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A peculiar nature of the ferroelectric phase transition of isotope exchanged SrTi18O3 (STO18) are discussed by comparing three independent Raman studies which have been recently published. The results reported in a paper by the present authors (Phys.Rev. B 74, 174121 (2006)) are quite different from others as follows: (a) Contrary to the report by Takesada et al. (Phys. Rev. Lett. 96, 227602 (2006)), the perfect softening does not take place. Instead, a quasi-elastic mode appears near Tc indicating the order-disorder nature of STO18; (b) Contrary to the report by Taniguchi et al. (Phys.Rev.Lett. 99, 017602 (2007)), the ferroelectric phase of STO18 is intrinsically inhomogeneous regardless of the isotope concentration. By comparison, it is shown that the conclusions in the latter two papers are not the case. The reason is that in these papers the spectra for only a single phonon propagation direction Kp were measured and analyzed without taking into account the consistency to the spectra for other Kp's. Contrary to other ordinary ferroelectric crystals, the transition in STO18 is peculiar because the ferroelectric domains are generated from the polar nano-region (PNR) and its percolation. [ABSTRACT FROM AUTHOR]

The guest editors introduce the papers published within this Special Issue on the Applications of Ferroelectrics in the IEEE Transactions of Ultrasonics, Ferroelectric, and Frequency Control (TUFFC).

The article discusses various reports published within the issue, including an overview of the fundamental materials science required to advance the discipline, as well as papers on the applications of ferroelectric materials and another on the applications of ferroelectrics.

This paper gives closed-form equations for the intermodulation and third harmonic signals generated in a nonlinear transmission line with distributed quadratic nonlinearities in the conductor and dielectric. Although the formulation developed is general, it is intended to be used in planar devices combining high-temperature superconductor (HTS) and oxide ferroelectrics. The analysis in this paper shows that the intermodulation and third harmonic signals produced by an HTS tend to cancel those of a ferroelectric, and that full cancellation is theoretically possible. This opens the way for using HTS/ferroelectric multilayers, not (only) for their tunable or phase-shifting properties, but for highly linear spurious-free planar HTS devices. [ABSTRACT FROM AUTHOR]

The present paper shows a detailed analysis on the thermally stimulated processes in barium modified SrBi2Nb2O9 ferroelectric bi-layered perovskite, which is one of the most promising candidates for non-volatile random access memory applications because of its excellent fatigue-resistant properties. A numerical method is used to separate the real pyroelectric current from the other thermally stimulated processes. A discharge due to the space-charge injected during the poling process, the pyroelectric response, and a conductive process are discussed in a wide temperature range from ferroelectric to paraelectric phase. The pyroelectric response is separated from the other components to evaluate the polarization behavior and some pyroelectric parameters. The remanent polarization, the pyroelectric coefficient, and the merit figure are evaluated, which show good results. [ABSTRACT FROM AUTHOR]

In this paper, we report the phase transition behavior of ternary relaxor ferroelectric single crystals of 0.25Pb(In1/2Nb1/2)O3-0.44Pb(Mg1/3Nb2/3)O3-0.31PbTiO3 subject to a uniaxial mechanical stress up to 400 MPa. The resultant in situ neutron diffraction data are interpreted in terms of the polarization rotation theory and provide direct structural evidence for the stress-induced polarization rotation pathway deduced from studies of macroscopic physical properties under stress. It is suggested that an intermediate, metastable orthorhombic phase is induced above a critical pressure of ∼75 MPa. This critical stress level appears to be unaffected by sample poling although the ground states (at zero stress) for the poled and unpoled crystals are different. The critical stress level, however, does decrease with increasing temperature. The elastic behavior of the intermediate phases is also studied based on a calculation of the associated lattice strains. [ABSTRACT FROM AUTHOR]

Thin film dielectrics have broad applications, and the performance degradation due to charge trapping in these thin films is an important and pervasive reliability concern. It has been presumed since the 1960s that current transport in intermediate-thickness (IT) oxides (∼10-100 nm) can be described by Frenkel-Poole (FP) conduction (originally developed for ∼mm-thick films) and algorithms based on the FP theory can be used to extract defect energy levels and charging-limited lifetime. In this paper, we review the published results to show that the presumption of FP-dominated current in IT oxides is incorrect, and therefore, the methods to extract trap-depths to predict lifetime should be revised. We generalize/adapt the bulk FP current conduction model by including additional tunneling-based current injection. Steady state characteristics are obtained by a flux balance between contacts and the IT oxide. An analytical approximation of the generalized FP model yields a steady state leakage current J ∝ exp(-B[Square_Root]E)(1 - C[Square_Root]E - D/E), where B, C, and D are material-specific constants. This reformulation provides a new algorithm for extracting defect levels to predict the corresponding charging limited device lifetime. The validity and robustness of the new algorithm are confirmed by simulations and published experimental data. [ABSTRACT FROM AUTHOR]

This paper examines the process of domain nucleation in ferroelectric perovskites at a free surface due to electrical fields applied through a charged tip above the surface. We use a real-space phase-field model to model the ferroelectric, and apply a boundary element-based numerical method that enables us to accurately account for the stray electric fields outside the ferroelectric and the interactions through electric fields between the external tip and ferroelectric. We calculate the induced domain patterns, the stress and internal electric fields, and the induced surface displacement for various relative orientations of the crystal lattice with respect to the free surface. The effect of the external spatially inhomogeneous electric field leads to the formation of complex domain patterns and nominally incompatible microstructures. Two key findings are: first, in c axis films, a new domain forms beneath the tip through 180° switching and this new domain has the opposite piezo-response as the original domain, leading to a distinct displacement signature on the surface; and second, in a axis films, domain nucleation occurs at lower applied field because polarization rotates to align with the applied field, whereas in c axis films, the polarization magnitude reduces until 180° switching occurs at a higher applied field. We also see that the calculated domain patterns differ significantly from analytical approximations that are often used. [ABSTRACT FROM AUTHOR]

For the past 40 years, Eric Cross has been the worldwide leader of the international ferroelectrics community, organising meetings, advising students and colleagues, and building up an outstanding research programme at Penn State University. This paper describes the beginnings of the Penn State programme and some of the people involved, including George Brindley, Wilhelm Buessem, Ray Pepinsky and Rustum Roy. Three important events in its history were the work on multilayer capacitors with Erie Technological Products and Sprague Electric leading to the formation of the NSF Center for Dielectric Studies; the longstanding programme on piezoelectric transducers sponsored by the ONR which led to new families of composite ferroelectrics, to phased array ultrasound, and to near perfect electromechanical coupling factors; and the electrostriction measurements on relaxor ferroelectrics which played a key role in the development of reliable active optics systems. These were exciting times, and I am proud to have been a member of the Penn State ferroelectrics group and to express my gratitude to Eric Cross for his advice, leadership and friendship. He has a great mind and a big heart. [ABSTRACT FROM AUTHOR]

This paper provides explicit expressions for the orientation-dependent piezoelectric Eshelby S-tensor with a lamellar structure in a transversely isotropic medium. Many piezoelectric or ferroelectric materials prefer to form a lamellar structure during a change of nano-scale microstructure and domain switch; such a lamellar morphology is energetically more favorable than other shapes in a diffusionless process. According to the above observation, this paper seeks to derive the Eshelby tensor in a coupled field with the consideration of lamellar structure. In general, Eshelby's tensor can be obtained through a Green's function technique, but it is usually given in an integral form. Due to the geometric simplicity of a lamellar structure, a simple explicit form of piezoelectric S-tensor can be obtained directly from the interfacial continuous conditions. In a transversely isotropic medium, the angle between the global symmetric axis and one of the local parallel to the surface of the lamellar inclusion is the key geometrical factor in the construction of the S-tensor. Two special cases with 90° and 180° orientation that bear significant relevance to domain switch in ferroelectric ceramics are discussed in detail. [ABSTRACT FROM AUTHOR]

Ferroelectric memories (FeRAMs) are more and more using stack cells in 1T1C configuration. While none of these are already in real production, a great progress has been made when comparing these with strapped cells in 2T2C configuration. However the FeRAM community must be ready to face another challenging step in the evolution, i.e. the transition from planar to 3D capacitors. There's no consensus on the best approach to address this issue, which is probably a must at the 130 nm node. This paper reviews the limitations of the most popular approaches, then starts comparing two possible 3D FeCap structures (pin and cup-shaped). The final sections are dedicated to the introduction of a different strategy, trying to use a evolutionary approach. This is pursued starting with the development of a "quasi planar" FeCap in 0.35 μm technology that can evolve into a "quasi 3D" one at 0.18 μm node, and in a true one for 0.13 μm (or finer) rules. [ABSTRACT FROM AUTHOR]

Lead oxide-based ferroelectrics, represented by lead zirconate titanate [Pb(Zr,Ti)O3] or PZT), are the most widely used materials for piezoelectric actuators, sensors, and transducers due to their excellent piezoelectric properties. Most of these piezoelectric materials are employed under a variety of strains (stress, electrical field, and temperature). It would thus be interesting to predict their behaviors under different excitations without having to perform too much experimental work, i.e., just carry out a single experiment and still be able to provide the other experimental values. The purpose of this paper has thus been to propose several behavioral laws linking the electrical field, temperature and mechanical stress. The first law rendered it possible to express the mechanical stress by an equivalent electric field [ΔE≡αΔT×P(E,T0)]. Subsequently, a law linking the electrical field and temperature {ΔE≡[2β×P(E,θ0)]×Δθ} was proposed. From these two laws, a third law was identified reflecting the mechanical stress as an equivalent temperature; each expressed by a temperature equivalent stress (T≡δ×Δθ). After experimental validation of these laws, the mapping could be extended in order to predict the polarization behavior in the tensile stress zone as well as that as a function of the negative temperature. [ABSTRACT FROM AUTHOR]

In this paper we show that experimentally realizable apparently piezoelectric thin-film superlattices can be created from nonpiezoelectric materials provided an odd-order (e.g., trilayer) stacking sequence is used. The size-dependent mechanism of flexoelectricity, which couples gradients of strain to polarization, allows such a possibility. We present closed-form analytical expressions for the response of various thin-film and superlattice configurations. We also clarify some of the subtleties that arise in considering interface boundary conditions in the theory of flexoelectricity as well as the relationship of flexoelectricity to the frequently used polarization gradient terms used in modeling ferroelectrics. We find that for certain (optimum) material combinations and length scales, thin-film superlattices yielding apparent piezoelectricity close to 75% of ferroelectric barium titanate may be achievable. [ABSTRACT FROM AUTHOR]

Polymers with strong piezo-, pyro-, and ferroelectricity are attractive for a wide range of applications. In particular, semicrystalline ferroelectric polymers are suitable for a large variety of piezo- and pyroelectric transducers or sensors, while amorphous polymers containing chromophore molecules are particularly interesting for photonic devices. Recently, a new class of polymer materials has been added to this family: internally charged cellular space-charge polymer electrets (so-called “ferroelectrets”), whose piezoelectricity can be orders of magnitude higher than that of conventional ferroelectric polymers. Suitable patterning of these materials leads to improved or unusual macroscopic piezo-, pyro-, and ferroelectric or nonlinear optical properties that may be particularly useful for advanced transducer or waveguide applications. In the present paper, the piezo-, pyro-, and ferroelectricity of poled polymers is briefly introduced, an overview on the preparation of polymer electrets with patterned piezo-, pyro-, and ferroelectricity is provided and a survey of selected applications is presented. [ABSTRACT FROM AUTHOR]

As a form of free-space-type optical switch, the authors have proposed a planar polarization control-type optical switch. The present paper reports the design theory for a liquid crystal polarization control device with a tilted incidence angle as a key device for this switch. Since the switching of the optical paths by the polarization control of a liquid crystal is used as the operating principle, it is necessary to develop a device that can accurately change the direction of polarization of the beam incidence tilted from the crystal plane by 90° by an applied voltage. It has been known experimentally that a device with a characteristic close to this requirement can exist. A general design method has not been reported. In this paper, for the device made of ferroelectric liquid crystal, the polarization control characteristic is theoretically analyzed by the Jones matrix so that the condition for changing the polarization direction of the output light exactly by 90° is derived. Based on this finding, the optimum design values of the layer thickness and optical axis of the liquid crystal are numerically obtained. The polarization control characteristics of the fabricated device for a wavelength of 0.85 µm are measured and the validity of the present design method is demonstrated. © 2002 Scripta Technica, Electron Comm Jpn Pt 2, 85(3): 30–39, 2002 [ABSTRACT FROM AUTHOR]

The experimental characteristics of polarization fatigue in thin-film, bulk ceramic, and single-crystalline ferroelectrics have been reviewed in detail. Various scenarios and models proposed for fatigue in ferroelectric materials during the past few decades have been discussed, together with our own model developed very recently [Phys. Rev. Lett. 97, 177601 (2006); Phys. Rev. B 75, 244104 (2007)]. Interpretations for the experimental data reviewed in this paper but untreated in our previous work [Phys. Rev. B 75, 244104 (2007)] as well as the methods of improving the fatigue endurance in ferroelectrics are given based on this model. Finally, the results on polarization fatigue in some special classes of ferroelectrics such as multiferroics (e.g., BiFeO3-based materials), ferroelectric polymers, and antiferroelectric thin films and ceramics are discussed and accounted for in light of our model. [ABSTRACT FROM AUTHOR]

Tunable photonic crystals (PCs) have attracted much attention in the past decade because of their various applications, such as ultrafast optical filters and optical waveguides with add–drop functionalities. One way of achieving tunability is to make use of ferroelectric materials since the refractive index of ferroelectric materials can be electrically tuned through the electro-optic effect. In this paper, we present our work on developing a tunable one-dimensional (1D) PC based on a Ba0.7Sr0.3TiO3/MgO multilayer structure. The photonic band structures and band gap maps of the PC were calculated by using the plane-wave expansion (PWE) method. It is found that the gap center linearly shifts with the change in the refractive index of Ba0.7Sr0.3TiO3. A ferroelectric 1D PC consisting of a Ba0.7Sr0.3TiO3/MgO multilayer thin film was epitaxially deposited on a MgO (001) single-crystal substrate by pulsed laser deposition. A photonic band gap in the visible region is observed in the transmission spectrum of the multilayer thin film. The center wavelength of the band gap is ∼464 nm, which agrees with the simulation results obtained by the transfer matrix method. The band gap can be tuned by applying an electric field E. The band gap shifts by about 2 nm when the thin film is subjected to a dc voltage of 240 V (E∼12 MV/m). This shift corresponds to an ∼0.5% change in the refractive index of the Ba0.7Sr0.3TiO3 layer, as calculated by the PWE method. [ABSTRACT FROM AUTHOR]

In this paper, we illuminated the observation of asymmetric ferroelectric switching phenomena in fatigued P(VDF-TrFE) copolymer films. Two types of asymmetric switching were observed: one was the occurrence of switching dual peaks obtained from films with asymmetric electrode structure and the other was the jump of remanent polarization during fatigue process, as was obtained mostly from films with asymmetric electrodes and occasionally from films with symmetric electrodes. No evidence indicated the dependence between the switching dual peaks and the jump of remanent polarization. The possible mechanism of such asymmetric phenomena was also discussed. [ABSTRACT FROM AUTHOR]

Saturated domain orientation textures of three types of pseudocubic (tetragonal, rhombohedral, and orthorhombic) ferroelectric ceramics after complete electric and uniaxial tension (compression) poling is studied analytically in this paper. A one-dimensional orientation distribution function (ODF) of the domain polar vectors is explicitly derived from the uniform inverse pole figures of the poling field axes on a stereographic projection with respect to the fixed crystallite coordinates. The analytical ODF is used to obtain the analytical solutions of saturated polarization and strain after electric/mechanical poling. Based on the closed form solution of the saturated domain orientation textures, the resultant intrinsic electromechanical properties of ferroelectric ceramics, which depend only on the ODF and properties of the corresponding single crystals, are obtained. The results show how the macroscopic symmetries of ferroelectric crystals change from 4mm (tetragonal), 3m (rhombohedral), and mm2 (orthorhombic) single crystals to a ∞mm (transversely isotropic) completely poled ceramic. [ABSTRACT FROM AUTHOR]

In a poled ferroelectric ceramic, the probability of crystallographic poles oriented in any given specimen direction is the multiple of both the initial crystallographic texture and the domain switching fraction. In this paper, the non-180° domain switching fraction is shown to be dependent on the initial crystallographic texture and poling direction in tape cast Na0.5Bi4.5Ti4O15 ceramics. The domain switching fraction is 0.18 out of a maximum of 0.50 when poled in a direction in which most of the possible ferroelastic structural distortions are oriented (tape casting plane) whereas no non-180° domain switching is discernable when poled in a less-preferred direction. The mechanism for domain switching anisotropy in textured bismuth titanate ceramics is suggested to be the synergistic alignment of ferroelastic structural distortions, analogous to the mechanical clamping conditions in poling ferroelastic thin films. [ABSTRACT FROM AUTHOR]

This paper demonstrates the possibility of inducing an antiferroelectric phase from an intrinsically ferroelectric phase-only liquid crystal by doping with linear-shaped molecules, thus separating the neighboring smectic layers of the ferroelectric liquid crystal from each other. Such an intrinsically impossible process is, in fact, shown to be quite possible due to its entropy-related origin. When the temperature of the doped cell is increased, the antiferroelectric phase reverts to the ferroelectric phase as the dopant molecules change position from interlayer space to intralayer space, a result that coincides with the sawtooth model suggested by Glaser and Clark [Phys. Rev. E 66, 021711 (2002)]. The macroscopic spontaneous polarization of the induced antiferroelectric phase (13.5 nC/cm2) is smaller than that of the ferroelectric phase (73.3 nC/cm2), which shows that the charge fluctuation is not the origin of the conversion. [ABSTRACT FROM AUTHOR]

The optic tensor configurations (director profiles) in surface stabilized ferroelectric liquid crystal cells with homeotropic alignment are considerably simpler than in cells with the more conventional homogeneous alignment and, with the exception of thin surface regions, are essentially that of an unconstrained or "free" FLC sample. Previously the half-leaky guided mode (HLGM) technique, in which angle dependent reflectivity only is measured, has been used to characterize the director profile in such cells. The extended HLGM technique reported in this paper enables detection of both angle dependent reflectivity and transmissivity data. Combined analysis of these features significantly enhances the sensitivity of the original HLGM technique enabling the director profile in cells with homeotropic alignment to be explored in even greater detail. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

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One potential use of ferroelectrics is as active material in electrocaloric cooling systems. These systems promise a more energy efficient cooling process than vapor compression, thermoelectric or other current cooling systems. Currently different design types of electrocaloric cooling devices are in the focus of research. In this paper, we present an electrocaloric cooling device demonstrator working as “Active Electrocaloric Regenerator” (AER) and employing relaxor ferroelectric elements as active material. The device design is such that it allows the integration of different material systems and regenerator designs as well as a broad variation of operational parameters. [ABSTRACT FROM PUBLISHER]

The first-principles calculations are employed to investigate the Ce doping effects on the ferroelectricity of the Aurivillius-structured CaBi 2 Nb 2 O 9 (CBN). The formation energy is calculated for the Ce substituting the Bi site model and the Ce substituting the Ca site model, it is noted that the former is more stable than the latter. The NbO 6 octahedron distortion of the Ce/Bi model is increased due to the long-range effect of the Ce doping. By analyzing the partial density of states (PDOS), the Bader charge and the electron localization function (ELF), it is found that the extra electrons are introduced by the Ce doping, and transferred to the atoms of O2, O5, Nb and Bi. Thus, the electronic orbital hybridizations of O2-Nb, O5-Bi, and O2-Bi are enhanced by the extra electrons, and the enhancement of the orbital hybridization is the main reason of the enhancement of the spontaneous polarization (P s) comparing with intrinsic CBN. These findings could be used as a theoretical reference for future researches on the bismuth layer-structured ferroelectrics (BLSFs). In this paper, there are the following two highlights. • Comparing the formation energy of the Ce substituting the Bi site of CBN (Ce/Bi) model and that of the Ce doping in the Ca site of CBN (Ce/Ca) model, it is found that the former is more stable than the latter. Our calculations clarify the long time puzzle of the substituting of the Ce doping in CBN. • By analyzing the PDOS, the Bader charge and the ELF, it is found that extra electrons are introduced in the Ce/Bi model by the Ce doping, and are transferred to the atoms of O2, O5, Nb, and Bi. The electronic orbital hybridizations of the Ce/Bi model are enhanced due to the introduction of the extra electrons, and the enhancement of the orbital hybridization is just the reason of the enhancement of the spontaneous polarization comparing with intrinsic CBN. [ABSTRACT FROM AUTHOR]

Electric polarization typically originates from non-centrosymmetric charge distributions in compounds. In elemental crystalline materials, chemical bonds between atoms of the same element favor symmetrically distributed electron charges and centrosymmetric structures, making elemental ferroelectrics rare. Compared to atoms, elemental clusters are intrinsically less symmetric and can have various preferred orientations when they are assembled to form crystals. Consequently, the assembly of clusters with different orientations tends to break the inversion symmetry. By exploiting this concept, we show that sliding ferroelectricity naturally emerges in trilayer quasi-hexagonal phase (qHP) C60, a cluster-assembled carbon allotrope recently synthesized. Compared to many metallic or semi-metallic elemental ferroelectrics, trilayer qHP C60's have sizable band gaps and several ferroelectric structures, which are distinguishable by measuring their second-harmonic generation (SHG) responses. Some of these phases show both switchable out-of-plane and in-plane polarizations on the order of 0.2 pC/m. The out-of-plane and in-plane polarizations can be switched independently and enable an easy-to-implement construction of Van der Waals homostructures with ferroelectrically switchable chirality. [ABSTRACT FROM AUTHOR]

Recent advances have uncovered an exotic sliding ferroelectric mechanism, which endows to design atomically thin ferroelectrics from non-ferroelectric parent monolayers. Although notable progress has been witnessed in understanding the fundamental properties, functional devices based on sliding ferroelectrics remain elusive. Here, we demonstrate the rewritable, non-volatile memories at room-temperature with a two-dimensional (2D) sliding ferroelectric semiconductor of rhombohedral-stacked bilayer MoS2. The 2D sliding ferroelectric memories (SFeMs) show superior performances with a large memory window of >8 V, a high conductance ratio of above 106, a long retention time of >10 years, and a programming endurance greater than 104 cycles. Remarkably, flexible SFeMs are achieved with state-of-the-art performances competitive to their rigid counterparts and maintain their performances post bending over 103 cycles. Furthermore, synapse-specific Hebbian forms of plasticity and image recognition with a high accuracy of 97.81% are demonstrated based on flexible SFeMs. Functional devices based on sliding ferroelectrics remain elusive. This work demonstrates the rewritable, non-volatile memory devices at room-temperature with two-dimensional sliding ferroelectric rhombohedral-stacked bilayer MoS2. The device shows overall good performance and can be made flexible. [ABSTRACT FROM AUTHOR]

The discovery of nanoscale ferroelectricity in hafnia (HfO2) has paved the way for next generation high‐density, non‐volatile devices. Although the surface conditions of nanoscale HfO2 present one of the fundamental mechanism origins, the impact of external environment on HfO2 ferroelectricity remains unknown. In this study, the deleterious effect of ambient moisture is examined on the stability of ferroelectricity using Hf0.5Zr0.5O2 (HZO) films as a model system. It is found that the development of an intrinsic electric field due to the adsorption of atmospheric water molecules onto the film's surface significantly impairs the properties of domain retention and polarization stability. Nonetheless, vacuum heating efficiently counteracts the adverse effects of water adsorption, which restores the symmetric electrical characteristics and polarization stability. This work furnishes a novel perspective on previous extensive studies, demonstrating significant impact of surface water on HfO2‐based ferroelectrics, and establishes the design paradigm for the future evolution of HfO2‐based multifunctional electronic devices. [ABSTRACT FROM AUTHOR]

We report on the theoretical/numerical investigation of simultaneous second- and third-harmonic generation from a single wavelength input in quasi-phase-matched crystals. The presented technique consists of a quadratic crystal with two first-order quasi-phase-matched sections: one designed for quasi-phase-matching to second-harmonic generation and the other for quasi-phase-matching to third-harmonic generation via sum-frequency generation. We identify an optimal length ratio (optimal number of domains) for these sections in order to enhance the conversion to the third harmonic, achieving nearly complete energy transfer. The advantages of the method are demonstrated both numerically and analytically, with a specific example using periodically poled lithium niobate. Quadratic cascading with quasi-phase-matching proves to be an effective approach for achieving cubic-like effects with high conversion efficiencies. [ABSTRACT FROM AUTHOR]

An interdigital transducer structure was fabricated from multilayer graphene on the surface of the Y Z -cut of a LiNbO3 ferroelectric crystal. The multilayer graphene was prepared by CVD method and transferred onto the surface of the LiNbO3 substrate. The properties of the multilayer graphene film were studied by Raman spectroscopy. A multilayer graphene (MLG) interdigital transducer (IDT) structure for surface acoustic wave (SAW) excitation with a wavelength of Λ = 60 μm was fabricated on the surface of the LiNbO3 crystal using electron beam lithography (EBL) and plasma chemical etching. The amplitude–frequency response of the SAW delay time line was measured. The process of SAW excitation by graphene IDT was visualized by scanning electron microscopy. It was demonstrated that the increase in the SAW velocity using graphene was related to the minimization of the IDT mass. [ABSTRACT FROM AUTHOR]

B 2020 b , I 10 i , 2001726 DOI: 10.1002/aenm.202001726 The polarization I P i ( I z i ) shown in B Figure b 1c in the original paper and reproduced here as Figure 1A was calculated by moving the Cu-atom sheets in a synchronous (concerted) way. For each transition, all Cu atoms are initially in the I P i SB 1 sb polarization state and the Cu atoms are moved over the respective barrier one at a time until all Cu atoms are in I P i SB 2 sb . In the ACM, as viewed in each unit cell, the average position of the Cu ions is identical to the actual positions of the SCM Cu sheets only while transiting within the layers from -HP to +HP. [Extracted from the article]

Centimeter-sized Ca2Nb2O7 crystals were successfully grown using the conventional Czochralski pulling method with an optimized crystal growth technique. Single-crystal X-ray diffraction studies indicated that the Ca2Nb2O7 crystal belongs to the Pna21 space group with orthorhombic symmetry. The unit cell parameters were determined to be a = 26.471 Å, b = 7.688 Å, and c = 5.490 Å, while the thermal expansion coefficients were measured to be α11 = 5.83, α22 = 7.94, and α33 = 13.32 (10−6 °C−1). In addition, the ferroelectric properties of the crystal were also determined (i.e., Pr = 5.62 μC cm−1, Ec = 99.1 kV cm−1). Furthermore, simultaneous thermal analysis showed that the ferroelectric phase exists stably even when the temperature rises to 1400 °C. The full set of electro-elastic constants for the Ca2Nb2O7 crystal were determined by the resonance method, wherein the piezoelectric coefficient d33 was 8.5 pC N−1 and the electromechanical coupling factor k33 was 20.4%. As a ferroelectric crystal with a high Curie temperature, Ca2Nb2O7 exhibits a high piezoelectric coefficient, a high electromechanical coupling coefficient, and excellent potential for use in high-temperature piezoelectric sensing applications. [ABSTRACT FROM AUTHOR]

A continuous exponential rise has been observed in the storage and processing of the data that may not curtail in the foreseeable future. The required data processing speed and power consumption are restricted by the buses between the logic and memory devices that are characteristic of the von Neumann computing architecture. Bio‐mimicking neuromorphic computing has garnered considerable academic and industrial interest to resolve these challenges. Additionally, devices based on emerging nonvolatile memories capable of mimicking the behaviors of synapses and neurons, which are the main elements in biological computing systems (brains), are attracting significant interest from the device community. With the discovery of ferroelectricity in fluorite‐structured oxides, such as HfO2 and ZrO2, which are compatible with the state‐of‐the‐art complementary‐metal‐oxide‐semiconductor processes, ferroelectric devices have rapidly evolved as the main direction of these research and development activities. Fundamental science related to fluorite‐structured ferroelectrics has been intensively studied over the last decade. At present, the focus is gradually moving to practical applications, including neuromorphic computing and advanced classical processing or memory units in the conventional von Neumann architecture. However, despite its rapid development, the wealth of recent progress in neuromorphic computing devices based on fluorite‐structured ferroelectrics has not been reviewed and systemized. This progress report comprehensively reviews and systemizes the recent progress in artificial synaptic and spiking neuron devices for neuromorphic computing based on fluorite‐structured ferroelectrics. [ABSTRACT FROM AUTHOR]

We report the structures of three new materials in the MDABCO-based perovskite family. Analysis of the Goldschmidt tolerance factor and octahedral factor enable us to propose compositional limits for pseudo-cubic perovskite phase formation and suggest directions for further materials discovery in this family of new ferroelectrics. [ABSTRACT FROM AUTHOR]

The present paper is concerned with the piezoelectric properties and related parameters of the 2–2-type parallel-connected composites wherein rotations of the main crystallographic axes in ferroelectric single crystal components are analyzed. The composite consists of layers of two types that are regularly arranged along the non-polar axis. The Type I layer is a single domain 0.63Pb(Mg1/3Nb2/3)O3–0.37PbTiO3 single crystal (either tetragonal in Composite I or orthorhombic in Composite II). The Type II layer is a Li2B4O7 single crystal/polyethylene medium with 0–3 connectivity. The composite as a whole is characterized by 2–0–2 connectivity. The following parameters of the composite are studied by taking into account the polarization orientation effect in the Type I layer and the microgeometry of the composite in the Type II layer: piezoelectric coefficients and their hydrostatic analogs and hydrostatic squared figure of merit piezoelectric anisotropy factors / and / It is shown that large values of the studied piezoelectric coefficients, hydrostatic parameters and anisotropy factors make Composite II more preferable in comparison to Composite I for hydroacoustic, piezoelectric sensor and energy-harvesting applications. [ABSTRACT FROM AUTHOR]

A method for obtaining vector flow images using the transverse oscillation (TO) approach on a convex array is presented. The paper presents optimization schemes for TO fields and evaluates their performance using simulations and measurements with an experimental scanner. A 3-MHz 192-element convex array probe (pitch 0.33 mm) is used in both simulations and measurements. A parabolic velocity profile is simulated at a beam-to-flow angle of 90?. The optimization routine changes the lateral oscillation period λ࠭ as a function of depth to yield the best possible estimates based on the energy ratio between positive and negative spatial frequencies in the ultrasound field. The energy ratio is reduced from ?17.1 dB to ?22.1 dB. Parabolic profiles are estimated on simulated data using 16 emissions. The optimization gives a reduction in standard deviation from 8.81% to 7.4% for 16 emissions, with a reduction in lateral velocity bias from ?15.93% to 0.78% at 90? (transverse flow) at a depth of 40 mm. Measurements have been performed using the experimental ultrasound scanner and a convex array transducer. A bias of ?0.93% was obtained at 87? for a parabolic velocity profile along with a standard deviation of 6.37%. The livers of two healthy volunteers were scanned using the experimental setup. The in vivo images demonstrate that the method yields realistic estimates with a consistent angle and mean velocity across three heart cycles. [ABSTRACT FROM AUTHOR]

In this paper periodically domain-inverted (PDI) ferroelectric crystals are studied using high-resolution X-ray diffraction. Rocking curves and reciprocal-space maps of the principal symmetric Bragg reflections in LiNbO3 (LN) (Λ = 5 µm), KTiOPO4 (KTP) (Λ = 9 µm) and KTiOAsO4 (KTA) (Λ = 39 µm) are presented. For all the samples strong satellite reflections were observed as a consequence of the PDI structure. Analysis of the satellites showed that they were caused by a combination of coherent and incoherent scattering between the adjacent domains. Whilst the satellites contained phase information regarding the structure of the domain wall, this information could not be rigorously extracted without a priori knowledge of the twinning mechanism. Analysis of the profiles reveals strain distributions of Δ d/ d = 1.6 × 10−4 and 2.0 × 10−4 perpendicular to domain walls in KTP and LN samples, respectively, and lateral correlation lengths of 63 µm (KTP), 194 µm (KTA) and 10 µm (LN). The decay of crystal truncation rods in LN and KTP was found to support the occurrence of surface corrugations. [ABSTRACT FROM AUTHOR]

This paper deals with the application of the model presented in the first part Schrade et al. [1] to ferroelectric composites filled with electrically conducting inclusions as well as to ferroelectric polycrystals. Composites are analyzed through the use of a computational homogenization framework for phase field methods proposed in Zäh & Miehe [2]. This will give insights into the coupled phenomena taking place on the microscale and on their relation to the overall behavior. Both will be of special interest for the development of advanced composite materials with tailored properties like, for example, particulate magneto-electric composites, which are composed of a ferroelectric matrix and magnetic rare-earth elements or metals. Furthermore, we analyze the behavior of ferroelectric polycrystals with a focus on size effects. This will enable us to reveal preferred microstructure configurations depending on the system and grain size. In addition to that, it will serve as basis for the extraction of the directional properties of polycrystals with respect to their switching behavior in the different grains of the polycrystal. Associated simulations could then be used to supply coarser models with the needed directional informations. (© 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [ABSTRACT FROM AUTHOR]

The "National Seminar on Ferroelectrics and Dielectrics" (NSFD) is a biennial seminar that has been held in India since 1980. The seminar focuses on the physics, chemistry, and engineering aspects of ferroelectrics and dielectrics, which are materials used in modern technology for applications such as data storage and wireless communications. The 22nd NSFD took place at VIT-AP University in Andhra Pradesh, India, and covered topics including materials design, characterization, and theoretical modeling. The seminar facilitated the exchange of scientific ideas and resulted in the publication of 89 papers in a special issue of Ferroelectrics. [Extracted from the article]

Relaxor ferroelectric single crystals of Pb(Mg1/3Nb2/3)O3–PbTiO3 (PMN–PT) have outstanding electromechanical properties in the linear regime. When operated across a phase transition, these properties are significantly enhanced. Understanding the phase transition mechanism under electromechanical external fields is crucial for the new application of PMN–PT that takes advantage of this phase transition. In the present study, the phase transition of PMN–0.3PT single crystals subjected to a mechanical loading/unloading process and the effects of electric field on the phase transition and electromechanical responses of PMN–0.3PT single crystal under coupled mechanical-electrical loading were systematically investigated using a thermodynamics-based phase-field model. The roles the different energy terms play in the evolution of domain and phase structures were assessed. These findings have important implications for both understanding of the phase transition of relaxor ferroelectric single crystal PMN–0.3PT and applications that take advantage of phase transitions in these materials. The model results for the reversible/irreversible phase transition of PMN–0.3PT during the mechanical loading/unloading process are qualitatively consistent with experimental results. [ABSTRACT FROM AUTHOR]

Pb(Zr1-xTix)O3 (PZT) piezoelectric ceramics have been used extensively due to their comprehensive performance. Compared with direct current poling (DCP) and alternating current poling (ACP) methods, the combining DCP and ACP method can further improve the piezoelectric properties of relaxor-based ferroelectric single crystals. Here, the dielectric and piezoelectric properties of DCP, ACP, and ACP + DCP PZT-4 piezoelectric ceramics. The optimal poling conditions of DCP, ACP, and ACP + DCP were studied. The d33 of ACP + DCP PZT-4 piezoelectric ceramics reported in this paper is 350 pC/N, which is 15% and 9% higher than that of DCP (305 pC/N) and ACP (320 pC/N) samples. The strain value under electric field of the ACP PZT-4 ceramic (0. 08%) is higher than that of the DCP sample (0. 05%), indicating that ACP can effectively improve the strain value of PZT-4 ceramics. However, the increased hysteresis of the strain curve for ACP sample is not conducive to application. The effect of ACP on hard PZT piezoelectric ceramics needs to be further explored. [ABSTRACT FROM AUTHOR]

• Relaxor Ferroelectric Single Crystal (RFSC) Linear Array for Modal Decomposition and Analysis (LAMDA) design leverages RFSC's exceptional sensitivity to detect microjoule energy acoustic emission events. • Performs modal decomposition and identifies guided wave modes of a 6.6μJ pencil lead break over a broad bandwidth up to 1.4 MHz. • RFSC-LAMDA outperforms laser vibrometry and wideband AE sensors, demonstrating superior sensitivity and detection for field applications. This paper reports on an acoustic emission (AE) sensor based on relaxor ferroelectric single crystal (RFSC) transduction. The sensor crystal is arranged into a Linear Array for Modal Decomposition and Analysis (LAMDA), with the sensor interrogated by a bespoke high-bandwidth instrument. The efficacy of RFSC LAMDA sensors is showcased through a series of comparative experiments, which include the simultaneous acquisition of pencil lead break (PLB) AEs in a 1.6 mm thick aluminium plate using RFSC LAMDA, a wideband commercial sensor, and laser vibrometry. Subsequent modal decomposition and analysis of the PLB AE signals, as detected by RFSC LAMDA, identified the guided wave modes below 1.4 MHz. Furthermore, it was found that RFSC LAMDA exhibits, on average, 26.6 times greater improvement in sensitivity compared with polyvinylidene fluoride LAMDA variant with near-identical geometry. [ABSTRACT FROM AUTHOR]

This paper explores theoretically a model for third harmonic generation in antiferroelectric crystals which, being resonant in the far infrared, will also respond to microwave frequencies. The essential idea is that the tripling of the frequency components of microwave radiation incident on the antiferroelectric brought about by third harmonic generation will produce waves in the terahertz region. The response of antiferroelectric crystals in their interaction with microwaves of frequencies in the range 100 to 200 GHz makes this a viable proposal, together with the fact that, as with ferroelectrics, the nonlinear processes generated in antiferroelectrics tend to be stronger that in conventional dielectrics. Landau-Devonshire theory has been used to calculate nonlinear susceptibility coefficients. Here the susceptibility coefficient for third harmonic generation for the most straightforward one-dimensional case is given and it is shown how the slowly varying amplitude approximation can be used to solve the wave equation to describe the propagation of the generated waves in the crystal. Conditions on the length through which the waves travel that optimize the phase matching are a useful result of this analysis. [ABSTRACT FROM AUTHOR]

Recently, a number of two-dimensional van der Waals (vdW) ferroelectrics have been reported, showing the potential to develop various ultra-thin smart devices down to the atomic monolayer limit. In particular, they have been demonstrated to exhibit intriguing polar domain structures. However, phenomenological thermodynamic models of vdW ferroelectrics, which can capture their ferroic domain structure evolution, are still lacking, limiting our further exploration of domain-structure-related applications. In this work, combining first-principles calculations, we construct a phenomenological phase field model for monolayer ferroelectrics, FEβ-In2Se3. Based on the model, one can calculate the phase stability, ferroelectric hysteresis curves, and domain structures of FEβ-In2Se3 under different loading conditions, showing the feasibility of electromechanically driving the rotation of in-plane polarization and manipulation of the domain structures. By including the second-order partial derivative gradient energy term, the model further captures well the antiferroelectric–ferroelastic domain structures of β′-In2Se3 observed in previous experiments. The developed phase field model should help better understand the domain structure evolution behavior in low-dimensional materials and promote further exploration of domain-structure-related applications. [ABSTRACT FROM AUTHOR]

This paper presents modification for a model to retrace magnetic hysteresis loop and calculate hysteresis energy loss (HEL) in YBa2Cu3O7 (YBCO). In comparison with reported experimental results, it is revealed that the modified model could retrace successfully magnetic hysteresis loop for YBCO. As an application of this model, the calculation formula of HEL has been included in this article. The results show also that HEL in YBCO increases by 14% with the addition of the magnetic NiW substrate. This leads to conclude that the type of substrate has an effect on HEL of YBCO. This modified model can help us to explain experimental results and expect the functioning of superconductor tapes. [ABSTRACT FROM AUTHOR]

Phonon-polariton is the coupled excitation between optical phonon and photon. The remarkable frequency vs. wavevector dispersion relation of phonon-polariton contributes to important technological applications such as tunable terahertz radiation sources and basic materials science to clarify the terahertz dynamics of condensed matter such as lattice instability in ferroelectrics. This paper studies the broadband dispersion relation of phonon-polariton between 10 cm-1 and 1200 cm-1 in uniaxial ferroeletric crystals, LiNbO3 (LN) and LiTaO3 (LT) with polar trigonal system on the basis of the observed results using THz-Raman spectroscopy, THz time domain spectroscopy, and far-infrared spectroscopy. The dispersion on the lowest-frequency TO mode with crystals, which are assigned as ferroelectric soft modes, is discussed. [ABSTRACT FROM AUTHOR]

In this paper, we report synthesis, structural, microstructure and electrical study of Mn3O4. Manganese oxide in the form of Mn3O4 was prepared by co-precipitation technique using manganese nitrate as source at the calcination temperature of 400 °C. The crystal structure has been refined by least squire fitting method using powder X-ray diffraction data. The structure refinement showed the formation of single phase with no any secondary phases. The lattice parameter and cell volume has been calculated manually from standard equations and verified by UNITCELL software program. The particle size was also determined from the XRD pattern using Scherrer's equation. The microstructure of calcined and sintered sample was characterized by scanning electron microscopy. The temperature dependent dc conductivity of the Mn3O4 pellet was studied in the temperature range between room temperature to 500 °C. The conductivity of this spinal was very less at room temperature and increased with increasing temperature exhibiting negative temperature of coefficient of resistance behavior with activation energy 0.91eV. [ABSTRACT FROM AUTHOR]

Pd nano particles have been widely used as catalyst in chemical industry. However, the catalytic efficiency has been limited by the Aggregation of the Pd. In this paper, the surface aggregation dynamics of Pd on different ferroelectric polarization surface and temperature were reported. Meanwhile, reducing the particle size to obtain the dispersed morphology of Pd was discussed by the dissipative particle dynamics method and density functional theory. The negatively poled surface offered dispersed Pd morphology, the temperature influence will be discussed in the simulation. [ABSTRACT FROM AUTHOR]