Activation Energy Of Relaxation Research Articles

Ultrahigh thermal stability of dielectric permittivity in 0.6Bi(Mg1/2Ti1/2)O3–0.4Ba0.8Ca0.2(Ti0.875Nb0.125)O3

0.6Bi(Mg1/2Ti1/2)O3–0.4Ba0.8Ca0.2(Nb0.125Ti0.875)O3 ceramics with a pseudo-cubic structure and re-entrant dipole glass behavior have been investigated via x-ray diffraction and dielectric permittivity–temperature spectra. It shows excellent dielectric–temperature stability with small variations of dielectric permittivity (±5%, 420–802 K) and dielectric loss tangent (tanδ < 2.5%, 441–647 K) in a wide temperature range. Three dielectric anomalies are observed from 290 to 1050 K. The low-temperature, weakly coupled re-entrant relaxor behavior was described using the Vogel–Fulcher law and the new glass model. The mid- and high-temperature dielectric anomalies are characterized by isothermal impedance and electrical modulus. The activation energy of both dielectric relaxation and conductivity follows the Arrhenius law in the temperature ranges of 633–753 and 833–973 K, respectively. The ultrahigh thermal stability of dielectric permittivity is attributed to the weak coupling of polar clusters, the formation of diffuse phase transition, and the local phase transition of calcium-containing perovskite. The results provide new insights into the defects behavior and the modification way of re-entrant relaxor behavior.

Thermo-kinetic and structural characterization of Ce-doped glasses based on Bioglass 45S5

Thermo-kinetic behavior of Ce-doped 45S5 bioactive glass (addition of CeO2 up to 1.5 mol.%) was explored by means of calorimetry and thermomechanical analysis. The apparent activation energy of structural relaxation was estimated to vary in the 540–670 kJ mol−1 range. The relaxation process exhibited broad distribution of relaxation times and the relaxation motions were found to only weakly depend on the material's structure. The activation energy of viscous flow was found to vary in the 585–615 kJ mol−1 range; the viscosity itself showed Arrhenian behavior within 107–1011 Pa s. Thermal stability of the glasses was found to be non-monotonous and generally very low, with the most stable glass composition being 45S5 + 0.5 mol.% CeO2. The cold crystallization was found to behave autocatalytically, with the activation energy decreasing from 360 to 310 kJ mol−1 with the gradual addition of CeO2. While the bulk glasses were crystallization-resistant up to 620 °C, the powdered material with CeO2 content ≥1 mol.% was predicted to crystallize even at temperatures slightly above the glass transition temperature.

Crystal structure, photomagnetic and dielectric properties of a cyanido-bridged Cu-Mo assembly film

A film of a cyanido-bridged Cu-Mo assembly CuII2[MoIV(CN)8]·8H2O (CuMo-film) was electrochemically synthesized. Unlike analogs with a formula of MII2[MoIV(CN)8]·zH2O (M = Mn, Fe, Co), which show tetragonal crystal structures, the CuMo-film shows a monoclinic structure in the C2/m space group with cell parameters of a = 17.2461 Å, b = 11.1681 Å, c = 11.2618 Å, β = 125.1089°, and V = 1774.44 Å3. Extended X-ray absorption fine structure analysis traced the bond distances around the Cu site as 1.93–2.30 Å for Cu-N and 2.01–2.40 Å for Cu-O. CuMo-film exhibits photo-switchable magnetization with TC = 18 K and dielectric relaxation related to the hydrogen bond network. The change of activation energy (Ea) of the dielectric relaxation around 157 K (from Ea = 49.9 kJ mol−1 to Ea = 27.3 kJ mol−1 on cooling) suggests that the development of the hydrogen bond network occurs below 157 K.

Structure ordering and glass transition in size-asymmetric ternary mixtures of hard spheres: Variation from fragile to strong glasses.

We investigate the structure and activated dynamics of a binary mixture of colloidal particles dispersed in a solvent of much smaller-sized particles. The solvent degrees of freedom are traced out from the grand partition function of the colloid-solvent mixture which reduces the system from ternary to effective binary mixture of colloidal particles. In the effective binary mixture colloidal particles interact via effective potential that consists of bare potential plus the solvent-induced interaction. Expressions for the effective potentials and pair correlation functions are derived. We used the result of pair correlation functions to determine the number of particles in a cooperatively reorganizing cluster (CRC) in which localized particles form "long-lived" nonchemical bonds with the central particle. For an event of relaxation to take place these bonds have to reorganize irreversibly, the energy involved in the processes is the effective activation energy of relaxation. Results are reported for hard sphere colloidal particles dispersed in a solvent of hard sphere particles. Our results show that the concentration of solvent can be used as a control parameter to fine-tune the microscopic structural ordering and the size of CRC that governs the glassy dynamics. We show that a small variation in the concentration of solvent creates a bigger change in the kinetic fragility which highlights a wide variation in behavior, ranging from fragile to strong glasses. We conclude that the CRC which is determined from the static pair correlation function and the fluctuations embedded in the system is probably the sole player in the physics of glass transition.

Influence of confined phase transition on dielectric relaxation characteristics of thermochromic epoxy insulating materials

The dielectric relaxation characteristic and mechanism of thermochromic microcapsule-epoxy insulating material are investigated. The results show that thermochromic microcapsule-epoxy insulating material exhibits non-monotonic dielectric relaxation characteristic, namely the dielectric relaxation time gradually increases with the temperature rising in a range of about 58–66 ℃, which cannot be depicted by the conventional Arrhenius equation or Vogel-Fulcher-Tammann equation. It is proposed that the non-monotonic dielectric relaxation characteristic is derived from the free volume variation induced by the confined phase transition in microcapsule. With the increase of temperature, the solid-liquid phase transition occurs in the limited space of microcapsule, reducing the free volume inside the microcapsule, which could restrict the reorientation of dipole with the external electric field and lead to the increase of dielectric relaxation time. The non-monotonic dielectric relaxation characteristic of thermochromic epoxy specimen is fitted based on the confined dielectric relaxation model, obtaining the activation energy of dielectric relaxation. The relaxation activation energy values of thermochromic epoxy insulating materials with different microcapsule content are of the same order of magnitude, indicating that the non-monotonic dielectric relaxations occur inside the thermochromic microcapsule, verifying the role of confined phase transition in the non-monotonic dielectric relaxation characteristic.

Influences of intergrowth structure construction on the structural and electrical properties of the BBT-BiT ceramics.

Bismuth Layer Structured Ferroelectrics (BLSFs) have always been an important research direction of high Curie temperature piezoelectrical ceramics, and the construction of intergrowth structure has been considered as an effective method to improve the electric properties of BLSFs. There are many literatures about intergrowth structure improving electrical performance, but few reports analyze the influence of the construction of intergrowth structure on the internal defects and electrical properties in BLSFs. In this study, (1-x) BaBi4Ti4O15 - x Bi4Ti3O12 ceramic samples with intergrowth bismuth layer structure were fabricated by a conventional solid-state reaction method, and the mechanism of the influence of intergrowth structure construction on the structure and electrical properties of BLSFs has been discussed. The crystal structure, phase composition, microstructure, dielectric and piezoelectric performance, relaxation behavior and AC conductivity of ceramic samples were systematically investigated. It has been found that the construction of intergrowth structure can significantly inhibit the generation of oxygen vacancies. The concentration of the oxygen vacancies plays an important role, and its reduction will lead to the inhibition of grain growth and the increase of the relaxation activation energy of ceramics. In addition, the intergrowth structure construction also affects the symmetry of ceramics in the c-axis direction, thus affecting the electrical properties of ceramics.

Triblock Elastomeric Vitrimers: Preparation, Morphology, Rheology, and Applications

Vitrimer chemistry of boronic transesterification was introduced into a triblock thermoplastic elastomer to allow associative bond exchange in its highly ordered nanoscale domains. The purpose of this localized dynamic cross-linking is to enable reprocessing while also improving creep resistance. Triblock poly(styrene-b-butadiene-b-styrene) (SBS) was used as an elastomeric vitrimer precursor to gain understanding of fundamental structure–property effects of localized dynamical cross-linking. The occurrence of the UV-induced thiol–ene reaction was corroborated by Fourier transform infrared (FTIR) spectroscopy and swelling experiments. Transmission electron microscopy (TEM) images and small-angle X-ray scattering (SAXS) profiles demonstrate a prominently lamellar morphology with domain spacings that decline with the increase of cross-linking degree. Short and long relaxation modes of triblock SBS vitrimers (vSBSs) were found to have opposite temperature dependence, which caused thermorheological complexity in linear viscoelasticity. As compared to its random analog, vSBS shows much slower stress relaxation and higher activation energy, as well as superior resistance to creep under a steady load. The enhanced rheological properties are attributed to the high concentration of localized cross-links in the soft phase and to additional constraints that hinder network strand diffusion in the microphase-separated structure. The mechanical properties of vSBSs at low strain were substantially enhanced by the associative dynamic cross-links between the soft segments, increasing the maximum stress to 7.5 MPa at 100% strain. Its Young’s modulus of 88.1 MPa is about 2.8 times that of neat SBS. Applications of vSBSs as hot-melt adhesives were explored, showing excellent lap shear strength on iron plates. Due to the dynamic exchange of boronic ester bonds, adhesive joints can efficiently rebind at least three times and the lap shear strength remains almost unchanged.

Electrical characterisation and analysis of dominant contributions in disordered semiconducting systems with an application to the pure bentonite material for civil engineering applications

Semiconductors and clay materials have significant applications in environmental, civil engineering and optoelectronic sectors. The application of an electric field to such systems is subject of many works. However, to understand the behaviour of such materials under the influence of an electric field, the perception of its electrical properties is essential. In the present study, the powerful technique of complex impedance spectroscopy (CIS) is introduced to illustrate the electrical characteristics of two types of disordered semiconducting materials. These are Cu5In9Se16, an ordered defect compound of the I-III-VI2 family and a novel bentonite clay system which is an insulator at room temperature and semiconductor above 400 °C. Na-bentonite has been studied extensively because of its strong adsorption capacity and complexation ability while Cu5In9Se16 is considered for its use in solar and phtovoltaique domain. Some of selenides have turned out to be leading materials for electro-optical devices and the tellurides for thermoelectric power generation. It is very likely that study of bentonite clay and other similar materials may lead to the technology of heterojunction and clay composite. The frequency dependence of conductivity of bentonite was investigated using an impedance analyzer in the frequency range (20 Hz–1 MHz). The experimental data of CIS are analyzed using some analytical methods that take into account the effect of the grains and grain boundaries. The impedance data confirm the non-Debye behavior in these systems. Some important parameters related to the identified dominant contribution such as relaxation time and activation energies are estimated for the studied materials in the considered temperature and frequency ranges

Electrical conductivity and relaxation in lithium-doped barium vanadate glasses investigated by impedance spectroscopy

We present herein a detailed study of the electric and dielectric properties of glasses with the composition 60V2O5–(40–x)BaO–xLi2O, where x = 10, 15, 20, or 25 mol%. The conduction and relaxation mechanisms have been studied by impedance spectroscopy over the frequency range from 40 Hz to 10 MHz and at various temperatures. With constant transition metal oxide content, the conductivity variation in the glasses is assumed to be mainly due to an ionic contribution. The dependence of electrical conductivity on frequency has been analysed using Jonscher's power law. Properties of the glasses, such as electric modulus loss and relaxation mechanism, have been analysed in terms of electric modulus using the Kohlrausch–William–Watts (KWW) equation, which describes the relaxation behaviour of the mobile ions as non-Debye in nature. Scaling of ac conductivity and electric modulus data has shown that conductivity relaxation is independent of temperature. The non-monotonic variation in the stretching parameter β has been found to show a positive correlation with various activation energies, namely electrical activation energy, relaxation activation energy, and the activation energy from the Anderson–Stuart model. The anomalous behaviour of activation energy with respect to conductivity has been substantiated through structural insight. The conductivity was found to be highest in glasses with 25 mol% Li2O, while coupling between the mobile ions was best for glasses with 20 mol% Li2O.

Transition of the colossal permittivity related dielectric relaxation in V-doped CaCu3Ti4O12 ceramics

The co-achieving of stable colossal permittivity (CP) and low dielectric loss in dielectric materials has been a challenge. In this paper, a transition in CP was observed in V-doped CaCu3Ti4O12 (CCTO) ceramics. The fast high-frequency dielectric relaxation that mainly contributed to CP of CCTO ceramics was greatly suppressed in V-doped CCTO samples. Its relaxation activation energy remained ∼0.10 eV, while its magnitude dropped from thousands in CCTO to dozens in V-doped CCTO. Instead, CP of V-doped CCTO ceramics mainly arose from another slow dielectric relaxation, which appeared in a much lower frequency range. Moreover, this dielectric relaxation gradually turned from a “carrier-dominated” relaxation into a “dipole-dominated” one with the increase in temperature. Its relaxation activation energy also changed from ∼0.06 to 0.42 eV in the meanwhile. These results indicated important roles of multiple point defects and their relating charge transport in CP behaviors. It supported that CP arose from electron trapping behaviors at the edge of double Schottky barriers at grain boundaries. On this basis, suppression of any deep-level point defects was concluded to be a potential clue to achieve both stable CP and sufficiently low dielectric loss in CCTO ceramics and other CP materials.

Stress Relaxation Behavior of Poly(Methyl Methacrylate)/Graphene Composites: Ultraviolet Irradiation.

The graphene/poly (methyl methacrylate) (PMMA) composites are a promising candidate for electronic, optoelectrical, and environmental applications. Understanding the mechanical degradation of PMMA-based materials is of practical importance in improving the reliability and lifespan of the associated structures and systems. In this study, we investigate the effects of functionalized graphene (FG) and UV irradiation on the stress–relaxation of PMMA. Uniaxial tensile and stress –relaxation tests are performed to evaluate the mechanical properties of the composites. The mechanical strength and elongation at the break increase with the graphene concentration but decrease with the increase of the irradiation dose. Raman spectroscopy and intrinsic viscosity measurement are applied to examine the root cause of the degradation in the composites. UV irradiation leads to polymer chain scission and loss of molecular weight. The Kelvin representation of the standard linear solid model (SLSM) is used to describe the stress–relaxation curves of the composites. The value of the elastic modulus in the Kelvin element decreases with the increase in temperature. The viscosity follows the Arrhenius equation. The activation energy of viscosity increases with the increasing FGs concentration because the FGs hinder the chain motion of PMMA. However, UV irradiation makes chain scission of PMMA/FGs composite so that the polymer chain moves more easily and the activation energy of stress relaxation lowers. The steady-state stress follows the van ’t Hoff equation that stress relaxation is an exothermal deformation process. Although Maxwell’s representation of SLSM is mathematically identical to the Kelvin representation of SLSM, the former cannot interpret the stress–relaxation behavior of PMMA/FGs composite, which is against the concept of Young’s modulus as a decreasing temperature function.

Electrical Performance and Conduction Mechanism of Potassium Sodium Niobate-Based Lead-Free Piezoceramics via Two-Step Sintering Route

(1-x)(Li0.02Na0.48K0.48Ag0.02)(Nb0.95Sb0.05)O3-x(Ba0.4Bi0.3Na0.3)ZrO3 (LNKANbS-xBBiNZ, x = 0.04, 0.045, 0.05, 0.055 and 0.06) lead-free piezoelectric ceramics were prepared by the conventional solid-state reaction method via the two-step sintering route. The effects of the content of BBiNZ on electrical properties and microstructural morphology of the LNKANbS-xBBiNZ ceramics were studied systematically. The designing of forming rhombohedral-tetragonal phase boundary in the LNKANbS-xBBiNZ system is confirmed by XRD Rietveld refinement and Raman spectroscopy, whose phase proportion is affected greatly by the BBiNZ amount. The LNKANbS-xBBiNZ ceramics exhibit complicated dielectric behavior, whose dielectric response characteristic can be fitted by the quadratic law and the Curie-Weiss law, and both having some deviation. The high-temperature conductivity of the LNKANbS-0.045BBiNZ ceramics is controlled by oxygen vacancies detected by both conductive activation energy and relaxation activation energy fitting. The LNKANbS-0.045BBiNZ ceramics exhibit excellent electrical properties, correlating with appropriate R-T phase composition proportion and improved densification and microstructural homogeneity obtained by adjusting the BBiNZ content and using the two-step sintering method.

Deep understanding of structural and physical properties of BaTiO3 over a broad temperature range

BaTiO3 (BT) ceramic has been prepared by the solid-state reaction method. The Rietveld refinement and the Raman spectroscopy have been employed to characterize the structural information of the BT ceramic based on the analysis of dielectric at room temperature (RT). Detailed microstructure has been observed by scanning electron microscopy. The dielectric properties of our ceramic have been investigated over wide frequency (102-106 Hz) and temperature (−100–600 °C) ranges. At high temperature region (250–600 °C), a dielectric relaxation phenomenon has been observed. To better understand the physical mechanisms at high temperature, a macroscopic and phenomenological statistical model has been used. The calculated activation energy for relaxation and conduction was approximated to 1 eV. This suggests that relaxation in our studied sample at high temperature region is associated with the short-range hopping of ions. This is caused by oxygen vacancies in the bulk of the material. The BT ceramic demonstrated optimum electrical properties: εr = 1105, tanδ = 0.079, TC = 130 °C, εmax = 4050, Pmax = 18.35 μC/cm2, Pr = 7.93 μC/cm2, EC = 2.65 kV/cm, |Y| = 1.86*1011 N/m2, d33 = 197 pC/N, kp = 14%, and Qm = 196. In addition, the evolution of energy storage performance with an increase in the applied electric field has been investigated. The energy storage efficiently has achieved 40 % at RT, under an electrical field of 30 kV/cm.

Analysis of frequency dependence of complex impedance and electrical characterization of Fe2O3/kaolin ceramics for civil engineering applications

The complex impedance spectroscopy (CIS) method is usually used in order to analyze the electrical response of different semiconducting disordered materials as a function of frequency at different temperatures. The real and imaginary parts of the complex impedance can show different semicircles in the complex plane that give evidence for the presence of both bulk and grain boundary contributions. Many parameters can be deduced from the analysis of CIS data, such as relaxation times and activation energies. There are some literature data concerning electrical properties of clays and (semiconductor, sand, cement,…)/clay mixtures. Most of the published works are related to the AC conductivity of rocks with the effect of water or oil content but there are no similar studies on the characterization of the microstructure of individual clays as ceramic materials by analyzing their temperature and frequency dependence of their electrical conductivities. Hence, this paper presents an analysis of electric complex impedance of the Fe2O3/Kaolin composite in the high temperature range up to 740 °C. Sinusoidal voltage with frequency in the range [100 Hz, 1 MHz] is applied to the material in order to measure the electrical conductivity for various concentrations of Fe2O3 from zero to 100 %. The activation energies for the conduction and for the relaxation processes are determined and their dependence on the density of Fe2O3 analyzed. Furthermore, let’s found that Fe2O3 have the effect to increase the electrical conductivity in our samples. From the Nyquist diagrams, only one semi-circle related to the contribution of the grains to the total electrical conduction is identified for all investigated samples.

Influence of Microalloying Process on Dynamic Mechanical Relaxation of ZrCo-Based Amorphous Alloy

In this study, the dynamic mechanical spectroscopy was used to characterize the effects of minor Ni addition on the relaxation behavior of ZrCoAl bulk metallic glass (BMG). For this purpose, the Kohlrausch–Williams–Watts (KWW) function and quasi-point defect (QPD) model were used for evaluation of relaxation under the different aging temperatures. The results indicated that the Ni addition shifted the relaxation process to the higher temperatures. Moreover, the estimations showed that the activation energy of relaxation was 5.951 eV and 6.205 eV for ZrCoAl and ZrCoAlNi, respectively. It was also revealed that the microalloying process enhanced the structural defects in the system and led to the improvement of dynamic heterogeneity in the BMG. Comparing the physical models, it is suggested that a small change in the structural defects intensifies the dynamic heterogeneity in the material.

The Ubiquitous Memristive Response in Solids

Basic ingredients universally available in the carrier transport of conductive solids are proved to be sufficient (not necessary) conditions for the formation of memory while symmetry, or the lack of it, plays a decisive role in the nature of this response. It suffices that the input driving frequency is of the order of the inverse relaxation time and that the nonequilibrium carrier densities are in the order of the quasi-equilibrium ones. Thus, memristive response with ON and OFF states at zero voltage, Type I, and vanishing ON– OFF ratio, Type II, arise naturally according to simple symmetry constraints and are contrasted here in a fully analytical picture. Figures of merit for the conductance and the robustness of the memory response are presented in the form of concise correlations between general intrinsic microscopic parameters such as relaxation times, activation energies, and efficiencies with external drives: voltage pulses, temperature, and illumination. Explicit analytical expressions unveil the mimicry of inductive- and capacitive-like leaning impedances without the need of relaxing the interpretation of flux that has been used for more stringent definitions of memristors.

Evolution of the distribution of flow units of a metallic glass under cyclic loading

Dynamic mechanical relaxation processes (i.e., β relaxation and α relaxation) are closely connected with the mechanical and physical properties of metallic glasses. In the current work, the β relaxation of La60Ni15Al25 metallic glass was studied in sequential heating and cooling experiments by dynamic mechanical analysis. The values of the loss modulus peak were found to reach a relatively stable state during the progress of the heating-cooling cycles. The evolution of the flow unit distribution during thermal cycling was revealed by stress relaxation tests. The experimental results of stress relaxation were well described by a generalized Maxwell model, allowing the analysis of the underlying relaxation time and activation energy distributions. We also show here a suppressed relaxation behavior observed under repeated loading cycles, which is attributed to the annihilation of flow units and the modification of the relaxation time spectrum obtained in the framework of the generalized Maxwell model.

Influence of minor Zn additions on grain boundary anelasticity, grain boundary sliding, and superplasticity of Al-Mg-based alloys

Al-Mg alloys (AA5083-type) are widely used for superplastic forming. Limited grain boundary sliding as compared to other superplastic alloys limits the formability of Al-Mg based alloys. Grain boundary sliding intensity depends on the grain size, grain boundaries structure, and chemical composition of alloys. To improve superplastic properties of Al-Mg based alloys, we investigated the influence of a minor addition of Zn on the grain boundary relaxation effect and grain boundary sliding ability. The temperature dependence internal friction, superplastic deformation behavior, and microstructural changes during superplastic deformation for the AA5083 alloy and Zn modified alloy were compared. A minor Zn addition of 0.7 wt% does not influence the mean grain size but decreases the relaxation strength and the activation energy of grain boundary relaxation. The mechanisms of superplastic deformation and their contributions to the total strain were analyzed using FIB-milled grids evolution on the samples’ surface. Grain boundary sliding, grain rotations, and intragranular strain included both dislocation slip/creep and diffusional creep were involved in the deformation process. The contribution of grain boundary sliding increased from 10% to 25% for the Zn-free AA5083 alloy to 30–50% for the Zn-modified alloy. In result, a minor Zn addition proved to stimulate grain boundary sliding that decreases stress and increases strain rate sensitivity and elongation-to-failure of the studied alloy.

Non‐destructive thermal ageing evaluation of P (VDF‐HFP) film based on broadband dielectric response

Capacitors and sensors based on polymer dielectric materials are key components in electrical systems and electronic devices. Considering the temperature rise during operation, an effective evaluation method for the thermal ageing of polymer matrix is urgently needed. P(VDF-HFP) film with a thickness of 20 μm is manufactured by solution casting and a thermal ageing experiment up to 1000 h is conducted. Dielectric responses of wide ranges of temperatures and frequencies are measured for samples with different ageing durations. The universal relaxation law and Dissado–Hill dielectric response model are applied to further investigate the results. The characteristics of individual processes are obtained, which demonstrate that the main chain relaxation following the Vogel−Fulcher−Tammann equation and side chain relaxation following the Arrhenius equation both remain unchanged after thermal ageing. However, the activation energies of those two processes change significantly during the process and show different variation trends. The activation energy of the side chain relaxation gets larger monotonically due to the influence of annealing and the breaking of crystalline region. As a result, a non-destructive evaluation method for the thermal ageing of P(VDF-HFP) is proposed accordingly.

Dielectric Relaxation and Ferroelectric Properties of PNN–PZT Ceramics with Different Ni/Nb Ratios

0.35Pb(NixNb1−x)O3–0.65Pb(Zr0.39Ti0.61)O3 (x = 1/4,1/3,1/2 and 2/3) ceramics are prepared by the conventional solid reaction method and their structure, dielectric, and ferroelectric properties are studied. All compositions show tetragonal perovskite structure and Ni2+ segregated at grain boundaries in ceramics with high Ni/Nb (x = 1/2,2/3). Oxygen vacancies exist in nonstoichiometric ceramics and increase with the increase in Ni/Nb. Due to the pinning effect of defects, the P–E loops become unsaturated, accompanied by a softening–hardening transition. Dielectric relaxation is detected in both PNN–PZT(x = 1/2) and PNN–PZT(x = 2/3), and the activation energies of relaxation and conduction are calculated by Arrhenius law. The results show that both grain and grain boundary contribute to dielectric relaxation which can be explained on the basis of equivalent circuit containing two parallel RC elements connected in series. The relaxation at low frequency is induced by dipoles concentrating on the grain boundary while the relaxation at high frequency is attributed to the first ionization of oxygen vacancies in the grain.