Permittivity Peak Research Articles

Magneto-thermally activated spin-state transition in La0.95Ca0.05CoO3: magnetically-tunable dipolar glass and giant magneto-electricity.

The magneto-dielectric spectroscopy of La0.95Ca0.05CoO3 covering the crossover of spin states reveals the strong coupling of its spin and dipolar degrees of freedom. The signature of the spin-state transition at 30 K clearly manifests in the magnetization data at a 1 Tesla optimal field. Our Co L3,2-edge X-ray absorption spectrum on the doped specimen is consistent with its suppressed low-to-intermediate spin-state transition temperature at ∼30 K compared to ∼150 K, documented for pure LaCoO3. The dispersive activation step in the dielectric constant with the associated relaxation peak in imaginary permittivity characterize the allied influence of coexistent spin-states on the dielectric character. Dipolar relaxation in the low-spin regime below the transition temperature is partly segmental (Vogel-Fulcher-Tamman (VFT) kinetics) and features magnetic-field tunability, whereas in the low/intermediate-spin disordered state above ∼30 K, it is uncorrelated (Arrhenic kinetics) and almost impervious to the magnetic field H. Kinetics-switchover defines the dipolar-glass transition temperature Tg(H) (=27 K|0T), below which their magneto-thermally-activated cooperative relaxations freeze out by the VFT temperature T0(H) (=15 K|0T). An applied magnetic field facilitates thermal activation in toggling the low spins up into the intermediate states. Consequently, the downsized dipolar-glass segments in the low-spin state and the independent dipoles in the intermediate state exhibit accelerated dynamics. A critical 5 Tesla field collapses the entire relaxation kinetics into a single Arrhenic behaviour, signaling that the dipolar glass is completely devitrified under all higher fields. The magneto-electricity (ME) spanning sizeable thermo-spectral range registers diverse signatures here in kinetic, spectral, and field behaviors, in contrast to the static/perturbative ME observed close to the spin-ordering in typical multiferroics. Intrinsic magneto-dielectricity (50%) along with vanishing magneto-loss is obtained at (27 K/50 kHz)9T. The sub-linear deviant and field-hysteretic split seen in above 4 Tesla suggests the emergence of robust dipoles organized into nano-clusters, induced by the internally-generated high magneto-electric field. An elaborate ω-T multi-dispersions diagram maps the rich variety of phase/response patterns, revealing highly-interacting magnetic and electric moments in the system.

Dispersion behaviors of Gaussian-type distribution of Curie temperature in relaxor ferroelectrics

ABSTRACTWhen the contributions of dipole and soften vibration mode are assigned to a complex impermeability and a real impermeability, respectively, the total complex permeability with frequency can be derived to modify the classical Landau-Devonshire theory. In a gaussian distribution and a skewed gaussian distribution of Curie temperature of second-order phase transition, the functions derived have the form of dispersion behavior of relaxor ferroelectrics. By comparing with experiment result, slight deviations appear on the two sides of peak of permittivity for the gaussian distribution, and improved by the skewed gaussian distribution. The relevant problems to be solved are proposed.

Highly accelerated resistance degradation and thermally stimulated relaxation in BaTiO3-based multilayer ceramic capacitors with Y5V specification

Correlation between resistance degradation and thermally stimulated relaxation in commercial BaTiO3-based multilayer ceramic capacitors (MLCCs) with Y5V specification were analyzed. The temperature dependence of dielectric behavior shows that the polarization response is activated by increasing AC electric field, especially the dielectric permittivity peak value. Highly accelerated degradation test and thermally stimulated depolarization current (TSDC) measurements were performed. It has been found that the reliability of capacitors greatly depends on temperature and electric field. TSDC of capacitor dielectrics before and after degradation were also investigated for a fundamental understanding of the resistance degradation mechanism. Two TSDC relaxation peaks were detected, and were correspondingly assigned to in-grain and across-grain boundary migration of oxygen vacancies. Contrary to our predictions, the degraded sample shows an evident decrease in TSDC density and activation energy of the across-grain boundary relaxation compared with the ceramic capacitor without degradation. It is demonstrated that the insulation resistance degradation is associated with the migration of oxygen vacancy defects. The strong degradation indicates that more oxygen vacancies may jump out of potential well and probably form defect clusters. Such clusters will not have the mobility to relax back, subsequently causing the decrease in the measured relaxation current.

Influence of FeNb codoping on the dielectric and electrical properties of CaCu3Ti4O12 ceramics

The CaCu3 (Ti1−xFex/2Nbx/2)4O12 (x = 0.00, 0.50, 0.53, 0.57, 0.60) ceramics were prepared by the solid-state reaction method via the pre-synthesis of the monoclinic precursor FeNbO4. The temperature dependence of dielectric properties showed that the dielectric permittivity of pure CaCu3Ti4O12 sample increased rapidly with the rising temperature, while a broad peak of dielectric permittivity of the FeNb codoped CaCu3Ti4O12 samples was observed in the temperature range. The frequency dependence of dielectric spectra was measured in frequency range from 20 Hz to 1 GHz for pure CaCu3Ti4O12 sample, two Debye-type relaxations were shown in low and high frequency, respectively, and the giant dielectric plateau of pure CaCu3Ti4O12 sample was attributed to the interfacial polarization at grain boundaries. A reduce of dielectric permittivity of the FeNb codoped CaCu3Ti4O12 samples occurred in low frequency, indicating the existence of a Debye-type relaxation related to the surface layer effect. By the complex impedance spectroscopy measurement, three semi-circle arcs of the FeNb codoped CaCu3Ti4O12 samples were revealed, which represented the responses of surface layer, grain boundary and grain, respectively. The nonlinear I–V characteristics revealed the existence of Schottky potential barrier and the heights of Schottky potential barrier of FeNb codoped CaCu3Ti4O12 were lower than that of pure CaCu3Ti4O12.

Monitoring time course of human whole blood coagulation using a microfluidic dielectric sensor with a 3D capacitive structure.

This paper reports on the design, fabrication, and testing of a microfluidic sensor for dielectric spectroscopy (DS) of human whole blood during coagulation. The sensor employs a three-dimensional (3D), parallel-plate, capacitive sensing structure with a floating electrode integrated into a microfluidic channel. Using an impedance analyzer and after a 5-point calibration, the sensor is shown to measure the real part of complex relative dielectric permittivity of human whole blood in a frequency range of 10kHz to 100MHz. The temporal variation of dielectric permittivity at 1MHz for human whole blood from three different healthy donors shows a peak in permittivity at ~ 4 to 5 minutes, which also corresponds to the onset of CaCl2-initiated coagulation of the blood sample verified visually.

Phase transitions, ferroelectric, and piezoelectric properties of lead-free piezoelectric xBaZrO3–(0.25−x)CaTiO3–0.75BaTiO3 ceramics

Lead-free xBaZrO3–(0.25−x)CaTiO3–0.75BaTiO3; x = 0.00–0.25 ceramics were successfully prepared using the conventional solid-state reaction method. Analysis of the sintered ceramics showed that all compositions exhibited a pure phase perovskite. The effects of composition on the phase transition, ferroelectric properties, and piezoelectric properties were studied. With the increasing BaZrO3 content, the phase transition temperature (T C) decreased and the coercive field E c decreased. The phase diagram featuring a cubic–rhombohedral–tetragonal triple point (x ~ 0.125) was derived from X-ray diffraction data and dielectric data as a function of temperature. Compositions near the convergence region exhibited the maximum peak in permittivity of ~11,400 at T C. In addition, the morphotropic phase boundary compositions showed an enhancement in ferroelectric and piezoelectric properties. The composition 0.125BaZrO3–0.125CaTiO3–0.75BaTiO3 exhibited the highest strain values of 0.14 % and a d 33 * of 474 pm/V.

Phase evolution and enhanced electrical properties of (Ba0.85Ca0.15−x Y x )(Zr0.1Ti0.9)O3 lead-free ceramics

(Ba0.85Ca0.15−x Y x )(Zr0.1Ti0.9)O3 (x = 0.00, 0.01, 0.02, 0.03 and 0.04) lead-free ceramics with excellent performance were fabricated using a solid-state reaction method. The effects of Y2O3 substitution on the crystal structure and electrical properties were investigated in detail. On the basis of the X-ray diffraction, it was clear that Y2O3 additive induced phase transition from orthorhombic phase to the coexistence of orthorhombic and tetragonal phases, and then to single tetragonal phase at room temperature with increasing x. Dielectric measurements revealed that a gradual change presented from typical ferroelectric behavior in (Ba0.85Ca0.15)(Zr0.1Ti0.9)O3 to dispersive relaxor-like characteristics in substituted samples. In addition, double permittivity peaks were presented in plots of relative permittivity versus temperature (e r − T ) with the sample of 0.01 ≤ x ≤ 0.04, which could be associated with composition fluctuation on account of the incorporation of Y2O3. The enhanced temperature stabilities of ferroelectric and piezoelectric properties were obtained in the temperature range from 20 to 140 °C. This result was found to be consistent with the change of dielectric properties. Besides, the outstanding electrical properties were obtained (d 33 = 564 pC/N, k p = 58 %, strain = 0.09 %, P r = 8.38 μC/cm2, e r = 3078, and tanδ = 0.03) at x = 0.02 due to the coexistence of orthorhombic and tetragonal phases.

Magnetic and dielectric properties of [N(C2 H5 )4 ]2 CoClBr3 solid solution: A new potential multiferroic

Thermodynamically induced structural transformation to a polar phase in the tetraethylammonium tetrahalogenocobaltate solid solution of [N(C2H5)4]2CoClBr3 (TEACCB-3) is found to be accompanied with a large dielectric permittivity peak near 258 K. It was also found that the sample undergoes a ferrimagnetic ordering on further cooling below 8 K. Our results demonstrate that crystalline ferroics with an alkylammonium cation can develop strong magnetic interactions reaching 2.3 μB fu−1 at 14 T that can potentially coexist with electric polarization at the same temperature region.

Fluctuating defects in the incipient relaxorK1−xLixTaO3(x=0.02)

We report neutron scattering measurements of the structural correlations associated with the apparent relaxor transition in K$_{1-x}$Li$_x$TaO$_3$ for $x=0.02$ (KLT(0.02)). This compound displays a broad and frequency-dependent peak in the dielectric permittivity, which is the accepted hallmark of all relaxors. However, no evidence of elastic diffuse scattering or any soft mode anomaly is observed in KLT(0.02) [J. Wen et al., Phys. Rev. B 78, 144202 (2008)], a situation that diverges from that in other relaxors such as PbMg$_{1/3}$Nb$_{2/3}$O$_3$. We resolve this dichotomy by showing that the structural correlations associated with the transition in KLT(0.02) are purely dynamic at all temperatures, having a timescale on the order of $\sim$THz. These fluctuations are overdamped, non-propagating, and spatially uncorrelated. Identical measurements made on pure KTaO$_3$ show that they are absent (within experimental error) in the undoped parent material. They exhibit a temperature dependence that correlates well with the dielectric response, which suggests that they are associated with local ferroelectric regions induced by the Li$^+$ doping. The ferroelectric transition that is induced by the introduction of Li$^+$ cations is therefore characterized by quasistatic fluctuations, which represents a stark contrast to the soft harmonic-mode-driven transition observed in conventional perovskite ferroelectrics like PbTiO$_3$. The dynamic, glass-like, structural correlations in KLT(0.02) are much faster than those measured in random-field-based lead-based relaxors, which exhibit a frequency scale of order of $\sim$GHz and are comparatively better correlated spatially. Our results support the view that random fields give rise to the relaxor phenomena, and that the glass-like dynamics observed here characterize a nascent response.

Structure and properties of (1 − x)BiFeO3 · xPbFe2/3W1/3O3 (0 ≤ x ≤ 1) solid solutions

(1 − x)BiFeO3 · xPbFe2/3W1/3O3 ((1 − x)BFO · xPFWO) samples with 0 ≤ x ≤ 1 have been prepared by a standard ceramic processing technique and characterized by X-ray diffraction, dielectric measurements, and Mossbauer spectroscopy. The system has been shown to contain a continuous series of perovskite solid solutions. The solid solutions in the range 0 ≤ x < 0.32 have a rhombohedral structure and those with 0.32 ≤ x ≤ 1 have a cubic structure. Increasing the BFO content from 0 to 40% leads to rapid degradation of the dielectric permittivity peak that occurs at 180 K in PFWO and is due to the relaxor behavior of this component. At higher BFO concentrations, the electrical conductivity of the solid solutions increases by about two orders of magnitude. The temperature dependences of permittivity for the samples containing ∼80% BFO have prominent maxima around 430 and 520 K, whose position is frequency-independent. The solid solutions exhibited no piezoelectric or pyroelectric effect, probably because they were insufficiently poled in a field of 10 kV/cm at 300 K. At higher electric field intensities, the samples experienced breakdown.

Dielectric, thermal and ferroelectric properties of Na0.997Li0.003NbO3 ceramics

Na0.997Li0.003NbO3 ceramics of 93% density have been prepared by a solid-state chemical reaction of stoichiometric mixtures of the component oxides and carbonates. The dielectric, thermal expansion, heat capacity, Raman and ferroelectric studies of these ceramics have been performed. The electric permittivity peak shows rather a small dispersion and no change of the maximum position with increasing frequency can be observed. The results clearly show a first-order phase transition at about 375 °C on heating and near 310 °C on cooling and ambiguously indicated another phase transitions. The pyroelectric measurements show for the first time that the material has weak ferroelectric properties, which are rather metastable. The results show that the investigated ceramics are one of the promising lead-free materials for electronic applications.

Dielectric and ferroelectric responses of Ba0.99 − xBi2x/3Ca0.01Zr0.02Ti0.98O3 ceramics

Structure, dielectric and ferroelectric properties of Ba0.99−xBi2x/3Ca0.01Zr0.02Ti0.98O3 (x=0.00, 0.03, 0.06 and 0.12) ceramics have been investigated. X-ray diffraction and Raman results show that Bi3+ ions enter the crystal lattice, maintaining the perovskite structure. Dielectric spectroscopy shows that all compositions sintered at 1350°C show a normal ferroelectric characteristics. Interestingly, the sample with x=0.12 sintered at 1150°C exhibits a relaxor behavior with the frequency dependence of permittivity peak obeying the Vogel–Fulcher formula, which may be ascribed to the defect pair [BiBa⋅−VBa′′]. As the Bi3+ substitution level is increased, the spontaneous polarization is decreased, whereas the coercive field is increased.

Relationship between electromechanical properties and phase diagram in the Ba(Zr0.2Ti0.8)O3–x(Ba0.7Ca0.3)TiO3 lead-free piezoceramic

The Ba(Zr0.2Ti0.8)O3–x(Ba0.7Ca0.3)TiO3 system was synthesized in a wide compositional range in order to study the relationship between its phase diagram and electromechanical properties. Phase transitions were marked using peaks in temperature-dependent permittivity, providing up to three transitions from the rhombohedral phase to an orthorhombic, tetragonal and finally cubic phase, which meet in a region that is termed the phase convergence region in this work. In situ small and large signal electromechanical properties were studied as a function of temperature with specific emphasis on these transitions. A small signal piezoelectric coefficient, d33, presents maximized values at the transition from the orthorhombic to the tetragonal phase, while a large signal piezoelectric coefficient, d33∗, does so at both rhombohedral to orthorhombic and to tetragonal phase transitions. Maximum polarization Pmax was the only quantity determined that had a clear maximum at the phase convergence region.

Structure, Dielectric Relaxor Behavior and Ferroelectric Properties of Sr&lt;sub&gt;1-x&lt;/sub&gt;La&lt;sub&gt;x&lt;/sub&gt;Bi&lt;sub&gt;2&lt;/sub&gt;Nb&lt;sub&gt;2-x/5&lt;/sub&gt;O&lt;sub&gt;9&lt;/sub&gt; Ferroelectric Ceramics

Ferroelectric ceramics, Sr1-xLaxBi2Nb2-x/5O9 (SLBNO), were prepared using the conventional solid-state reaction method. Effect of lanthanum substitution on dielectric and ferroelectric properties of SrBi2Nb2O9 (SBN) ceramics were investigated. X-ray diffraction analyses (XRD) revealed that all the specimens had a single phase with orthorhombic space group A21am. The maximum dielectric permittivity peak broadened gradually with the increase in lanthanum substitution indicated that the phase transition from normal ferroelectrics to relaxor ferroelectrics occurred in SLBNO ceramics. The modified Curie-Weiss (CW) law was used to describe the relaxor behavior of the SLBNO ceramics. The relaxation indication coefficient (γ) was estimated from a quadratic fit of modified CW law and was found to be 1.7 and 2.0 for the SLBN20 and SLBN30 specimens, respectively. Curie temperature (Tc) of the SBN ceramic was decreased gradually with the increase in lanthanum substitution. In addition, the ferroelectric properties of the SBN ceramic were enhanced significantly by the introduction of lanthanum ions and the maximum of remnant polarization (Pr) was found to be 4.35 μC/cm2 for the SLCB20 specimen. Nature of relaxor behavior of the SLBNO ceramic is attributed to the cationic disordering at nanoscale on A site by the introduction of lanthanum ions.

Electromagnetic wave absorption properties of composites with ultrafine hollow magnetic fibers

Ultrafine hollow magnetic fibers were prepared by electroless plating using hydrolyzed polyester fiber as a sacrificial substrate. These hollow fibers can be served for lightweight and efficient electromagnetic (EM) absorbing materials. As observed from SEM and EDS analysis, hollow structures consisting of Ni inner layer and Fe or Fe–Co outer layer were obtained. By introducing Co onto Fe, oxidation of the Fe layer was successfully prevented making it possible to enhance the complex permeability compared to a case in which only Fe was used. Polymeric composites containing the hollow fibers with different weight fractions and fiber lengths were prepared by a simple mixing process. The electromagnetic wave properties of the composites were measured by a vector network analyzer and it was found that the hollow magnetic fibers show a clear resonance peak of the complex permittivity around the X-band range (8–12GHz) and the resonance frequency strongly depends on the fiber concentration and length. A possible explanation for the unique resonance is that the hollow fibers possess relatively low electrical conductivity and a long mean free path due to their oxidized phase and hollow structure. The calculated EM wave absorption with the measured EM wave properties showed that the composite containing 30wt% hollow Ni/Fe–Co (7:3) fibers in length of 180μm exhibited multiple absorbance peaks resulting in a broad absorption bandwidth of 4.2GHz. It is obvious that this multiple absorbance is attributed to the resonance characteristic of the composite.

Large Remanent Polarization and Low Leakage Current in High-&lt;i&gt;T&lt;sub&gt;c&lt;/sub&gt; &lt;/i&gt;0.2Bi (Ni&lt;sub&gt;1/2&lt;/sub&gt;Ti&lt;sub&gt;1/2&lt;/sub&gt;)O&lt;sub&gt;3&lt;/sub&gt;-0.8PbTiO&lt;sub&gt;3&lt;/sub&gt; Ferroelectric Thin Films

High Curie-temperature (Tc) polycrystalline 0.2Bi (Ni1/2Ti1/2)O3-0.8PbTiO3 (0.2BNT-0.8PT) thin films were fabricated on Pt (111)/Ti/SiO2/Si substrates via an aqueous chemical solution deposition (CSD) technique. The thin films exhibited good crystalline quality and dense, uniform microstructures with an average grain size of 55 nm. The dielectric, piezoelectric and ferroelectric properties of the films was investigated. The permittivity peak appeared at 485 °C, which was 100 °C higher than that of Pb (Zr,Ti)O3 thin films. The local effective piezoelectric coefficient d33 was 45 pm/V at 3V. Moreover, a large remnant polarization with 2Pr up to 92 uC/cm2 and a small leakage current of 2.2×10-5 A/cm2 under an electric field of 400 kV/cm were obtained. The magnitude of the measured polarization and the high Curie temperature make the 0.2BNT-0.8PT films promising candidates for application in high-temperature ferroelectric and piezoelectric devices.

Pb(Mg1/3Nb2/3)O3: A minimal induced-moment soft pseudospin glass perspective

An argument that relaxor ferroelectricity in the isovalent alloy $\mathrm{Ba}({\mathrm{Zr}}_{1\ensuremath{-}x}{\mathrm{Ti}}_{x}){\mathrm{O}}_{3}$ can be understood as an induced-moment soft pseudospin glass on the $B$ ions of the $AB{\mathrm{O}}_{3}$ matrix [Sherrington, Phys. Rev. Lett. 111, 227601 (2013)] is extended to the experimentally paradigmatic but theoretically more complex heterovalent relaxor $\mathrm{Pb}({\mathrm{Mg}}_{1/3}{\mathrm{Nb}}_{2/3}){\mathrm{O}}_{3}$. It is argued that interesting behavior of the onset of nonergodicity, frequency-dependent permittivity peaks, and precursor nanodomains can be understood from analogous considerations of the $B$ ions, with the displacements of the Pb ions a largely independent, but distracting, side feature. This contrasts with conventional conceptualizations.

Structure and Dielectric Properties of BaTiO3–BiYO3 Perovskite Solid Solutions

(1−x)BaTiO3–xBiYO3 [(1−x)BT–xBY] polycrystalline ceramics were prepared by solid‐state reaction method. The ceramics are in tetragonal phase when x ≤ 0.04, transform to pseudocubic at x ≥ 0.06, showing a classic ferroelectric to relaxor transition at x = 0.06, where the phase transition temperature was found to shift to higher temperature with increasing frequency. The dielectric permittivity peaks were analyzed by the modified Curie–Weiss law. Both parameters ΔTdiffuse and ΔTrelaxor were found to increase with increasing BY content, demonstrating a stronger relaxor characteristic.

Role of random electric fields in relaxors

PbZr(1-x)Ti(x)O3 (PZT) and Pb(Mg1/3Nb2/3)(1-x)Ti(x)O3 (PMN-xPT) are complex lead-oxide perovskites that display exceptional piezoelectric properties for pseudorhombohedral compositions near a tetragonal phase boundary. In PZT these compositions are ferroelectrics, but in PMN-xPT they are relaxors because the dielectric permittivity is frequency dependent and exhibits non-Arrhenius behavior. We show that the nanoscale structure unique to PMN-xPT and other lead-oxide perovskite relaxors is absent in PZT and correlates with a greater than 100% enhancement of the longitudinal piezoelectric coefficient in PMN-xPT relative to that in PZT. By comparing dielectric, structural, lattice dynamical, and piezoelectric measurements on PZT and PMN-xPT, two nearly identical compounds that represent weak and strong random electric field limits, we show that quenched (static) random fields establish the relaxor phase and identify the order parameter.

Electrical properties of niobium doped Bi4Ti3O12-SrBi4Ti4O15 intergrowth ferroelectrics

Nb-doped Bi4Ti3O12-SrBi4Ti4O15 intergrowth ceramics have been prepared by modified oxalate route. XRD phase analysis confirmed the formation of single phase compound. Nb-doping does not affect the basic crystal structure of the intergrowth. SEM micrographs showed that the grain size of the ceramics decreases with Nb-doping. The temperature dependence of dielectric constant and losses was investigated in the temperature range 30–800°C and frequency range 1kHz–1MHz. With Nb-doping, the Tc of the ferroelectrics reduces and peak permittivity increases. Doping also introduces small relaxor behavior in the ferroelectrics. The dc conductivity of the ceramics decreases with doping. The remnant polarization (Pr) of the intergrowth ferroelectrics is increased with Nb doping.