Showing papers on "Ferroelectric ceramics published in 2011"
TL;DR: In this paper, the temperature-dependent dielectric permittivity of BNT-6BT was studied to disentangle the existing unclear issues over the crystallographic aspects and phase stability of the system.
Abstract: Temperature-dependent dielectric permittivity of 0.94(Bi1/2Na1/2)TiO3-0.06BaTiO3 (BNT-6BT) lead-free piezoceramics was studied to disentangle the existing unclear issues over the crystallographic aspects and phase stability of the system. Application of existing phenomenological relaxor models enabled the relaxor contribution to the entire dielectric permittivity spectra to be deconvoluted. The deconvoluted data in comparison with the temperature-dependent dielectric permittivity of a classical perovskite relaxor, La-modified lead zirconate titanate, clearly suggest that BNT-6BT belongs to the same relaxor category, which was also confirmed by a comparative study on the temperature- dependent polarization hysteresis loops of both materials. Based on these results, we propose that the low-temperature dielectric anomaly does not involve any phase transition such as ferroelectric- to-antiferroelectric. Supported by transmission electron microscopy and X-ray diffraction experiments at ambient temperature, we propose that the commonly observed two dielectric anomalies are attributed to thermal evolution of ferroelectric polar nanoregions of R3c and P4bm symmetry, which coexist nearly throughout the entire temperature range and reversibly transform into each other with temperature.
716 citations
TL;DR: The correlation between structure and electrical properties of lead-free polycrystalline piezoceramics was investigated systematically by in situ synchrotron diffraction technique, combined with electrical property characterization as discussed by the authors.
Abstract: The correlation between structure and electrical properties of lead-free (1−x)(Bi1/2Na1/2)TiO3–xBaTiO3 (BNT-100xBT) polycrystalline piezoceramics was investigated systematically by in situ synchrotron diffraction technique, combined with electrical property characterization It was found that the morphotropic phase boundary (MPB) between a rhombohedral and a tetragonal phase evolved into a morphotropic phase region with electric field In the unpoled material, the MPB was positioned at the transition from space group R3m to P4mm (BNT-11BT) with optimized permittivity throughout a broad single-phase R3m composition regime Upon poling, a range of compositions from BNT-6BT to BNT-11BT became two-phase mixture, and maximum piezoelectric coefficient was observed in BNT-7BT It was shown that optimized electrical properties are related primarily to the capacity for domain texturing and not to phase coexistence
384 citations
TL;DR: In this paper, high-resolution powder x-ray diffraction patterns reveal peak splitting in the room temperature phase that evidence the true structure as monoclinic with space group Cc.
Abstract: Bismuth-based ferroelectric ceramics are currently under intense investigation for their potential as Pb-free alternatives to lead zirconate titanate-based piezoelectrics. Na0.5Bi0.5TiO3 (NBT), one of the widely studied compositions, has been assumed thus far to exhibit the rhombohedral space group R3c at room temperature. High-resolution powder x-ray diffraction patterns, however, reveal peak splitting in the room temperature phase that evidence the true structure as monoclinic with space group Cc. This peak splitting and Cc space group is only revealed in sintered powders; calcined powders are equally fit to an R3c model because microstructural contributions to peak broadening obscure the peak splitting.
268 citations
TL;DR: In this paper, the energy density of 0.89BNT and 0.5NbO3 (0.89Bi0.5Na0.6BT-0.05KNN) lead-free ceramics was investigated.
Abstract: Energy-storage properties of 0.89Bi0.5Na0.5TiO3–0.06BaTiO3–0.05K0.5Na0.5NbO3 (0.89BNT–0.06BT–0.05KNN) lead-free ceramics were first investigated. Measurements of dielectric properties together with switching current curves indicate a rather diffuse ferroelectric (FE) to anti-ferroelectric (AFE) phase transition when heating from 20°C to 90°C. The energy density (W), which was calculated from P–E hysteresis loops, increases linearly with the external electric field when E exceeds AFE-FE transition field. W is independent of temperature and frequency, and maintains around 0.59 J/cm3 under 5.6 kV/mm in the stable AFE phase region. These properties indicate that 0.89BNT–0.06BT–0.05KNN ceramics might be a promising lead-free AFE material for energy-storage capacitor application.
262 citations
TL;DR: In this paper, Liu et al. designed a Pb-free pseudo-binary system, Ba(Sn012Ti088)O3-x(Ba07Ca03)-O3 (BTS-xBCT), characterized by a phase boundary starting from a tricritical triple point of a paraelectric cubic phase, ferroelectric rhombohedral, and tetragonal phases.
Abstract: We designed a Pb-free pseudo-binary system, Ba(Sn012Ti088)O3-x(Ba07Ca03)O3 (BTS-xBCT), characterized by a phase boundary starting from a tricritical triple point of a paraelectric cubic phase, ferroelectric rhombohedral, and tetragonal phases The optimal composition BTS-30BCT exhibits a high piezoelectric coefficient d33 � 530 pC/N at room temperature In view of the recent report of high piezoelectricity in another Pb-free system BZT-BCT (Liu and Ren, Phys Rev Lett 103, 257602 (2009)), which possesses a similar tricritical triple point in the phase diagram, it seems that forming a suitable phase boundary starting from a tricritical triple point could be an effective way to develop high-performance Pb-free piezoelectrics V C 2011 American Institute of Physics
249 citations
TL;DR: In this paper, the electrocaloric effect (ECE) of lead-free ferroelectric ceramics was characterized via P-T curves under different electric fields, which indicated that the NBT has an abnormal ECE with a negative temperature change (ΔT140 −−0.33 −kV/cm) opposite to that of the normal ferroelectrics.
240 citations
TL;DR: In this article, the authors measured a full set of elastic, piezoelectric, and dielectric properties for the MPB composition, Ba(Zr0.2Ti0.8)O3-50(Ba0.7Ca0.3)TiO3 (BZT-50BCT), by using a resonance method.
Abstract: There is an urgent demand for high performance Pb-free piezoelectrics to substitute for the current workhorse, the lead zirconate titanate (PZT) family. Recently, a triple point (also tricritical point) type morphotropic phase boundary (MPB) in Pb-free Ba(Zr0.2Ti0.8)O3-x(Ba0.7Ca0.3)TiO3 system has been reported that shows equally as excellent piezoelectricity as soft PZT at room temperature (Liu and Ren6). In the present study, we measured a full set of elastic, piezoelectric, and dielectric properties for the MPB composition, Ba(Zr0.2Ti0.8)O3-50(Ba0.7Ca0.3)TiO3 (BZT-50BCT), by using a resonance method. The resonant method gives piezoelectric properties d33 = 546 pC/N, g33 = 15.3 × 10−3 Vm/N, electromechanical coupling factor k33 = 65%, and the elastic constant s33E = 19.7 × 10−12 m2/N, c33E = 11.3 × 1010 N/m2, which are close to the properties of soft PZT (PZT-5A). Furthermore, the piezoelectric coefficients (k33, d33), the ferroelectric properties (coercive field, remnant polarization), and the elastic ...
238 citations
TL;DR: A strategy for integrating nanoribbons of one of the most widely used ferroelectric ceramics, lead zirconate titanate, in "wavy" geometries, on soft, elastomeric supports to achieve reversible, linear elastic responses to large strain deformations, without any loss in ferro electric or piezoelectric properties is reported.
Abstract: Applications of ferroelectric ceramics, ranging from components for sensors, memory devices, microelectromechanical systems, and energy convertors, all involve planar and rigid layouts. The brittle nature of such materials and their high-temperature processing requirements limit applications to devices that involve only very small mechanical deformations and narrow classes of substrates. Here, we report a strategy for integrating nanoribbons of one of the most widely used ferroelectric ceramics, lead zirconate titanate, in “wavy” geometries, on soft, elastomeric supports to achieve reversible, linear elastic responses to large strain deformations (i.e., stretchable properties), without any loss in ferroelectric or piezoelectric properties. Theoretical and computational analysis of the mechanics account for these characteristics and also show that the amplitudes of the waves can be continuously tuned with an applied electric field, to achieve a vertical (normal) displacement range that is near 1000 times l...
194 citations
TL;DR: In this article, the photoluminescence of Pr doped (Bi 0.5Na0.5)TiO3 ferroelectric ceramics prepared by conventional solid-state reaction were investigated.
Abstract: The photoluminescence of Pr doped (Bi0.5Na0.5)TiO3 ferroelectric ceramics prepared by conventional solid-state reaction were investigated. A bright red emission is observed at room temperature, which ascribed to 1D2→3H4 transition. The excitation bands are mainly located at 440 ∼ 505 nm, which is adaptable to the emission band of commercial blue light-emitting diodes (LEDs) chips. The optimal emission intensity was also obtained when Pr doping level was 0.003 mol. Meanwhile, the enhanced ferroelectric properties were obtained by Pr doping. The results show that Pr doped (Bi0.5Na0.5)TiO3 ceramics as a multifunctional material may be useful for white LEDs, sensor, and optical-electro integration.
112 citations
TL;DR: In this paper, nonlinear ceramics that provide the basis for high energy density and high-temperature capacitors, as well as tunable microwave dielectrics, and their applications are discussed.
Abstract: Nonlinear ceramics that provide the basis for high-energy-density and high-temperature capacitors, as well as tunable microwave dielectrics, and their applications are discussed in this article
109 citations
TL;DR: In this paper, an electric field-induced phase transition in bismuth-based ceramics is used at a relatively low field of 40 kV/cm, where the phase transition is attributed to the transition from non-polar to ferroelectric phases in BNKT-BA small grains with BNT large grains during external electric field execution.
Abstract: In this study, a method in which an electric field-induced phase transition in bismuth-based ceramics is used at a relatively low field of 40 kV/cm is proposed. This study investigated the electrical properties and electric field-induced strain of Bi0.5Na0.5TiO3 (BNT) single particle-added Bi0.5(Na0.75K0.25)0.5TiO3-BiAlO3 (BNKT-BA) ceramics. Strains of 0.27% and 0.29%, for 0.94BNKT-0.06BA with 10% BNT and 0.93BNKT-0.07BA with 20% BNT, were observed, respectively. These strains were attributed to the transition from non-polar to ferroelectric phases in BNKT-BA small grains with ferroelectric BNT large grains during external electric field execution.
TL;DR: In this paper, a single-phase, low-loss, room-temperature multiferroic with magnetoelectric coupling was proposed, which combines x-ray scattering, magnetic and polarization hysteresis in both phases, plus a second-order dielectric divergence for an unambiguous assignment as a C2v-C4v (Pmm2-P4mm) transition.
Abstract: Mixing 60-70% lead zirconate titanate with 40-30% lead iron tantalate produces a single-phase, low-loss, room-temperature multiferroic with magnetoelectric coupling: (PbZr0.53Ti0.47O3) (1-x)- (PbFe0.5Ta0.5O3)x. The present study combines x-ray scattering, magnetic and polarization hysteresis in both phases, plus a second-order dielectric divergence (to epsilon = 6000 at 475 K for 0.4 PFT; to 4000 at 520 K for 0.3 PFT) for an unambiguous assignment as a C2v-C4v (Pmm2-P4mm) transition. The material exhibits square saturated magnetic hysteresis loops with 0.1 emu/g at 295 K and saturation polarization Pr = 25 μC/cm2, which actually increases (to 40 μC/cm2) in the high-T tetragonal phase, representing an exciting new room temperature oxide multiferroic to compete with BiFeO3. Additional transitions at high temperatures (cubic at T>1300 K) and low temperatures (rhombohedral or monoclinic at T<250 K) are found. These are the lowest-loss room-temperature multiferroics known, which is a great advantage for magnetoelectric devices.
TL;DR: In this article, a range of ceramics were prepared by substituting 0.5-2 at.% of Fe or Mn for TiO 3 and it was found that a low dopant concentration (0.5 at.%) increases the depolarization temperature (T d ) with a minimal loss in room temperature d 33, allowing for high piezoelectric coefficients at elevated temperatures.
Abstract: Bismuth-based ferroelectric ceramics are currently under intense investigation for their potential as Pb-free alternatives to lead zirconate titanate-based piezoelectrics. The present work evaluated the thermal depoling behavior of various compositions of Na 0.5 Bi 0.5 TiO 3 (NBT), one of the Bi-based materials of broad interest, through in situ and ex situ measurements of the piezoelectric constant (d 33 ). A range of ceramics was prepared by substituting 0.5-2 at.% of Fe or Mn for Ti. It was found that a low dopant concentration (0.5 at.%) increases the depolarization temperature (T d ) with a minimal loss in room temperature d 33 , allowing for high piezoelectric coefficients at elevated temperatures. For example, 0.5 at.% Fe substitution leads to an enhanced piezoelectric coefficient of d 33 of 133 pm/V at an elevated temperature of 180°C. However, with further increase of dopant concentration, T d decreases in both Mn- and Fe-doped NBT. The in situ depoling measurements of 0.5 at.% Fe- and Mn-doped NBT in the present work exhibit the potential for higher temperature applications.
TL;DR: In this paper, major modifications of magnetic anisotropies and magnetic coercivity induced by the application of electric fields perpendicular to the interface have been found in Fe/BaTiO3(001) heterostructures.
Abstract: Magnetoelectric effects in Fe/BaTiO3(001) heterostructures have been investigated via magneto-optical Kerr effect as a function of temperature. We find major modifications of magnetic anisotropies and magnetic coercivity induced by the application of electric fields perpendicular to the interface. Changes in the coercive magnetic field, on the order of 100% at 250 K (in the orthorhombic phase of BaTiO3) and 40% at 300 K (in the tetragonal phase), which are linked to the ferroelectric behavior of BaTiO3, are reported.
TL;DR: In this article, the dielectric properties of BaBi4Ti4O15 ceramics were investigated as a function of frequency (10(2)-10(6) Hz) at various temperatures (30 degrees C-470 degrees C), covering the phase transition temperature.
TL;DR: In this paper, the dielectric response of all samples was studied by means of broadband dielectoric spectroscopy, over a wide temperature (from 30°C to 160°C) and frequency (from 10 −1 ǫ to 10ÂMHz) range.
Abstract: Ceramic–polymer composites incorporating ferroelectric and piezoelectric crystal particles, randomly distributed within the polymer matrix represent a novel class of materials. Composites including ferroelectric and/or piezoelectric particles are expected to exhibit functional properties because of the varying polarization of the ceramic particles. In the present study polymer matrix/ZnO/BaTiO 3 composites were prepared, in different filler concentrations. The dielectric response of all samples was studied by means of broadband dielectric spectroscopy, over a wide temperature (from 30 °C to 160 °C) and frequency (from 10 −1 Hz to 10 MHz) range. Experimental data were analyzed by means of dielectric permittivity and electric modulus formalisms. Dielectric permittivity and loss are increasing with ceramic filler and diminishing rapidly with frequency. The functionality of the composite systems is related to the abrupt variation of the real part of permittivity, in the vicinity of the characteristic Curie temperature of BaTiO 3 , and to the relaxing polarization of the ZnO particles.
TL;DR: In this article, the authors reported a large d31 piezoelectric coefficient and corresponding electromechanical coupling factor, Kp, for lead-free piezoceramics.
Abstract: We report a large d31 piezoelectric coefficient and corresponding electromechanical coupling factor, Kp, of 0.5Ba(Zr0.2Ti0.8)O3–0.5(Ba0.7Ca0.3)TiO3 (BCTZ50) and 0.68Ba(Zr0.2Ti0.8)O3–0.32(Ba0.7Ca0.3)TiO3 (BCTZ32) lead-free piezoceramics. The piezoelectric coefficient, d31, reaches a high value of 200 pC/N for BCTZ50 at room temperature which is comparable to the one of the soft PZT. This confirms the previously reported d33 for the same material. A useful way to achieve such performances at the expense of a smaller thermal budget is suggested, enabling better control of the ceramics composition and microstructure. Based on pyroelectric and ferroelectric hysteresis loops measurements, we show that such outstanding properties are likely due to the high flexibility of polarization under thermal and electric stresses.
TL;DR: In this paper, a multiferroic La0.1Bi0.9FeO3 (LBFO) ceramics with high resistivity were synthesized by using a modified rapid thermal process.
Abstract: Multiferroic La0.1Bi0.9FeO3 (LBFO) ceramics with high resistivity were synthesized by using a modified rapid thermal process. The LBFO ceramics show very low leakage and low dielectric loss. Well saturated ferroelectric hysteresis loops and polarization switching currents have been observed. For a maximum applied electric field of 145 kV/cm, the remanent polarization is 17.8 μC/cm2 and the coercive filed is 75 kV/cm. The dominant conduction mechanism in the LBFO ceramics has been found to be the space-charge-limited current mechanism rather than the thermal excitation mechanism. Electrical reliability related to the fatigue and polarization retention of the LBFO ceramics has also been discussed with the leakage mechanisms.
TL;DR: In this article, the influence of the oxygen vacancies on the dielectric response of BaZr0.10Ti0.90O3 ceramics prepared by solid-state reaction and sintered at 1400 °C for 2 h was investigated.
Abstract: The influence of the oxygen vacancies on the dielectric response of BaZr0.10Ti0.90O3 ceramics prepared by solid-state reaction and sintered at 1400 °C for 2 h was investigated. The as-sintered ceramic exhibits a giant relaxation with a shift of the transition temperature from ∼85 °C to above 170 °C in the frequency ranges of 1 Hz–100 kHz, with high losses above unity and two components in the complex impedance plot. A complex dielectric relaxation response, with at least two thermally activated defect mechanisms with activation energies of ∼0.2 eV below the transition temperature and ∼0.7 eV for higher temperatures in the range of 85 °C–170 °C was determined. The observed giant relaxation is an extrinsic effect related to the oxygen deficiency, inhomogeneous distributed in the ceramic grain and not to the relaxor behavior of this system. After a post-annealing treatment at 1000 °C for 50 h, the dielectric response is completely changed: the permittivity vs. temperature dependences present maxima located a...
TL;DR: In this paper, two series of lead-free piezoelectric solid solutions of 1−x−y(Bi0.5Na 0.5K 0.20)NbO3 (BNT-BKT-KNN) ceramics are presented.
Abstract: Results on two series of lead-free piezoelectric solid solutions of 1−x−y(Bi0.5Na0.5)TiO3−x(Bi0.5K0.5TiO3)−y(Na0.5K0.5)NbO3 (BNT-BKT-KNN) ceramics, synthesized in the vicinity of ferroelectric rhombohedral (x=0.17) and ferroelectric tetragonal (x=0.20) phase boundary of 1−x(BNT)–xBKT are presented. Orthorhombic KNN in stoichiometric proportion as third component with 0.0≤y≤0.06 is added to prepare these two series (i) with x=0.17 and (ii) with x=0.20. Addition of KNN up to a critical y is observed to improve tetragonality in both series and solid solubility of KNN was verified at least up to y=0.1 in this system. Depolarization temperature Td of these stoichiometric BNT-BKT-KNN series were found to be considerably lower than that of their parent BNT-BKT compositions. As a result of this, coexistence of polar and nonpolar phases for compositions at morphotropic phase boundary (MPB) were indicated at room temperature, resulting in pinched polarization versus electric field (P-E) loops and large strain (stra...
TL;DR: In situ high-resolution synchrotron x-ray diffraction reveals a local minimum in rhombohedral distortion angle αR (associated with an inflection in the lattice constant aR) near 400 and 350 °C in BiFeO3 (BFO) and (BiFeO 3)0.95(BaTiO3) 0.05 (B FO-5%BT), respectively as discussed by the authors.
Abstract: In situ high-resolution synchrotron x-ray diffraction reveals a local minimum in rhombohedral distortion angle αR (associated with an inflection in the lattice constant aR) near 400 and 350 °C in BiFeO3 (BFO) and (BiFeO3)0.95(BaTiO3)0.05 (BFO–5%BT), respectively. It suggests a coupling between ferroelectric and magnetic parameters near the antiferromagnetic–paramagnetic transition, which is responsible for the broad frequency-dependent dielectric maxima. A rhombohedral (R)–orthorhombic (O)–cubic (C) transition sequence takes place near 820 and 850 °C in BFO upon heating. BFO–5%BT exhibits a R–C transition near 830 °C. The BaTiO3 substitution can enhance dielectric and ferromagnetic responses and reduce electric leakage. The dielectric loss of BFO–5%BT remains less than 0.04 below 150 °C.
TL;DR: In this article, the depoling mechanism of the (0.54 − 0.70) compositions close to the morphotropic phase boundary (MPB) was systematically investigated as a function of PbTiO3 content.
Abstract: The structure, electrical properties, and depoling mechanism of the (0.95−x)BiScO3−xPbTiO3−0.05Pb(Zn1/3Nb2/3)O3 (BS-xPT-PZN, x=0.54–0.70) compositions close to the morphotropic phase boundary (MPB) have been systematically investigated as a function of PbTiO3 content (x). The phase approached from the rhombohedral toward the tetragonal phase when the PbTiO3 contents increased. The composition with high PT content exhibited normal ferroelectric behavior while it showed a diffused phase transition characteristic as PT decreased. In the vicinity of the MPB, the ceramics showed enhanced piezoelectric, electromechanical, and ferroelectric properties with piezoelectric constant d33=490 pC/N, planar electromechanical coupling factors kp=57.4%, remnant polarization Pr=40.1 μC/cm2, and coercive field Ec=28.5 kV/cm with a high transition temperature Tm∼417 °C, respectively. The thermal depoling experiments of the polarization for samples with different phase structures were investigated and the possible depoling me...
TL;DR: In this paper, structural, dielectric and ferroelectric properties of BaZr0025Ti0975O3 Ferroelectric ceramics have been investigated using solid state reaction technique.
TL;DR: Weak relaxor behavior was observed in K 1−xBixNb1−xYbxO3 ceramics with x 0.20 and X 0.30.
Abstract: Weak-relaxor behaviour was observed in K1−xBixNb1−xYbxO3 ceramics with x = 0.20 and x = 0.30. According to x-ray diffraction analysis, the crystal structure of these ceramics can be described by the cubic centrosymmetric Pm3¯m space group; however Raman spectroscopy reveals both the occurrence of local lattice distortions and the disruption of the long-range ferroelectric order. The local lattice strain caused by the larger Yb3+ combined with the presence of Bi3+, which lone-pair of electrons induces further local distortions, gives rise to polar nanoregions (PNRs). Nevertheless, the interaction between the PNRs appears weak and proper relaxor behaviour does not develop.
TL;DR: In this paper, a double hysteresis loop and small fingerprint domains with uniform distribution observed for 3/75/25 indicate an intermediate ferroelectric state, and it is proposed that the unstable intermediate Ferroelectric states which would experience obvious field-induced phase transition is the origin of the giant electro-optic Kerr effect observed in La-doped Pb(Mg1/3Nb2/3)O3-PbTiO3 (PMN-PT) 3/ 75/25.
Abstract: Transparent ceramics of La-doped Pb(Mg1/3Nb2/3)O3-PbTiO3 (PMN-PT) x/75/25 are prepared, and the ferroelectric domains, dielectric, and ferroelectric properties of x/75/25 are investigated. A double hysteresis loop and small fingerprint domains with uniform distribution observed for 3/75/25 indicate an intermediate ferroelectric state. The dielectric behavior under dc bias and the evolution of the hysteresis loop with increasing electric field for 3/75/25 indicate an electric field-induced phase transition, and it is proposed that the unstable intermediate ferroelectric state which would experience obvious field-induced phase transition is the origin of the giant electro-optic Kerr effect observed in La-doped PMN-PT 3/75/25.
TL;DR: Distinct anomalies of dielectric and piezoelectric parameters, corresponding to the transition between rhombohedral (monoclinic) and tetragonal ferroelectric phases, have been observed in pure PFN and PFN-xPT compositions with PbTiO content up to 8 mol%.
Abstract: Dielectric, X-ray, and piezoelectric studies of highly-resistive Li-doped (1-x)PbFe1/2Nb1/2O3-(x)PbTiO3 (PFN-xPT) ceramics from the 0 ≤ x ≤ 0.2 range fabricated by solid-state synthesis and usual sintering have been carried out. Distinct anomalies of dielectric and piezoelectric parameters, corresponding to the transition between rhombohedral (monoclinic) and tetragonal ferroelectric phases, have been observed in pure PFN and PFN-xPT compositions with PbTiO3 content up to 8 mol.%. The x,T-phase diagram of the PFN-xPT solid solution system has been constructed using these data.
TL;DR: In this paper, the polarization state in three-dimensional porous polycrystalline ferroelectric networks has been modelled to eliminate the oversimplification of these idealized unit cells.
Abstract: Micromechanical models of porous ferroelectric ceramics have often assumed that the material is fully polarized in a particular direction and/or consists of a single isolated pore. In this work the polarization state in three-dimensional porous polycrystalline ferroelectric networks has been modelled to eradicate the oversimplification of these idealized unit cells. This work reveals that microstructural network models more closely represent a porous ferroelectric microstructure since they are able to take into account the complex polarization distribution in the material due to the presence of high and low permittivity regions. The modelling approach enables the prediction of the distribution of poled and unpoled material within the structure. The hydrostatic figures of merit and permittivity were determined for a variety of porous lead zirconate titanate microstructures and found to be in good agreement with experimental data. The decrease in piezoelectric activity with porosity was observed to be associated with the complex polarization state within the material. Model results were shown to be much improved when compared to a model assuming a fully polarized model.
TL;DR: In this article, a lead free Sodium Bismuth Titanate (NBT) (Na 0.5Bi0.5TiO3) composition was synthesized by conventional ceramic method (CS) and microwave sintering (MS).
Abstract: Dielectric studies were carried out on a lead free Sodium Bismuth Titanate, NBT, (Na0.5Bi0.5TiO3) composition. The material was synthesized by conventional ceramic method (CS) and microwave sintering (MS). The presence of single phase has been confirmed by X-ray diffraction and scanning electron microscopy of NBT ceramic. The later technique (MS) resulted in material with high density, dielectric properties and improved microstructure. The transition temperature was observed slightly higher for microwave sintered (MS) material. Longitudinal modulus measurements are very sensitive property to identify the phase transitions in ceramics. Longitudinal modulus (L) measurements were also employed on these samples in the frequency 136 kHz and can be studied in the wide temperature range 30°C to 400°C. The elastic behavior (L) showed a break at two temperatures (~200°C and 350°C) in both the conventional and microwave sintered ceramics. In NBT ceramics, permittivity anomalies are connected to modulus anomalies. The results are correlated with the dielectric measurements. This behavior explained in the light of structural phase transitions in the ferroelectric ceramics.
TL;DR: In this article, a sample of the layered perovskite phase was successfully obtained, even if little Bi-deficient pyrochlore Bi2Ti2O7 also existed.
Abstract: Ceramics of Nd/Co co-substituted Bi5Ti3FeO15, i.e., (Bi4Nd)Ti3(Fe0.5Co0.5)O15 were prepared by the conventional solid-state reaction method. The X-ray diffraction pattern demonstrates that the sample of the layered perovskite phase was successfully obtained, even if little Bi-deficient pyrochlore Bi2Ti2O7 also existed. The ferroelectric and magnetic Curie temperatures were determined to be 1077 K and 497 K, respectively. The multiferroic property of the sample at room temperature was demonstrated by ferroelectric and magnetic measurements. Remarkably, by Nd/Co co-substituting, the sample exhibited large magnetic response with 2Mr = 330 memu/g and 2Hc = 562 Oe at applied magnetic field of 8 kOe at room temperature. The present work suggests the possibility of doped Bi5Ti3FeO15 as a potential multiferroic.
TL;DR: In this article, a tunable bandpass filter base on an evanescentmode dielectric cavity, which is loaded by a pair of tunable mushroom-type complementary split-ring resonators, is presented.
Abstract: This letter presents the design and the realization of a compact tunable filter integrated in ferroelectric ceramic substrate. The bandpass filter bases on an evanescent-mode dielectric cavity, which is loaded by a pair of tunable mushroom-type complementary split-ring resonators. Tunable impedance matching networks are additionally implemented to improve passband insertion loss across the tuning range. A prototype has been realized in a 12.5 mm × 9.5 mm × 0.8 mm planar module. Measurements confirm a frequency coverage from 2.95 to 3.57 GHz, a 3 dB fractional bandwidth below 5.4%, with an insertion loss between 3.3 dB and 2.6 dB.