Showing papers on "Ferroelectric ceramics published in 2012"
TL;DR: In this paper, high aspect ratio fillers are used to increase the dielectric constant of polymer composites more efficiently than spherical fillers according to the rule of mixtures.
Abstract: High aspect ratio fillers are predicted to increase the dielectric constant of polymer composites more efficiently than spherical fillers according to the rule of mixtures. Using high aspect ratio fillers is a promising route for creating high dielectric constant, low loss materials at a low filler volume fraction, for use as capacitor and electric field grading materials. In this work, two high aspect ratio fillers were mixed into a polymer matrix, and the dielectric properties of composites were studied. Barium titanate fibers were synthesized by electrospinning a sol-gel, followed by a heat treatment to obtain a perovskite crystal structure. The heat treatment conditions were found to be crucial for obtaining tetragonal barium titanate fibers with high dielectric constant. Graphene platelets were prepared by a thermal shock method, which was found to result in a larger dielectric constant. A combination of barium titanate and graphene platelets yielded the highest dielectric constant when used in a polydimethyl siloxane matrix. The increase in dielectric loss over the pure matrix was small when the volume fraction was below the percolation threshold of graphene platelets. Electric flux density-electric field (D-E) measurements showed a linear dielectric constant in barium titanate filled composites and higher loss when graphene was added. The ac breakdown strength was reduced compared to the neat polymer and was affected by filler aspect ratio. The mechanisms that lead to the observed phenomena are discussed.
102 citations
TL;DR: In this paper, the detection of specific features related to the ferroelectric-to-relaxor crossover with increasing Sn content is possible by combining techniques, and the results confirm the conclusions from the Raman and dielectric studies.
Abstract: BaSnxTi1−xO3 solid solutions with compositions in the range x = 0–0.20 were studied by combining analysis of the field-induced dielectric and ferroelectric properties with Raman spectroscopic investigations. By combining techniques, the detection of specific features related to the ferroelectric-to-relaxor crossover with increasing Sn content is possible. Detailed tunability analysis of the x = 0.05 composition indicated that multiple components contribute to the dc-field induced permittivity response; these components are active in different temperature and field ranges and could be assigned to a few polarization mechanisms. First order reversal curves (FORC) for the material clearly show a transition from ferroelectric-to-relaxor behavior with increasing x, confirming the conclusions from the Raman and dielectric studies. This was evidenced by the shift of the FORC distribution over coercivities toward zero field values. Raman measurements allow the identification of the separate phases with varying Sn ...
90 citations
Abstract: High quality Bi1−xDyxFeO3 (0 ≤ x ≤ 0.15) ceramics have been fabricated by sintering Dy-doped BiFeO3 (BFO) precursor powders at a low temperature of 780 °C. The magnetic properties of BFO were improved by the introduction of Dy on the Bi-site. More importantly, well saturated ferroelectric hysteresis loops and polarization switching currents have been observed at room temperature. A large remnant polarization (2Pr) value of 62 μC/cm2 is achieved, which is the highest value reported so far for rare-earth-doped BFO ceramics. Moreover, mechanisms for improved multiferroic properties depending on chemical doping-caused structure evolutions have also been discussed.
87 citations
TL;DR: In this article, complex dielectric susceptibility was used to investigate the relaxor properties and the ferroelectric phase transitions in (Na1/2Bi 1/2)1 − xBaxTiO3 (0.08) ceramics.
Abstract: Complex dielectric susceptibility was used to investigate the relaxor properties and the ferroelectric phase transitions in (Na1/2Bi1/2)1 − xBaxTiO3 (0 ≤ x ≤ 0.08) ceramics. XRD was used to characterize the ground states of poled and unpoled samples. Dielectric susceptibility vs. temperature studies allowed to obtain the relaxor properties and to identify the electric field-induced phase transitions in the morphotropic phase boundary (MPB) compositions (0.06 < x < 0.08) and the spontaneous relaxor-ferroelectric phase transitions in the rhombohedral compositions (x < 0.06). The frequency dispersion of the dielectric maximum at Tm was observed for all compositions, although of decreased extension for lower x. The relaxor properties have been analysed with Vogel-Fulcher law. The activation energy and attempt frequency for the MPB compositions are similar to those of classical relaxors like Pb(Mg1/3Nb2/3)O3, while for rhombohedral compositions, they are similar to relaxor ferroelectrics with spontaneous relaxor-ferroelectric phase transitions, like Pb(Sc1/2Nb1/2)O3. A relationship has been found between the relaxor dispersion degree and the hysteresis of the ferroelectric transition.
77 citations
TL;DR: In this article, textured lead-free piezoelectric ceramics were prepared by a templated-grain growth method using BaTiO3 as template, and the degree of orientation and the microstructure of the textured-ceramics with different amount of template were investigated.
Abstract: 〈001〉 textured (Ba0.85Ca0.15)(Ti0.9Zr0.1)O3 (BCTZ) lead-free piezoelectric ceramics were prepared by templated-grain growth method using BaTiO3 as template. The degree of orientation and the microstructure of the ceramics with different amount of template were investigated. The electrical properties of the textured-ceramics in the optimized condition were dramatically enhanced compared with randomly-oriented BCTZ ceramics. The textured BCTZ ceramics showed high piezoelectric constants d33 = 470 pC/N and d31 = −170 pC/N, and high electromechanical coupling factors kp = 44% and k31 = 22%. In addition, the Curie point of the textured ceramics revealed an increase with the template content.
73 citations
TL;DR: In this article, the piezoelectric fatigue behavior of Pb-free ceramics based on solid solutions of Bi(Zn0.5Ti 0.5)O3 was characterized at 50 kV/cm after 106 bipolar cycles.
Abstract: The piezoelectric fatigue behavior of Pb-free ceramics based on solid solutions of Bi(Zn0.5Ti0.5)O3-(Bi0.5K0.5)TiO3-(Bi0.5Na0.5)TiO3 was characterized at 50 kV/cm after 106 bipolar cycles. Ferroelectric compositions containing 2.5% Bi(Zn0.5Ti0.5)O3 exhibited only minor losses in maximum strain (∼10%). In compositions with 5% Bi(Zn0.5Ti0.5)O3 that exhibit large electric field-induced strains, the electromechanical strain actually increased 4%, exhibiting essentially fatigue free behavior. This finding demonstrates that these materials have excellent potential for demanding high cycle applications such as microelectromechanical systems actuators.
68 citations
TL;DR: In this article, the occurrence of phase-change functional responses in the BiFeO3-PbTiO3 perovskite solid solution was investigated, analogous to those anticipated by a recent first-principles study of BiFe3-BiCoO3.
Abstract: We have investigated the occurrence of phase-change functional responses in the BiFeO3-PbTiO3 perovskite solid solution, analogous to those anticipated by a recent first-principles study of BiFeO3-BiCoO3. Like the former system, BiFeO3-PbTiO3 shows a morphotropic phase boundary (MPB) between multiferroic polymorphs of rhombohedral and tetragonal symmetries. MPB BiFeO3-PbTiO3 is a high temperature ferroelectric with the phase transition around 900 K, and a room temperature square-shape hysteresis loop with remnant polarization as high as 62 μC cm−2. Strain under the electric field was studied, and a phase-change response was found. Analogous magnetoelectric effects are expected from the multiferroic nature of this MPB.
64 citations
TL;DR: In this paper, the basic principles governing ferroelectricity and various materials which exhibit these properties are described. And some important applications of the microstructure examination as well as powerful techniques are briefly discussed.
Abstract: New advances in the sol–gel processing of ferroelectric ceramic powders and thin films and recently, scientific and technological interests in ferroelectric ceramics have been focused particularly on thin films. This is mainly due to their great potential applications in integrated electronics as passive components and as non-volatile ferroelectric memories, optoelectronic devices, etc. Special attention has been paid to the effects of the microstructure and composition on the piezoelectric properties of ferroelectric ceramic powders and thin films, and various characterization techniques are reported. This paper introduces the basic principles governing ferroelectricity and lists the various materials which exhibit these properties. The processing of ferroelectric ceramics and thin films in general and sol–gel processing in particular, with some examples are described. Finally, important applications of ferroelectric films and microstructure examination as well as powerful techniques are briefly discussed.
62 citations
TL;DR: In this paper, a systematic impedance spectroscopy study on Y0.5Ca 0.5MnO3 and La 1.5NiO4 ceramics reveals that the high permittivity and its temperature-and frequency-dependence over the ranges of 10-300 K and 10 Hz-1 MHz, respectively, are mainly associated with an extrinsic non-ohmic sample-electrode contact effect, rather than an intrinsic response.
Abstract: Recently, many charge-ordered compounds containing mixed-valence transition metal ions have been considered as possible multiferroics. Theoretically it has been proposed that charge (orbital) ordering could generate “electronic ferroelectricity” in some of these compounds. Experimentally, temperature- and frequency-dependent high permittivity is commonly presented as evidence of ferroelectricity in these materials. Here, systematic impedance spectroscopy studies on Y0.5Ca0.5MnO3 and La1.5Sr0.5NiO4 ceramics reveal, however, the high permittivity and its temperature- and frequency-dependence over the ranges of 10–300 K and 10 Hz–1 MHz, respectively, are mainly associated with an extrinsic non-ohmic sample-electrode contact effect, rather than an intrinsic response. A general strategy to distinguish the intrinsic dielectric properties of these charge-ordered compounds from extrinsic contributions using impedance spectroscopy is also demonstrated.
61 citations
TL;DR: In this paper, the lead-free Ba0.5 Na0.3-xBaTiO3 (BNT-xBT) ceramics prepared by citrate method are investigated at temperatures of 30-250°C.
Abstract: Electro-caloric (EC) properties of lead-free Ba0.5Na0.5TiO3-xBaTiO3 (BNT-xBT) ceramics prepared by citrate method are investigated at temperatures of 30–250°C. Based on thermodynamics calculations, BNT-xBT (x = 0, 0.05, 0.06, 0.1, 0.25, 0.3) are found to show EC effects different with other lead-based or lead-free ferroelectric ceramics, i.e., they absorb heats (refrigeration effect) during the processes of field application while other ferroelectric ceramics show refrigeration effect during the processes of field removal. The EC temperature change of BNT-xBT can be as large as 2.1°C under an electric field of 60 kV/cm, which is larger than most of the lead-free ferroelectric bulk ceramics. When x is close to the morphotropic phase boundary (x ~ 0.06–0.1), the EC temperature change of BNT-xBT shows a maximum near the ferroelectric to anti-ferroelectric transition temperature, which is characterized by dynamic mechanical analysis. This study suggests that these lead-free ferroelectric materials are promising in the practical application as EC coolers.
56 citations
TL;DR: In this article, phase pure ferroelectric ceramics in the (1-x)Bi0.5K 0.5TiO3-xBiFeO3 system have been examined in a wide range of composition (0.1 ≤ x ≤ 0.9).
Abstract: Highly dense and phase-pure ferroelectric ceramics in the (1-x)Bi0.5K0.5TiO3–xBiFeO3 system have been prepared and examined in a wide range of composition (0.1 ≤ x ≤ 0.9). The dielectric and electromechanical properties have been shown to reach a maximum value at x ≈ 0.25 demonstrating a high strain performance (250–370 pm/V in the temperature range 25–175 °C). Stability of the strain response with respect to temperature, as well as frequency and amplitude of the driving electric field is reported and discussed.
TL;DR: In this paper, a single phase using x-ray diffraction of the Bi(Zn0.5TiO3)-O3 ternary system for <20 mol.
Abstract: Solid solutions ceramics of the Bi(Zn0.5Ti0.5)O3–(Bi0.5K0.5)TiO3–(Bi0.5Na0.5)TiO3 ternary system for <20 mol. % BZT were created and confirmed to be single phase using x-ray diffraction. The dielectric dispersion showed decreasing Tmax of the dielectric spectrum with a broadening of the transition with increasing BZT content. At 2.5BZT–40BKT–57.5BNT, a secondary transition commonly observed for morphotropic phase boundary (MPB) BNT–BKT was observed. The ferroelectric behavior of the system was characterized by a transition where the polarization hysteresis showed a severe pinching effect on remanent polarization (20.8 μC/cm2 at 2.5% BZT) as BZT contents was increased (Pr = 2.3 μC/cm2 at 20% BZT). Similarly, as the temperature increased to 175 °C, the remanent polarization of the 2.5% BZT composition significantly reduced to 2.1 μC/cm2. The onset of this transition corresponds to the lower temperature frequency dispersion observed in the dielectric spectrum. The strain hysteresis experienced analogous tran...
TL;DR: In this article, the effect of grain size on the electric field dependence of the dielectric constant in ferroelectric nanoceramics was studied using a detailed model and the predicted behavior compared to experimental data obtained for BaTiO${}_{3}$.
Abstract: The grain size (GS) effect on the electric field dependence of the dielectric constant in ferroelectric nanoceramics was studied using a detailed model and the predicted behavior compared to experimental data obtained for BaTiO${}_{3}$. In the finest ceramics the permittivity reduces below 1000 and a tendency to linearization of the permittivity vs field dependence is observed. The composite structure of ferroelectric ceramics corresponding to ferroelectric grain cores separated by nonferroelectric grain boundaries determines a progressive increase of the electrical inhomogeneity of the system with decreasing GS. The local electric field was computed at various applied voltages for different GSs by a finite element approach, and then the effective permittivity-field response ${\ensuremath{\varepsilon}}_{\mathrm{eff}}$($E$) was determined by taking into consideration the local field distribution. A remarkable agreement between the model and experimental data was obtained for BaTiO${}_{3}$ ceramics. The local field distribution explains with considerable accuracy the reduction of permittivity and tunability observed with decreasing GS as well as the tendency towards linearization of ${\ensuremath{\varepsilon}}_{\mathrm{eff}}$($E$) in nanoceramics.
TL;DR: In this paper, a monoclinic ferroelectric phase with space group Pm has been discovered in lead-free (K0.5Na 0.5)-5% LiNbO3 solid solution ceramics by high energy synchrotron x-ray powder diffraction measurements.
Abstract: A monoclinic ferroelectric phase with space group Pm has been discovered in lead-free (K0.5Na0.5)NbO3-5%LiNbO3 solid solution ceramics by high energy synchrotron x-ray powder diffraction measurements. At ambient temperature, the lattice parameters of this monoclinic structure were (am, bm, cm; β) = (4.015 A, 3.944 A, 3.987 A; 90.34°). This monoclinic phase transformed to a tetragonal (P4mm) one on heating between 340 K and 360 K. The results demonstrate the presence of structurally bridging low symmetry monoclinic phase in (K0.5Na0.5)NbO3-x%LiNbO3 solid solution system: indicating a means to achieve high piezoelectricity in Pb-free systems via domain engineering.
TL;DR: In this article, the ferroelectric properties and strain behaviors of 0-3-type-ceramic composites were investigated, and it was found from the strain curve that two contributions, phase stabilization and phase transition activation, were involved in the strain behavior of the ceramic composites.
Abstract: The ferroelectric properties and strain behaviors of 0-3-type-ceramic composites were investigated. (100-x)Bi0.5(Na0.75K0.25)TiO3-xBiAlO3 (x = 5, 6, and 7: abbreviated as 95BNKT-5BA, 94BNKT-6BA, and 93BNKT-7BA, respectively, and the three compositions are altogether designated as BNKT-BA) were chosen as a matrix materials, and ferroelectric Bi0.5Na0.5TiO3 (f-BNT), Bi0.5(Na0.8K0.2)0.5TiO3 (f-BNKT), and 98.5Bi0.5(Na0.8K0.2)0.5TiO3-1.5BiAlO3 (f-BNKTBA) grains as inclusions. Large f-BNT, f-BNKT, and f-BNKTBA grains strongly affect the ferroelectric properties and strain behaviors of the BNKT-BA matrix in the composite. In 95BNKT-5BA with f-BNT and f-BNKT, negative strain was observed, indicating that the ferroelectric phase is formed and stabilized. 93BNKT-7BA with f-BNT, f-BNKT and f-BNKTBA showed an increase in positive strain, which is associated with low field-induced phase transition. It was found from the strain curve that two contributions, ferroelectric phase stabilization and phase transition activation, were involved in the strain behaviors of the ceramic composites.
TL;DR: Dielectric studies of PFN single crystals show that, in contrast to the commonly adopted view, the ferroelectric phase transition in PFN is non-diffused and the relaxor-like behavior usually observed in ceramic samples has an extrinsic nature.
Abstract: In the present study, we diluted either A- or B- sublattice of perovskite multiferroic PbFe0.5Nb0.5O3 (PFN) and studied the changes of the magnetic and ferroelectric phase transition temperatures and dielectric properties caused by such dilution. Dielectric studies of PFN single crystals show that, in contrast to the commonly adopted view, the ferroelectric phase transition in PFN is non-diffused and the relaxor-like behavior usually observed in ceramic samples has an extrinsic nature. A-site substitutions (Ba, Ca) lead to the smearing of the permittivity-temperature maximum, lowering its maximum temperature, Tm and inducing relaxor behavior. B-site diluting of PFN by Ti increases Tm and only slightly affects the permittivity maximum diffuseness. Both A-site and B-site substitutions in PFN lead to lowering of its Neel temperature, TN. However, above a certain compositional threshold, fast lowering of TN stops and a new magnetic state with comparatively high (~50K) transition temperature becomes stable in a rather wide compositional range.
TL;DR: In this article, BTF7C3O and Bi5Ti3Fe0.7Mn0.3O15 (BTF7M3O) thin films on α-quartz substrates were fabricated by a chemical solution deposition method and the room temperature ferroelectric and magnetic properties of this candidate multiferroic were compared with those of thin films of Mn3+ substituted, Bi5 Ti3Fe 0.7Co0.
Abstract: Aurivillius phase Bi5Ti3Fe0.7Co0.3O15 (BTF7C3O) thin films on α-quartz substrates were fabricated by a chemical solution deposition method and the room temperature ferroelectric and magnetic properties of this candidate multiferroic were compared with those of thin films of Mn3+ substituted, Bi5Ti3Fe0.7Mn0.3O15 (BTF7M3O). Vertical and lateral piezoresponse force microscopy (PFM) measurements of the films conclusively demonstrate that BTF7C3O and BTF7M3O thin films are piezoelectric and ferroelectric at room temperature, with the major polarization vector in the lateral plane of the films. No net magnetization was observed for the in-plane superconducting quantum interference device (SQUID) magnetometry measurements of BTF7M3O thin films. In contrast, SQUID measurements of the BTF7C3O films clearly demonstrated ferromagnetic behavior, with a remanent magnetization, Br, of 6.37 emu/cm3 (or 804 memu/g), remanent moment = 4.99 × 10−5 emu. The BTF7C3O films were scrutinized by x-ray diffraction, high resolutio...
TL;DR: In this article, a method to control the nonlinear dielectric properties in porous anisotropic ceramics is proposed, where the local field distributions in an isotropic porous ceramic structures were determined and the field-induced permittivity was estimated in parallel and perpendicular configurations (with respect to the pore orientation vs. the applied field direction).
Abstract: A method to control the nonlinear dielectric properties in porous anisotropic ceramics is proposed. The local field distributions in anisotropic porous ceramic structures were determined and the field-induced permittivity was estimated in parallel and perpendicular configurations (with respect to the pore orientation vs. the applied field direction). The predicted tunability behavior agrees well with the measured values obtained for Pb(Zr0.52Ti0.48)Nb0.024O3 ceramics with different anisotropic porosity levels. The paper demonstrates the concept of engineered local fields in porous microstructures for tailoring the permittivity and tunability values and the possibility to increase tunability with reducing permittivity for small porosity levels.
TL;DR: In this article, a simplified account for electric displacement saturation on the hysteretic behavior of initially unpoled ferroelectric ceramics as well as on the initiation and propagation of cracks within the linear regime of piezoelectricity is presented.
Abstract: This paper presents a computational investigation of a proposed simplified account for electric displacement saturation on the hysteretic behavior of initially unpoled ferroelectric ceramics as well as on the initiation and propagation of cracks in poled ferroelectric ceramics within the linear regime of piezoelectricity. For the latter case, experimental observations suggest an odd dependency of the onset of crack initiation in these brittle materials on the orientation of the applied electric field with respect to their poling direction which contradicts theoretical results which propose an even dependency of the energy release rate on the applied electric field within the framework of anisotropic linear piezoelectricity. Electric non-linearities arising at regions of inhomogeneities such as inclusions or at the crack tip are proposed in the literature to avoid this discrepancy. Electric displacement saturation is one such non-linear effect which is investigated in this work. A simplified account of this effect is proposed based on an exponential saturation model of the identified material parameters which can be related to this non-linearity. Its advantage over the superposition of a complex function onto the singular solution of a crack within the framework of linear piezoelectricity lies in the straightforward extension of the proposed approach to problems where no analytical solutions exist. This is outlined based on its incorporation into a rate-dependent ferroelectric model accounting for polarization switching as well as based on its incorporation into a finite element framework capable of simulating the initiation and propagation of cracks in piezoelectric ceramics through strong discontinuities in the displacement field and the electric potential. It is shown that besides the determination of the crack initiation onset also the crack propagation direction is influenced by the appearance of saturation zones arising at the crack tip normal to the polarization direction. The numerically obtained crack paths are found to be close to the experimentally reported results.
TL;DR: In this article, the polarization reversal and dynamic hysteresis of ferroelectrics with double hystresis-like loops were investigated by using CuO-doped (Na 0.5K0.5)NbO3 ceramics.
Abstract: The polarization reversal and dynamic hysteresis of ferroelectrics specially with double hysteresis-like loops were investigated by using CuO-doped (Na0.5K0.5)NbO3 ceramics. The variation of the hysteresis area and current density clearly suggests three stages of the polarization reversal. It was found that the hysteresis behavior of the dynamics can be scaled as power law relationships apart from the second stage, where different numbers of domains can be rapidly activated. The main polarization mechanism was ascribed to the reversible domain wall motion (field amplitude Eo 3.5 kV/mm) for the third stage.
TL;DR: In this article, Ba5LaTi3Nb7O30 tungsten-bronze ferroelectric ceramics were synthesized and characterized, and a broad permittivity peak with strong frequency dispersion was observed around 250 K where the peak points well fitted the Vogel-Fulcher relationship.
Abstract: Ba5LaTi3Nb7O30 tungsten-bronze ferroelectric ceramics were synthesized and characterized. The tetragonal tungsten bronze structure in space group P4/mbm was confirmed, and a broad permittivity peak with strong frequency dispersion was observed around 250 K where the peak points well fitted the Vogel-Fulcher relationship [H. Vogel, Phys. Zeit. 22, 645 (1921); G. S. Fulcher, J. Am. Ceram. Soc. 8, 339 (1925)]. The temperature dependence of the ferroelectric hysteresis indicated the paraelectric to ferroelectric phase transition in the temperature range between 153 and 273 K. The high temperature permittivity curve deviated from the Curie-Weiss law in quite a narrow temperature region above Tmax, which reflected the weak correlations between the polar nanoregions. The Curie-Weiss constant (C) was 1.218 × 105 K, which was consistent with that for the displacive type ferroelectric. No DSC peak was detected over the temperature region investigated here. Moreover, the Curie-Weiss constant below Tmax (C′) was just...
TL;DR: In this paper, the frequency and stress dependence of the direct piezoelectric d33 coefficient in BiFeO3 ceramics was investigated using transmission electron microscopy.
Abstract: We report on the frequency and stress dependence of the direct piezoelectric d33 coefficient in BiFeO3 ceramics. The measurements reveal considerable piezoelectric nonlinearity, i.e., dependence of d33 on the amplitude of the dynamic stress. The nonlinear response suggests a large irreversible contribution of non-180 domain walls to the piezoelectric response of the ferrite, which, at present measurement conditions, reached a maximum of 38% of the total measured d33. In agreement with this interpretation, both types of non-180 domain walls, characteristic for the rhombohedral BiFeO3, i.e., 71 and 109, were identified in the poled ceramics using transmission electron microscopy. In support to the link between nonlinearity and non-180 domain-wall contribution, we found a correlation between nonlinearity and processes leading to depinning of domain walls from defects, such as quenching from above the Curie temperature and high-temperature sintering. In addition, the nonlinear piezoelectric response of BiFeO3 showed a frequency dependence that is qualitatively different from that measured in other nonlinear ferroelectric ceramics, such as “soft” (donor-doped) Pb(Zr,Ti)O3 (PZT), i.e., in the case of the BiFeO3 large nonlinearities were observed only at low field frequencies (<0.1Hz); possible origins of this dispersion are discussed. Finally, we show that, once released from pinning centers, the domain walls can contribute extensively to the electromechanical response of BiFeO3; in fact, the extrinsic domain-wall contribution is relatively as large as in Pb-based ferroelectric ceramics with morphotropic phase boundary (MPB) composition, such as PZT. This finding might be important in the search of new lead-free MPB compositions based on BiFeO3 as it suggests that such compositions might also exhibit large extrinsic domain-wall contribution to the piezoelectric response.
TL;DR: Er3+ doped SrBi4Ti4O15 (SBT) bismuth layered-structure ferroelectric ceramics were synthesized by the traditional solid-state method, and their upconversion photoluminescent (UC) properties were investigated as a function of Er3+ concentration and incident pump power as discussed by the authors.
Abstract: Er3+ doped SrBi4Ti4O15 (SBT) bismuth layered-structure ferroelectric ceramics were synthesized by the traditional solid-state method, and their upconversion photoluminescent (UC) properties were investigated as a function of Er3+ concentration and incident pump power. Green (555 nm) and red (670 nm) emission bands were obtained under 980 nm excitation at room temperature, which corresponded to the radiative transitions from 4S3/2, and 4F9/2 to 4I15/2, respectively. The emission color of the samples could be changed with moderating the doping concentrations. The dependence of UC intensity on pumping power indicated a two-photon emission process. Studies on dielectric properties indicated that the introduction of Er increased the ferroelectric-paraelectric phase transition temperature (Tc) of SBT, thus making this ceramic suitable for piezoelectric sensor applications at higher temperatures. Piezoelectric measurement showed that the doped SBT had a relative higher piezoelectric constant d33 compared with th...
TL;DR: In this paper, the effects of Ca-substitution on the crystal structure and dielectric properties were investigated for Ba5SmTi3Nb7O30 tungsten bronze ceramics.
Abstract: Effects of Ca-substitution on the crystal structure and dielectric properties were investigated for Ba5SmTi3Nb7O30 tungsten bronze ceramics. The tetragonal tungsten bronze structure in space group P4bm was determined in Ba4CaSmTi3Nb7O30 ceramics, which was the same for Ba5SmTi3Nb7O30. The c-axis off center displacement in both B1 and B2-sites for Ba5SmTi3Nb7O30 was slightly larger than that in BaCaSmTi3Nb7O30, while the distortion of Ti/Nb(2)O6 octahedra in Ba4CaSmTi3Nb7O30 was obviously suppressed compared with that in Ba5SmTi3Nb7O30. Though there were also two dielectric anomalies observed in Ba4CaSmTi3Nb7O30, the relaxor ferroelectric nature was changed to the normal ferroelectric one, and both the endothermal peak in differential scanning calorimetry curve and the significant thermal hysteresis of the phase transition confirmed the first order ferroelectric transition. These results indicated that the ferroelectric nature of Ba4CaSmTi3Nb7O30 was more close to that in Ba4Sm2Ti4Nb6O30, and it could be c...
TL;DR: In this paper, the frequency dependence of large signal properties of (1−x)(0.81Bi1/2Na 1/2TiO3-0.19Bi1/(2K1/ 2TiOO3)-xBi(Zn1)/2Ti1/3)O3 with x = 0.02, 0.03 and 0.04 on the measurement frequency was investigated for a wide range of frequencies from 0.1 Hz to 100
Abstract: The dependence of large signal properties of (1−x)(0.81Bi1/2Na1/2TiO3-0.19Bi1/2K1/2TiO3)-xBi(Zn1/2Ti1/2)O3 with x = 0.02, 0.03, and 0.04 on the measurement frequency was investigated for a wide range of frequencies from 0.1 Hz to 100 Hz. A significant frequency dispersion in the characteristic parameters representatively maximum and coercive values was denoted. On extension with the temperature dependent dielectric permittivity measurement, it was shown that the observed frequency dependence is primarily correlated with the dynamics of field-induced phase transition from a relaxor state to a long-range ferroelectric state. Increasing the substitutional disorder introduced by Bi(Zn1/2Ti1/2)O3 addition was demonstrated to pronounce the frequency dependence. It was proposed that the change be due to the increase in random fields and consequent dominance of ergodicity, based on the frequency-dependent hysteresis measurements at an elevated temperature above so-called induced-ferroelectric-to-relaxor transition temperature.
TL;DR: In this article, the Raman spectrum of NKN fibers was analyzed using high-resolution electron microscopy and x-ray diffraction, which revealed preferential cube-on-cube growth of fibers in [1] direction.
Abstract: Dense homogeneous textile composed from continuous bead-free sodium potassium niobate (NKN) nanofibers 100 μm long and 50-200 nm in diameter was sintered by sol-gel calcination assisted electrospinning. High resolution electron microscopy and x-ray diffraction revealed preferential cube-on-cube growth of fibers in [001] direction. Raman spectrum of NKN fibers contains all the features characteristic to electrically poled orthorhombic phase. In contrast to polycrystalline ceramics, it shows relative enhancement of the Raman cross section of isotropic A1g(ν1) mode compared with polar axis defined F2g(ν5) and Eg(ν2) vibrations. We interpret this as an evidence for superparaelectric state of NKN nanofibers. Spontaneous polarization inside highly crystalline nanofiber exists at room temperature though big distance between fibers prevents the settling of a net macroscopic polarization.
TL;DR: In this article, the Vogel-Fulcher analysis is compared to other relaxors, and a frequency-dependent dielectric relaxation was observed, consistent with relaxor behaviour. But the authors did not consider the effect of temperature on the dielectrics.
Abstract: Dielectric properties of (1 − x)K0.5Bi0.5TiO3 − xBiScO3 ceramics have been studied for compositions x ≤ 0.5. Single-phase solid solutions occurred for compositions x < 0.25. A frequency-dependent dielectric relaxation was observed, consistent with relaxor behaviour. This gave rise to a relatively stable dielectric permittivity at high temperatures, for example, ɛr = 2880% ± 3%, between temperatures of 500 and 700 K (1 kHz) for composition x = 0.15. This consistency in relative permittivity occurs at higher temperatures than for other lead-free dielectrics. Parameters from Vogel-Fulcher analysis are compared to other relaxors.
TL;DR: The relationship between photovoltaic responses and light intensity can be described by exponential equations, EOC, JSC, ES, and JS are open-circuit photiovoltage (V/cm), shortcircuit photocurrent density (A/cm2), saturated photivoltage, and saturated photocurrent densities, respectively.
Abstract: Open-circuit photovoltage and short-circuit photocurrent were investigated in BiFeO3 (BFO) ceramics as functions of laser wavelength (λ = 373 and 532 nm), illumination intensity, and sample thickness. BFO ceramics exhibit significant photovoltaic responses under near-ultraviolet illumination of λ = 373 nm. The photovoltaic responses strongly depend on wavelength, light intensity, and sample thickness. The relation between photovoltaic responses and light intensity can be described by exponential equations, EOC = ES[1 – exp(–I/α)] and JSC = JS[1 – exp(−I/β)]. EOC, JSC, ES, and JS are open-circuit photovoltage (V/cm), short-circuit photocurrent density (A/cm2), saturated photovoltage (V/cm), and saturated photocurrent density, respectively. This work suggests that BFO ceramic exhibits stronger photovoltaic responses than the ferroelectric WO3-doped Pb1-xLax(ZryTiz)1-x/4O3 ceramics and Pb(Mg1/3Nb2/3)1-xTixO3 crystals.
TL;DR: In this article, the authors showed that the difference in dielectric and ferroelectric properties among the ceramics with various Na amount was associated with the generation of Na and/or oxygen vacancies.
TL;DR: In this paper, the fabrication of highly piezoelectric biocompatible soft fibers containing barium titanate ferroelectric ceramic particles dispersed in electrospun poly lactic acid (PLA) was reported.
Abstract: We report the fabrication of highly piezoelectric biocompatible soft fibers containing barium titanate ferroelectric ceramic particles dispersed in electrospun poly lactic acid (PLA). These fibers form mats that have two orders of magnitude larger piezoelectric constant per weight than single crystal barium titanate films. We propose that the observed apparent piezoelectricity results from the electrospinning induced polar alignment of the ferroelectric particles that pole the fibers similar to ferroelectret polymer foams that are poled by corona discharge. Due to the biocompatibility of PLA that encases the ferroelectric particles, these mats can be used in biological applications such as bio-sensors, artificial muscles, and energy harvesting devices.