Dielectric Relaxation Phenomena Research Articles

Octahedral distortion due to oxygen vacancy reduction in La3+ modified BNT-BTO solid solutions near morphotropic phase boundary

Currently, there is great interest in perovskite compounds (ABO3) due to their various applications as well as fundamental research that has taken place. However, oxygen vacancy in the perovskite is a very important parameter to control its physical properties. Hence, the polycrystalline ((Bi1−xLax)0.5Na0.5)0.94Ba0.06TiO3 (BLNBTO) with x = 0.00, 0.02, 0.04, 0.06, 0.08 and 0.10 solid solutions was synthesized via a conventional solid-state reaction process to study the oxygen vacancies and its influence on dielectric property. Structural phase formation of the solid solutions has been studied by x-ray diffraction (XRD) technique. Rietveld analysis of the XRD pattern reveals the decrease of octahedral distortion with the increase of La3+ concentration in BNBTO (x = 0.00) solid solution. The reduction of octahedral distortion in the solid solutions was also supported by Raman spectra analysis. The presence of oxygen vacancy has been observed from the analysis of x-ray photoelectron spectroscopy spectra corresponding to the different elements of the solid solutions. Furthermore, the distinct peak at high-temperature range (250 °C–350 °C) in impedance plots is ascribed to the presence of oxygen vacancy related dielectric relaxation phenomenon. The activation energy increases from 0.99 to 1.53 eV with the increase of La3+ mole fraction in BNBTO solid solution, which is obtained from impedance data using the Arrhenius equation. The increase of activation energy has been correlated with the reduction of oxygen vacancy.

Dielectric relaxation phenomenon and conductivity in lead-free ceramics

Relaxation phenomena and electric conductivity of (1-x) KNbO3-xK0.5Bi0.5TiO3 system where x = 0, 0.025, 0.05, 0.075, 0.1, 0.2, 0.3 have been studied at high temperature. A relaxation behavior was observed in temperature range 400 K ≤ T ≤ 550 K for orthorhombic solid solutions at room temperature. The activation energy (Ea) of this phenomenon was range from 0.68 eV for x = 0–0.489 eV for x = 0.075 with τ0 = 10−13 s. The relaxation was attributed to hopping of oxygen vacancies for solid solutions x ≤ 0.075. Substitution by K0.5Bi0.5TiO3 does not affect the electrical conductivity of KNbO3 too much, while the mobility of species such as oxygen vacancies and oxygen ions allow the increase of the conductivity σac at high temperatures.

Effect of space charge on dielectric and magneto-dielectric behaviors in Ba0.85Ca0.15Zr0.1Ti0.9O3/La0.67Sr0.33MnO3 heterostructure

The Ba0.85Ca0.15Zr0.1Ti0.9O3/La0.67Sr0.33MnO3 (BCZT/LSMO) heterostructures were deposited on LaAlO3 (111) substrates through radio-frequency magnetron sputtering technique. Dielectric behaviors as a function of frequency, temperature and magnetic field were investigated. The frequency dependence of dielectric permittivity exhibited apparent relaxation behavior. The corresponding activation energy estimated from Arrhenius plot was 2 meV. Abnormal point at 120 K was detected from the real part of dielectric permittivity vs temperature plot and magnetodielectricity (MD) vs temperature plot simultaneously, which refer to rhombohedral to orthorhombic phase transition in BCZT. A maximum of 20 percent was obtained in MD-temperature pattern, indicating obvious magneto-electric (ME) coupling. The dielectric permittivity relaxation phenomena as well as magneto-dielectric effect can be ascribed to the role of space charges, which arise at interface of BCZT and LSMO owing to lattice mismatch. The dependence of magneto-dielectric on temperature results from the variation of lattice mismatch degree induced by phase transition of BCZT.

Structural, optical, magnetic and electrical properties of hematite (α-Fe2O3) nanoparticles synthesized by two methods: polyol and precipitation

Hematite (α-Fe2O3) nanoparticles have been successfully synthesized via two methods: (1) polyol and (2) precipitation in water. The influence of synthesis methods on the crystalline structure, morphological, optical, magnetic and electrical properties were investigated using X-ray diffraction, RAMAN spectroscopy, scanning electron microscopy, transmission electron microscopy, UV–visible diffuse reflectance spectroscopy (UV–vis DRS), superconducting quantum interference device and impedance spectroscopy. The structural properties showed that the obtained hematite α-Fe2O3 nanoparticles with two preparation methods exhibit hexagonal phase with high crystallinity and high-phase stability at room temperature. It was found that the average hematite nanoparticle size is estimated to be 36.86 nm for the sample synthesized by precipitation and 54.14 nm for the sample synthesized by polyol. Moreover, the optical properties showed that the band gap energy value of α-Fe2O3 synthesized by precipitation (2.07 eV) was higher than that of α-Fe2O3 synthesized by polyol (1.97 eV) and they showed a red shift to the visible region. Furthermore, the measurements of magnetic properties indicated a magnetization loop typical of ferromagnetic systems at room temperature. Measurements of electrical properties show higher dielectric permittivity (5.64 × 103) and relaxation phenomenon for α-Fe2O3 issued from the precipitation method than the other sample.

Thermal, electrical, and dielectric properties of reduced graphene oxide–polyaniline nanotubes hybrid nanocomposites synthesized by in situ reduction and varying graphene oxide concentration

ABSTRACTIn this study, reduced graphene oxide (RGO) has been introduced as conductive filler within polyaniline (PAni) nanotubes (PAniNTs) by in situ chemical reduction method to enhance the properties of PAniNTs. The effect of varied concentration of in situ reduced GO on the structural, thermal, electrical, and dielectric properties of RGO–PAniNTs nanocomposites have been investigated by high resolution transmission electron microscope, X‐ray diffraction, Fourier transform infrared, thermogravimetric analysis, I–V characteristics, and impedance analyzer. The enhanced thermal stability of the nanocomposites has been analyzed from the derivative thermogravimetric curves in terms of onset and rapid decomposition temperature. The transport mechanisms have been studied by fitting the nonlinear I–V characteristics to the Kaiser model. The dielectric relaxation phenomena have been investigated by permittivity and modulus formalisms. Characteristic relaxation frequency of RGO–PAniNTs nanocomposites shifts toward higher frequency with increasing RGO concentration indicating a distribution in conductivity relaxation. The distribution of relaxation time has been studied by fitting the imaginary modulus spectra of the nanocomposites to Bergman modified KWW function. The ac conductivity spectra are fitted to the Jonscher's power law equation and enhanced conductivity value of 1.26 × 10−3 S cm−1 is obtained for 40 wt % of RGO compared to 1.22 × 10−4 S cm−1 for PAniNTs. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018, 135, 45883.

Dielectric Relaxation Phenomenon between Aniline and 2-Alkoxyethanols in Different Non Polar Solvents by Frequency Domain Technique

Dielectric Relaxation Phenomenon between Aniline and 2-Alkoxyethanols in Different Non Polar Solvents by Frequency Domain Technique

Gamma-ray irradiation effects on electrical properties of bismuth layer-structured ferroelectric ceramics

Abstract In this study, we prepared the bismuth layer-structured ferroelectric (BLSF)-type Bi 4 Ti 3 O 12 (BiT), Bi 3.25 La 0.75 Ti 3 O 12 (BLaT), and Bi 3.1 Nd 0.9 Ti 3 O 12 (BNdT) ceramics using the solid-state reaction method. The prepared ceramics were irradiated at room temperature by using a 60 Co gamma-ray source in a dose range of 0–3000 kGy with a dose rate of 10 kGy/h to compare the structure and electrical properties of the irradiated ceramics. The X-ray diffraction analysis shows that the BLSF structure was well formed in all ceramics without a secondary phase. There was no structural change such as grain size change and secondary phase formation despite the cumulative gamma-ray dose of 3000 kGy. A comparison of the electrical properties with gamma-ray irradiation shows that the BiT ceramics exhibits a larger reduction ratio compared to the BLaT and BNdT ceramics. The rate of change of the remnant polarization (2 P r ) value with the gamma-ray irradiation doses was − 14.2%, − 8%, and − 3.4% in BiT, BLaT, and BNdT ceramics, respectively, at a cumulative gamma-ray dose of up to 3000 kGy. Furthermore, the dielectric relaxation phenomenon in BiT ceramics at low frequency was observed when gamma rays of 1000 kGy or more were irradiated. Based on these results, in this study, we investigated the structure and electrical properties of BLSF ceramics with gamma-ray irradiation.

Dielectric properties of polyaniline composites

ABSTRACTThis study presents a comparison of the dielectric properties of composite materials consisting of insulating polymers (polyamides 6 and 12) containing polyaniline as a conductive phase. Samples were obtained by in situ polymerization of the aniline monomer in the presence of the insulating matrices. The results obtained by dielectric relaxation spectroscopy showed that it was possible to increase the permittivity of the samples by increasing the polyaniline content. Polyamide12-based films exhibit high dielectric permittivities above the percolation threshold. Polyaniline also induces relaxation phenomena, clearly visible at low temperature. It was also shown that the dielectric relaxation phenomena are thermally activated. Some relaxations seem to be of the same nature in polyamides 6 and 12 films because they require nearly the same activation energy.

Dielectric relaxation and pinning phenomenon of (Sr,Pb)TiO3 ceramics for dielectric tunable device application.

The behavior of ferroelectric domain under applied electric field is very sensitive to point defects, which can lead to high temperature dielectric relaxation behaviors. In this work, the phases, dielectric properties and ferroelectric switching behavior of strontium lead titanate ceramics were investigated. The structural characterization is confirmed by X-ray diffraction. The high dielectric tunability and high figure of merit of ceramics, especially Sr0.7Pb0.3TiO3 (SPT), imply that SPT ceramics are promising materials for tunable capacitor applications. Oxygen vacancies induced dielectric relaxation phenomenon is observed. Pinched shape hysteresis loops appeared in low temperature, low electric field or high frequency, whereas these pinched hysteresis loops also can become normal by rising temperature, enhancing electric field or lowering frequency. The pinning and depinning effect can be ascribed to the interaction between oxygen vacancies and domain switching. A qualitative model and a quantitative model are used to explain this phenomenon. Besides, polarization and oxygen treated experiment can exert an enormous influence on pinning effect and the machanisms are also discussed in this work.

Dielectric properties of FeNbO4 ceramics prepared by the sol-gel method

In this work, FeNbO4 powders were prepared using the sol-gel method. The fine powder particles were pressed into pellets and sintered at temperatures between 500 and 1200 °C. The powder was studied by X-ray diffraction and Raman spectroscopy. The morphology of the grains was investigated by scanning electron microscopy. Heat-treatment of the particles results in higher crystallinity, larger grains, and a decrease in the porosity of the material.The dielectric properties were measured in the frequency range of 102–106 Hz, in function of temperature (200–370 K). In all samples the real (ε′) and imaginary (ε″) parts of the complex permittivity increase with increasing annealing temperature. The sample heat treated at 1200 °C shows the highest ε′, > 104 at 300 K. All samples show a dielectric relaxation phenomenon, analysed using the modulus formalism. The evolution of the ac conduction activation energy and of the activation energy associated with the relaxation mechanism, is directly related with the changes promoted by the heat treatment in the structure and in the morphology of the base powders.

Preparation of novel (Sb1/2Na1/2)(Fe2/3W1/3)O3 compound by solid state reaction technique and their multiferroic property

Large leakage current and poor magnetizations are the two major shortcomings observed in known multiferroic BiFeO3 which hinders its practical utility. Na and W co-doped SbFeO3 i.e. (Sb1/2Na1/2)(Fe2/3W1/3)O3 with enhanced electric and magnetic properties compared to BiFeO3 is prepared by solid state reaction technique. To understand the structure of the compound, X-ray diffraction analysis has been carried out which shows its orthorhombic crystal structure with crystallite size of 20 nm. The obtained crystallite size is same as the particle size, calculated by transmission electron microscope. The scanning electron microscope analysis reveals the formation of grain and grain boundary of the compound with average grain size of 108 nm. Energy dispersive X-ray spectroscopy studies shows that the elemental composition of the compound before and after heat treatment process is almost same. Dielectric and impedance study of the material in a wide range of temperature (30–400 °C) at different frequencies (100 Hz–1 MHz) shows the dielectric relaxation phenomena and the properties of grain and grain boundary respectively. It also reveals the non-Debye type relaxation and negative temperature coefficient of resistance (NTCR) behavior of the compound. DC conductivity of the material is found to obey Arrhenius relation whereas ac conductivity is governed by Jonscher’s universal power law. The appearance of room temperature P–E loop shows the ferroelectric nature of the compound. The material shows the weak ferromagnetic property with remnant magnetization (Mr) of 0.00582 emu/g and coercive field (Hc) of 369 Oe.

Synthesis of polyaniline/ZrO2 nanocomposites and their performance in AC conductivity and electrochemical supercapacitance

Polyaniline/zirconium oxide (PANI/ZrO2) nanocomposites have been synthesized by incorporating ZrO2 nanoparticles into the PANI matrix via liquid–liquid interfacial polymerization method. The composite formation and structural changes in PANI/ZrO2 nanocomposites were investigated by powder X-ray diffraction (PXRD), scanning electron microscopy (SEM) and Fourier transform infrared spectroscopy (FT-IR). PXRD pattern of PANI/ZrO2 nanocomposites exhibited sharp and well-defined peaks of monoclinic phase of ZrO2 in PANI matrix. SEM images of the composites showed that ZrO2 nanoparticles were dispersed in the PANI matrix. The FT-IR analysis revealed that there was strong interaction between PANI and ZrO2. AC conductivity and dielectric properties of the nanocomposites were studied in the frequency range, 50–106 Hz. AC conductivity of the nanocomposites obeyed the power law indicating the universal behaviour of disordered media. The nanocomposites showed high dielectric constant in the order of 104, which could be related to dielectric relaxation phenomenon. Further, the materials were checked for their supercapacitance performance by using cyclic voltammetry (CV), chronopotentiometry (CP) and electrochemical impedance spectroscopy (EIS). Among the synthesized nanocomposites, PANI/ZrO2-25 wt.% showed a higher specific capacitance of 341 F g−1 at 2 m Vs−1 and good cyclic stability with capacitance retention of about 88% even after 500 charge–discharge cycles.

Relaxation Associated with Oxygen Vacancies at High Temperatures and Leakage Current in Ba x Sr1−x TiO3 Ceramics

Ba x Sr1−x TiO3 (x = 0.7, 0.8, 0.9, 1.0) ceramics were synthesized using traditional solid state reaction methods. The structure, microstructure, ferroelectric and dielectric properties of the ceramics were investigated. X-ray diffraction results show that a pure phase was obtained. For all compositions, a sharp phase transition was observed in the dielectric data and the substitution of Ba2+ by Sr2+ gradually reduced the Curie temperature. A dielectric relaxation phenomenon was observed at high temperatures (300–550°C). From impedance measurements, the activation energy for relaxation and conduction was calculated as approximately 1 eV, which suggests that relaxation in Ba x Sr1−x TiO3 ceramics at high temperatures is associated with the short-range hopping of ions caused by oxygen vacancies. An oxygenation treatment, the variation of dielectric behaviors and activation energy verified that the oxygen vacancies were the origin of the dielectric relaxation. The leakage current of Ba x Sr1−x TiO3 ceramics may be associated with the combined effect of oxygen vacancies and the size of the largest grains.

High‐Temperature Dielectric Relaxation Behaviors of Relaxer‐Like PbZrO3–SrTiO3 Ceramics for Energy‐Storage Applications

Abstract(1−x)PbZrO3–xSrTiO3 (x: 10, 20, and 30 mol %) ceramics were prepared by a conventional mixed‐oxide solid‐state reaction method. The relaxer behaviors of the PbZrO3–SrTiO3 ceramics were examined in the temperature range of 120–523 K. A broad dielectric maximum that shifted to higher temperature with increasing frequency signified the relaxer‐type behaviors of these ceramics. The value of the relaxation parameter of γ=1.73, estimated from the linear fit of the modified Curie–Weiss law, indicated the relaxer nature. High‐temperature dielectric relaxation phenomena were found in the temperature region of 600‐850 K. The activation energy, calculated from impedance measurements of samples, suggested that the dielectric relaxation was a result of oxygen vacancies generated during the sintering process. The energy‐storage density calculated from hysteresis loops reached about 0.46 J cm−3 for the PSZT30 ceramic at room temperature.

Dielectric and Conduction Processes and Behaviours in Ni<sub>0.3</sub>Zn<sub>0.7</sub>Fe<sub>2</sub>O<sub>4</sub>

Dielectric relaxation and conductivity of Ni0.3Zn0.7Fe2O4 (NZF) were studied in the frequency range between 0.01 Hz to 3 MHz and temperature range within 313 K to 473 K. The sample was prepared by mixing Zinc Oxide, Nickel Oxide and Iron Oxide and sintered at 1573 K for 10 hours long. Dielectric properties were studied using Novo Control Dielectric Spectrometer. Dielectric relaxation and conductivity phenomena were discussed using an empirical model to key out the dielectric relaxation process. Analyze peak frequency relaxation process consist of four slopes to explain the dielectric relaxation process. The conductivity of the sample indicates an activated process and activation energy of dc conductivity is 0.44 ± 0.01 eV.

Effects of swift heavy ion irradiation on dielectric relaxation and conduction mechanism in Ba0.90Sr0.10TiO3

The effects of 100MeV O8+ ion beam irradiation on the structural and dielectric behavior of Ba0.90Sr0.10TiO3 ceramics have been analyzed. Ion irradiation does not change the crystalline structure, however the tetragonal distortion increases. The low frequency dielectric dispersion especially at high temperatures increases significantly after ion irradiation. The dielectric relaxation phenomenon has been probed through complex impedance and electric modulus approaches. The observed dielectric relaxation has distributed relaxation times and is a thermally activated process. Ion irradiation enhances the cationic disordering. The contributions of grains and grains boundaries towards impedance have been separated. It is inferred that the grain boundaries become more resistive due to ion irradiation and is associated to oxygen vacancies annihilation. Ion irradiation also decreases the bulk ferroelectric polarization demonstrating that the surface or near surface modifications may tune the bulk properties in polar dielectrics.

Energy-storage properties and high-temperature dielectric relaxation behaviors of relaxor ferroelectric Pb(Mg1/3Nb2/3)O3–PbTiO3 ceramics

(1 − x)Pb(Mg1/3Nb2/3)O3−xPbTiO3 (x = 0, 5, and 10 mol%) ceramics were prepared using a conventional mixed oxide solid state reaction method. The low-temperature relaxor behavior of (1 − x)Pb(Mg1/3Nb2/3)O3–xPbTiO3 ceramics were examined in the temperature range from 120 to 523 K. A broad dielectric maximum that shifted to higher temperatures with increasing frequency, signified the relaxor-type behavior of these ceramics. The value of the relaxation parameter γ = 1.61–1.94 estimated from the linear fit of the modified Curie–Weiss law indicated the relaxor nature. High-temperature dielectric relaxation phenomena were found in the temperature region 600–850 K. Energy-storage properties were also analyzed, and the energy-storage density calculated from hysteresis loops reached about 0.47 J cm−3 at room temperature.

Observation of large dielectric permittivity and dielectric relaxation phenomenon in Mn-doped lanthanum gallate

Shifting of tan δ-peaks (100 Hz to 1 MHz) towards higher temperature; featuring dielectric relaxation.

Dielectric relaxation phenomena in flax fibers composite

In this work, a study of the dynamic dielectric analysis of the unidirectional epoxy composite: flax-fibre-reinforced epoxy (FFRE) was investigated. In this composite, three relaxation processes were identified. The first one is the water dipoles polarization imputed to the presence of polar water molecules in flax fiber. The second relaxation process associated with conductivity occurs as a result of the carriers charges diffusion. As for the third dielectric relaxation associated with the interfacial polarization effect is attributable to the accumulation of charges at the fibers/matrix interface. The analysis of the Maxwell-Wagner-Sillars (MWS) and the water dipoles polarizations using the Havriliak-Negami model revealed the high adhesion of flax fibers in the matrix. This analysis was supported by the thermal properties using a Differential Scanning Calorimety (DSC).

Structural Properties, Impedance Spectroscopy and Dielectric Spin Relaxation of Ni-Zn Ferrite Synthesized by Double Sintering Technique

Structural properties, impedance, dielectric and electric modulus spectra have been used to investigate the sintering temperature (Ts) effect on the single phase cubic spinel Ni0.6Zn0.4Fe2O4 (NZFO) ceramics synthesized by standard ceramic technique. Enhancement of dielectric constants is observed with increasing Ts. The collective contribution of n-type and p-type carriers yields a clear peak in notable unusual dielectric behavior is successfully explained by the Rezlescu model. The non-Debye type long range dielectric relaxation phenomena is explained by electric modulus formalism. Fast response of the grain boundaries of the sample sintered at lower Ts sample leading to small dielectric spin relaxation time, t (several nanoseconds) have been determined using electric modulus spectra for the samples sintered at different Ts. Two clear semicircles in impedance Cole-Cole plot have also been successfully explained by employing two parallel RC equivalent circuits in series configuration taking into account no electrode contribution. Such a long relaxation time in NZFO ceramics could suitably be used in nanoscale spintronic devices.