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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 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]

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]

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]

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]

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]

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 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]

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]

The paper reviews the results of our studies concerning the ferroelastic domain structure in the crystals exhibiting superprotonic conductivity. We would like to show the ferroelastic domain structure and its temperature behaviour in solid acids which belong to the family of crystals with a general formula MxLiyHz(XO4)(x + y + z)/2 (M = Rb,K,Cs,NH4; X = S and Se). For the majority of crystals, which belong to that family, the transition to the phase with high proton conductivity is simultaneously the ferroelastic-paraelastic one. However, this does not apply to all crystals of the family. Therefore, a question arises about the role of the phenomenon of ferroelasticity in the superprotonic phase transition. Depending on x,y and z, there are different groups of crystals. Our paper presents the results of temperature evolution of ferroelastic domain pattern at ferroelastic-superprotonic phase transitions as well as at other structural phase transitions, which appear in different crystal groups. [ABSTRACT FROM AUTHOR]

This paper reviews the spontaneous polarization of ferroelectric ceramics and its variations with applied electric field, stress and temperature, especially at induced phase transitions. Normally, there are two kinds of field dependence of the induced polarization, the linear and nonlinear dependence. In this paper the nonlinear relationship will be emphasized. The application of these ceramics for underwater transducers, shock wave power generators, pyroelectric energy converters and pyroelectric voltage transformers are listed. [ABSTRACT FROM AUTHOR]

Travelling wave ultrasonic motors, TWUM, are based on the friction transmission of mechanical travelling waves excited on the stator by using high Q piezoelectric ceramics. When reducing the analysis to the optimal design of the motor stator, the electromechanical coupling factor can be defined as one of the objective function in the optimisation process. The present paper describes the work carried out in the process of optimising TWUM operation. First, the paper describes a novel modelling suitable for parametric optimisation of the motor performance. secondly, parameters having the most relevant influence on motor performance are identified as optimisation parameters. Finally, the proposed objective functions and the optimisation results are discussed. [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]

Tunability of ferroelectric complex oxides is achieved by applied bias voltage. Many applications require usage of relatively low voltage which is achievable by using a ferroelectric thin-film. Recently developed dielectric metamaterials were implemented in bulk and in thick films. Metamaterials are resonant structures. The frequency range of 0.1–1.5 THz is of special interest for such applications as non-destructive evaluation of materials and detection of chemical and biological hazards. This paper numerically investigates the possibility of a resonant effect in a thin-film ferroelectric metamaterial and the effects of increased dielectric constant and thickness on the thin-film's resonance frequency. [ABSTRACT FROM AUTHOR]

Effect of lower ionic radii (Na and Nd) substitution in A-site on the structure, dielectric, ferroelectric and piezoelectric properties of SrBi4Ti4O15(SBT) is investigated in this paper. The samples are prepared by solid state double sintering method and sol gel method based on pechini process. Substitution of smaller ions reduced the dielectric constant and remanent polarization values. But sol gel samples showed good dielectric and ferroelectric properties. A-site substitution has resulted in improved Curie temperature and piezoelectric properties. As a result, Na and Nd modified SBT ceramics are found to be excellent high temperature piezoelectric materials. [ABSTRACT FROM PUBLISHER]

Solution for BaTiO3was prepared via sol-gel route in this paper. Ceramic fibers of BaTiO3were then obtained by gel-spinning technique with the solution. FTIR spectra of the samples of fibers were characterized. TG-DTA spectra of the gel fibers were also conducted by a thermal analyzer. Different sintering conditions were performed, in order to obtain ceramic fibers with better ferroelectric and piezoelectric properties. The crystal structures of the samples were identified with XRD. The microstructures of the ceramic fibers were observed with SEM, Meanwhile, ferroelectric and piezoelectric properties of the BaTiO3ceramic fibers were characterized by using of a workstation measurement system, with the remnant polarization of 9.41 μC/cm2, coercive field of 3.13 kV/cm, piezoelectric constant of 172 pC/N and mechanical-electrical parameter of 0.56. [ABSTRACT FROM AUTHOR]

This paper presents the design and modeling of micro-electromechanical systems (MEMS) on the ternary ferroelectric compounds (PZT) based by using finite element model (FEM) simulation. The conceptual framework establishes five steps to perform the critical analysis: design a novel structure, define the failure mechanisms under the given conditions, analyze different vibrations, analyze the operation principle, and detect resonance modes. In addition, MEMS failure modes were analyzed under different scenarios and the obtained results discussed. [ABSTRACT FROM AUTHOR]

In this paper scanning probe microscopy investigations of surface morphology and local ferroelectric properties of sol-gel deposited PZT thin films are presented. It is shown that the films have sufficiently low surface roughness about 2 nm and small grain size about 20 nm. Possibility of the film polarization by applying both positive and negative DC voltage between the SPM probe and the sample is demonstrated. Additionally, times of residual piezoresponse signal relaxation are measured and domain wall velocity for the PZT films is calculated. [ABSTRACT FROM AUTHOR]

Ferroelectricity and piezoelectricity are two of the common ferroelectric material properties, which have widespread observations in many biological systems, and these are referred to as biopiezoelectricity and bioferroelectricity. This paper presents a short overview of the main issues of piezoelectricity and ferroelectricity, their manifestation in organic, biological, and molecular systems. As a showcase of novel biopiezomaterials, the investigation of diphenylalanine (FF) peptide nanotubes (PNTs) is described by computational molecular modeling, as well by experimental AFM/PFM measurements. FF PNTs present a unique class of self-assembled functional biomaterials, owing to their wide range of useful properties, including nanostructural piezoelectric and ferroelectric properties. [ABSTRACT FROM AUTHOR]

This paper highlights the structural, dielectric and pyroelectric properties of two complex tungsten bonze ceramics (K2Pb2Pr2W2Ti4Nb4O30and K2Pb2Pr2W2Ti4Ta4O30) which were prepared by high temperature mixed oxide method. Room temperature X-ray structural analysis confirms the formation of the compounds in single phase. SEM micrographs show uniform distribution of densely packed rod like grains. Variation of dielectric parameters with temperature and frequency shows the phase transition at 350°C and 426°C for the respective samples. Temperature dependent hysteresis loop confirms the existence of ferroelectricity in the materials. The current variation with voltage at different temperatures shows the semiconductor like behaviour of the materials. The temperature dependent dc conductivity follows the Arrhenius equation, and reveals the negative temperature coefficient of resistance (NTCR) behaviour of the materials. The current (for a fixed voltage) variation with temperature shows that the materials have high pyroelectric co-efficient and figure of merit, thus making them useful for pyroelectric sensors. [ABSTRACT FROM AUTHOR]

In this paper we report the mechanism and nature of relaxor ferroelectric behavior in the environmental friendly lead free Barium Zirconate Titanate (BZT) system. A revised complete (Structure:Property) phase diagram of Ba(ZrxTi1-x)O3, with compositions 0.00≤ × ≤1.00 has been developed based on their electrical properties. Two different kinds of relaxor behaviors have been observed in the BZT system; one is dominated by polar Ti-rich regions and another by non-polar Zr-rich regions. All the BZT relaxor compositions are characterized by dielectric properties with and without bias, pyroelectric and thermal expansion measurements in the wide range of temperatures. The structure of the BZT compositions has been evaluated by XRD, Neutron diffraction study. Further the local structure of the BZT compositions has been probed by micro-Raman spectra. Although the global structure of BZT relaxors is cubic as observed in Neutron diffraction studies, the local symmetry is non-cubic as evident in the micro-Raman spectra of BZT relaxors as well as in their thermal strain measurement, dielectric and pyroelectric behavior. [ABSTRACT FROM PUBLISHER]

This paper is devoted to the problem of the electromechanical coupling of advanced composites based on relaxor-ferroelectric single crystals with large piezoelectric activity. A novel 0–3–0 PMN–0.33PT single crystal/porous araldite composite is considered as a material with large values of electromechanical coupling factors with a variable anisotropy. The role of physical and microstructural factors in achieving the considerable electromechanical coupling is discussed for 0–3–0 connectivity. [ABSTRACT FROM PUBLISHER]

In spite of a number of studies on the ferroelectricity of the isotope exchanged SrTi18O3, it has not been clarified yet why the spontaneous polarization P in the isotope exchanged SrTi18O3 is not parallel to [100]c as expected from the Slater mode but parallel to [110]c. In this paper it is shown that the dipole-dipole interaction between the rhombohedral polar clusters which exist from well above Tc is closely related to the formation of the P parallel to [110]c. The results are consistent with the appearance of the relaxational mode in the Raman spectra and suggest the existence of the order-disorder nature of this transition. [ABSTRACT FROM AUTHOR]

This paper proposed an application of Artificial Neural Network (ANN) to concurrently model ferroelectric hysteresis properties of Barium Titanate in both single-crystal and bulk-ceramics forms. In the ANN modeling, there are 3 inputs, which are type of materials (single or bulk), field amplitude and frequency, and 1 output, which is hysteresis area. Appropriate number of hidden layer and hidden node were achieved through a search of up to 2 layers and 30 neurons in each layer. After ANN had been properly trained, a network with highest accuracy was selected. Query file of unseen input data was then input to the selected network to obtain the predicted hysteresis area. From the results, the target and predicted data were found to match very well. This therefore suggests that ANN can be successfully used to concurrently model ferroelectric hysteresis property even though the considered ferroelectrics are with different domains, grains and microscopic crystal structures. [ABSTRACT FROM AUTHOR]

The National Aeronautics and Space Administration (NASA) is developing high-tolerance, radiation-hardened electronics for missions in and beyond Low Earth orbit. Ferroelectric-based electronics are highly viable candidates for these electronics because of their inherent radiation-hardened property. Since standard memory devices are prone to damage caused by radiation, ferroelectric memory may provide the needed radiation-tolerance. To test the effectiveness of ferroelectric random access memory (FRAM) in Low Earth orbit, a 512 K Ramtron FRAM will be flown on a Low Earth orbit satellite that will be launched by NASA. This paper discusses the advantages of ferroelectric electronics and outlines the Low Earth orbit ferroelectric memory test experiment. [ABSTRACT FROM AUTHOR]

This paper describes an automated-measurement system of ferroelectric hysteresis loops, which was developed in LabView environment based on Virtual Instrument. The system provides a function obtaining nonlinear polarization current from measured current data, which is important for properly estimating ferroelectricity of a dielectric, especially for one with high electric loss. In addition, the relationship between nonlinear polarization current density and external electric field of a ferroelectric reveals more information which is helpful for researches of polar order and/or ferroelectric characteristics. [ABSTRACT FROM AUTHOR]

This paper investigated the ferroelectric and dielectric properties of Sm-doped BaTiO3 sintered in different atmosphere. The influence of variable doping concentration on microstructure, ferroelectric and dielectric properties was studied. The results showed that the dielectric-temperature curve of Sm-doped BaTiO3 was smoother than that of pure BaTiO3. And tunability of Sm-doped BaTiO3 was smaller than that of pure BaTiO3. Dielectric constant of the samples sintered in nitrogen was smaller than that of samples sintered in air. The hysteresis loop displayed that ferroelectric polarization decreased with Sm doping. [ABSTRACT FROM AUTHOR]

This paper uses structured diffuse scattering to compare and contrast the local crystal structure behaviour of the normal ferroelectric BaTiO3 with a range of relaxor ferroelectric substituted BaTiO3 materials. The results strongly suggest that both normal ferroelectric BaTiO3 and the relaxor ferroelectric substituted BaTiO3's have the same underlying polarisation mechanism i.e. inherent 1-D correlated Ti cation and neighbouring O anion displacements forming 1-D dipole clusters (or polar nano regions). The role of the substituting ions is not to induce the PNR's but rather to suppress homogeneous strain distortion, transverse correlation of the 1-D PNR's and a transition into a long range ordered ferroelctric state. [ABSTRACT FROM AUTHOR]

In a recent paper, the modified model by P. Weiss was applied to ferroelectrics. Typical ferroelectric properties could be simulated. A further generalization of the Weiss model is the assumption of a power law feedback with an exponent κ between the polarization of the permanent dipoles and the local field. The Weiss model is included for the exponent κ = 1 and we obtain a second-order type phase transition. For values κ > 1 the simulations yield first-order type phase transitions whereas we obtain diffusive-type phase transitions for values κ < 1. [ABSTRACT FROM AUTHOR]

In the paper we present analytical calculations of the profiles and average values of the correlation radius of polarization fluctuations and generalized susceptibility in thin ferroelectric films with in-plane and out-of-plane polarization orientation. The contribution of polarization gradient, surface energy and depolarization field were taken into account. For the second order ferroelectrics the correlation radius and generalized susceptibility diverge at the film critical thickness as anticipated. The surface energy, inhomogeneous distribution of polarization and depolarization field related with incomplete screening govern the size effects such as thickness-induced phase transition, corresponding correlation radius and a generalized susceptibility divergence in the phase transition point. [ABSTRACT FROM AUTHOR]

In the present paper the dielectric investigation results of NaNO2 and NaNO3 confined in porous glass are presented. The phase transition in nanoconfined NaNO2 with pore size 20 nm remains nearly at the same temperature. Two phase transitions can be seen in the dielectric spectra. The increase in the frequency dependent dielectric permittivity on heating is mainly the result of a conductivity effects. The relaxational soft mode contribution is present as well but is small as compared to the conductivity contribution. Such huge conductivity is caused by a premelting phase, which is visible even at temperatures below the phase transition. Relaxational soft mode temperature behaviour is also different from classical ferroelectrics. Only change in the activation energy can be identified as a phase transition. Due to that contribution of this mode, the static dielectric permittivity also behaves completely different—it has minima at TC. Present results confirmed value of TC obtained from neutron scattering experiments. Obtained results are compared between NaNO3 and NaNO2. [ABSTRACT FROM AUTHOR]

Microwave characterisation of dielectric materials is vital to implement the material in communication devices and circuits. The microwave characterisation parameters are the dielectric constant, loss tangent, Q0 × f0, temperature coefficient of frequency and temperature coefficient of permittivity. This paper examines the microwave characterisation data of four different dielectric materials. From several experiments on different dielectric materials, it has been concluded that the concept of using Q0 × f0 and temperature coefficient of frequency, as a material property will not reflect on material's fundamental behaviour. On the other hand, it has been interesting to note that the temperature coefficient of permittivity of a material is a constant irrespective of the measurement technique and hence it is a material parameter. The studies on temperature dependent permittivity will reveal the knack of a material to operate as a frequency stable circuit or device. [ABSTRACT FROM AUTHOR]

Two-step phase transition model, displacive to order-disorder, is proposed. The driving forces for these two transitions are fundamentally different. The displacive phase transition is one type of the structural phase transitions. We clearly define the structural phase transition as the symmetry broking of the unit cell and the electric dipole starts to form in the unit cell. Then the dipole-dipole interaction takes place as soon as the dipoles in unit cells are formed. We believe that the dipole-dipole interaction may cause an order-disorder phase transition following the displacive phase transition. Both structural and order-disorder phase transition can be first-order or second-order or in between. We found that the structural transition temperatures can be lower or equal or higher than the order-disorder transition temperature. The para-ferroelectric phase transition is the combination of the displacive and order-disorder phase transitions. It generates a variety of transition configurations along with confusions. In this paper, we discuss all these configurations using our displacive to order-disorder two-step phase transition model and clarified all the confusions. [ABSTRACT FROM AUTHOR]

Diamond-like carbon (DLC) films have received much attention due to their excellent hardness, chemical inertness, and low surface friction coefficient. But DLC films needed to be combined with one piezoelectric layer such like ZnO or AlN film for surface acoustic wave (SAW) applications. In this paper, we study the effect of DLC thin film fabricated by RF magnetron sputtering on the characteristics of the SAW devices (IDT/ZnO/DLC/Si). The comparison of the phase velocity of the ZnO/DLC/Si layered structure with different thickness of the DLC thin films is discussed. We use a two-step process for the deposition of ZnO film on DLC thin film to enhance the adhesion between them. The full width at half maximum intensity of ZnO(002) orientation obtained is only 0.19° from the X-ray diffraction. The phase velocity of the SAW devices will be increased when the thickness of the DLC thin film is increased. The results show that the characteristics of the SAW devices could be improved by the DLC films in raising the SAW phase velocity. [ABSTRACT FROM AUTHOR]

Minimally invasive surgery (MIS) is the most exciting and rapidly developing area where force sensing is actually of central importance. Micro-machined piezoelectric sensors can be integrated onto MIS tools for improved diagnosis and treatment monitoring. A micro-machined freestanding vanadium doped-lead zirconate titanate (PZTV) force sensor is fabricated using five masks process incorporating deep reactive ion, ion beam and wet-chemical etching techniques. The PZTV sensor is designed as a parallel plate capacitor structure in which the sol-gel prepared 1-μ m thick PZTV film is sandwiched between top (Au/Cr) and bottom (Pt/Ti) metal electrodes mounted on a thin Si membrane. This paper also describes a new wet chemical approach for patterning vanadium doped-PbZr0.53Ti0.47O3 films. The etch recipe provided excellent etch control, minimized undercut, preserved the photoresist mask, and effectively removed the residues on the etched surfaces. A high etch rate (200 nm/min), high selectivity with respect to photoresist, and limited under-cutting (1.5:1, lateral : thickness) were obtained. The fabricated force sensor exhibited good ferroelectric properties. The current fabrication procedure and electrical analysis can be considered as a breakthrough for fabricating freestanding PZT force sensor in any desired shape and dimensions, as well as a good example of ferroelectric microdevices. [ABSTRACT FROM AUTHOR]

This paper is a review article that emphasizes that dynamical processes of electromagnetic wave interaction with ferroelectrics proceed in such a way that characteristic frequencies of various excitations related to polarization lie in microwave range: i) a soft mode frequency in a number of displacive ferroelectrics on approaching the Curie temperature drops into the millimeter wave range or splits to components, the lower of which lies at microwaves and explains the static permittivity; ii) a frequency of relaxation soft mode in a number of order-disorder ferroelectrics lies also in the microwave range, and iii) relaxation of permittivity in relaxors and dipolar glasses also occurs at microwaves. Results of the complete dielectric spectra of the fundamental dielectric dispersion in the frequency range 1 MHz to 1012 Hz and its microscopic description in the most characteristic materials are presented and discussed. [ABSTRACT FROM AUTHOR]

Piezoelectric ceramics, constituting an active element, make a stator vibrate generating a rotational force in ultrasonic motors. In the drive of ultrasonic motors, many factors exist that can affect the resonance characteristics of piezoelectric ceramics. For example, those factors are the bonding conditions with the elastic body, the magnitude of the electric field, the normal force for the frictional drive, the emission of heat due to vibration and friction, and so on. Therefore, it is important to properly research the inclination for variation of piezoelectric ceramics in the circumstance where complex elements are involved. In this paper, we focus on the analysis of the resonance characteristics of an ultrasonic motor due to the magnitude of the input voltage and normal force. [ABSTRACT FROM AUTHOR]

This paper focuses on the effect of back-etching on the electrical properties in (001)&(100) oriented Pb(Zr0.3Ti0.7)O3 (PZT30) thin films. The PZT30 thin films were deposited by chemical solution deposition (CSD) on a Pt/Ti/SiO2/Si substrate with different back-etching depth. The back-etching depth was controlled by changing the etching time in the range from 287 μ m to 98 μ m (residual Si thickness; TSi = 13-202 μ m). The residual stress in PZT30 thin film was estimated at the back etched part and the un-etched part by Raman analysis. In addition, the dielectric and ferroelectric properties in PZT30 thin film were measured to estimate the effect of the back-etching depth on the electrical properties. [ABSTRACT FROM AUTHOR]

Isotope exchanged SrTi18O3(STO18) undergoes a ferroelectric transition at about Tc = 24 K. Its origin and mechanism have been investigated by many authors but even the direction of spontaneous polarization has not been clarified yet. In this paper from optical and Raman scattering studies, we report that the spontaneous polarizations are parallel to [1, ± 1,0]c, which is the crystal axes of the tetragonal phase. In Raman spectra, softening of TO modes are observed but the softening is not perfect. The displacement of soft mode is not parallel to the cubic axis [1, 0, 0]ccontrary to the expectation from Slater mode. Near Tc, a quasi-elastic mode appears which suggests the order-disorder nature of this transition. Although at temperatures far from Tc this transition is triggered by the soft TO mode, ferroelectricity in STO18 is a result of the percolation of polar clusters which exist already above Tc. The structure of STO18 below Tc is inhomogeneous mixture of the orthorhombic (C2v) ferroelectric domains with [image omitted] / / [110]c and [image omitted] / / [1[image omitted]0]c in the matrix of the tetragonal (D4h) structure. [ABSTRACT FROM AUTHOR]

The paper deals with the non-linear properties of the piezoelectric ceramics Pb(ZrxTi1 - x)O3 (PZT) at room temperature. The influence of DC electric field on the material parameters, such as piezoelectric coefficients d31 and d33 of PZT ceramics, was studied using the resonance method. The dependence of the resonance and antiresonance frequencies of PZT resonators on DC electric field was measured. Hydrostatic piezoelectric coefficients dh, calculated from d33 and d31 piezoelectric coefficients, were compared with dh coefficients, that were measured directly by dynamic hydrostatic method. Electric field limits for application on PZT ceramics were determined. A remarkable influence of the DC electric field on d31 and d33 piezoelectric coefficients values was exhibited for soft PZT ceramics (APC 850 and APC 856). [ABSTRACT FROM AUTHOR]

In the present work six-port reflectometer suitable for the dielectric measurements in the frequency range 80-120 GHz is described. Complex dielectic constant is very difficult to obtain the higher is the value and the higher the frequency of measurements. Presented method is presented with superior calibration method, which implies higher precision. In this paper, results of actual measurements of relaxor ceramics PLZT 8/65/35 and comparison to previous work are presented. [ABSTRACT FROM AUTHOR]

In this paper certain peculiarities of the ferroelectric behavior of the TGS crystals with tailored non-uniform distribution of the impurity Cr3 + are considered. The dielectric hysteresis loops of the TGS:Cr samples were characterized by the large shifts both along the polarization P axis and along the electric field axis. It is established that the unipolarity coefficient and pyroelectric signal of the samples with the impurity gradient have remained stable at the repeated cycles of heating - cooling. The obtained results are explicated within the framework of the phenomenological approach taking into consideration the gradient term in the Landau-Ginzburg free energy. [ABSTRACT FROM AUTHOR]

Various perovskite structure electroceramic thin films have been studied for semiconductor memory applications. The high permittivity and ferroelectric remanent polarization properties of these materials give the promise of a new generation of advanced dynamic and/or nonvolatile memory devices. The recent study indicates that perovskite oxide showing bistable resistance switching behavior is a highly promising candidate for nonvolatile semiconductor device, the so-called resistance random access memory (RRAM). RRAMs exhibit sufficiently fast switching capability and low operation voltages as compared with flash memory, and bring about the current upsurge in research. This paper summarizes the fabrication and characterization of these potential materials, and provides a broad view of the current status and future trends for perovskite oxides-based RRAMs. The associated conduction mechanisms are also discussed with specific examples from recent literature. [ABSTRACT FROM AUTHOR]

The structural, dielectric and ferroelectric studies of SrBi2Ta2O9 (SBT) ferroelectric ceramics, partially substituted with wolframium (W) for tantalum (Ta), are reported in this paper. Polycrystalline samples of wolframium substituted SBT ceramics of compositions SrBi2(WxTa1 - x)2O9 (SBWT); x = 0.0-0.20 were synthesized by solid state reaction method. X-ray analysis confirm that the single phase layered perovskite structure is maintained up to x = 0.05. The microstructural studies reveal that the average grain size increases with the increase in W- content. Dielectric properties studied as a function of temperature at 100 kHz show an increase in Curie temperature over the composition range of x = 0.025 to 0.20. The dielectric loss reduces significantly with wolframium addition. The temperature dependence of dc conductivity of the samples vis-à-vis wolframium content exhibits the typical negative temperature coefficient of resistance (NTCR) and a decrease in conductivity by as much as two to three orders of magnitude is observed. The ferroelectric properties improved with W-doping and the maximum value of remanent polarization was observed for composition with x = 0.075. The observed results have been discussed in terms of contribution from the cation vacancies which are introduced into the lattice structure so as to compensate the charge imbalance due to donor doping. [ABSTRACT FROM AUTHOR]

Aurivillius type bismuth layer structured ferroelectrics (BLSF) have been found to possess strong relationship between tetragonal strain (c/a) and extrinsic/ intrinsic conductivity. The extrinsic part of the conductivity is known to depend upon space charge in the sample. The present paper discusses effects of 30 atomic % doping of Ca, La and Pb on tetragonal strain, conductivity and dielectric constant/loss with temperature and frequency. Tetragonal strain increases on doping calcium and lead while it shows a decrease on doping lanthanum. The calcium and lanthanum doped samples show pronounced space charge part of dielectric constant while lead doped sample shows nearly constant permittivity values. No phase transition is observed in the calcium doped sample up to 600°C while for the lanthanum doped sample a decrease of 141°C is observed in the value of Curie temperature compared to that for the undoped sample. [ABSTRACT FROM AUTHOR]

Preparation of KNbO3 powder from aqueous solution of layered perovskite K2NbO3F has been investigated. The prepared powders showed a pseudo-cubic KNbO3 structure, and need heat treatment at 1000°C to convert in the crystal structure to orthorhombic ferroelectrics. In this paper, we report a modified processing for the preparation of a better organized orthorhombic KNbO3 powders by firing at lower temperature of 800°C by the introduction of Pechini method. [ABSTRACT FROM AUTHOR]

We have examined whether or not it would be possible to obtain a giant spontaneous polarization in BiFeO3 (BFO) thin films, in agreement to our experimental data showing values of nearly 150 μ C/cm2. As our previous calculations have shown such values can only be obtained in a giant tetragonality structure of a perfect crystal, in this paper we are studying the defects' influence on the spontaneous polarization in a structure with a low tetragonality. We have found that, alike in conventional perovskite ferroelectrics such as BaTiO3 and PbTiO3, hole doping can enhance the ionic off-centering in BFO. [ABSTRACT FROM AUTHOR]

Relaxors have a wide variety of industrial applications because of their high permittivity and piezoelectricity around room temperature. Although the microscopic mechanism of the relaxor behavior has not been fully elucidated yet, there are some fundamental developments in the experimental studies in the last decade, which are briefly reviewed in this paper with particular reference to pioneering works of Professor Ginzburg on phase transitions in ferroelectricity. [ABSTRACT FROM AUTHOR]