}{\mathrm{O}}_{3}\text{\ensuremath{-}}x\mathrm{BaTi}{\mathrm{O}}_{3}(\mathrm{NBT}\text{\ensuremath{-}}x\mathrm{BT})$ single crystal, as one of the most promising candidates to replace lead-based ferroelectrics, is a typical and unique lead-free system with morphotropic phase boundary (MPB) by far. In this paper, the phase transition process of NBT-0.06BT crystal in a wide temperature range of $20\ensuremath{\sim}550{\phantom{\rule{0.16em}{0ex}}}^{\ensuremath{\circ}}\mathrm{C}$ was analyzed at atomic scale by theoretical fitting to the measured synchrotron radiation x-ray absorption fine structure spectra quantitatively. Detailed analysis revealed a gradually transition of local structure at the point of phase transition from rhombohedral to tetragonal phase in NBT-0.06BT crystal on the bond lengths of Bi-O and Bi-Ti. The continuous evolution of local structure with no obvious barrier to overcome is one of the intrinsic characteristics of MPB at atomic scale and is responsible for the high piezoelectric properties. These results could promote the understanding of the origin of the high piezoelectric performance around the MPB and meanwhile guide new lead-free material designs.

Recent investigations have shown that highly oxygen defective cerium oxides generate non-classical electrostriction that is superior to lead-based ferroelectrics. In this work, we report the effect of field-assisted spark plasma sintering (SPS) on electro-chemo-mechanical properties of calcium doped ceria (CDC). Nanometric powders of Ca.10 nm are rapidly consolidated to form polycrystalline nanostructures with a high degree of crystalline disorder. Remarkably, the resultant material demonstrates a large electromechanical strain without a frequency-related relaxation effect. We conclude that electromechanical activity in CDC materials strictly depends on the Ca2+- V o ¨ interaction, while disorder at the crystalline boundaries has a minor effect.

Single crystals of x at.% Nb + 0.94(Na0.5Bi0.5)TiO3–0.06BaTiO3 (x%-Nb:NBT-6BT, x = 0.12, 0.23, and 0.48) show improved ferroelectric and piezoelectric properties. In particular, the large piezoelectric constant (d33 = 532 pC/N) and high field-induced strains (Smax = 0.57%) in 0.23%-Nb:NBT-6BT single crystal demonstrate its promising application potential. The underlying mechanisms were investigated directively by atomistic scale simulations. We found that, Nb5+ cations prefer to substitute Ti4+ cations on B-site and will first fill up the oxygen vacancies generated due to the loss of Bi2O3 and/or Na2O. Higher concentration of Nb2O5, however, will be compensated by Ti and/or Bi vacancies. The ions positions surrounding the defect center(s) were identified.

Ion migration in Na0.5Bi0.5TiO3 (NBT) was investigated by molecular dynamics (MD) simulations and molecular static (MS) simulations. In MD simulations (>104 ions), performed for simulation times of tsim = 0.3 ns and at simulation temperatures in the range 1200 ≤ T/K ≤ 2400, oxide ions exhibited appreciable diffusivity, with derived activation enthalpies lower than 0.8 eV, whereas sodium and bismuth cations displayed no diffusion at the temperatures and on the time scale of the simulations. MS calculations yielded high activation barriers (>2 eV) for the migration of these cations. These results strongly suggest that the contribution of A-site cations to the total ionic conductivity is negligible. Bismuth vacancies and sodium vacancies were found to be detrimental to the rate of oxygen diffusion. The effect of ordered arrangements of Bi3+/Na+ cations on oxygen tracer diffusion was also examined by MD simulations. The (111)-ordered structure was seen to display higher rates of oxygen diffusion than the (100)- and (110)-ordered structures. MS calculations of the individual barriers for oxygen-ion jumps provided insights into this behavior. Our simulation results thus suggest design rules for developing superior low-temperature oxide ion conductors based on NBT perovskites and related materials.

Density-functional-theory (DFT) calculations within the generalised gradient approximation (GGA) were used to examine the behaviour of point defects in the cubic BVIO3 perovskite-type oxide, ReO3. Energies of reduction and of hydration were calculated, and the results are compared with literature data for ABO3 perovskite oxides. The activation energies of migration were determined for O2−, H+, Li+, Na+, K+ and H3O+. An occupied A site in ReO3 is found to be beneficial to oxide-ion migration by a vacancy mechanism as well as to proton migration by a Grotthuss mechanism. Na+, K+ and H3O+ exhibit activation energies of migration higher than 2 eV, whereas Li+ is characterised by a very low migration barrier of 0.1 eV. Reasons for this behaviour are discussed. Our results suggest that H+, O2−, and especially Li+, are highly mobile ions in ReO3.

The understanding of surface chemistry changes on oxygen electrodes is critical for the development of reversible solid oxide fuel cell (RSOFC). Here, we report for the first time that the electrochemical potentials can drastically affect the surface composition and hence the electrochemical activity and stability of PrBaCo2 O5+δ (PBCO) electrodes. Anodic polarization degrades the activity of the PBCO electrode, whereas the cathodic bias could recover its performance. Alternating anodic/cathodic polarization for 180 h confirms this behavior. Microstructure and chemical analysis clearly show that anodic bias leads to the accumulation and segregation of insulating nanosized BaO on the electrode surface, whereas cathodic polarization depletes the surface species. Therefore, a mechanism based on the segregation and incorporation of BaO species under electrochemical potentials is considered to be responsible for the observed deactivation and recovery process, respectively.

A combination of polarized Raman technique, infrared reflectance spectra, and first-principles density-functional theoretical calculations were used to investigate structure transformation and lattice vibrations of Na0.5Bi0.5TiO3, Na0.5Bi0.5TiO3–5%BaTiO3, and Na0.5Bi0.5TiO3–8%K0.5Bi0.5TiO3 single crystals. It was found that Na0.5Bi0.5TiO3 is of a two-phase mixture with rhombohedral and monoclinic structures at room temperature. Correspondingly, three Raman-active phonon modes located at 395, 790, and 868 cm−1, which were previously assumed as A1 modes of rhombohedral phase have been reassigned as A′′, A′, and A′ modes of monoclinic phase in the present work. In particular, a strong low-frequency A′′ mode at 49 cm−1 was found and its temperature dependence was revealed. Two deviations from linearity for the abrupt frequency variation in the A′′ mode and Ti–O bond have been detected at temperatures of ferroelectric to antiferroelectric phase transition TF–AF and dielectric maximum temperature Tmax. The appearance of Na–O vibrations at 150 cm−1 was found below Tmax, indicating the existence of nanosized Na+TiO3 clusters. The observed Raman and infrared active modes belonging to distinct irreducible representations are in good agreement with group-theory predictions, which suggests 9A1+9E and 36A′′+24A′ modes for the rhombohedral and monoclinic phases of Na0.5Bi0.5TiO3, respectively.

Paeonia ostii var. lishizhenii, a well-known medicinal and horticultural plant, is indigenous to China. Recent studies have shown that its seed has a high oil content, and it was approved as a novel resource of edible oil with a high level of α-linolenic acid by the Chinese Government. This study measured the seed oil contents and fatty acid components of P. ostii var. lishizhenii and six other peonies, P. suffruticosa, P. ludlowii, P. decomposita, P. rockii, and P. lactiflora Pall. 'Heze' and 'Gansu'. The results show that P. ostii var. lishizhenii exhibits the average oil characteristics of tested peonies, with an oil content of 21.3%, α-linolenic acid 43.8%, and unsaturated fatty acids around 92.1%. Hygiene indicators for the seven peony seed oils met the Chinese national food standards. P. ostii var. lishizhenii seeds were used to analyze transcriptome gene regulation networks on endosperm development and oil biosynthesis. In total, 124,117 transcripts were obtained from six endosperm developing stages (S0-S5). The significant changes in differential expression genes (DEGs) clarify three peony endosperm developmental phases: the endosperm cell mitotic phase (S0-S1), the TAG biosynthesis phase (S1-S4), and the mature phase (S5). The DEGs in plant hormone signal transduction, DNA replication, cell division, differentiation, transcription factors, and seed dormancy pathways regulate the endosperm development process. Another 199 functional DEGs participate in glycolysis, pentose phosphate pathway, citrate cycle, FA biosynthesis, TAG assembly, and other pathways. A key transcription factor (WRI1) and some important target genes (ACCase, FATA, LPCAT, FADs, and DGAT etc.) were found in the comprehensive genetic networks of oil biosynthesis.

A new relaxor-based ferroelectric ternary system Pb(Lu 1/2 Nb 1/2 )O 3 –Pb(Mg 1/3 Nb 2/3 )O 3 –PbTiO 3 (PLN–PMN–PT), with a combination of a high-Curie temperature system Pb(Lu 1/2 Nb 1/2 )O 3 –PbTiO 3 (PLN–PT) and a high piezoelectricity system Pb(Mg 1/3 Nb 2/3 )O 3 –PbTiO 3 (PMN–PT), was investigated in this paper. Single crystal PLN–PMN–PT with dimensions of Φ20×45 mm 3 was grown successfully by the modified Bridgman technique for the first time. The studies of structure and composition of the as-grown crystal showed structural consistency but compositional deviation along the growth direction. The 〈0 0 1〉-oriented wafers of the PLN–PMN–PT single crystal showed excellent electrical properties at room temperature: e 33 ~4500, tan δ ~0.5%, d 33 ~2300 pC/N. The crystal was found to exhibit high Curie temperature ( T C ~176°C), rhombohedral–tetragonal phase transition temperature ( T RT ~108 °C) and coercive field ( E C ~8.1 kV/cm), superior to those of PMN–0.3PT single crystal. Studies of temperature dependence ferroelectric properties showed that high values of k 33 and d 33 could be maintained up to the T RT . These results showed that PLN–PMN–PT piezoelectric single crystal has a higher Curie temperature and coercive field with excellent electrical properties, making the crystal a promising candidate for high-power transducer applications in a broad temperature range.

A series of (Na0.5Bi0.5)TiO3–PbTiO3 (NBT–PT) single crystals with compositions near the morphotropic phase boundary (MPB) region were grown by the modified Bridgman technique. The dependence of structure on composition was measured, and the MPB region of the NBT–PT system was confirmed. The dielectric properties of the NBT–PT single crystals were investigated, and the phase transition behaviour of the NBT–PT single crystals during heating was examined. With increasing addition of PT, the coercive field of the NBT–PT crystals decreased to levels much lower than that of the pure NBT system; such a change allowed easy poling of the NBT–PT crystals and the resultant piezoelectric properties were significantly enhanced. The electromechanical coupling factor of the crystals showed relatively constant thermal stability at the depolarization temperature (Td). Finally, studies of the domain evolution of NBT–0.09PT showed the disappearance of domains at the Td, which indicates that phase transition at the Td is related to changes in domain structures.

Much attention is drawn to the preparation, structure and properties investigation of lead-free ferroelectrics for the next generation of piezoelectric devices. (Na0.5Bi0.5)TiO3-BaTiO3 (NBT-BT) lead-free solid solution piezoelectric single crystals with composition x in the range of 0–0.05 as a materials with high piezoelectric properties were successfully grown from platinum crucible by using the top-seeded solution growth (TSSG) method. The dimensions of NBT-BT crystal is Ø40 × 10 mm2. X-ray powder diffraction patterns reveal that the crystal structure of NBT-BT crystal changes from rhombohedral to tetragonal symmetry with increasing amounts of BT(x). The dielectric, ferroelectric and piezoelectric properties of NBT-BT crystals with different compositions near the morphotropic phase boundary (MPB) were studied systematically. Ions (Mn, Eu, Zn) doped NBT and NBT-BT 95/5 crystals were also grown and studied. In addition, their piezoelectric and ferroelectric properties are investigated. Further, a high-quality and large-sized (K0.25Na0.75)NbO3 (KNN25/75) single crystal has been achieved by a carefully controlled TSSG method. The dimensions of the as-grown KNN25/75 single crystal reached up to Ø30 × 10 mm2. The obtained KNN crystals provided us a superb material for the dielectric, piezoelectric, ferroelectric and electromechanical coupling property characterization along different orientations.

In situ observations of the phase symmetry and domain evolution of (K0.25Na0.75)NbO3 single crystals under bipolar electric fields have been performed for both pseudocubic (110) and (001) orientations using polarized light microscopy and X-ray diffraction. The macroscopic symmetry was identified to be a monoclinic C type phase with the spontaneous polarization direction close to . The electric field-driven domain morphology and evolution model were also presented. It was found that, under an antiparallel electric field, the approximately 180° domain switching process in a pseudocubic (101) sample consists of three steps: two ~60° domain switching and a ~90° domain switching, and the ~90° domain switching process in the pseudocubic (001) sample is composed of two ~60° switching steps.

Dielectric, ferroelectric and piezoelectric properties of lead-free Na1/2Bi1/2TiO3–xK1/2Bi1/2TiO3 (NBT–xKBT) ferroelectric single crystals were characterized systematically. With increasing KBT concentration, the remanent polarization and coercive electric field decrease, while the piezoelectric constant and the electromechanical coupling coefficient increase. The evolution of average and local structures as a function of temperature and composition was investigated using in-situ X-ray diffraction and Raman spectroscopy. The structure/property relationship of NBT–xKBT single crystals was discussed in detail.

Peculiar L-shaped diffuse streaks along pc were observed in (Na 0.5 Bi 0.5 )TiO 3 (NBT) below the Burns temperature, revealing the existence of polar nanoregions (PNRs). The displacement of Bi 3+ cations is ∼0.26 A along pc in the PNRs, with a size of ∼13 A in NBT. The BaTiO 3 doping drives the diffuse scattering patterns to evolve from the L-shape into an ellipsoidal along pc in (Na 0.5 Bi 0.5 )TiO 3 –x BaTiO 3 . An abnormally large correlation length was observed in the morphotropic phase boundary composition with x = 0.05.

Giant bipolar and unipolar strains i.e. S max > 0.5%, e max / E max > 1000 pm V –1 have been observed in Mn-doped Na 0.5 Bi 0.5 TiO 3 –6BaTiO 3 single crystals after being annealed. Temperature-dependent impedance spectra were studied and activation energies of oxygen vacancies were calculated accordingly. The two different binding energies present in X-ray photoelectron spectra for Na and Bi were assigned to different coordinate environments. However, titanium exhibits only one oxidation state (e.g. Ti 4+ ). The site occupation and valence fluctuation of Mn were characterized by electric paramagnetic resonance spectra.

Lead-free single crystal (Na1/2Bi1/2)TiO3–1.5 at.%Bi(Zn1/2Ti1/2)O3 (NBT–1.5BZT) with dimension of Φ35 mm × 12 mm was successfully grown by a top-seeded solution growth technique. The average and local structure were studied by a combination of X-ray diffraction and Raman spectroscopy. The electric and optical properties of -oriented single crystals were investigated systematically. Compared with pure NBT, the piezoelectric constant and transmission coefficient were both enhanced, that is, from 62 pC/N and ~60% to 121 pC/N and ~70%, respectively. Furthermore, domain structure observation suggested that the -oriented tetragonal ferroelastic domains in NBT were suppressed at room temperature with addition of BZT, which was responsible for the improved piezoelectric and optical properties of NBT–1.5BZT single crystal.

Compositional segregation usually has negative effects on the growth of solid solution ferroelectric single crystals of Pb(In1/2Nb1/2)O3-Pb(Mg1/3Nb2/3)O3-PbTiO3 (abbr. PIN-PMN-PT or PIMNT). A modified Bridgman method was adopted in this work to control the segregation and improve the compositional homogeneity significantly. The characteristic of this work is to use multiround growths and gradient composition raw materials in order to keep the PbTiO3 concentration constant during the crystal growth. As an example, the two-round growth of ternary PIN-PMN-PT single crystal is conducted in the same Pt crucible with gradient raw materials, where the first-round boule was used as the seed crystal for the second-round growth. Our results show that the as-grown (Ф80 mm × 270 mm) PIN-PMN-PT crystals exhibit higher phase transition temperatures (Tc∼180 °C, Tr/t∼110 °C) and larger coercive field (Ec∼5–5.5 kV/cm), which are much better than the performances of Pb(Mg1/3Nb2/3)O3-PbTiO3 crystals, and similar dielectric and piezoelectric performances (e∼5000, tanδ∼1.25%, d33∼1500 pC/N, kt∼60%). And about 85 percent of the crystal boule grown by the two-round growth technique could maintain its compositions around the morphotropic phase boundary.

Single crystals of x at% Fe + 0.95(Na1/2Bi1/2)TiO3-0.05BaTiO3 (x%-Fe:NBBT5, x = 0.1, 0.2 and 0.5) with ultrahigh ferroelectric response were developed by introducing defect associations. The very large field-induced bipolar and unipolar strains, i.e., Smax ∼ 1.1%, emax/Emax ∼ 1300 pm V−1, d33 ∼ 600 pC N−1 and permittivity tunability ∼120%, demonstrate that these crystals are promising candidates as lead-free ferroelectrics. The presence of ferromagnetic properties further provides their new application potential as multiferroic materials. The defect chemistry and domain structure were studied systematically. The effects of microscopic defect functional centers on macroscopic properties were discussed in detail.

Eu3+-doped Na0.5Bi0.5TiO3 (Eu:NBT) single crystals were grown by a top-seeded solution growth method. Photoluminescence emission and excitation spectra of Eu:NBT were investigated. The two transitions in 7F0 → 5D0 excitation spectra reveal that Eu3+ ions were incorporated into two adjacent crystallographic sites in NBT, i.e., Bi3+ and Na+ sites. The former has a symmetrical surrounding, while the later has a disordered environment, which was confirmed by decay curve measurements. The dielectric dispersion behavior was depressed and the piezoelectric and ferroelectric properties were improved after Eu doping.

A large-size 0.88Na0.5Bi0.5TiO3–0.12K0.5Bi0.5TiO3 lead-free piezoelectric single crystal with dimensions of ∅30 mm ×10 mm was successfully grown by the top-seeded solution growth method. X-ray powder diffraction measurement showed that the as-grown crystal possesses a rhombohedral perovskite structure at room temperature. The temperature dependence of dielectric constant and loss, polarization hysteresis loop, electric-field-induced strain, and the electromechanical coupling property were investigated for the -oriented as-grown crystal. The remanent polarization P r, the piezoelectric constant d 33, and the electromechanical coupling coefficient k t at room temperature are 13.8 pC/cm2, 205 pC/N, and 51 %, respectively. The maximum strain of 0.23 % was obtained under 30 kV/cm. The temperature dependence of k t demonstrated a relatively stable thermal electromechanical coupling property over the temperature range of 20–150 °C.

0.95Na 0.5 Bi 0.5 TiO 3 –0.05K 0.5 Bi 0.5 TiO 3 lead-free piezoelectric single crystal with rhombohedral structure was grown by the top-seeded solution growth method. The temperature dependence of dielectric constant and loss, polarization hysteresis loops, the optimum poling condition and the electromechanical coupling property were investigated for the 〈100〉-oriented as-grown crystal. The curves e ( T ) show two anomalies, which are related to the two phase transformations at the temperature range of 130–340 °C. The piezoelectric constant d 33 and electromechanical coupling coefficient k t for the 〈001〉-oriented crystal at room temperature reached 147 pC/N and 0.52, respectively. The value of k t demonstrated a relatively stable thermal electromechanical coupling property over the temperature range of 15–130 °C.

A pure Cu (99.995 wt%) has been subjected to dynamic plastic deformation at cryogenic temperature to a strain of 2.1. Three types of microstructures that are related to dislocation slip, twinning and shear banding have been quantitatively characterized by transmission electron microscopy (TEM) assisted by convergent beam electron diffraction (CBED) analysis. Microstructures originated from dislocation slip inside or outside the shear bands are characterized by low angle boundaries ( ) up to the maximum angle of 9 degrees. The quantitative structural characteristics are compared with those in conventionally deformed Cu at low strain rates, and allowed a quantitative analysis of the flow stress-structural parameter relationship.

The 0.96Na0.5Bi0.5TiO3–0.04K0.5Bi0.5TiO3 (NKBT96/4) lead-free single crystal was successfully grown by top-seeded solution growth method. The effective segregation coefficient for K was calculated to be 0.20. X-ray powder diffraction measurement showed that the as-grown crystal possesses rhombohedral perovskite structure at room temperature. X-ray rock curve measure indicated that the as-grown single crystal owned relatively higher quality. The NKBT96/4 single crystal exhibits apparent diffused dielectric behavior, where the diffusiveness index α is 1.79 for the [001]-oriented crystal planes. A notable thermal hysteresis, ΔT h , of 25°C was disclosed for the tetragonal antiferroelectric-tetragonal paraelectric phase transition in the dielectric property studies between heating and cooling. The highest remnant polarization, P r , 16.8 μC/cm2, was obtained at 100°C. The electromechanical coupling coefficient kt of the [001]-oriented crystal planes at room temperature was determined to be 38% using resonance–antiresonance technique. The room temperature piezoelectric constant d33 reaches 120 pC/N.

The formation kinetics of e-Fe3–2N phase in a nanocrystalline α-Fe, which was processed by surface mechanical attrition treatment, is found to be obviously increased with respect to that in the coarse-grained form. This can be attributed to the much enhanced heterogeneous nucleation rate at numerous grain boundaries in the nanocrystalline α-Fe.

The dynamical phase transition mechanism of $({\mathrm{Na}}_{1/2}{\mathrm{Bi}}_{1/2}){\mathrm{TiO}}_{3}$ (NBT) was studied using inelastic neutron scattering. Softening was observed of multiple phonon modes in the phase transition sequence of NBT. As usual, the softening of the zone center transverse optical modes ${\ensuremath{\Delta}}_{5}$ and ${\ensuremath{\Sigma}}_{3}$ was observed in the (200) and (220) zones, showing the Ti vibration instabilities in ${\mathrm{TiO}}_{6}$ octahedra for both cubic-tetragonal (C-T) and tetragonal-rhombohedral (T-R) phase transitions. In these two phase transitions, however, ${\mathrm{Ti}}^{4+}$ has different preferential displacement directions. Surprisingly, the longitudinal optic mode also softens significantly toward the zone center in the range of the transition temperature, indicating the ${\mathrm{Na}}^{+}/{\mathrm{Bi}}^{3+}$ vibration instability against ${\mathrm{TiO}}_{6}$ octahedra during the T-R phase transition. Strong inelastic diffuse scattering shows up near $M$(1.5, 0.5, 0) and $R$(1.5, 1.5, 0.5) in the tetragonal and rhombohedral phases, respectively, indicating the condensations of the ${M}_{3}$ and ${R}_{25}$ optic modes for the corresponding transitions. This reveals the different rotation instabilities of ${\mathrm{TiO}}_{6}$ in the corresponding transition temperature range. Bottleneck or waterfall features were observed in the dispersion curves at certain temperatures but did not show close correlations to the formation of polar nanoregions. Additional instabilities could be the origin of the complexity of phase transitions and crystallographic structures in NBT.

We have investigated the impact of covalent hybridization on martensitic structure and magnetic properties of Ni50Mn5+xGa35-xCu10 shape memory alloys. We found that the lattice distortion ((c-a)/a) of L10 martensite monotonously changes with the substitution of Mn for Ga atoms and shows a kink behavior at Ga(at.%)= 25 due to the weakened covalent effect between main-group and transition-metal atoms. Moreover, owing to the competition between covalence hybridization and magnetic ordering of introduced Mn atoms, the molecular magnetic moment and Curie temperature coincidently show maximums at Ga(at.%)=25 as well. These behaviors are closely associated with corresponding changes of the strength of covalent hybridization. The results therefore suggest that careful control of the concentration of main-group atoms in Heusler alloys can serve as an additional general tuning parameter for searching new multifunctional materials., 22 pages, 4 figures and 1 table, supplementary info, submitted for publication

A lead-free single crystal 0.92(Na0.5Bi0.5)TiO3-0.06BaTiO3-0.02(K0.5Na0.5)NbO3 (NBT-6BT-2KNN) with dimension of Φ35 mm × 10 mm is grown by a precisely controlled top seeded solution growth method. The 〈001〉 oriented single crystals have excellent piezoelectric properties with a giant strain of 0.83% at 28 kV/cm. Application of an electric-field ≥14 kV/cm leads to a phase transition from pseudocubic to coexistence of tetragonal and pseudocubic. A strong ferroelectric domain texture occurs during the phase transition. Furthermore, the variation of tetragonal phase fraction agrees well with the macroscopic strain curve, demonstrating that the induced tetragonal phase plays a critical role in the high strain property.

A GaAs MMIC technology of the novel compact left-handed bandpass filter consisting of one left-handed (LH) transmission line (TL) and one dual composite right/left- handed (D-CRLH) TL is presented. The D-CRLH is the dual of the conventional CRLH in the sense that it consists of a LC parallel-tank impedance and of a LC series-tank admittance. In contrast to the conventional CRLH TL which has LH operation at low-frequency and RH one at high-frequency, the D-LH TL exhibits its LH band at high frequencies and its RH band at low frequencies. Thus, utilizing the high pass property of LH and low pass property of D-CRLH, a bandpass filter can be constructed. In this paper, this novel idea is realized by MMIC technology. The proposed filter exhibits a broad passband from 6.2 GHz to 20.8 GHz with a size of 1.43 mm2. (6 pages)

Linear magnetoelectric (ME) and nonlinear magnetoelectric effects are considered systematically in this paper. We have prepared 3 multi-push-pull magnetoelectric laminated composites Metglas/PMNT/Metglas with n layers metglas (n = 1, 2, and 3). When n increases from 1 to 3, the linear magnetoelectric charge coefficients increase from 1900 to 2200 and then to 2600 pC/Oe at 2 Hz under their each optimal magnetic bias. By using these 3 ME composites, we have also prepared 3 ME sensors, the sensitivity of which are as low as 130, 168, and 199 pT/√Hz at 1 Hz for n = 1, 2, and 3, respectively, via nonlinear modulation method. Therefore, the nonlinear ME charge coefficients decrease as layer numbers of metglas increase, which is different with the ME charge linear coefficient's increasing trend, also demonstrated coupled with the finite element analysis method. The factors that result in the higher nonlinear ME charge coefficient in ME composites with fewer metglas layers are analyzed and discussed in detail.

Polarized Raman spectroscopy has been performed to investigate the effects of the electric field on 0.68PbMg1/3Nb2/3O3–0.32PbTiO3 (PMN–32PT) relaxor single crystal. Based on the group theory analysis, the Raman modes of PMN–32PT single crystal at zero-field are assigned to the monoclinic structure. The electric-field-evolution of Raman spectra reveal that a structural transition to tetragonal phase is initiated at a threshold electric field E1 and completed at higher field E2. In the intermediate field range from E1 to E2, the structure of the crystal is determined to be a coexistence of monoclinic and tetragonal phases. These results of the Raman spectra allow us to better understand the field-induced ultrahigh macroscopic strain in the relaxor ferroelectrics.

A micro-Raman scattering technique was used to investigate the electric-field and temperature dependent phase stability of Mn-doped Na1/2Bi1/2TiO3-5.0at. %BaTiO3 single crystal. The Ti–O mode was found to exhibit a slight shift at a low electric field (E = 10 kV/cm) and splitting at higher electric field (E ≥ 30 kV/cm), ascribed to field-induced local distortion and phase transition, respectively. The temperature-dependent Raman scattering was also measured over a wide range of 150–800 K to study the phase stability of poled samples. A new Raman mode at about 200 cm−1 and an anomaly in intensity of the Ti-O modes were detected at 390 K, indicating a ferroelectric to antiferroelectric phase transition. The frequency shift of TiO6 octahedral modes implied a transition to a paraelectric state at 550 K. Furthermore, the Ti-O and TiO6 octahedral modes were found to be sustained in the high-temperature paraelectric state.