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In a semi-review paper, the fundamentals of the vibronic (pseudo Jahn-Teller) theory of ferroelectricity in perovskite crystals of ABO3 type, its main achievements and significant applications, are given. The theory is derived from first principles. First, the pseudo Jahn-Teller effect (PJTE) is introduced and shown to be the only source of polar instability that triggers the spontaneous polarization of the crystal. The driving force of the PJTE is added covalency by distortion, which is essentially of local (chemical) origin. Then, the earlier more qualitative, but physical transparent results in application of the PJTE theory to ABO3 perovskites are presented, followed by the rigorous formulation in terms of Greens' functions theory. The form of the adiabatic potential energy surface (APES) for the metal B sites with eight equivalent minima, obtained analytically, is confirmed by DFT calculations, and its parameter numerical values were estimated for BaTiO3. It explains the occurrence of the three ferroelectric and one paraelectric phases, and order-disorder transitions between them as due to temperature dependent gradual overcome of the consecutive barriers between its eight equivalent minima. The theoretical treatment of the phase transitions is carried out in the mean-field approximation yielding near-to-experimental Curie temperatures. An important further development of this theory was reached more recently, for the first time revealing the role of spin in ferroelectric polarization of perovskites with the electronic dn configuration of the B ion. It was shown that, subject to the PJTE, not only d0 configurations may be unstable to produce ferroelectricity ("the d0 mystery"), but some other specific dn configurations with unpaired electrons may be dipolar active too, the crystal being thus both magnetic and ferroelectric (multiferroic). The necessary conditions for such multiferroicity are formulated for the whole n = 0,1,...10 variety of perovskites, and it is shown to be different in the two (or more) possible spin arrangements of the same ion, high-spin or low-spin for n = 3, 4, ...7. In conditions of spin crossover this leads to a magnetic-ferroelectric crossover that can be manipulated by external perturbations, including electric magnetization, already realized experimentally. A novel chapter is opened in application of the vibronic PJTE theory to important problems of materials science by analyzing the interaction of the ferroelectric perovskites with external perturbations. For the paraelectric phase of BaTiO3 with local dynamic-polar instability, any external electric field, strain, or stress violates the equivalency of the eight minima of the APES, quenching the polar dynamics, thus contributing an orientational polarization (like in polar liquids). It increases the permittivity, flexoelectricity, electrostriction, and external pressure effects by several orders of magnitude, confirmed experimentally. The theory explains also the formation of polar nanoregions and laxor properties in the paraelectric phase as due to the "local drops formation" when two phases may coexist locally (which is not possible in displacive theories where the formation of a polarized phase requires long-range interaction). A significant part of the paper is devoted to discussion and comparison of the vibronic PJTE theory of ferroelectricity with other theories and empirical data. It is shown that a series of experimentally observed specific properties of perovskite ferroelectrics encounter fundamental difficulties in attempt to explain their origin by means of displacive theories. This is related to the B ion being (instantly) polar displaced along the trigonal axis in all the phases, the order-disorder character of the phase transitions, the role of the spin of the B ion in the ferroelectric polarization, the strong dependence of ferroelectricity and multiferroicity on the chemical composition, the giant effects in interaction with external perturbations, the formation of polar nanoregions in nonpolar phases leading to relaxor behavior, etc. All these unique properties of perovskite ferroelectrics follow directly from the vibronic (PJTE) theory. [ABSTRACT FROM AUTHOR]

In this paper, microstructural, ferroelectric and magnetic properties of multiferroic composite system (1-x) Ba0.5Sr0.5TiO3(BST) – (x) Ni0.4Co0.2Zn0.4Fe2O4(NCZF), where x = 0.1, 0.2, 0.3, 0.4 molar ratio have been studied. Grains of NCZF are larger in size and more symmetrical in comparison to BST grains. Overall grain size of BST grains in the composite samples decreases with increase in NCZF content. Polarization vs Electric Field (P-E) loops of the composite samples are unsaturated. The values of remanant polarization of the composite samples increase with increase in NCZF content. The composite samples possess saturated M-H loops with the values of remanant and saturation magnetization increases with increase in NCZF content. [ABSTRACT FROM AUTHOR]

Dielectric properties of 2,3,6,7,10,11-hexahydroxytriphenylene tetrahydrate crystallites are examined in this paper. We observe a first order, order-disorder phase transition at a temperature of 251 K. The frequency dependence revealed four relaxation regions, where two relaxations follow the Arrhenius law with activation energy of 300 meV. Our investigation shows the experimental data below the phase transition to follow the Curie-Weiss law, however, ferroelectric ordering is not observed. [ABSTRACT FROM AUTHOR]

Silver nano particles have been widely used as catalyst for chemical industry. However, the catalytic efficiency of the silver has been limited by the aggregation of the silver, as the active sites are only located on the surface of the catalyst particles. In this paper we report the surface aggregation dynamics of silver on different ferroelectric polarization surface and temperature dependent behaviors. Meanwhile, reducing the particle size to obtain the dispersed morphology of silver was discussed by the dissipative particle dynamics method and density functional theory. The surface with upward polarization provides more electrons to the silver, which is responsible for the dispersed morphology of the silver. [ABSTRACT FROM AUTHOR]

The paper presents synthesis of (1-x)PMN-(x)PT (PMN-PT) near morphotropic phase boundary (MPB) i.e. for x = 0.25, 0.31, 0.33 and 0.35, using hydroxide co-precipitation method. Further, PMN-PT compositions under investigation were systematically characterized for density, structural, morphological, dielectric and ferroelectric properties. X-ray diffraction data reveals single phase formation of PMN-PT. The scanning electron microscopy (SEM) images were recorded and used to understand morphology of the samples. In present study, it was noted that the PMN-PT composition with x = 0.25 exhibits the maximum value of dielectric constant (ϵ) and saturation polarization (Pmax) amongst the PMN-PT compositions under investigation. [ABSTRACT FROM AUTHOR]

In this paper we report on the investigation of longitudinal ultrasonic wave attenuation, velocity and ultrasonically induced piezoelectric voltage in P(VDF-TrFE) composites with fillers of conductive carbon nanotubes (CNT). Moreover, temperature dependences of ultrasonic attenuation in the composites were shown to be sensitive to thermal cycling over the ferroelectric phase transition. [ABSTRACT FROM AUTHOR]

Sodium metavanadate has pyroxene-type one dimensional VO4-tetrahedral chains, which is analogous to the SiO4-chains in Bi2SiO5. Although it is known to undergo ferroelectric phase transition, its mechanism has not been clarified. This paper shows the spectroscopic results of simultaneous measurement of Raman/Brillouin scattering by utilizing ultra-narrowband holographic notch filters. The spectroscopic anomalies accompanying to the phase transition were observed for the first time in both Raman and Brillouin regimes. [ABSTRACT FROM AUTHOR]

In this paper, we established the origin of the experimentally observed topological instability representing the change of the plane domain wall shape by formation of so-called “fingers” during fast polarization reversal of the ferroelectric capacitor. By means of a simplified model we show that the topological instability of the domain wall can be attributed to retardation of the bulk screening of residual depolarization field. [ABSTRACT FROM PUBLISHER]

The paper first introduces the basic physics behind perovskite multiferroics. Then the recent progress on simple, complex perovskites, and manganites are briefly reviewed. The review discloses two important directions on achievement multiferrocity in perovskite: pay with strain engineering and adjust octahedral deformation. The authors also suggest that specific issues like leakage current and characterization platforms are also very important for the study of multiferroics. [ABSTRACT FROM PUBLISHER]

Nature has always amused us; sometimes it holds us in awe and sometimes it leaves us spellbound with its mysterious and inscrutable ways of working. The most significant and fundamental understanding of materials observed today is based on their constituent elements and position of the elements in the periodic table; which decides their property, behavior, reactivity and affinity with other elements. Given this primary aspects what comes secondary is the specificity or the multiplicity of functions that can be achieved from a material. In the present era, there is an incredible and massive increase in the number of functional materials to meet the ever-increasing need of electronic devices and their miniaturization. Functional materials have carved a special niche for itself in the field of material science. This review is exclusively intended to highlight and satiate the academic curiosity of novices about functional aspects of ferroelectric materials. It explores the various intricate and inherent principles and mechanisms which underpins the functional dimensions of ferroelectric materials. Ferroelectrics span a huge fraction of functional materials. Phenomenon like photovoltaic effect in ferroelectric materials, ferroelectric emission of electrons and their multifaceated applications are also discussed. Low dimensional ferroelectrics and their multifunctional prospects are also briefly covered in this review. It also includes brief idea of ferroelectric meta-materials, dielectric super-capacitors and its advantage over other preexisting ones. It is mostly informative and resourceful in providing multifunctional aspects of ferroelectrics. This review assures researchers who are genuinely interested in broadening their information base along with getting a fresh perspective into this emerging field of ferroelectrics as functional materials. [ABSTRACT FROM AUTHOR]

The concept of local ferroelectricity discussed in this paper belongs to the emerging field of ultrathin multiferroics. The idea of the ferroelectric polarization associated with the domain walls in magnets proposed by V.G. Bar'yakhtar et al. more than thirty years ago has recently got experimental evidence including electric field driven magnetic domain wall motion and electric field induced Stark shift in the single molecule microscopy. The special attention is paid here to the magnetoelectric properties of dislocation in stripe domain structure (i.e. the stripe domain heads) that differ considerably from the ones of straight domain wall segments. It is shown that the electric field induced displacement of the domain wall can be increased by an order of value with external constant magnetic field. [ABSTRACT FROM PUBLISHER]

The year 2020 marks hundred years since the watershed discovery of the phenomenon of ferroelectricity although at that time its importance was hardly realized. We provide a historical account of this event and its impact in terms of new materials discovery, novel fundamental physics concepts and technological applications on a decadal basis. We emphasize how ferroelectrics and the broader class of ferroics enriched our understanding of not only a wide variety of functional materials including multiferroics but also numerous device concepts and even a slew of topological defects these materials can harbor. Finally, we touch upon the current as well as future research topics in this ever growing and fecund area of interdisciplinary science. [ABSTRACT FROM AUTHOR]

One of the negative effects of ferroelectric applications, particularly for electrocaloric effect (ECE) applications, is temperature hysteresis (ΔTHyst). Temperature hysteresis is the difference between the temperatures corresponding to the maximum dielectric permittivity in heating and cooling modes. The value of ΔTHyst is commensurate with the value of the ECE temperature change. The ECE is a phenomenon in which a material shows a reversible temperature change under an applied electric field. The aim of this work is to study the possibilities of temperature hysteresis reduction by varying the ceramic sintering temperature, changing the stoichiometry of BaxSr1-xTiO3 solid solutions, and changing the rate of the heating-cooling cycle. [ABSTRACT FROM AUTHOR]

We report the preparation and characterization of vanadium substituted four-layer Aurivillius compound Bi5Fe1.5V0.5Ti2O15 using spin coating method. Ferroelectricity in the prepared films are confirmed from the well saturated polarization vs electric field (P-E) loops having remnant polarization (2 Pr) around 12.94 µC/cm2 at room temperature. In addition, low temperature P-E measurements show a decrease in Pmax and 2 Pr, which is attributed to the stabilization of defect dipole complexes and domain pinning, as seen in bismuth-based ferroelectrics. Additionally, this decrease in polarization is accompanied by an increase in imprint, confirming the presence of defect dipoles manifested as internal fields. [ABSTRACT FROM AUTHOR]

In this review we concentrate on the work of K. Alex Müller in connection with his activities on oxide perovskites and ferroelectrics which were central to his research career long before he successfully discovered the first high temperature superconductor (HTSC) together with J. G. Bednorz in 1986. Not accidentally, but taking his long experience in perovskite ferroelectrics into account, the first HTSC was an oxide perovskite which had never been considered before to be superconducting. [ABSTRACT FROM AUTHOR]

We review recent understanding of the crystallographic phases and its relation to ferroelectricity in ammonium lithium sulphate (NH4LiSO4) using the crystal structural data reported before and present our recent idea about its ferroelectricity. In this paper, we also report phase transitions and crystal structure at room temperature of tori-ammonium lithium di-sulphate ((NH4)3Li(SO4)2) from our recent experimental results. NH4LiSO4which is one of the (NH4)2SO4family ferroelectrics and (NH4)3Li(SO4)2which is one of theA3B(XY4)2-type derived from theABXY4-type were crystallized by evaporating the aqueous solution at room temperature. The phase transition and crystal structure were studied by means of thermogravimetric analysis, differential scanning calorimetry and single-crystal X-ray diffraction. In addition, phase transitions and ferroelectricity of NH4LiSO4will be discussed from the crystal structural changes. [ABSTRACT FROM PUBLISHER]

Structural transition, tetragonality, and dielectric properties are investigated along with thermal and compositional expansion of lead strontium titanate in order to reveal composition dependence and structure-property relation of the ferroelectric structure. Based on the available structural and dielectric data, dielectric stiffness and temperature-dependent paraelectric cubic lattice parameters are analyzed. Non-zero sixth-order free energy coefficients are derived for strontium titanate. Spontaneous polarization, spontaneous strain, volumetric change, and dielectric permittivity are modeled as a function of composition, and the theoretical results are in agreement with experimental data reported in the literature and reveal solid solution effect. [ABSTRACT FROM AUTHOR]

The hysteresis loops and the transition properties of a ferroelectric (FE) thin film with seeding layers are studied using the effective field theory with a probability distribution technique that accounts for the self-spin correlation functions. The effect of the interaction parameters for the seeding layer on the hysteresis loops and phase diagram are also examined. We calculated the critical temperature and the polarization of the FE thin film for different seeding layer structures. We find that the seeding layer can greatly increase the Curie temperature and the polarization of the whole FE thin film. The hysteresis loops are obtained for some typical value of the exchange interaction and the transverse field for a film with one or two seeding layers. [ABSTRACT FROM AUTHOR]

We present the results of structural and magnetic properties of two types of heterostructures composed of ferroelectric BaTiO3 and dielectrics LaMnO3 or SrTiO3. By means of the first principle calculations we analyze structures of BaTiO3/LaMnO3 and BaTiO3/SrTiO3 interfaces and investigate magnetic properties and an impact of ferroelectric polarization. Experimental results of magnetic susceptibility measurements for Ba0.8Sr0.2TiO3/LaMnO3 heterostructure are presented. [ABSTRACT FROM AUTHOR]

The unconventional Si-compatible ferroelectricity in hafnia-based systems, which becomes robust only at nanoscopic sizes, has attracted a lot of interest. While a metastable polar orthorhombic (o-) phase (Pca21) is widely regarded as the responsible phase for ferroelectricity, a higher energy polar rhombohedral (r-) phase is recently reported on epitaxial HfZrO4 (HZO) films grown on (001) SrTiO3 (R3m or R3), (0001) GaN (R3), and Si (111). Armed with results on these systems, here we report a systematic study leading toward identifying comprehensive global trends for stabilizing r-phase polymorphs in epitaxially grown HZO thin films (6 nm) on various substrates (perovskites, hexagonal and Si). [ABSTRACT FROM AUTHOR]

The temperature evolution of crystal structure and ferroelectric order parameter η(T) in nanocomposite materials "SBA-15 + NaNO2" have been studied by neutron diffraction. The large (∼15 K) temperature hysteresis in dependences of η(T) on heating and on cooling has been observed. It is shown that a cause of this effect is an influence of elastic strains arising upon heating and leading to a change in the temperature of the ferroelectric phase transition. [ABSTRACT FROM AUTHOR]

The origin of size effects in polycrystalline ferroelectric films of Pb(Zr1-xTix)O3 having the frequency dependence of coercive field in the form ln(ν/ν0)∼1/Ec2 is investigated. A model of a surface source emitting thin ferroelectric domains with reversed polarization is employed to explain this unusual frequency dependence of polarization switching in polycrystalline films in a wide range of frequencies. The model also predicts that the activation energy for domain nucleation increases with the source size, indicating an increase in the coercive field as minimum size sources deteriorate. The proposed mechanism for the domain nucleation in polycrystalline PZT films can explain the electrode size dependence of the limiting frequency. This dependence is related with increasing role of the athermal domain growth in strongly inhomogeneous electric field near electrode edges. [ABSTRACT FROM AUTHOR]

Domain switching by triangular field pulses was studied in (111)-cut rhombohedral PMN-PT crystal in the temperature range from 25 to 130 °C. The usual ferroelectric behavior with smooth switching current shape and well-defined threshold field (Eth) was obtained for temperatures below Tf (115 °C). At the temperatures above Tf, the switching current consisted of the pulses and complete backswitching was obtained. The sample image evolution investigated during: (1) zero-field heating and subsequent zero-field cooling, and (2) zero-field heating and field-cooling was attributed to a known domain structure behavior. The single-domain volume was achieved in the sample completely covered by electrode after field-cooling. [ABSTRACT FROM AUTHOR]

Ishibashi and Takagi considered 'ferroelectric domain switching' just equivalent to 'phase evolution during crystal growth'. They slightly modified Kolmogorov and Avrami's classical theory of 'phase transformations in crystal growth' and applied it to the switching data in ferroelectrics. Here an effort is made to elucidate mathematical steps in evolution of this new KAI model used to fit experimental switching data to estimate microscopic switching parameters. In mixed composite system (x = 0.09), the domain growth dimension () is found to expand from to when signal amplitude changed from to The cesium substitution is supposed to have enabled lone pairs on central nitrogen of nitrite group to orient constituting branches into more ordered state in the matrix of molecular chains of the PVA facilitating control of crystallization process which led to lowering of strain giving rise to the increased change in with change in pulse amplitude. [ABSTRACT FROM AUTHOR]

The temperature dependences of the linear permittivity ε' and the harmonic coefficient γ of composite materials obtained by introducing the ferroelectric NH4IO3 into the porous Al2O3 alumina matrix with a pore diameter of 60 nm are studied. It is found that the phase transition is smeared out and the Curie temperature shifts to the low-temperature region ΔT ∼ 25 K. The results obtained are consistent with the Ising model and are discussed within the framework of the phenomenological Landau theory. [ABSTRACT FROM AUTHOR]

Detailed study of the X-ray diffuse scattering in the paraelectric phase of the PbZr0.985Ti0.015O3 was carried out. We concentrated on the analysis of the scattering peculiarities in the vicinities of M- and R- points of the Brillouin zone. We have observed a critical increase of the diffuse scattering at the position Q ≈ (0.47 + h 0.53 + k l) slightly aside of M point on cooling to the intermediate phase. We attribute observed critical scattering to a mixed mode containing both oxygen octahedral tilts and antiparallel cationic displacements. Tentative conclusion is made describing earlier reported complicated set of the satellite peaks around M-point as the result of the soft-mode driven incommensurate phase transition. [ABSTRACT FROM AUTHOR]

Hysteresis phenomena were observed under electric fields two orders of magnitude lower than the coercive ones in ferroelectric copolymer vinylidene fluoride–tetrafluoroethylene. From the field dependences of the electrical displacement hysteresis, the volumetric energy density of electric loss was calculated. Its value increases with increasing amplitude of the sawtooth external field and is higher in case of lower external field frequency. Complex dielectric permittivity measurements indicate that the noted high-voltage hysteresis phenomena at polarization should be related to the process of space charge formation, which is due to the presence of heterogeneity in the copolymer under study. [ABSTRACT FROM AUTHOR]

The effect of sodium nitrite and barium titanate particle inclusions on the dielectric properties and the Curie temperature of the ferroelectric AgNa(NO2)2 is studied. It is shown that the presence of 10 volume percent of BaTiO3 particles increases the permittivity 4 times and raises the temperature of the phase transition by ΔТc ≈ 10 K. The presence of the NaNO2 particles leads to the increase of dielectric permittivity of the composite, but it does not influence the Curie temperature. [ABSTRACT FROM AUTHOR]

The effect of sodium nitrite and barium titanate particle inclusions on the dielectric properties and the Curie temperature of the ferroelectric AgNa(NO2)2 is studied. It is shown that the presence of 10 volume percent of BaTiO3 particles increases the permittivity 4 times and raises the temperature of the phase transition by ΔТc ≈ 10 K. The presence of the NaNO2 particles leads to the increase of dielectric permittivity of the composite, but it does not influence the Curie temperature. [ABSTRACT FROM AUTHOR]

Whether the intrinsic screening of depolarization by electrons and holes exists is essential for the fundamental ferroelectric properties such as domains and size effect. Despite many studies of domain boundary conduction, only clean BaTiO3 polar surfaces in ultrahigh vacuum (UHV) exhibit ohmic conductance at low field, clear polarization dependence and consistent temperature dependence, which prove the existence of electron and hole layer induced by depolarization field. Therefore, we study TiO2 polar surface (c+, c− surface) of BaTiO3 local density functional theory (LDA) with a large supercell consisting of 11 layers of TiO2 and10 layers of BaO. These calculations confirm the electron and hole layer formation at the surface shown by experiments in ultrahigh vacuum and Ginzburg-Landau theory and resolve some inconsistencies between them. [ABSTRACT FROM AUTHOR]

The structural, dielectric, ferroelectric, and ferromagnetic properties of multiferroic ceramics (1-x)Ba(Zr0.2Ti0.8)O3-xBa0.7Ca0.3FeTaO5 (abbreviated as (1-x)BZT-xBCFT where x = 0.2, 0.25, and 0.4) were investigated systematically. Ceramics possess a tetragonal phase of a perovskite structure. Dielectric-temperature spectrums exhibit a dielectric relaxation phenomenon that behaves as a dielectric step and frequency dispersion. X-ray photoemission spectroscopy confirmed the coexistence of Fe2+ and Fe3+. It is concluded that the dielectric relaxation in (1-x)BZT-xBCFT originates from the electron hopping in the dipole formed by Fe2+ and Fe3+. Multiferroic behavior that coexisted with ferroelectricity and ferromagnetism was well established by magnetic and ferroelectric measurements. [ABSTRACT FROM AUTHOR]

We employ electron paramagnetic resonance (EPR) of the spin probe Mn2+ to study the paraelectric − ferroelectric transition in Dimethylammonium Manganese Formate (DMMnF) and Mn2+-doped Dimethylammonium Zinc Formate (DMZnF), which are considered model metal − organic frameworks (MOF) with a Pb-free perovskite architecture. In DMMnF, we study the variation of the Mn2+ EPR line shape and intensity at the X-band (∼9.4 GHz) and over 80 to 300 K, and we show the absence of magnetoelectric coupling at the ferroelectric transition. At the antiferromagnetic transition in DMMnF, we detect a magnetoelectric coupling caused by weak ferromagnetism in the AFM phase. In DMZnF, EPR spectra of the Mn2+ probe combined with DFT show that the crystal field is predominantly determined by the Dimethylammonium (DMA+) cations. [ABSTRACT FROM AUTHOR]

The Raman spectra of novel ferroelectric ceramics SnxSr1-xTiO3 (x = 0.1, 0.05 and 0.02) were obtained to clarify the mechanism of their ferroelectric phase transitions. Two transverse-optic modes in the ferroelectric phase showed softening toward the ferroelectric transition temperature. A comparison of the spectra obtained for SnxSr1-xTiO3 with the spectrum of PbxSr1-xTiO3 facilitated the assignment of the observed modes under the assumption of the ferroelectric phase in symmetry. However, several peaks violating the Raman selection rules were observed, suggesting the emergence and growth of polar regions even in the paraelectric phase. [ABSTRACT FROM AUTHOR]

Effect of nanocrystalline size of the particles on ferroelectric properties of KNbO3 is studied. Properties like hysteresis parameters, phase transition temperatures and domain morphology in nanocrystallites were studied by using P-E hysteresis, differential scanning calorimetry (DSC) and transmission electron microscopy (TEM) techniques, respectively. Nanocrystalline KNbO3 compound was synthesized by a modified polymerized complex method and room-temperature structural phase was characterized by X-ray diffraction (XRD) and Fourier transform infrared (FTIR) spectroscopy. Field emission gun-scanning electron microscopy (FEG-SEM) was used to reveal the size and morphology of the particles. It was found that the present nanoparticles of sizes ranging from 50 to 250 nm bears polarization values <1 μC/cm2, and undergo cubic-tetragonal and tetragonal-orthorhombic phase transitions at 312 and 87 °C respectively. Although the value of polarization is small as compared to the bulk reported in the literature, the nature of P-E loops along with phase transitions and presence of 60, 90 and 180° domain structures indicates retention of ferroelectric nature in KNbO3 even at the nanolevel. [ABSTRACT FROM AUTHOR]

Piezoelectric ceramics of the perovskite solid solution 0.655Pb(Mg1/3Nb2/3)O3-0.345PbTiO3 (0.655PMN-0.345PT) were synthesized by tape-casting process. Highly dense ceramics lacking parasitic pyrochlore phases were fabricated by using precursor method and adding moderate PbO. The influences from sintering temperature on the physical and electrical properties of the 0.655PMN-0.345PT ceramics were initially investigated by phase and microstructure analyses. High piezoelectric, dielectric and ferroelectric properties of d33=700 pC/N, kp=0.605, εr=4770, tanδ = 0.016, Pr=30.68 μC/cm2 were obtained for the specimens sintered at 1200 °C. Compared with the traditional solid-state sintering method, the performance of ceramics formed by tape-casting achieved an improvement. [ABSTRACT FROM AUTHOR]

Structural changes in isotropic films of ferroelectric vinylidene fluoride (VDF)/tetrafluoroethylene (TFE) 94/6 copolymers in the metastable state have been studied on heating. The metastable state was ascribed to γ-crystals. The dielectric relaxation spectroscopy was employed to study space charge relaxation processes. Two relaxations were observed at high temperatures. One of them was attributed to relaxation of space charge accumulated on the Al electrode which may be partially blocked due to new functional groups formed in the polymer surface. Recrystallization of the film from the melt is accompanied by small α-crystals formation. This results in a decrease in activation energy of the space-charge relaxation process. [ABSTRACT FROM AUTHOR]

We present a comparative study on the investigation of memory hysteresis and leakage current characteristics of the MFIS structure with Lead-Zirconate-Titanate (100 nm) and different insulating layers of thickness 5 nm. Effect of introducing buffer layer grown/deposited by different technique and processed under different conditions has been observed. For SiO2, Si3N4and HfO2layers, the memory window reduces from 6.5 to 4 V at the annealing temperature of 500°C. XRD data indicates phase change in deposited PZT film from tetrahedral to rhombohedral. Multiple angle ellipsometry indicates an increase in refractive index of the deposited HfO2and PZT films with annealing temperature. [ABSTRACT FROM PUBLISHER]

A lead free polycrystalline material Ba(Bi0.5Ta0.5)O3was prepared by a standard mixed oxide method using high-purity precursor materials. A preliminary X-ray diffraction study confirmed the formation of a single-phase material, crystallized in monoclinic phase and homogeneous morphology for the sample. The dielectric properties (ϵrandtanδ) have been studied for a wide range of temperature at some selected frequencies. The temperature dependence of relative permittivity suggests that the material may exhibit ferroelectricity of diffuse type around 315°C. The frequency dependence of ac conductivity follows the Jonscher's power lawreveals the material exhibit NTCR behavior similar to that of a semiconductor. [ABSTRACT FROM PUBLISHER]

Zr-substituted Ba0.6Sr0.4TiO3((Ba0.6Sr0.4)(Ti0.8Zr0.2)O3) - BSZT) thin films are deposited by using Pulsed Laser Deposition method with different fluence at optimized conditions on amorphous fused silica substrates. The X-ray diffraction (XRD) pattern of the films confirms the formation of cubic phase. Raman studies are performed to understand vibrational modes present in the films. The optical band gap of deposited BSZT thin films were calculated from the transmittance measurements. Microwave dielectric properties of the thin films deposited at 2 J/cm2were measured. These results show BSZT thin films are useful in tunable microwave devices. [ABSTRACT FROM AUTHOR]

The dielectric properties of newly synthesized AgCrP2S6and Cu0.2Ag0.8CrP2S6phosphorous chalcogenide crystals are presented. The measurements were performed in the frequency and temperature ranges 20 Hz to 1 MHz and 110 K to 470 K, respectively. No anomalies of complex dielectric permittivity indicating the polar phase transition can be detected in the measured temperature range. Dielectric spectra at high temperatures are mostly influenced by the electrical conductivity. From DC conductivity the activation energies have been calculated and compared with CuCrP2S6. The activation energies of the conductivity were found to be 1.26 eV and 0.75 eV for AgCrP2S6and Cu0.2Ag0.8CrP2S6, respectively. [ABSTRACT FROM PUBLISHER]

Size effect and lattice strain effect for charge ordered structure and magnetic properties were investigated on the nano particles of geometrically spin and charge frustrated system YbFe2O4. The lattice strain of the nano particle was controlled with the ratio of Yb and Fe (2.00 ≤ Fe/Yb ≤ 2.04) in liquid synthesizing method. It was found that the lattice strain is not affected by the magnetic transition temperature, however the anomalous behavior at a lower magnetic transition (TLT) with an increment of the Fe / Yb ratio was detected. The development of charge ordering was two-dimensional and magnetic ordering goes down for all samples in spite of the variation of the local lattice strain. This is the first report of the coupling of charge and spin ordering to the size effect in this material. These results suggest that the discussion on the electric polarization induced from the charge ordering in this material need to care the long-range interaction like surface effect. [ABSTRACT FROM AUTHOR]

The ferroelectric phase transition of copolymers of vinylidene fluoride (VDF) with trifluoroethylene (TrFE) is well known and related to conformational changes in the polymer chain. Contrary to the expected paraelectric behaviour in the high temperature phase a pyroelectric investigation of the phase transition in the range from 0°C to 130°C combined with X-ray diffraction indicate the copolymer as ferroelectric when prepared and polarised in the high-temperature phase. Based on this finding the orthorhombic space-groupFmm2 is proposed for the polar high-temperature phase. Above the Curie temperature the material exhibits pyroelectricity with inverted sign, whose origin is interpreted as flexoelectricity. [ABSTRACT FROM AUTHOR]