Showing papers on "Ferroelectric ceramics published in 2007"

Giant strain in lead-free piezoceramics Bi0.5Na0.5TiO3–BaTiO3–K0.5Na0.5NbO3 system

Abstract: Piezoelectric actuators convert electrical into mechanical energy and are implemented for many large-scale applications such as piezoinjectors and ink jet printers. The performance of these devices is governed by the electric-field-induced strain. Here, the authors describe the development of a class of lead-free (0.94−x)Bi0.5Na0.5TiO3–0.06BaTiO3–xK0.5Na0.5NbO3 ceramics. These can deliver a giant strain (0.45%) under both unipolar and bipolar field loadings, which is even higher than the strain obtained with established ferroelectric Pb(Zr,Ti)O3 ceramics and is comparable to strains obtained in Pb-based antiferroelectrics.

Modified (K0.5Na0.5)NbO3 based lead-free piezoelectrics with broad temperature usage range

Abstract: (K0.5Na0.5)NbO3 (KNN) based lead-free materials exhibit arguably, comparable piezoelectric properties to conventional Pb(Zr,Ti)O3 ceramics owing to an orthorhombic to tetragonal polymorphic phase transition (TO-T) occurring near room temperature. However, this transition correspondingly results in a strong temperature dependence of the dielectric and piezoelectric properties, being limited further by domain instability, during thermal cycling between the two ferroelectric phases. Analogous to BaTiO3 based piezoelectrics, the addition of CaTiO3 in KNN materials was found to shift the TO-T well below room temperature. Piezoelectric and electromechanical values of KNN–LiSbO3–CaTiO3 material were found to be d33∼210pC∕N, d15∼268pC∕N and k33∼61%, k15∼56%, respectively, with greatly improved temperature stability over the temperature range of −50–200°C, demonstrating practical potential for actuator and/or ultrasonic transducer applications.

Phase structures and electrical properties of new lead-free (Na0.5K0.5)NbO3–(Bi0.5Na0.5)TiO3 ceramics

Abstract: Highly dense (1−x)(Na0.5K0.5)NbO3–x(Bi0.5Na0.5)TiO3 (NKN-BST) solid solution piezoelectric ceramics have been fabricated by ordinary sintering. All compositions show pure perovskite structures, showing room-temperature symmetries of orthorhombic at x⩽0.02, of tetragonal at 0.03⩽x⩽0.09, of cubic at 0.09 0.20. A morphotropic phase boundary (MPB) between orthorhombic and tetragonal ferroelectric phases was identified in the composition range of 0.02

Domain wall contributions to the properties of piezoelectric thin films

Abstract: In bulk ferroelectric ceramics, extrinsic contributions associated with motion of domain walls and phase boundaries are a significant component of the measured dielectric and piezoelectric response. In thin films, the small grain sizes, substantial residual stresses, and the high concentration of point and line defects change the relative mobility of these boundaries. One of the consequences of this is that thin films typically act as hard piezoelectrics. This paper reviews the literature in this field, emphasizing the difference between the nonlinearities observed in the dielectric and piezoelectric properties of films. The effect of ac field excitation levels, dc bias fields, temperature, and applied mechanical stress are discussed.

Large bulk polarization and regular domain structure in ceramic BiFeO3

Abstract: Regularly twinned domain structures are observed by scanning piezoforce microscopy on single crystalline grains of BiFeO3 ceramics being grown by a special low temperature sintering process. The domains are considerably larger than those observed in thin films. Their spontaneous polarization comes close to that predicted theoretically and overcomes restrictions hitherto being set to bulk single crystals. The observed ferroelastic twin domain structure resembles that of classic T domains in rhombohedrally distorted NiO, but is additionally superimposed by ferroelectric twin domain patterns.

Ferroelectric to relaxor crossover and dielectric phase diagram in the BaTiO3–BaSnO3 system

Abstract: The (1−x)BaTiO3–xBaSnO3 (0⩽x⩽0.30) perovskite solid solution ceramics were prepared by solid state reaction and studied by dielectric spectroscopy. The complex dielectric permittivity was measured as a function of frequency (0.1Hz–100kHz) in the temperature (T) range of 123–573K. The transition from the high-temperature paraelectric state where the dielectric constant obeys the Curie-Weiss law to the ergodic cluster state is found to occur at the same temperature of 485K in all the compositions of x⩾0.04 and at lower temperatures in those with a smaller x. For 0⩽x⩽xc=0.19, the temperature of the dielectric peak Tm, corresponding to the diffuse transition from the ergodic polar cluster state to the ferroelectric state, decreases with increasing x and does not depend on frequency. The diffuseness of the peak gradually increases. For x>xc, the permittivity exhibits relaxor behavior with the frequency-dependent Tm satisfying the Vogel-Fulcher law. The temperature variation of the permittivity on the high-temp...

Dielectric relaxations and formation mechanism of giant dielectric constant step in CaCu3Ti4O12 ceramics

Abstract: The dielectric relaxation behaviors of CaCu3Ti4O12 ceramics were evaluated together with the mixed-valence structure, and the formation mechanism of a giant dielectric constant step was discussed. The giant dielectric constant step was bounded by two dielectric relaxations in low and high temperature ranges. The low-temperature dielectric relaxation was intrinsic, and it was very similar to the electronic ferroelectricity, while the high temperature relaxorlike dielectric peak was assigned to be the result of defect ordering since it could be suppressed by O2 annealing. Both the low and high temperature dielectric relaxations were the thermal activated relaxation process following the Arrhenius law. Moreover, it was supposed that the giant dielectric constant step resulted from the competing balance between the low and high temperature dielectric relaxations.

Effect of composition on coupled electric, magnetic, and dielectric properties of two phase particulate magnetoelectric composite

Abstract: The particulate composite materials of ferrite-ferroelectric ceramics viz. nickel-cobalt-copper ferrite (i.e., Ni0.94Co0.01Cu0.05Fe2O4) and barium titanate were synthesized by the double sintering ceramic technique. The presence of constituent phases in the composites was confirmed by x-ray diffraction studies. The average grain size was calculated by using a scanning electron micrograph. The electrical properties such as dc resistivity and thermo-emf were measured as a function of temperature and volume fraction of constituent phases. The ac conductivity was calculated from dielectric data in the frequency range from 100Hzto1MHz. It is concluded that the conduction in the present composites is due to small polarons. The relative dielectric constant measured as a function of applied frequency varies with the variation in the dc resistivity and molar fraction of constituent phases. It shows dispersion in the lower frequency range. The hysteresis behavior was studied to understand the magnetic properties su...

A study of the phase diagram of (K,Na,Li)NbO3 determined by dielectric and piezoelectric measurements, and Raman spectroscopy

Abstract: A composition-temperature phase diagram of the system (1−x)(K0.5Na0.5)NbO3–xLiNbO3 is presented for 0⩽x⩽0.1. Using dielectric and piezoelectric resonance measurements, and Raman spectroscopy, ceramic samples containing 2%–10% LiNbO3 were studied over a temperature range of 7–770K showing a complex sequence of phase transitions. Analysis of the different Raman, piezoelectric, and dielectric data shows distinct transitions from cubic to tetragonal to orthorhombic to rhombohedral phase for x=0.02–0.05. The symmetries of the phases were assigned using analogy to phase diagram of (K0.5Na0.5)NbO3 single crystals and ceramics (x=0). At x>0.07 only one transition between ferroelectric phases occurs where tetragonal phase transforms to another phase, possibly of rhombohedral, orthorhombic, or monoclinic symmetry. In the region between x=0.05 and x=0.08, the phase transition sequence is more complex. Below 100K this phase with unidentified symmetry creates a vertical boundary with the rhombohedral phase present nea...

Synthesis and multiferroic properties of Bi0.8A0.2FeO3 (A=Ca,Sr, Pb) ceramics

Abstract: Bi1−xAxFeO3 ceramics (A=Ca,Sr,Pb) were sintered by conventional mixed oxide route. The crystallographic structure of all samples is characterized by the rhombohedral symmetry (space group R3c). The existence of switchable ferroelectric polarization is verified by piezoresponse force microscopy that is proven to be a useful technique in semi-insulating ferroelectrics. Magnetic properties of Ca and Sr-doped ceramics are found to reproduce the antiferromagnetic behavior of undoped BiFeO3 without any enhancement of the magnetization. On the contrary, Pb-doped compound demonstrates appearance of a weak ferromagnetism. It is thus shown that Pb doping of BiFeO3 is a promising way for preparing multiferroic materials.

Raman scattering spectra and ferroelectric properties of Bi1−xNdxFeO3 (x=0–0.2) multiferroic ceramics

Abstract: Single-phase Bi1−xNdxFeO3 (BNFOx) (x=0–0.2) multiferroic ceramics were prepared to study the effects of Nd substitution on their crystal structures, Raman scattering spectra, and ferroelectric properties. Rietveld refinement of x-ray diffraction data showed a gradual change in crystal structure from rhombohedral to pseudotetragonal via triclinic with increasing x. The evolvement of Raman normal modes with increasing x suggested that such structural change is accompanied by the weakening of long-range ferroelectric order. The simultaneous occurrence of abrupt mode evolvement and ferroelectric-paraelectric transition in BNFOx=0.175 and BNFOx=0.2 was explained according to the change of Bi–O covalent bonds as a result of the decline in the stereochemical activity of the Bi lone electron pair at 0.175⩽x⩽0.2.

Compositional Inhomogeneity in Li‐ and Ta‐Modified (K, Na)NbO3 Ceramics

Abstract: Reference LC-ARTICLE-2008-016doi:10.1111/j.1551-2916.2007.01962.xView record in Web of Science Record created on 2008-04-11, modified on 2017-05-10

Property-processing relationship in lead-free (K, Na, Li) NbO3-solid solution system

Abstract: There has been a significant driving force to eliminate the utilization, recycling, and disposal of ferroelectric ceramics with high content of toxic element (Pb). Recently, the ternary system of KNN-LT-LS has proven to be an outstanding lead-free piezoceramic with properties almost comparable to their lead-based counterpart, PZT. This study reports the effect of various processing conditions on the electromechanical properties of (K0.44Na0.52Li0.04)(Nb0.84Ta0.10Sb0.06)O3 system. This includes powder processing, humidity, and exposure to oxygen rich environment during sintering. The Perovskite and Mixed-Oxide methods are used to prepare the stoichiometric powders. It will be shown that both processing methods are notably sensitive to the moisture of as received raw materials and the humidity of environment. Optimum results are obtained when the raw materials undergo a pre-heat treatment followed by formulating the desired composition in an inert atmosphere. The highest electromechanical properties are achieved when the ceramics are completely exposed to oxygen with a high flow rate. Sintered at 1150 °C for 1 h with an oxygen flow rate of 180 cm3/min, the KNN-LT-LS ceramics prepared by Perovskite and Mixed-Oxide routes have d 33 ≥ 300 pC/N, $$\varepsilon ^{T}_{{33}} = 1865$$ , tan δ = 0.02, k 33 = 0.65.

Dielectric tunable properties of low dielectric constant Ba0.5Sr0.5TiO3–Mg2TiO4 microwave composite ceramics

Abstract: Ba0.5Sr0.5TiO3–Mg2TiO4 composite ceramics are fabricated via the conventional solid-state reaction method. The microstructures, dielectric tunability, and microwave properties of composite ceramics are investigated. The dielectric constant is tailored from 335 to 35 by manipulating the addition of Mg2TiO4 from 50% to 80% weight ratio and the tunability is 10.8% measured at 10kHz for the 80% Mg2TiO4 addition. The composite ceramics with high Q value (>200) at L band are useful for potential tunable microwave device applications in the wireless communication system.

Effects of pore shape and porosity on the properties of porous PZT 95/5 ceramics

Abstract: Porous lead zirconate titanate (PZT 95/5) ferroelectric ceramics were prepared by sintering compacts consisting of PZT and pore formers. The piezoelectric, dielectric and ferroelectric properties of porous PZT ceramics were investigated as a function of pore shape and porosity. Piezoelectric coefficient ( d 33 ), dielectric constant ( ɛ 33 ) and remnant polarization ( P r ) decreased with an increase in porosity, and the porous PZT ceramics with spherical pores exhibited better properties than that with irregular pores. Furthermore, the electrical conductivities of PZT ceramics were investigated to explain the phenomena that porous PZT ceramics exhibited lower dielectric loss (tan δ ) than dense PZT ceramics in the temperature range from 250 to 500 °C.

Rapid liquid phase sintered Mn doped BiFeO3 ceramics with enhanced polarization and weak magnetization

Abstract: Single-phase BiFe1−xMnxO3 multiferroic ceramics have been synthesized by rapid liquid phase sintering method to study the influence of Mn substitution on their crystal structure, dielectric, magnetic, and ferroelectric behaviors. From XRD analysis it is seen that Mn substitution does not affect the crystal structure of the BiFe1−xMnxO3 system. An enhancement in magnetization was observed for BiFe1−xMnxO3 ceramics. However, the ferooelectric hysteresis loops were not really saturated, we observed a spontaneous polarization of 10.23μC∕cm2 under the applied field of 42kV∕cm and remanent polarization of 3.99μC∕cm2 for x=0.3 ceramic.

Influence of Electric Field and Mechanical Stresses on the Fracture of Ferroelectrics

Abstract: This chapter reviews experimental results that allow one to interpret the essential features of fracture in ferroelectric ceramics under electric and mechanical load. First, crack growth measurements on unpoled and poled ferroelectric ceramics are reviewed, and numerous experiments that demonstrate the existence and relevance of a domain-switching zone are presented. Thereafter the review concentrates on results of fracture experiments with applied electric fields and addresses the controversial outcomes of such experiments. Theoretical fracture mechanical concepts are then introduced. One part of the discussion focuses on electrical boundary conditions used at the crack surface because they decisively determine the predicted energy release rate. The other part of the discussion, which concerns theoretical concepts, discusses the predicted switching zones around cracks and their influence on the stress intensity factor and energy release rate. Finally, this chapter attempts to mirror the tremendou...

Ferrite-ferroelectric hybrid wave phase shifters

Abstract: A dual, electric and magnetic field tunable microwave phase shifter based on the propagation of hybrid spin-electromagnetic waves in a ferrite-ferroelectric bilayer is discussed. The bilayer consists of a single-crystal yttrium iron garnet film and a ceramic barium strontium titanate slab. The electrical tunability of the differential phase shift Δφ is achieved through the application of a voltage across barium strontium titanate. An insertion loss of 20dB and a continuously variable Δφ as high as 650° in the frequency range of 4.5–8GHz are measured.

Giant dielectric response and relaxor behaviors induced by charge and defect ordering in Sr(Fe1∕2Nb1∕2)O3 ceramics

Abstract: Dielectric spectra of Sr(Fe1∕2Nb1∕2)O3 ceramics were characterized in wide temperature (123–623K) and frequency (100Hz–1MHz) ranges. Two dielectric relaxations with strong frequency dispersion and following the Arrhenius law were detected in low and high temperature ranges, respectively, and between them there was a giant dielectric constant step. The high temperature relaxorlike dielectric peak could be almost completely removed by annealing in O2, and it should be assigned to be a defect ordering induced relaxor behavior, while the low temperature dielectric relaxation was proposed to stem from the electronic ferroelectricity. Moreover, it was speculated that the giant dielectric constant step resulted from the competing balance between the low and high temperature dielectric relaxations.

Ultrawide range dielectric spectroscopy of BaTiO3-based perovskite dielectrics

Abstract: Ultrawide range dielectric spectra from the kilohertz to terahertz range of BaTiO3 (BT), Ba(Zr0.25Ti0.75)O3 (BZT), (Ba0.6Sr0.4)TiO3 (BST), and SrTiO3 ceramics were presented by analyzing dielectric permittivity and IR reflectivity data. It was found that the permittivity of the ST was determined only by the ionic polarization while that of the BT was determined by the ionic polarization as well as the dipole polarization due to the domain contribution. The high permittivity of the BZT ceramics was attributed to the dipole polarization of polar nanoregions in the relaxors. The dipole and ionic polarizations overlapped in the BST.

Dielectric relaxations in Ba(Fe1∕2Ta1∕2)O3 giant dielectric constant ceramics

Abstract: Dielectric relaxations of Ba(Fe1∕2Ta1∕2)O3 ceramics were investigated and discussed over a broad temperature and frequency range. Two dielectric relaxations following Arrhenius law were observed at 153–382 and 440–623K, where there was a giant dielectric constant step between them. The frequency dependent rapid drop of dielectric constant at 153–382K was nearly a Debye relaxation with the intrinsic nature, while the high temperature dielectric relaxation with an extremely high dielectric constant peak and very strong frequency dispersion was attributed to the defect ordering but not a typical relaxor ferroelectric behavior. The O2 annealing almost completely suppressed the dielectric peak and subsequently extended the giant dielectric step, while the low temperature dielectric relaxation and the magnitude of such step were not obviously affected.

Microstructure and piezoelectric properties of lead-free (1 -x)(Na0.5K0.5)NbO3-xCaTiO3 ceramics

Abstract: The crystal structure of (1−x)(Na0.5K0.5)NbO3-xCaTiO3 ceramics began to change from orthorhombic to tetragonal at x≥0.03, then became a morphotropic phase boundary in which both the orthogonal and tetragonal phases coexisted at 0.03

Processing and properties of Yb-doped BiFeO3 ceramics

Abstract: The authors prepared Yb-doped bismuth iron oxide ceramics (Bi1−xYbxFeO3, with 0⩽x⩽0.20) by rapid liquid phase sintering method and investigated the material’s structures and electrical properties. The x-ray diffraction measurements showed that the doping of Yb has induced noticeable lattice distortion in the ceramics, and a largest distortion was observed when the concentration of Yb was 15%. By doping electrical resistivity, ferroelectric and dielectric properties of the ceramics were improved. Among all samples, BiFeO3 doped with 15% Yb was found to have the smallest leakage current density (<10−7A∕cm2) and the largest remnant polarization (8.5μC∕cm2).

Enhanced electric field tunable dielectric properties of BaZrxTi1−xO3 relaxor ferroelectrics

Abstract: The environmental friendly lead-free perovskite BaZrxTi1−xO3 (x=0.35, 0.40, and 0.45) relaxor ceramics are developed for the tunable microwave device applications such as tunable filters, phase shifters, antennas, etc. Electric field dependence of dielectric behavior of the ceramic samples has been studied in the temperature range from 300to15K for the tunable dielectric devices. The results have been analyzed in relation to tunability (%) and K factor of the tunable dielectric materials. Very high tunability (∼93%) as well as extremely high K factor (∼468) has been achieved by manipulating the Zr:Ti concentration in BaZrxTi1−xO3 ceramics.

Texture and Anisotropy of Polycrystalline Piezoelectrics

Abstract: Piezoelectricity is manifested in ferroelectric ceramics by inducing a preferred volume fraction of one ferroelectric domain variant orientation at the expense of degenerate orientations. The piezoelectric effect is therefore largely controlled by the effectiveness of the electrical poling in producing a bias in ferroelectric (180°) and ferroelastic (non-180°) domain orientations. Further enhancement of the piezoelectric effect in bulk ceramics can be accomplished by inducing preferred orientation through grain-orientation processes such as hot forging or tape casting that precede the electrical-poling process. Coupled crystal orientation and domain orientation processing yields ceramics with an even greater piezoelectric response. In this paper, preferred orientations of domains and grains in polycrystalline piezoelectric ceramics generated through both domain- and grain-orientation processing are characterized through pole figures and orientation distribution functions obtained using data from a variety of diffraction techniques. The processing methods used to produce these materials and the methods used to evaluate preferred orientation and texture are described and discussed in the context of prior research. Different sample and crystal symmetries are explored across a range of commercial and laboratory-prepared materials. Some of the variables presented in this work include the effects of in situ thermal depoling and the detailed processing parameters used in tape casting of materials with preferred crystallite orientations. Preferred orientation is also correlated with anisotropic properties, demonstrating a clear influence of both grain and domain orientations on piezoelectricity.

Dielectric and structural studies of Ba2MTi2Nb3O15 (BMTNO15, M=Bi3+,La3+,Nd3+,Sm3+,Gd3+) tetragonal tungsten bronze-structured ceramics

Abstract: The structure and dielectric properties of a new family of tetragonal tungsten bronze (TTB) ceramics with the general formula, Ba2MTi2Nb3O15 where M=Bi3+,La3+,Nd3+,Sm3+,Gd3+, have been investigated. Hereafter the compositions will be referred to by the abbreviation BMTNO15 where M=B(Bi3+), L(La3+), N(Nd3+), S(Sm3+) or G(Gd3+). BLTNO15 [permittivity maximum (Tm)∼−80°C] and BBTNO15 (Tm∼−100°C) exhibited relaxorlike dielectric behavior. In contrast, BNTNO15 (Tm∼165°C), BSTNO15 (Tm∼250°C), and BGTNO15 (Tm∼320°C) were classic ferroelectrics. Tm increased with decreasing radius of the M ion. Room temperature x-ray powder diffraction (XRD) patterns of all the compounds indexed on a prototype P4∕mbm (or P4bm) space group with lattice parameters a≈12.4A and c≈4A. However, electron diffraction revealed that the relaxor phases, BLTNO15 and BBTNO15, exhibited an incommensurate modulation, whereas the classic ferroelectric BNTNO15, BSTNO15, and BGTNO15 featured an orthorhombic superstructure with lattice parameters a≈...

Comment on the use of Calcium as a dopant in X8R BaTiO3-based ceramics

Abstract: BaTi1−xCaxO3−x ceramics, where 0⩽x⩽0.04, prepared by the mixed oxide route at 1500°C display a strong suppression of the Curie temperature and a significant increase in grain conductivity with increasing x. The ramifications of these results on the applicability of using Ca2+ as a dopant to achieve X8R specification in BaTiO3-based formulations are discussed.

Enhancement of dielectric characteristics in donor doped Aurivillius SrBi2Ta2O9 ferroelectric ceramics

Abstract: In this study, investigations have been made on the crystal structure, surface morphology, dielectric and electrical properties of tungsten doped SrBi 2 (W x Ta 1− x ) 2 O 9 (0.0 ≤ x ≤ 0.20) ferroelectric ceramics. Dielectric measurements performed as a function of temperature at 1, 10 and 100 kHz show an increase in Curie temperature ( T c ) over the composition range of x = 0.05–0.20. W 6+ substitution in perovskite-like units results in a sharp dielectric transition at the ferroelectric Curie temperature with the dielectric constant at their respective Curie temperature increasing with tungsten doping. The dielectric loss reduces significantly with tungsten addition. The temperature dependence of ac and dc conductivity vis-a-vis tungsten content shows a decrease in conductivity, which is attributed to the suppression of oxygen vacancies. The activation energy calculated from the Arrhenius plots is found to increase with tungsten content.

Phase transitions and ferroelectric properties in BiScO3-Bi(Zn1∕2Ti1∕2)O3-BaTiO3 solid solutions

Abstract: Ceramics solid solutions within the ternary perovskite system Bi(Zn1∕2Ti1∕2)O3-BiScO3-BaTiO3 were synthesized via solid-state processing techniques. The crystal structure of sintered ceramics was analyzed by x-ray diffraction. A stable perovskite phase was obtained for all compositions with a BaTiO3 content greater than 50 mol %. Furthermore, a change in symmetry from pseudocubic to tetragonal was observed as the mole fraction of BaTiO3 increased. Dielectric measurements show a dielectric anomaly associated with a phase transformation over the temperature range of 30 °C–210 °C for all compositions. Examination of the polarization hysteresis behavior revealed weakly nonlinear hysteresis loops. With these data, ferroelectric phase diagrams were derived showing the transition between the pseudocubic relaxor behavior to the tetragonal normal ferroelectric behavior. This transition was also correlated with changes in the diffuseness parameter.