Dielectric Relaxation Peaks Research Articles

Cerium doped strontium titanate with stable high permittivity and low dielectric loss

High permittivity materials continue to arouse considerable interest due to their applications in the field of high performance capacitors. However it is still a challenge to make material both with stable high permittivity and low dielectric loss. Here, the Sr1-3x/2CexTiO3 (SCT) ceramics are synthesized via solid-state reaction process and sintering in air. The sample (x = 0.01) exhibits a high permittivity of ∼7000 and low dielectric loss of ∼0.007 at room temperature and 1 kHz. Moreover, the dielectric properties are stable over a very broad temperature and frequency range. Further investigations reveal that the high permittivity is related to the defect chemistry caused by the trace Ce ions doping. The Ti3+ ions substitute the Ti4+ ions lead to the Ti-O octahedral off-center, which make a certain contribution to improve the permittivity. The low dielectric loss is owing to the fact that the defects are more likely to be in the form of defect clusters in the Ce doped SrTiO3 monophase solid solutions. The appropriate defect chemistry design suppresses the dielectric loss relaxation peak of Sr1-xCexTiO3 (x = 0.01) caused by the motion of oxygen vacancies.

Nanoscale compositional segregation and suppression of polar coupling in a relaxor ferroelectric

A number of relaxor ferroelectric ceramics have been demonstrated to possess a near stable value of relative permittivity over very wide temperature ranges. This cannot be explained by conventional theories of relaxors. One such system is based on the perovskite solid solution series: (1-x) (Ba0.8Ca0.2)TiO3-xBi(Mg0.5Ti0.5)O3, giving stable relative permittivity from 150 to 500 °C. We show by scanning transmission electron microscopy and electron energy loss spectroscopic elemental mapping that nanoscale compositional segregation occurs in the temperature stable relaxor composition (x = 0.55), with Ba/Ti clusters some 2–4 nm in extent, separated by Bi-rich regions of comparable size. This nanomosaic structure is consistent with phase separation into a ferroelectrically active BaTiO3 – type phase (Ba/Ti rich) and a weakly polar Bi/(Mg) rich perovskite solid solution. The possibility that nanophase segregation is the cause of weak dipole coupling and suppression of the dielectric relaxation peak is considered.

Understanding Thermal Admittance Spectroscopy in Low-Mobility Semiconductors

Thermal admittance spectroscopy (TAS) is frequently used to analyze the properties of trap states in semiconductor devices. We perform detailed simulations in combination with experiments to understand the effect of low carrier mobility on the analysis of trap states by TAS. We show that the apparent characteristic peak in the differential capacitance spectra is strongly dominated by the dielectric relaxation (DR) peak caused by low carrier mobilities for the case of shallow traps and low trap densities. The model for the DR dominated case is successfully applied to interpret the experimental results from poly(3-hexylthiophene-2,5-diyl) (P3HT) based diodes. In contrast, for deep states with high density of states, we are able to properly estimate the energetic position, but the low carrier mobility affects the correct determination of the attempt-to-escape frequency as well as the capture cross section. Our results reveal that low carrier mobilities cause inherent obstacles in accurately determining the t...

Nature of Dielectric Properties, Electric Modulus and AC Electrical Conductivity of Nanocrystalline ZnIn2Se4 Thin Films

The structural characteristics of thermally deposited ZnIn2Se4 thin films were indexed utilizing x-ray diffraction as well as scanning electron microscopy techniques. Dielectric properties, electric modulus and AC electrical conductivity of ZnIn2Se4 thin films were examined in the frequency range from 42 Hz to 106 Hz. The capacitance, conductance and impedance were measured at different temperatures. The dielectric constant and dielectric loss decrease with an increase in frequency. The maximum barrier height was determined from the analysis of the dielectric loss depending on the Giuntini model. The real part of the electric modulus revealed a constant maximum value at higher frequencies and the imaginary part of the electric modulus was characterized by the appearance of dielectric relaxation peaks. The AC electrical conductivity obeyed the Jonscher universal power law. Correlated barrier hopping model was the appropriate mechanism for AC conduction in ZnIn2Se4 thin films. Estimation of the density of states at the Fermi level and activation energy, for AC conduction, was carried out based on the temperature dependence of AC electrical conductivity.

Study of the structural, impedance spectroscopy and dielectric properties of Na and Si co-doped NiO ceramics

Sodium and silicon co-doped NiO (NSNO) of the formula NaxSiyNi1 – x−yO (x = 0.05, 0.1 and y = 0.02, 0.05) were prepared by solid state reaction. Structural, electrical conduction and dielectric properties of the NSNO ceramics were investigated. The current NSNO ceramics exhibited giant dielectric constant (ε′ ~ 104 at 1.1 KHz and 300 K) and three dielectric relaxation peaks were found on the curve of the frequency dependence of the imaginary part of electric modulus M″. The complex impedance diagrams showed three electrical responses, which have been attributed to the domain, domain-boundaries and grain-boundaries in the NSNO ceramics. Analysis of the temperature dependence of the conductivity for the current ceramics indicated that the electrical conduction mechanism changes from variable range hoping at low temperatures (T < 220 K) to nearest neighbor hopping mechanism at higher temperatures. The electrically heterogeneous structure, revealed by the complex impedance analysis, combined with considerable polarization due to defect dipoles are thought to be the cause for the giant dielectric response of NSNO ceramics.

Optical and dielectric relaxation of transition metal-based organic-inorganic hybrid materials

The [(CH3)3NH]CdCl3 (1) and [N(CH3)3H]CoCl3·2H2O (2) compounds were obtained by slow evaporation at room temperature and characterized by X-ray powder diffraction patterns. These compounds were crystallized in the orthorhombic system, in Pbnm and Pnma space groups, respectively. The optical properties were measured by means UV–Vis absorption spectrometry in order to deduce the absorption coefficient α and optical band gap Eg. The Tauc model was used to determine the optical gap energy of the synthesized compounds 1 and 2. Data analysis revealed the existence of two optical transition mechanisms. The calculated values of the direct and indirect band gaps (Egd, Egi) for both samples were estimated between 5.41 and 5.30 eV for compound 1; and between 4.02 and 3.82 eV for compound 2. The dependence of the optical constants, the refractive index (n) and the extinction coefficient (k) of compounds 1 and 2 were calculated and the results discussed. The normal dispersion of refractive index of the samples was described using the Wemple–DiDomenico single oscillator method. The optical dispersion parameters Eo and Ed were determined according to the above oscillator method. We employed dielectric spectroscopy to investigate the dipolar dynamics in the both compound. The evolution of the dielectric loss as a function of frequency showed a distribution of relaxation times; which is probably due to the reorientational dynamics of alkyl chains in compound 1, analyzed with the Cole–Cole formalism. Various relaxation processes and their locations of compound 2 were analyzed according to the fitted data of the Havriliak–Negami (HN) function. Different relaxation processes were found to belong to non-debye relaxation. The dielectric constants were composed of two dielectric relaxation peaks, DC conduction and electrode polarization (EP) effect. The determined values of relaxation time are characteristic of the co-operative reorientation of the trimethylammonium cation.

Magnetic and dielectric study of Fe-doped CdSe nanoparticles

Nanoparticles of cadmium selenide (CdSe) and Fe (5% and 10%) doped CdSe have been synthesized by soft chemical route and found to have cubic structure. The magnetic field dependent magnetization measurement of the doped samples indicates the presence of anti-ferromagnetic order. The temperature dependent magnetization (M-T) measurement under zero field cooled and field cooled conditions has also ruled out the presence of ferromagnetic component in the samples at room temperature as well as low temperature. In order to estimate the anti-ferromagnetic coupling among the doped Fe atoms, an M-T measurement at 500 Oe has been carried out, and the Curie-Weiss temperature θ of the samples has been estimated from the inverse of susceptibility versus temperature plots. The dielectric relaxation peaks are observed in the spectra of imaginary part of dielectric constant. The temperature dependent relaxation time is found to obey the Arrhenius law having activation energy ~ 0.4 eV for Fe doped samples. The frequency dependent conductivity spectra are found to obey the power law.

Synthesis and characterization of multiferroic Sm-doped BiFeO3 nanopowders and their bulk dielectric properties

Multiferroic Bi1−xSmxFeO3 (x=0, 0.05, 0.1, 0.2, and 0.3) nanopowders with particle sizes of 69–22.6nm were prepared by a simple co-precipitation method. The structure and morphology of the samples were examined using X-ray diffraction (XRD) and scanning electron microscopy (SEM). The XRD patterns confirmed the phase transition from rhombohedral to orthorhombic phases. The results of X-ray absorption spectroscopy (XAS) data indicate that the oxidation state of Fe in the sample was Fe3+. The results of magnetic properties revealed the enhancement of weak ferromagnetic property with increasing Sm doping in BFO nanopowders. SEM images revealed that the average grain size decreased with an increase in Sm concentration. Undoped BFO ceramics exhibited a high dielectric constant ε′ ∼1.1×104 and a low loss tangent of tan δ ∼0.5 at room temperature for 1kHz. The room temperature dielectric constant decreased with increasing concentration of Sm doping and the dielectric relaxation peaks were observed at x≤0.1. The dielectric relaxation peaks which were observed at all frequency ranges were x≤0.1 samples which were attributed to Maxwell-Wagner relaxation. As the temperature increased, great increases in dielectric permittivity were observed in all the Bi1−xSmxFeO3 samples. The effects of grain boundaries on the dielectric properties of Sm-doped BFO ceramics were investigated by measuring the dielectric responds in the frequencies of 100Hz–1MHz at room temperature under applied dc bias of 0–20V. It was found that, with an increase in applied dc bias voltage from 0 to 20V, the dielectric constant decreases at frequencies below 104Hz. However, the dielectric properties in the high-frequency region remained unchanged.

Dielectric relaxation behavior of Mn-modified Ca0.9Pr0.05[]0.05Bi2Nb2O9 –based high temperature piezoceramics

Pr/Mn- codoped Aurivillius type Ca0.95[]Bi2Nb2O9 ([] denoted as A-site vacancies) piezoelectric ceramics were prepared by a conventional solid state sintering method. The microstructure and correlated electrical properties were investigated. A set of dielectric relaxation peaks was observed in the high doping level of Pr/Mn-doped CBN ceramics. The primary and secondary processes dominate the dc conduction and dielectric relaxation processes owing to various activation energies. The localized hopping of oxygen vacancies near the Mn doping centers causes the dielectric relaxation behavior. On the other hand, the long-range continuous transformation of oxygen vacancies is responsible for the dc conduction process, which has a higher energy barrier than that of the localized hopping. The thermal depolarization behavior of piezoelectric properties was also studied.

Dielectric and impedance characteristics of Na1/3Ca1/3Y1/3Cu3Ti4O12 ceramic prepared by solid-state reaction method

Dielectric response of Na1/3Ca1/3Y1/3Cu3Ti4O12 ceramic, fabricated via a conventional solid-state method, has been investigated in the frequency range 100–2 MHz at temperatures from −80 to 200 °C. Single phase of Na1/3Ca1/3Y1/3Cu3Ti4O12 with cubic perovskite-related structure was confirmed by X-ray diffraction. High dielectric permittivity (>3 × 103) and low dielectric loss (~0.08) were observed at room temperature. The dielectric relaxation peaks of $$\varepsilon^{\prime \prime }$$ shifts to higher frequencies, indicating a thermally activated relaxation process. The activation energy for the dc conduction process (0.501 eV) is comparable to that for conduction at the grain boundaries (0.514 eV), indicating the dc conduction process is closely associated with the characteristics of grain boundaries in Na1/3Ca1/3Y1/3Cu3Ti4O12 ceramic.

Raman and dielectric spectroscopic analysis of magnetic phase transition in Y(Fe0.5Cr0.5)O3 multiferroic ceramics

Here, we report the Raman and dielectric spectroscopic studies as a function of temperature of orthorhombically distorted Y(Fe0.5Cr0.5)O3 (YFC) ceramics, measured from 80 to 300K. The dc-magnetization measurements under field cooled (FC)-zero field cooled (ZFC) protocol indicate a small onset of magnetic ordering at TN∼270K. The field dependent magnetization plot recorded at 50K, 150K and 200K show a clear opening in hysteresis loops. The linear dependence of magnetization plot at high field without any saturation of magnetization indicates the coexistence of weak ferromagnetic (WFM) component within the canting antiferromagnetic (CAFM) matrix. Temperature evolution of Raman line-shape parameter of B2g(4) phonon mode clearly exhibits an anomalous behavior of phonon shift near TN∼270K, indicating the spin-phonon coupling in the ceramics. From the temperature dependent dielectric permittivity (ε(T)) study, two dielectric relaxation peaks are detected below 200K and above 250K. The appearance of former relaxation peak is responsible for polaronic conduction mechanism, while the later one is associated with magnetic phase transition which might be relevant to the presence of magnetoelectric coupling in YFC ceramics. The observed P-E hysteresis loops at room temperature indicate weak ferroelectric nature of the ceramics.

Preparation, characterization and dielectric response of a high-breakdown-field ZnO-based varistor

In this study, ZnO-based varistors with a high breakdown field were obtained through BaCO3 doping and sintering at a low temperature of 950 °C. The grain size of the ZnO samples decreased to 1.28 μm, and the breakdown field was enhanced to 3845 V/mm, which is approximately one order of magnitude higher than that of ordinary ZnO-based varistors. The dielectric responses of the ZnO-based varistors were measured in a wide frequency and temperature range. At 193 K, two dielectric relaxation peaks with activation energies of 0.22 and 0.35 eV were observed and considered intrinsic defects; these peaks did not vary with the preparation process. Another dielectric relaxation peak observed in a wide temperature range (283–463 K) was characterized in an impedance plot. This relaxation peak was ascribed to extrinsic defects related to the grain boundary. The resistance values of the grain boundary increased by two orders of magnitude through BaCO3 doping and lowering of the sintering temperature. The corresponding activation energy also increased from 0.53 to 0.74 eV. A parallel resistance–capacitance circuit model was proposed to interpret the variation in the electrical properties of ZnO-based varistors.

Anomalous europium luminescence in LaF3

Optical spectra (absorption, emission, excitation, decay) and dielectric relaxation were measured for divalent europium and partially for ytterbium in lanthanum fluoride crystals. Optical absorption of LaF3–Eu2+ contains not only asymmetric weakly structured band at 245 nm but also less intense bands at 330, 380 nm. Broadband Eu2+ emission at 600 nm appeared below 80 K with decay time 2.2 μs at 7.5 K. Emission at 600 nm is attributed to so-called anomalous luminescence. Bulk conductivity is directly proportional to absorption coefficient of Eu2+ bands. Dielectric relaxation peak of LaF3–EuF3 is attributed to rotation of dipoles Eu2+-anion vacancy. The long-wavelength absorption at 300–400 nm region are assigned to transitions from 4f7Eu2+ ground state to states of neighbouring fluorine vacancy.

誘電緩和現象を用いた高分子樹脂に分布したマイクロフィラーの分散性評価手法の検討

Dielectric properties were measured of epoxy composites filled with ZnO micro fillers in the range of 1 mHz-1 MHz of frequency at room temperature. In order to observe loss peaks in the composite samples, obtained data were transformed to “electric modulus”. We found two main dielectric relaxation peaks, which were fitted with Havriliak-Negami equations. Fine structure of the samples was investigated and the dispersion of the micro fillers in epoxy resin was found. The difference in 2nd relaxations for the samples might express the dispersion of micro fillers.

Relaxor Behavior and Dielectric Relaxation in Lead-Free Solid Solutions of (1 − x)(Bi0.5Na0.5TiO3)–x(SrNb2O6)

Lead-free compositions (1 − x) (Bi0.5Na0.5TiO3)–x(SrNb2O6) (BNT-SN) are synthesized by a simple solid state reaction route. SN diffuse in distorted perovskite BNT for low concentrations of SN (x ≤ 0.03) and are stabilized in rhombohedral perovskite phase with experimentally observed relative density of the ceramics >92%. A temperature-dependent dielectric response exhibits a broad dielectric peak that shows frequency-dependent shifts towards higher temperatures reflecting typical relaxor behavior. Modified Curie–Weiss law and Lorentz-type empirical relationships are used to fit the dielectric data that exhibit almost complete diffuse phase transition characteristics. In addition, significant dielectric dispersion is observed in a low-frequency regime in both components of the dielectric response and a small dielectric relaxation peak is observed. Cole–Cole plots indicate the poly-dispersive nature of the dielectric relaxation.

Structural and AC conductivity study of CdTe nanomaterials

Cadmium telluride (CdTe) nanomaterials have been synthesized by soft chemical route using mercapto ethanol as a capping agent. Crystallization temperature of the sample is investigated using differential scanning calorimeter. X-ray diffraction and transmission electron microscope measurements show that the prepared sample belongs to cubic structure with the average particle size of 20nm. Impedance spectroscopy is applied to investigate the dielectric relaxation of the sample in a temperature range from 313 to 593K and in a frequency range from 42Hz to 1.1MHz. The complex impedance plane plot has been analyzed by an equivalent circuit consisting of two serially connected R-CPE units, each containing a resistance (R) and a constant phase element (CPE). Dielectric relaxation peaks are observed in the imaginary parts of the spectra. The frequency dependence of real and imaginary parts of dielectric permittivity is analyzed using modified Cole–Cole equation. The temperature dependence relaxation time is found to obey the Arrhenius law having activation energy ~0.704eV. The frequency dependent conductivity spectra are found to follow the power law. The frequency dependence ac conductivity is analyzed by power law.

The effect of Mn doping contents on the structural, dielectric and magnetic properties of multiferroic Bi5Ti3FeO15 Aurivillius ceramics

Aurivillius Bi5Ti3FeO15 (BTFO) multiferroic ceramics with different Mn doping contents were synthesized through the conventional solid state reaction. The effect of Mn doping on the structural, magnetic and dielectric behaviors of BTFO ceramics is investigated in detail. All these Mn-doped BTFO ceramics are determined to be layered Aurivillius structure by X-ray diffraction. No microstructure variation of plate-like grains is obviously confirmed due to Mn doping through field emission scanning electron microscopy. Similar evolution of ε and tanδ with frequency is found both in BTFO and 10% Mn-doped BTFO ceramics. However, obvious dielectric dispersion phenomena are presented as the Mn-doping content is beyond 0.1, and this dispersion behavior becomes strong with increasing Mn-doping content, clearly indicated by the appearance of dielectric loss relaxation peaks. Finally, the same magnetic orders of 10% Mn-doped BTFO ceramics as those of the BTFO one are unambiguously found while weak ferromagnetism is observed in BTFO ceramics with Mn-doping content beyond 0.2.

Dielectric Characteristics in BiFeO3-Modified SrTiO3 Incipient Ferroelectric Ceramics

We investigate the dielectric and ferroelectric properties of Sr1−xBixTi1−xFexO3 solid solutions (x = 0, 0.05, 0.1, 0.15 and 0.2) together with their structures. Through the analysis of Rietveld refinement of powder x-ray diffraction, a cubic structure in space group Pm3̄m is determined for all the compositions. An obvious dielectric relaxation peak differing from SrTiO3 is observed in the present ceramics. The peak temperature Tm increases with increasing x, and it approaches room temperature at x = 0.2. The Vogel—Fulcher law and Curie—Weiss law fittings further confirm the relaxor ferroelectricity in the present ceramics.

Magnetic, dielectric, and magneto-dielectric properties of rare-earth-substituted Aurivillius phase Bi6Fe1.4Co0.6Ti3O18

We investigate the magnetic, dielectric, and magnetodielectric properties of rare-earth-substituted Aurivillius phase Bi6Fe1.4Co0.6Ti3O18. The room-temperature ferromagnetic behavior is observed in all samples, and the rare-earth-substituted samples exhibit an enhanced magnetization. The weak ferromagnetism can be ascribed to the spin canting of the antiferromagnetic coupling of the Fe-based and Co-based sublattices via Dzyaloshinsky-Moriya interaction. The dielectric loss of all samples exhibits two dielectric relaxation peaks corresponding to two different relaxation mechanisms. One relaxation process with Ea = 0.5 eV is related to the hoping process of oxygen vacancies and the other one with Ea = 1.6 eV can be ascribed to the intrinsic conduction. The Gd-doped sample exhibits a remarkable magnetodielectric effect (9.4%) at RT implying this Aurivillius phase may be the potential candidate for magnetodielectric applications.

Colossal breakdown electric field and dielectric response of Al-doped CaCu3Ti4O12 ceramics

Abstract A greatly enhanced breakdown electric field of ∼21 kV/cm was achieved by liquid-phase doping of Al 2 O 3 in CaCu 3 Ti 4 O 12 (CCTO) ceramics. It was found that the dielectric loss of CCTO ceramics was composed of two dielectric relaxation peaks and dc conduction. Impedance analysis showed that the grain boundary resistance was increased from 0.37 MΩ to 13.55 MΩ and the corresponding activation energy of grain boundary was elevated from 0.63 eV to 0.81 eV. The frequency dependence of the conductivity was interpreted with the Jonscher's law, which indicated that the contribution of dc-like conduction at low frequency was effectively suppressed by Al 2 O 3 doping. In addition, dimensional effect of the CCTO ceramics was found and an inflection (or critical) point behavior can be observed for pure and Al-doped samples, which referred to the variation of the breakdown electric field with the thickness of the samples.