Differential Permittivity Research Articles

Influence of uniaxial pressure and aging on dielectric and ferroelectric properties of BaTiO3 ceramics

The effect of uniaxial pressure (0–3000 bar) applied parallel to the AC electric field and aging on dielectric and ferroelectric behavior of BaTiO3 ceramics were investigated. Applying uniaxial pressure leads to a reduction of the peak intensity of the electric permittivity (ε) of the polarization as well as of the dielectric hysteresis. The peak intensity of ε becomes diffused and shifts to a higher temperatures with increasing the pressure. The electrostrictive coefficient Q 11 and differential permittivity were evaluated from the obtained data. We interpreted our results based on the hardening of the soft-mode and domain switching processes under the action of pressure. The aging effect followed a logarithmic law and is related to the relaxation of the domain structure toward an equilibrium configuration. The aging rate was found to decrease with increasing frequency as a result of the pinning of polarization components by defects field.

Ca10.5 − x Pb x (PO4)7 and Ca9.5 − x Pb x M(PO4)7 ferroelectrics with the whitlockite structure

We have prepared Ca9.5 − xPbxM(PO4)7 (M = Mg, Zn, Cd) and Ca10.5 − xPbx(PO4)7 solid solutions. A polar whitlockite-like (sp. gr. R3c) crystal structure exists in the range 0 ≤ x ≤ 1.5 for all of the M cations in Ca9.5 − xPbxM(PO4)7 and in the range 0 ≤ x ≤ 2.5 for Ca10.5 − xPbx(PO4)7. X-ray powder diffraction profile analysis results for Ca8.5PbCd(PO4)7 powder demonstrate that the small divalent M cations reside predominantly on the octahedral site M5 of the whitlockite structure, the calcium cation occupy the M1–M3 sites, and the lead cations are located primarily on the M4 site. Differential scanning calorimetry, second-harmonic generation, and dielectric permittivity data indicate that all of the synthesized phosphates are high-temperature ferroelectrics. The highest Curie temperatures are offered by the x = 0.5 materials, in which most of the lead resides in the spacious oxygen polyhedra M4 and only a small amount of lead is incorporated into the smaller polyhedra around M1–M3. The nonlinear optical activity has a maximum in the middle of the solid-solution series and is an order of magnitude higher than that of the parent, lead-free phases.

Structure and properties of Ca9 − x Pb x R(PO4)7 (R = Sc, Cr, Fe, Ga, In) whitlockite-like solid solutions

We have prepared solid solutions based on whitlockite-structure ferroelectrics, Ca9 − x Pb x R(PO4)7 (R = Sc, Cr, Fe, Ga, In), through Pb substitution for Ca. Single-phase Ca9 − x Pb x R(PO4)7 materials with a polar whitlockite-like structure (sp. gr. R3c) exist in the range 0 ≤ x ≤ 1.5 for all of the R metals studied. X-ray powder diffraction profile analysis results for R = In (x = 0.5, 0.8, and 1.0) demonstrate that the trivalent cations reside on the octahedral site M5 of the whitlockite structure, the calcium cation occupy the M1–M3 sites, and the lead cations are located predominantly on the M3 site. Differential scanning calorimetry, dielectric permittivity, and second-harmonic generation data attest to a ferroelectric phase transition, whose temperature is 580–610°C in Ca9R(PO4)7 and decreases monotonically to 480–520°C as x increases to 1.5.

Uniaxial stress dependence of the dielectric and ferroelectric properties of the Na0.5K0.5NbO3 and Na0.5K0.5NbO3 + 0.5 mol%MnO2 ceramics

Na0.5K0.5NbO3 and Na0.5K0.5NbO3 + 0.5 mol%MnO2 lead-free ceramics have been produced by solid phase hot pressing sintering process at 1120–1145°C. The results of the X-ray diffraction measurements showed that the obtained samples possessed a perovskite structure. The micrograph of the fractured surface showed a dense ceramic structure, in compliance with 93% relative density determined by the Archimedes method. The dependence of dielectric and ferroelectric properties on the uniaxial compressive stress (0–3000 bar) of the Na0.5K0.5NbO3 and Na0.5K0.5NbO3 + 0.5 mol%MnO2 ceramics was investigated. Significant influence of the external stress on these properties was revealed. It includes a shift of the phase transition, diffuseness of the permittivity maxima, increase of the thermal hysteresis and decrease of polarization. The electrostrictive coefficient Q 11 and the differential permittivity were estimated from the obtained data. We discuss our results based on hardening of the soft-mode and domain switching processes under the action of pressure.

Conductivity Studies on Li<sub>1-X</sub>Al<sub>x</sub>Ti<sub>2-X</sub>(PO<sub>4</sub>)<sub>3</sub> (X=0.0-0.5) Due to the Addition of Al<sup>3+</sup> Trivalent Cation

The Li-ion fast conductor, Li1-XAlxTi2-X(PO4)3 (LATP) compound were synthesized by a sol-gel method. Effects due to the addition of Al3+ into Li1-XAlxTi2-X(PO4)3 (x=0.0-0.5) glass-ceramics system have been investigated using electrochemical impedance spectroscopy (EIS), X-ray differential analysis (XRD) and permittivity studies. The crystalline phase of the samples obtained confirming that they had a characteristic of glass-ceramics structure.

Soft and hybrid-doped Pb(Zr,Ti)O3 ceramics under stress, electric field, and temperature loading

We investigated the influence of uniaxial pressure (0–1000 bars) applied parallelly or perpendicularly to the ac or dc electric field (in a one-dimensional or two-dimensional manner) on dielectric and ferroelectric properties of selected soft and hybrid-doped PZT ceramics (1 mol. % Gd, 1 mol. % La and 1 mol. % (La+Fe)-doped Pb(Zr0.54Ti0.46) O3). Applying uniaxial pressure leads to a reduction of the peak intensity of the electric permittivity (ɛ), of the frequency dispersion, and of the dielectric hysteresis. The peak intensity of ɛ becomes diffused and shifts to a higher temperatures with increasing pressure. Simultaneous application of uniaxial pressure and dc electric field (perpendicular to each other) in the poling process implies in improvement of the ferroelectric properties, indicating a new possibility for poling materials with a high coercive field and/or high electric conductivity. It was also found that simultaneous application of uniaxial pressure and dc electric field (perpendicular to each other) allowed observation of the space charge in the depolarization process. The electrostrictive coefficient Q11 and differential permittivity were evaluated from obtained data. Our results show that applying uniaxial pressure induces similar effects as increasing the Ti-ion concentration in the PZT system. We interpreted our results based on the Cochran soft-mode and domain switching processes under the action of pressure.

A test bench for investigating the pulsed polarization dynamics of nonlinear dielectrics

A test bench for investigating the polarization of nonlinear dielectrics under the action of the leading edges of high-voltage pulses is described. The design of the bench ensures investigations of pulsed polarization of ferroelectrics under a monotonic increase in the electric-field strength within time intervals from tens of nanoseconds to tens of milliseconds at voltages ranging from several hundred volts to tens of kilovolts. In accordance with the technique described, experimental dependences of the electric induction, dielectric permittivity, and differential dielectric permittivity on the pulsed electric-field strength at various temperatures of ferroelectric ceramics on the basis of solid solutions of barium and strontium titanates have been obtained.

Study of microstructure in Ag x(As 0.33Se 0.67) 100−x chalcogenide glasses

Glasses with general formula Ag x (As 0.33Se 0.67) 100− x were studied by means of modulated differential scanning calorimetry (MDSC), conductivity and permittivity measurements and atomic force acoustic microscopy (AFAM). In the whole range of doping ( x = 2–12 at.% Ag) a phase separation was supposed. The proportional amount of the ion-conductive Ag rich phase increased with the Ag content. A rapid increase (almost four orders of magnitude) in the conductivity was observed in the Ag concentration range 4–8 at.%, which could be associated with the interconnection of this ion-conductive phase. The transition from a hole conductivity (at low Ag concentration) to a mixed ionic-hole conductivity at higher Ag concentration was studied by permittivity measurements.

The Frequency Dependence of the Conductivity and Dielectric Relaxation of [(CH2)3(NH3)2]Cu(II)Cl4

The structural, dielectric and conductive properties of [(CH2)3(NH3)2]Cu(II)Cl4 have been studied. The material shows an order-disorder transition at T1 = (333±2) K and a ferroelectric phase transitions at T2 = (434±3) K. Results of differential thermal analysis, infrared spectroscopy, X-ray diffraction, AC conductivity and permittivity measurements are reported and discussed. The conductivity results are interpreted in terms of barrier hopping at low and intermediate temperatures, and band-type conduction at high temperatures. - PACS: 81.05.-t, 77.22.-d

Uniaxial stress dependence of ferroelectric properties of xPMN-(1–x)PZT ceramic systems

Effects of uniaxial compressive pre-stress on the ferroelectric properties of ceramics in the PMN-PZT system are investigated. The ceramics with a formula xPb(Mg1/3Nb2/3)O3-(1-x)Pb(Zr0.52Ti0.48)O3 or xPMN-(1-x)PZT when x=0.0, 0.1, 0.3, 0.5, 0.7, 0.9, and 1.0 are prepared by a conventional mixed-oxide method. The ferroelectric properties under the uniaxial compressive pre-stress of the PMN-PZT ceramics are observed at the stress levels up to 13 MPa using a compressometer in conjunction with a modified Sawyer–Tower circuit. It is found that with increasing compressive pre-stress levels the area of the ferroelectric hysteresis (P–E) loops, the saturation polarization (Psat), the remanent polarization (Pr), and the coercive field (Ec) decrease. These results are interpreted through the non-180° ferroelastic domain-switching processes. Finally, the calculated differential permittivity for all the xPMN-(1-x)PZT ceramics, except for 0.5 PMN-0.5 PZT, decreases with increasing applied stress.

Modification of the structure and properties of poly(vinylidene fluoride–trifluoroethylene) 56/44 mol % copolymer by a proton‐irradiation treatment

AbstractThe effects of high‐energy proton irradiation on the structure and properties of 56/44 mol % poly(vinylidene fluoride–trifluoroethylene) copolymer were studied with differential scanning calorimetry (DSC), X‐ray diffraction (XRD), relative permittivity, and polarization hysteresis measurements. Copolymer films prepared by hot compression molding were irradiated with a broad range of proton dosages (10–107 Mrad) at room temperature. The DSC results showed that the ferroelectric transition was strongly affected by the proton dosages. The XRD data indicated the reduction of polar ordering in the copolymer by the proton‐irradiation treatment. From the relative permittivity and polarization behavior, the copolymer film was found to be converted from a normal ferroelectric material to a relaxor ferroelectric material as the proton dosage was increased to 50 Mrad. The electrostrictive coefficient of the 56/44 mol % copolymer was enhanced after irradiation, and the optimized proton dosage for attaining the highest electrostrictive strain response was determined. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 2334–2339, 2005

Model for ferroelectric semiconductors thin films accounting for the space varying permittivity

Reducing thickness of ferroelectric films typically comes with an apparent degradation of their ferroelectric and dielectric properties. The existence of low-dielectric interfacial layers is often invoked to explain such behaviors. Much work has been done on modeling ferroelectric thin films by considering a ferroelectric layer between two layers with low dielectric constant. In these models it is necessary to introduce extrinsic parameters; the dielectric constant and the polarization are step functions of the depth inside the film. We have developed a model for ferroelectric semiconductors based on the inhomogeneous Landau–Devonshire theory, including surface effects. The local electric field is determined by solving Poisson’s equation in which a differential permittivity replaces the dielectric constant. We have found that the hysteresis loops were strongly influenced by the correlation length. That point is discussed by examining the electric field, polarization, and differential permittivity profile inside the film. It is shown that the differential permittivity strongly decreases with the correlation length increases. That phenomena leads to high electric fields inside the film and especially close to the surface. As a consequence, an explanation for thin film ferroelectric properties can be given by invoking space charge density many orders of magnitude lower than those usually considered.

Non-linear dielectric response of ferrofluids under magnetic field

The dielectric response of a water-based magnetic fluid is investigated at room temperature and in the frequency range of 100–10 7 rad/s. The response is linear in the electric fields used. Upon application of a constant magnetic field of 40 mT, which is well below the sample saturation, the response becomes non-linear. Magnetic field effects are isolated by performing a differential analysis of the inverse dielectric permittivity with and without applied field in both perpendicular and parallel configurations. The imaginary part of the differential inverse permittivity displays two peaks. The low-frequency peak is seen to correspond to the orientation relaxation of aggregates also detected in SAXS, photon correlation and atomic force microscopy measurements. The high-frequency peak corresponds to single magnetic particle reorientation.

Ferroelectric Characterization of a Room Temperature Liquid Crystal: 2Cl.BAAP.180-BBP by Low Frequency Dielectric and Optical Methods

The isotropic to nematic(IN), nematic to cholesteric(NCh), cholesteric to smectic-A (ChA) and smectic-A to smectic-C* (AC*) phase transition temperatures exhibited by a room temperature ferroelectric liquid crystal RTFLC, viz., 2Cl.BAAP.180-BBP are determined by the observed anomaly in differential permittivity, d l '/dT. The low frequency dielectric dispersion along with the activation energy are detailed in the N, Ch, SmA and SmC* phases. The Soft mode and Goldstone mode relaxation in the vicinity of AC* phase transition are discussed. The trend of distribution parameter h-values for the off-centred Debye relaxation is discussed. Temperature variation of dilectric strength for the soft mode relaxation is estimated through ferrolectric Curie-Weiss law. Observed temperature variation of Spontaneous Polarization P s (T), Tilt angle θ(T), Response Time s (T), and Effective Torsional viscosity m (T) is found to agree with the Mean field expectation. Relative strength of P s among the reported values is discussed as a function of extended conjugation about the chiral centre.

Photoacoustic analysis of the ferroelectric ceramics specific heat

Knowing the thermal expansion of a material and the correlation analysis of the photoacoustic signals, it is possible to obtain the phase transition temperature and a qualitative curve of the specific heat at constant pressure (Cp) for ceramic materials. This analysis was applied to a BaTiO3 ferroelectric ceramic and a good agreement with previously published Cp versus temperature curves was obtained. Additionally, the phase transition temperature and the Cp curve of a samarium-doped lead titanate ceramic (Pb0.88Sm0.08TiO3) are presented. The phase transition temperature of the Pb0.88Sm0.08TiO3 obtained with this technique was corroborated with classical differential thermal analysis and dielectric permittivity measurements.

Photoacoustic phase transition of the ceramic BaTiO3

Photoacoustic signals from the ceramic BaTiO3 are analyzed, as a function of temperature close to structural phase transition from tetragonal to cubic at 110 °C. The amplitude of the signals depends on the changes of the thermoelastic properties in the ceramic with temperature. The Curie temperature value for the phase change was reproducible and was found to be 109±6 °C. A comparative analysis of this result with the differential thermal analysis and permittivity techniques is performed. Two changes of sign in the photoacoustic signal are observed, associated with the thermal expansion coefficient behavior in this material near the transition.

Comment on ‘‘A Comment on dielectric theory: Differential equations and permittivity’’

A number of models for the non-Debye dielectric response have been developed during the last few years. One such example reported by Kliem [J. Appl. Phys. 70, 1861 (1991)] from the work by Guo and Guo [J. Phys. C 16, 1955 (1983)] is not compatible with linear response theory, except under the condition of a step-function electric field; this has lead to a confusion of this model with those commensurate with linear response theory. The present communication resolves this ambiguity.

Reply to ‘‘Comment on ‘A Comment on dielectric theory: Differential equations and permittivity’ ’’

It is emphasized that in the comment of J. M. Alison on my communication [J. Appl. Phys. 70, 1861 (1991)] the time dependent coefficient f(t) in the equation of motion has been mistaken for the dielectric decay function φ(t).

A comment on dielectric theory: Differential equations and permittivity

For an explanation of the non-Debye response (NDR) several models have been developed during the last years. Some of these models use differential equations with time-dependent coefficients for the polarization or for the dielectric decay function. In this article it is investigated whether these differential equations may be used for an explanation of NDR. The conclusion is that they are not suitable.

(CH3)4NHgBrI2—A New polar organic-inorganic double halide

(CH3)4NHgBrI2 exhibits at room temperature a polar columnar structure based on edge-sharing anion tetrahedra with a double anion occupancy. Its orthorhombic space group is Pb2//1m. An unusual multiple phase transition sequence revealed by differential scanning calorimetry, dilatometry and permittivity vs. temperature measurements leads to a non-polar high temperature phase with a trigonal mercury coordination and the monoclinic space group P2//1/n.