Maxwell-Wagner Type Relaxation Research Articles

Mg2+ Doping Effects on the Structural and Dielectric Properties of CaCu3Ti4O12 Ceramics Obtained by Mechanochemical Synthesis.

In this study, ceramic CaCu3Ti4O12 (CCTO) and CaCu3−xMgxTi4O12 solid solutions in which 0.1 ≤ x ≤ 0.5 were prepared by the mechanochemical method, realized by a high-energy ball milling technique. The effects of the Mg2+ ion concentration and sintering time on the dielectric response in the prepared ceramics were investigated and discussed. It was demonstrated that, by the use of a sufficiently high energy of mechanochemical treatment, it is possible to produce a crystalline product after only 2 h of milling the mixture of the oxide substrates. Both the addition of magnesium ions and the longer sintering time of the mechanochemically-produced ceramics cause excessive grain growth and significantly affect the dielectric properties of the materials. The X-ray diffraction (XRD) analysis showed that all of the as-prepared solid solutions, CaCu3−xMgxTi4O12 (0.0 ≤ x ≤ 0.5), regardless of the sintering time, exhibit a cubic perovskite single phase. The dielectric study showed two major contributions associated with the grains and the grain boundaries. The analysis of the electric modules of these ceramics confirmed the occurrence of Maxwell–Wagner type relaxation, which is dependent on the temperature.

Structural, magnetic and dielectric properties in 3d–5d based Sr2FeIrO6 thin films

The structural, magnetic and dielectric properties have been investigated in 3d–5d based double perovskite Sr2FeIrO6 thin films deposited by pulse laser deposition technique. To understand the effect of strain, epitaxial films are grown with varying thickness as well as on different substrates i.e., SrTiO3 (100) and LaAlO3 (100). The films with highest thickness are found to be more relaxed. Atomic force microscope images indicate all films are of good quality where grain sizes increase with increase in film thickness. X-ray absorption (XAS) spectroscopy measurements indicate a Ir5+ charge state in present films while providing a detailed picture of hybridization between Fe/Ir-d and O-p orbitals. The bulk antiferromagnetic transition is retained in films though the transition temperature shifts to higher temperature. Both dielectric constant (ϵ r) and loss (tan δ) show change around the magnetic ordering temperatures of bulk Sr2FeIrO6 indicating a close relation between dielectric and magnetic behaviors. A Maxwell–Wagner type relaxation is found to follow over whole frequency range down to low temperature in present film. On changing the substrate i.e., LaAlO3 (100), the ϵ r(T) and (tan δ(T)) show almost similar behavior but ϵ r shows a higher value which is due to an increased strain coming from high mismatch of lattice parameters.

Dielectric behaviors and relaxor characteristics in Bi0.5Na0.5TiO3-BaTiO3 ceramics

Microstructure and dielectric behaviors of heating/cooling and bias-field were investigated in lead-free ceramics ([Formula: see text])[Formula: see text][Formula: see text][Formula: see text]BaTiO3 (BNT[Formula: see text]BT, [Formula: see text], 0.02, 0.04, 0.06, 0.08 and 0.10). The relaxor characters and the Vogel–Fulcher law of frequency-dependent dielectric properties were analyzed. Three dielectric anomalies with pronounced frequency dispersion at [Formula: see text], a maximum dielectric with variable frequency-dispersion at [Formula: see text] and a third Maxwell–Wagner-type relaxation over a wide temperature range in high-temperature region were observed. The significant dielectric thermal hysteresis, low barrier energy, high freezing temperature in heating process and the maximum dielectric tunability appeared in [Formula: see text] ceramic.

Effects of Dy on structural, dielectric and magnetic properties of Ni-Sr-Y co-precipitated hexaferrites

Dysprosium (Dy) doped Y-type strontium hexa ferrites of the following composition Ni2Sr2DyxFe12-xO22 where (x = 0.00, 0.05, 0.10, 0.15, 0.20, 0.25) were prepared through co-precipitation process. Phase analysis of the investigated samples was carried out by characterizing through (XRD) X-ray diffraction which confirmed the pure phase of Y-type hexaferrites. Dysprosium ion doping influenced lattice parameters i.e. lattice constants (a, c), crystallite size, (c/a) ratio, cell volume and porosity. The calculated crystallite size was in the range of 88–159 nm. FTIR plots showed that the characteristics bonds of Ni2Sr2DyxFe12-xO22 are appreciably influenced by the incorporation of Dy contents. The results of dielectric parameters revealed that dielectric constant, dielectric loss, tanloss were decreased with an increase in frequency. At 6.0 × 108 Hz, dielectric constant decreased from 5.55 to 3.69 with increasing Dy concentration. Owing to Maxwell-wagner type relaxation, the decrease in dielectric constant was noticed at higher frequency. The smaller dielectric constants and dielectric losses make these materials suitable for their applications in microwave devices fabrication.

Defect induced polarization and dielectric relaxation in Ga2–xFexO3

We report dielectric and pyroelectric responses of solid solutions of Ga2–xFexO3 (x = 0.75, 1.0, and 1.25), exhibiting combined relaxations (Maxwell-Wagner type relaxation and Debye relaxation); however, the dominating contribution is found to be from extrinsic Maxwell-Wagner type relaxation. Furthermore, the emergence of polarization in these systems is understood in terms of the thermally stimulated depolarization current effect caused by freezing of defect dipoles associated with charged oxygen vacancies rather than the intrinsic ferroelectric behavior.

Investigation of multiferroicity, spin-phonon coupling, and unusual magnetic ordering close to room temperature in LuMn0.5Fe0.5O3

We report the detailed experimental characteristics of LuMn0.5Fe0.5O3 synthesized by the wet chemical method and proclaim it as a new member of the multiferroic family. The compound stabilizes in P63cm crystal symmetry. It exhibits a spin re-orientation transition at TSR and an antiferromagnetic transition at TN. In addition, our magnetization vs. temperature data reveals an extra broad maximum close to room temperature; unseen in earlier studies. By invoking the compatible nature of the magnetic exchange path in P63cm symmetry, we have argued that the origin lies in the intraplane short-range spin ordering. Heat capacity is measured and analysed to elucidate the magnetic entropy. Though long-range antiferromagnetic ordering vanishes at TN ∼ 103 K, we find the experimental magnetic entropy calculated till 200 K is less by a significant amount from the value of theoretical spin randomization magnetic entropy; further supporting the existence of spin ordering beyond TN and even above 200 K. While the specific heat data and phonon modes of Raman spectra show a signature of spin-phonon coupling at TSR and TN both, dielectric anomaly indicating a magnetoelectric effect is seen only at TN. Piezoresponse force microscopy and ferroelectric hysteresis loop measurement confirm the room-temperature weak ferroelectricity with a saturation polarization value 0.007 μC/cm2 and low coercive field. Furthermore high-temperature dielectric characteristics reveal the ferroelectric transition at around 900 K and exhibit Maxwell-Wagner type relaxation. The present work serves as a bridge between h-RMnO3 and rare earth ferrite RFeO3. It assumes significance in the light of recent research developments in hexagonal RFeO3 (mainly h-LuFeO3) in the context of room-temperature multiferroicity and magnetoelectricity.

Preparation and physical properties of M-type hexaferrite SrCo2Ti2Fe8O19

ABSTRACTMeasurements of Raman spectra, dielectric constant and magnetization were performed on M-type hexaferrite SrCo2Ti2Fe8O19 single crystal, which was grown by travelling solvent method in an optical furnace. The Raman spectra measurements at room temperature revealed that main Raman modes, which are associated with the bipyramid FeO5, octahedra Fe(4)O6 and Fe(5)O6 as well with mixed octahedral vibration all with A1g symmetry, shift monotonously to higher wave numbers. In the low-frequency region (<10 kHz), permittivity rapidly decreases with increasing frequency, exhibiting a typical characteristic of Maxwell-Wagner type relaxation. The relaxation peak in dielectric losses centred on 100 kHz can be attributed to ionic relaxation processes caused by multiple valence states of iron ion (Fe2+ and Fe3+). M-type hexaferrite SrCo2Ti2Fe8O19 orders magnetically at 768 K and undergoes order-to-order magnetic phase transition at 380 K. Magnetic properties are almost isotropic around room temperatures with very low hysteresis having coercive field with induction lower than 3×10−3 T and with remnant magnetization lower than 0.17 μB/f.u. for magnetic fields applied along main crystallographic directions.

Origin of giant dielectric constant and conductivity behavior in Zn1−xMgxO (0 ≤ x ≤ 0.1) ceramics

Zn1−xMgxO (≤x≤0.1) ceramics were fabricated by conventional solid-state reaction of co-precipitated zinc oxide and magnesium hydroxide nanoparticles. Structural and morphological properties of the fabricated ceramics were studied using X-ray diffraction and scanning electron microscopic analysis. The dielectric measurements of the ceramics were carried out as a function of frequency and temperature respectively. Interestingly, Mg doped ZnO (MZO) samples exhibited colossal dielectric response (∼1×104 at 1kHz) with Debye like relaxation. The detailed dielectric studies and thermal analyses showed that the unusual dielectric response of the samples were originated from the defected grain and grain boundary (GB) conductivity relaxations due to the absorbed atmospheric water vapor (moisture). Impedance spectroscopy was employed to determine the defected grain and GB resistances, capacitances and which supported Maxwell–Wagner type relaxation phenomena.

Giant dielectric response and magnetoelectric behavior of 95BiFeO3–5BaTiO3 (95BFO–5BT) ceramics

A detailed study of electrical behavior of 95BiFeO3–5BaTiO3 (95BFO–5BT) ceramics through comprehensive analysis of temperature and frequency dependent dielectric behavior, ac impedance and magnetodielectric (MD) properties is reported here. Addition of insulating BaTiO3 into BiFeO3 have exhibited enhanced dielectric and ferromagnetic responses. The remnant polarization (Pr) was found to be 6 µC/cm2, while the dielectric constant was found to be very high ( $$\varepsilon_{\text{r}}^{\prime }$$ ≥ 102, for T ≥ 140 °C). Along with strong conductivity contribution to $$\varepsilon_{\text{r}}^{\prime }$$ , spectroscopic plots of $$\varepsilon_{\text{r}}^{\prime }$$ revealed the Maxwell–Wagner type relaxation in the sample, which ultimately could have led to an apparent high $$\varepsilon_{\text{r}}^{\prime }$$ in 95BFO–5BT ceramics. Origin of such a high $$\varepsilon_{\text{r}}^{\prime }$$ in BFO–BT was further investigated using impedance spectroscopy. MD studies revealed the magneto-electric coupling in the ceramics. The MD studies along with anomaly in dielectric data near antiferromagnetic ordering temperature (TN = 170 °C) of BFO suggests the magnetic bearing on the electrical properties of 95BFO–5BT ceramics.

Dielectric, AC-impedance, modulus studies on 0.5BaTiO3·0.5CaCu3Ti4O12 nano-composite ceramic synthesized by one-pot, glycine-assisted nitrate-gel route

A nano-composite electro-ceramic with the chemical formula 0.5BaTiO3·0.5CaCu3Ti4O12 (BTO–CCTO) has been synthesized by a glycine – assisted nitrate-gel route which is simpler and faster at relatively low temperature than the conventional solid-state synthesis method. X-ray diffraction (XRD) analysis showed the existence of BTO as a secondary phase alongside the major phase of CCTO. Transmission electron microscope (TEM) analysis of the composite shows that nano-particles (60±15nm) were obtained. Further, scanning electron microscope (SEM) images show that the morphology consists of a few large grains of CCTO (~1–5µm) embedded in small grains of BTO (~500nm–1µm) with a bimodal distribution. The impedance analysis shows two major contributions associated with the grains and the grain boundaries. Modulus analysis of this composite confirmed the presence of a Maxwell-Wagner type relaxation, which is temperature dependent. The activation energy value was found to be 0.80eV, and this composite is electrically conductive due to the mobility of the ionized oxygen defects.

Structural, electric and magnetic properties of Pb(Zr0.2Ti0.8)O3–CoFe2O4 heterostructures

Electric and magnetic properties of symmetric and asymmetric Pb(Zr0.2 Ti0.8)O3–CoFe2O4 (PZT/CFO) heterostructures, grown by pulsed laser deposition on SrTiO3 (100) substrates with a 25nm SrRuO3 (SRO) buffer layer as bottom electrode, were investigated by using hysteresis and capacitance measurements. X-ray diffraction, and transmission electron microscopy investigations reveal the high quality crystalline structure and the epitaxial relationship between SRO, PZT and CFO. The electric polarization–voltage hysteresis reveals that the remnant polarization and the coercive field are significantly affected by the CFO layer. The frequency dependence of capacitance suggests a Maxwell–Wagner type relaxation at low frequencies and is also affected by the presence of the PZT/CFO interface(s). The magnetic hysteresis measurements infer the possible presence of another spinel phase (Co3O4) in the CFO film, due to the lattice mismatch at the PZT/CFO interfaces, and with direct influence on the magnetic response of the structure. According to the electric and magnetic characterization, better room temperature multiferroic properties would be expected for the symmetric heterostructure.

High frequency electrical transport properties of CoFe2O4 and Sr2NiMnFe12O22 composite ferrites

Abstract Composite ferrite ceramic materials were obtained by mixing sol/gel derived CoFe 2 O 4 and Sr 2 NiMnFe 12 O 22 nanopowders sintered at 1050 °C for 3 h. The synthesized samples were characterized by XRD, Scanning Electron Microscopy, FT-IR, electrical resistivity and dielectric measurements. XRD analysis revealed that there is no new phase observed, indicating that no chemical reaction occurs between spinel and hexagonal phases and the intensity of Y-phase gradually decreased by increasing spinel concentration. Crystallite size calculated from XRD data decreased by increasing spinel concentration. Room temperature resistivity and activation energies of the samples increased with increasing spinel concentration. Dielectric constant of pure Y-type hexagonal ferrite decreased by increasing spinel concentration up to ~8.5. At higher frequency further decrease in dielectric constant was observed due to Maxwell-Wagner type relaxation with few resonance peaks beyond 2 GHz. Imaginary part of dielectric constant showed the similar behavior with frequency. Low dielectric constant, low dielectric losses and high resistivity make these composite ferrites useful in electromagnetic attenuation materials and microwave devices.

Structural and dielectric properties of La0.8Te0.2MnO3

We have studied the structural and dielectric properties of La0.8Te0.2MnO3 pervoskite compound, has a rhombohedral structure with space group R-3c, at room temperature. Infrared spectrum shows two active bands located at 611 and 410cm−1, which can be ascribed to the internal stretching and bending phonon modes. The additional bands observed at 925, 969 and 1383cm−1 are attributed to the multiphonon scattering. The dielectric constant ε′ shows a step like relaxation behaviour and has been discussed with in the frame work of the Kramers–Kronig transformation model. The ac conductivity follows a universal dielectric response (UDR), and the results were discussed and fitted with the Jump relaxation model (JRM). The occurrence of giant or colossal dielectric constant is most likely due to electrode polarization or interface polarization effect. The depletion layers are arising due to the formation of Schottky barriers at the metallic contacts of semiconducting samples, which may be formed by grain boundaries, can give rise to Maxwell–Wagner type relaxation and apparently very high dielectric constants.

High-temperature dielectric response in pulsed laser deposited Bi1.5Zn1.0Nb1.5O7 thin films

Cubic pyrochlore Bi1.5Zn1.0Nb1.5O7 thin films were deposited by pulsed laser ablation on Pt(200)/SiO2/Si at 500, 550, 600, and 650 °C. The thin films with (222) preferred orientation were found to grow at 650 °C with better crystallinity which was established by the lowest full-width half maxima of ∼0.38. The dielectric response of the thin films grown at 650 °C have been characterized within a temperature range of 270–650 K and a frequency window of 0.1–100 kHz. The dielectric dispersion in the thin films shows a Maxwell–Wagner type relaxation with two different kinds of response confirmed by temperature dependent Nyquist plots. The ac conduction of the films showed a varied behavior in two different frequency regions. The power law exponent values of more than 1 at high frequency are explained by a jump-relaxation-model. The possibility of grain boundary related large polaronic hopping, due to two different power law exponents and transformation of double to single response in Nyquist plots at high temperature, has been excluded. The “attempt jump frequency” obtained from temperature dependent tangent loss and real part of dielectric constants, has been found to lie in the range of their lattice vibronic frequencies (1012–1013 Hz). The activation energy arising from a large polaronic hopping due to trapped charge at low frequency region has been calculated from the ac conduction behavior. The range of activation energies (0.26–0.59 eV) suggests that the polaronic hopping at low frequency is mostly due to oxygen vacancies.

Room temperature stabilized cubic zirconia nanocrystal: a giant dielectric material

A giant low-frequency dielectric constant (∼105) has been observed in room temperature stabilized cubic zirconia nanocrystal of size range 4–8 nm. Dielectric constant strongly depends on the crystallite size. Electrical behaviour of nanocrystallites has been described by an equivalent circuit to obtain grain and grain boundary effects. Mixed valency of Zr (Zr4+, Zr3+) ions gives rise to electronic conduction. Giant dielectric constant has been explained by interfacial polarization because of Maxwell–Wagner type relaxation effect.

Colossal dielectric constants: A common phenomenon in CaCu3Ti4O12 related materials

In the present work we demonstrate that in addition to the well-known colossal-dielectric-constant material CaCu3Ti4O12 also various members of the series Ln2/3Cu3Ti4O12 with Ln = La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er and Tm, exhibit giant values of the dielectric constant. Just as CaCu3Ti4O12, all these materials show a Maxwell-Wagner type relaxation process. For the best material, Pr2/3Cu3Ti4O12, we provide a detailed investigation of its dielectric properties in a broad frequency range up to 1 GHz. Polarization at internal barriers, most likely grain boundaries, seems to be the reason for the observed very high values of the dielectric constant. Taking into account the present results and those reported in literature

Dielectric properties and ac-conductivity analysis of Bi 3.25La 0.75Ti 3O 12 ceramic using impedance spectroscopy

Investigations have been performed on lanthanum-modified layered ferroelectric bismuth titanate for composition Bi 3.25La 0.75Ti 3O 12 (BLT) using impedance spectroscopy to understand the role of microstructure on the dielectric properties of this important material. A wide range of frequency and a wide range of temperature passing through the Curie point were chosen for the measurement. The frequency dependence suggested an interfacial polarization controlled Maxwell–Wagner type relaxation at low frequencies, and the impedance spectrum correlated with the mathematical fitting indicated the presence of two types of interfaces, which were attributed to the metallurgical boundaries and the twinned planes parallel to the bismuth oxide layers inherent to the crystal structure within the metallurgical grains. A careful analysis of the dielectric properties, particularly the ac-conductivity analysis revealed that the grain boundaries did also follow their own Jonscher-like relaxation, and the overall relaxation of the sample changed to a purely grain boundary-limited response at low frequency to a pure grain-limited response at higher frequencies. And overall admittance of the ceramic sample neither follow unmodified nor modified Jonscher's law rather its behaviour can be well described by series addition of Jonscher's admittance corresponding to grain boundary and grain. It was demonstrated that the frequency response of the ac conductivity was related to the microstructure exactly in the same way as any other dielectric function, like the impedance or dielectric constant, a fact, which is not much emphasized in the open literature.

Effect of Boron Addition on the Dielectric Properties of Giant Dielectric CaCu3Ti4O12

The recently discovered giant dielectric CaCu 3 Ti 4 O 12 (CCTO) has been reported to show dielectric constant value as high as 80,000 for single crystals and around 10,000 for ceramics. However the dielectric constant is also associated with high dissipation factor. In the present study, it has been observed that the loss factor of CCTO can be reduced by B 2 O 3 addition. The low frequency dispersion of CCTO ceramics, which indicates Maxwell-Wagner type relaxation, is reduced by boron addition. Also the temperature dependence of dielectric constant is minimized by boron addition. From the present work it can be surmised that B 2 O 3 addition can favourably modify the dielectric properties of CCTO ceramic for its practical applications as a capacitor material.

Response time and electrorheology of semidiluted gellan, xanthan and cellulose suspensions

Response times with electrical fields of gellan and xanthan dry powder suspensions of 25, 32 and 53 μm average diameter and concentrations of 1.0, 1.5 and 2.0% (w/w) dispersed in commercial corn oil were optically measured through a specifically designed set up. In all cases, the delay time was proportional to 1/ E a, where E is the applied field and a is an adjustable parameter. The values of parameter a were very different from the typical value of some known electrorheolgical fluids. Response time of gellan suspensions was shorter than the one obtained for xanthan and it is comparable to the time found by using silica particles in silicon oil. Response times for cellulose were very large and the fibrillation phenomenon was negligible for E<1.0 kv/ mm. Viscosity measurements of semidiluted xanthan, gellan and cellulose suspensions (1.0 and 1.5% w/w) under the influence of electrical fields, were performed in a parallel plates rheometer. Results in the range of stress <70 Pa showed that viscosity values of gellan suspensions were larger than those obtained with xanthan or cellulose under the same applied electric field at shear rates higher than 10 s −1. However, cellulose suspensions showed larger viscosity values compared with the ones measured with xanthan and gellan suspensions at very low shear rates. Dielectric measurements of cellulose, xanthan and gellan 1.5% w/w suspensions were performed in the range 10 0–8×10 4 Hz. Results agree with a Maxwell–Wagner type relaxation model.

Interfacial electrical properties of diamond-like carbon/gallium arsenide heterostructures

Deposition onto GaAs of dielectric film with good interfacial properties is difficult owing to the high surface state densities at the GaAs surface. Study of diamond-like carbon (DLC)/GaAs heterostructures is worthwhile because of the advantageous properties of insulating DLC film and the low temperatures involved in its preparation. In this paper, we compare the electrical interfacial properties of DLC/GaAs with those of DLC/Si and DLC/Ge structures. The DLC films were prepared by r.f. plasma-assisted chemical vapour deposition using a mixture of propane and n-butane. Capacitance measurements were taken in the frequency range 400 Hz to 1 MHz. The interface trap density distribution N ss( E) was estimated for the DLCSi interface using Terman's method. Compared with the DLCSi and DLCGe interfaces, the DLCGaAs interface shows qualitatively different behaviour. There is an indication that the interfacial layer at the DLCGaAs interface is more conducting than the DLC film, giving rise to Maxwell-Wagner type relaxation. As a result, the effective permittivity of the DLC film is one order of magnitude higher. The formation of this interfacial layer could be related to pre-etching of the GaAs substrate using argon plasma.