Temperature Dependence Of Dielectric Properties Research Articles

Sintering dependent Ca2+ solubility in barium titanate synthesized by sol–gel auto combustion method

We report the preparation of ferroelectric Ba0.7Ca0.3TiO3 (BCT) ceramics by sol–gel auto combustion technique and its specific functional properties. The structural, dielectric and ferroelectric properties of BCT are strongly depending on the sintering temperature which also improves the phase purity and crystalline quality of the system. The formation of single-phase BCT is realized by sintering at 1450 °C for 4 h. suggesting the solubility limit of Ca2+ cation. Grain size and relative density are increased as the sintering temperature increased. The Rietveld refinement technique is employed for the detailed crystal structural analysis. The temperature and frequency dependent dielectric properties are investigated; the measured dielectric constant is er = 2680 at the transition temperature Tc=120 °C for the single phase ferroelectric BCT. Sintering and electrical poling improved the shape of the hysteresis curve and reduced the leakage current. Electrical conduction mechanism is also discussed.

Magnetic and dielectric studies of barium hexaferrite (BaFe12O19) ceramic synthesized by chemical route

Barium hexaferrite BaFe12O19 (BHF) ceramic was synthesized by chemical route on sintering at 1050 °C for 12 h. The synthesized material was characterized by XRD, SEM, AFM and TEM analysis. Metal oxide stretching frequencies corresponding to Fe-O, Ba-O, and Fe-O-Fe bands are confirmed by FTIR studies. The hexagonal nature of the BHF ceramic was confirmed by TEM analysis and Rietveld refinement with space group P63/mmc. The particle size observed by TEM is 175 nm. The root means square and average roughness were found to be 61.048 nm and 44.025 nm respectively. The M-T and M-H hysteresis loop indicates temperature dependent ferromagnetic behavior of BHF ceramic. The temperature and frequency dependent dielectric properties were explained by Maxwell-Wagner theory. The value of dielectric constant (e′) for BHF ceramic was found to be 22× 103 at 100 Hz and 483 K.

Tunable structural and electrical impedance properties of ordered and disordered iron oxide phases for capacitive applications

Having extensive knowledge of room temperature and temperature dependent dielectric and impedance properties of iron oxide nanostructures will help in extending the field of application from biomedical sciences to microelectronics industry. This aspect of iron oxide has long been neglected and the attention is mostly focused on magnetic investigations. To explore and extend the field of application of iron oxide this study is focused on detailed investigation of structural as well as temperature dependent (30–210 °C) dielectric along with impedance analysis. Iron oxide nanostructures are prepared using template free oleic acid assisted sol-gel method with variation in molarity of the finally synthesized sol in the range of 0.2–2.0 mM (interval 0.2 mM). Magnetite (Fe3O4) phase is observed at molarity of 0.2 mM whereas, vacancy ordered and disordered maghemite (γ-Fe2O3) phases are observed at molarities of 0.8–1.0 mM and 1.4–2.0 mM, respectively. Dielectric constant of 104.6, 74.5 and 98.43 (log f = 5.0) is observed at molarities of 0.2 mM, 1.0 mM and 2.0 mM for Fe3O4 and vacancy ordered (Vo) & disordered (Vd) γ-Fe2O3 phase, respectively. Zview software is used for the fitting of Nyquist plots. Fitted data reveals that dielectric constant strongly depends on grain boundary resistance (Rgb). Activation energy of 0.25 eV and 0.296 eV (log f = 5) is observed for Fe3O4 and Vd γ-Fe2O3 phase at 0.2 mM and 2.0 mM molarity of the final iron oxide sol.

Crystallinity mediated variation in optical and electrical properties of hydrothermally synthesized boehmite (γ-AlOOH) nanoparticles

In this article, nanostructures of boehmite (γ-AlOOH) have been successfully synthesized in a time varied, facile and cost effective hydrothermal route. The samples have been characterized by using X-Ray Diffraction (XRD), Field Emission Scanning Electron Microscopy (FESEM), Transmission Electron Microscopy (TEM) and Fourier Transform Infrared (FTIR) spectroscopy. Our samples exhibit remarkably high photoluminescence emission intensity and dielectric constant (3.71 × 106 for BH12 sample) with a nominal dielectric tangent loss. A detailed growth mechanism including the nucleation and self assembly of our nanomaterial has been discussed. Moreover, we are the first to report here the electrical properties of the boehmite nanoparticles. Present investigation also explores temperature dependent dielectric property and ac conductivity of these samples. The role of crystallinity in the optical and electrical enhancement of our samples has been illustrated with proper analytical details. Not only high emission intensity in the blue and green region of the spectrum makes our sample a strong candidate for bio-imaging and bio-sensing applications, but also high dielectric constant makes them desirable for cost-effective energy storing devices, such as supercapacitors and solar cells.

Studies on magnetocapacitance, dielectric, ferroelectric, and magnetic properties of microwave sintered (1-x) (Ba0.8Sr0.2TiO3) - x (Co0.9Ni0.1Fe2O4) multiferroic composite

Present paper reports the synthesis of multiferroic composite (1-x) [Ba0.8Sr0.2Ti)O3]-x[Co0.9Ni0.1Fe2O4] were x = 0.1, 0.2, 0.3 and 0.4. Both phases of the composite i.e. ferroelectric (BST) and ferrite (CNFO) are synthesized via hydroxide co-precipitation method followed by microwave sintering technique at 1100 °C. These composites were characterized for their structural, microstructural, dielectric analysis, magnetodielectric (MD) effect and ferroelectric properties. Presence of both the phases ferroelectric (BST) and ferromagnetic (CNFO) are confirmed by the x-ray diffraction and scanning electron microscopic analysis. Maxwell-Wagner type dielectric dispersion is observed in frequency dependent dielectric measurement. Temperature-dependent dielectric properties were measured from 25 °C to 500 °C at various applied frequencies. Ferroelectric behavior in the composites was confirmed by the polarization vs. Electric field analysis. The magnetodielectric effect was studied in the presence of applied magnetic field from 0 to 1 Tesla. Magnetocapacitance (%) increases with increase in the ferrite concentration in the ferroelectric phase. The maximum percentage of magnetocapacitance is observed in 60BST-40CNFO composite which is MC = 30% at the frequency 1 KHz with the applied magnetic field is 1-Tesla. Room temperature magnetic hysteresis loops show an increase in saturation magnetization (Ms) with an increase in ferrite concentration.

Effect of SiO2/B2O3 Ratio on the Crystallization Behavior and Dielectric Properties of Barium Strontium Titanate Glass–Ceramics Prepared by Sol–Gel Process

Ferroelectric glass–ceramics, with a basic composition 90 wt.% (Ba0.65Sr0.35)TiO3−10 wt.% (B2O3−nSiO2) (n = 0.5, 1, 3, 5) were synthesized by the sol–gel method and their phase development and dielectric properties were investigated by differential thermal analysis, x-ray diffraction, field emission scanning electron microscopy, dielectric temperature curves and impedance spectroscopy. From the differential thermal analysis, glass transition and crystallization behavior can be observed. From the x-ray diffraction study, two crystalline phases (Ba,Sr)TiO3 and Ba2TiSi2O8 were formed over the entire composition range of the glass–ceramics. In addition, the main crystal phase has undergone a transformation from (Ba,Sr)TiO3 to Ba2TiSi2O8 with the increase of n. A typical structure in which the crystal phase was surrounded by a glassy matrix has been observed in the scanning electron microscope images. As a result of temperature dependent dielectric property measurements, the dielectric constant increased obviously with the increase of n from 0.5 to 1. Further increasing n led to a reduction of the dielectric constant, which is in coincidence with the variation of the intensity of (Ba,Sr)TiO3 phase with n. According to the impedance spectroscopy analysis and the activation energy calculation, the relaxation peak in both Z″ and M″ data should be attributed to the crystal–glass interface, and the change of conduction mechanism with the increase of SiO2/B2O3 ratio may be attributed to the corresponding transition of the main crystal phase.

Analysis of temperature and frequency dependent dielectric properties, dynamic hysteresis loop and thermal energy conversion in BaZr0.05Ti0.95O3 ceramic

The barium zirconium titanate ceramic with formula BaZr0.05Ti0.95O3 has been synthesized by the conventional solid state reaction technique. The synthesized ceramic sample is characterized by X-ray diffraction, scanning electron microscopy, Raman spectroscopy, temperature dependent dielectric spectroscopy and ferroelectric behaviour. The Raman spectrum confirms the orthorhombic structure at room temperature and local distortions due to distorted octahedral structures. The temperature dependent dielectric study reveals the occurrence of three transition temperatures representing rhombohedra to orthorhombic, orthorhombic to tetragonal and tetragonal to cubic transition in the material. The area of the hysteresis loop decreases with temperature up to the transition temperature, followed by an increase at higher temperatures. Scaling relations for coercive field (Ec) and remnant polarization (Pr) are studied as a function of temperature. This exhibits back-switching polarization behaviour as a function of temperature. The thermal energy conversion potential of the studied sample is obtained by using Olsen cycle.

Enhanced relative permittivity in niobium and europium co-doped TiO2 ceramics

The appearance of colossal permittivity materials broadened the choice of materials for energy-storage applications. In this work, colossal permittivity in ceramics of TiO2 co-doped with niobium and europium ions ((Eu0.5Nb0.5)xTi1-xO2 ceramics) was reported. A large permittivity (εr ∼ 2.01 × 105) and a low dielectric loss (tanδ ∼ 0.095) were observed for (Eu0.5Nb0.5)xTi1-xO2 (x = 1%) ceramics at 1 kHz. Moreover, two significant relaxations were observed in the temperature dependence of dielectric properties for (Eu, Nb) co-doped TiO2 ceramics, which originated from defect dipoles and electron hopping, respectively. The low dielectric loss and high relative permittivity were ascribed to the electron-pinned defect-dipoles and electrons hopping. The (Eu0.5Nb0.5)xTi1-xO2 ceramic with great colossal permittivity is one of the most promising candidates for high-energy density storage applications.

The upper Manganese doping limit and its effects on physical properties of lead-free Bi0.5Na0.5TiO3 ceramics

The lead-free piezoelectric, Bi0.5Na0.5TiO3, was synthesized with varying amounts of Manganese (Mn) doping (x = 0.00, 0.02, 0.05, 0.10, 0.15) on the B-site to replace Ti4+ cations. Herein, the doping limit of Mn is explored along with its effects on the structure and properties of these materials. The temperature-dependent dielectric properties of the materials with a higher manganese doping level have also been comprehensively investigated in the temperature range of 10–700 K. All samples show a high dielectric permittivity, εr ~ 4979–3626 at Tm ~ 550–600 K, along with a low dielectric loss. The magnetic study shows that doping with Mn leads to a complex magnetic state, where there is possible clustering of Mn ions, with inter- or intra-cluster interactions becoming dominant at approximately 50 K. These samples may be considered as alternative to lead-free materials with magneto-electric coupling.

Dielectric properties of (K0.5Na0.5)NbO3–(Bi0.5Li0.5)ZrO3 lead-free ceramics as high-temperature ceramic capacitors

(1 − x)K0.5Na0.5NbO3–x(Bi0.5Li0.5)ZrO3 (labeled as (1 − x)KNN–xBLZ) lead-free ceramics were fabricated by a solid-state reaction method. A research was conducted on the effects of BLZ content on structure, dielectric properties and relaxation behavior of KNN ceramics. By combining the X-ray diffraction patterns with the temperature dependence of dielectric properties, an orthorhombic–tetragonal phase coexistence was identified for x = 0.03, a tetragonal phase was determined for x = 0.05, and a single rhombohedral structure occurred at x = 0.08. The 0.92KNN–0.08BLZ ceramic exhibits a high and stable permittivity (~ 1317, ± 15% variation) from 55 to 445 °C and low dielectric loss (≤ 6%) from 120 to 400 °C, which is hugely attractive for high-temperature capacitors. Activation energies of both high-temperature dielectric relaxation and dc conductivity first increase and then decline with the increase of BLZ, which might be attributed to the lattice distortion and concentration of oxygen vacancies.

Synthesis and study of structural, dielectric, magnetic and magnetoelectric properties of K0.5Na0.5NbO3–CoMn0.2Fe1.8O4 composites

Magnetoelectric (ME) composites consisting of K0.5Na0.5NbO3 (KNN) as ferroelectric phase and CoMn0.2Fe1.8O4 (CMFO) as ferrite phase with general formula (x) CoMn0.2Fe1.8O4–(1 − x) K0.5Na0.5NbO3 (x = 10, 20, 30, 40 and 50 wt%) were synthesized using solid state reaction method. X-ray diffraction analysis asserts the existence of component phases including spinel phase of CMFO and orthorhombic phase of KNN. Field emission scanning electron microscopy has been used for studying the morphology and calculation of average grain size. The temperature dependent dielectric properties including dielectric constant ( $$\varepsilon ^{\prime}$$ ) and dielectric loss (tan δ) at different frequencies has been studied and both are found to increase with incorporation of CMFO. Magnetic hysteresis loops have been measured at temperatures of 300 and 5 K. Variation of magnetization versus temperature has been studied in field cooled and zero field cooled modes. Polarization versus electric field (P–E) hysteresis loops are obtained at room temperature indicating presence of ferroelectric ordering in the composites at room temperature. The remnant polarization (2Pr) and coercive field (2Ec) are found to decrease linearly with incorporation of CMFO. ME voltage coefficient (αME) has been measured. The maximum value of αME is found to be 5.941 mV/cm-Oe for 10% CMFO–90% KNN bulk composite.

Thermal-induced structural transition and depolarization behavior in (Bi0.5Na0.5)TiO3-BiAlO3 ceramics

The depolarization temperature Td determines the upper temperature limit for the application of piezoelectric materials. However, the origin of depolarization behavior for Bi-based materials still remains controversial and the mechanism is intricate for different (Bi0.5Na0.5)TiO3-based systems. In this work, the structure and depolarization behavior of (1-x)(Bi0.5Na0.5)TiO3-xBiAlO3 (BNT-BA, x = 0, 0.02, 0.04, 0.06, 0.07) ceramics were investigated using a combination of X-ray diffraction and electrical measurements. It was found that as temperature increased, the induced long-range ferroelectric phase irreversibly transformed to the relaxor phase as evidenced by the temperature-dependent ferroelectric and dielectric properties, which corresponded to a gradual structural change from the rhombohedral to the pseudocubic phase. Therefore, the thermal depolarization behavior of BNT-BA ceramics was proposed to be directly related to the rhombohedral–pseudocubic transition. Furthermore, Td (obtained from thermally stimulated depolarization currents curves) was higher than the induced ferroelectric-relaxor phase transition temperature TFR (measured from dielectric curves). The phenomenon was quite different from other reported BNT-based systems, which may suggest the formation of polar nanoregions (PNRs) within macrodomains prior to the detexturation of short-range ferroelectric domains with PNRs or nanodomains.

Zn doped NiFe2O4- Pb (Zr0.58Ti0.42)O3 multiferroic nanocomposites: Magnetoelectric coupling, dielectric and electrical transport

We have investigated the room temperature magnetoelectric coupling, temperature dependent impedance and dielectric properties of xZn0.3Ni0.7Fe2O4 – (1-x) Pb (Zr0.58Ti0.42)O3 (x = 0.2, 0.3, 0.4 and 0.5) nanocomposites. The nanocomposites have been prepared through low temperature chemical pyrophoric reaction process followed by solid state reaction route. The magnetoelectric coupling has been measured as a function of applied magnetic field at different frequencies and different angles between applied magnetic field and measured electric field. The observed magnetoelectric coupling may be due to the field dependent magnetostriction of the piezomagnetic phase of the composite. Noticeably, the magnetoelectric coupling is strongly depended on the frequencies, angles and volume fraction of the piezomagnetic phase of the nanocomposites. Polarization – Electric field loop shows the room temperature ferroelectric nature of nanocomposites. The ac electrical properties of the nanocomposites have been studied employing impedance spectroscopy technique. The temperature dependent impedance studies reveal the grain boundaries plays the dominating role. Thermally tunable dielectric properties of nanocomposites exhibit the Maxwell – Wagner interfacial polarization in the system. Electromechanical resonance response is observed at the higher frequency region. The ac conductivity of the nanocomposites has been investigated at different temperatures and fitted by Jonscher's power law. The conduction mechanism is mainly due to the small and large polaronic hopping in the system.

Low temperature ferromagnetic behavior and temperature dependent anomalous dielectric relaxation of Zn0.90Ni0.05Mn0.05O diluted magnetic semiconductor

We report structural, magnetic and temperature dependent dielectric properties of diluted magnetic semiconductor Zn0.90Ni0.05Mn0.05O prepared by solid state reaction technique. X-ray diffraction analysis revealed formation of single phase hexagonal wurtzite structure. Scanning electron microscopy and atomic force microscopy images indicated increase in grain size and roughness respectively with increasing sintering temperature. Field dependent DC magnetization at low temperature exhibited ferromagnetic ordering with coercivity ~ 6 × 104 A/m and remanence ~ 17 A/m. Complex initial permeability values were found to be positive for the measurement frequency range (1 kHz–120 MHz) with a relaxation at lower frequency. Temperature dependent DC magnetization and AC susceptibility followed curie law with curie temperature below 65 K. Temperature dependent dielectric constants ($$\varepsilon ^{\prime}\,\& \,\varepsilon ^{\prime\prime}$$) and loss tangents ($$tan\delta$$) measured for selected frequencies were found to be an increasing function of temperature and decreasing function of frequency. AC conductivity ($${\sigma }_{ac}$$) values were found to be an increasing function of frequency and temperature. Clear signatures of relaxations were observed in $$\varepsilon ^{\prime},\,\varepsilon ^{\prime\prime},$$ $$tan\delta$$ and $${\sigma }_{ac}$$ for temperatures above 200 °C.

Retraction Note to: Effect of Temperature on the Dielectric Properties of Carbon Black-Filled Polyethylene Matrix Composites Below the Percolation Threshold

The temperature dependence of dielectric properties of carbon black-filled polyethylene matrix composites below the percolation threshold was studied based on the effect medium approximation theory (EMA theory). Although the literature on calculation based on the EMA theory by changing the parameters is vast, an overall discussion taking into account the EMA theory is required to explain the dielectric properties of the composites and their temperature dependence. Changes of the dielectric properties of carbon black-filled PMC and their temperature dependence below the percolation threshold for the volume fraction of carbon black have been discussed based on the EMA theory. The composites satisfy the universal law of conductivity above the percolation threshold, whereas it gives the critical exponent of s = 1 for dielectric constant below percolation threshold. The rates of the decrement of both % changes of dielectric constant and dielectric loss factor for temperature become larger with an increase in the volume fraction below percolation threshold. By incorporating the effect of thermal expansion into the EMA theory, the temperature dependence of dielectric properties is successfully explained.

Microwave-assisted rapid synthesis of poly(butylene succinate): principal effect of microwave irradiation of accelerating the polycondensation reaction

To determine the origin of the reaction rate acceleration in the synthesis of poly(butylene succinate) (PBS) upon microwave irradiation, we herein investigated the effect of the microwave-assisted activation of the reactants, viz. the monomers 1,4-butanediol (BD) and succinic acid (SA), and of the water produced as a by-product during the reaction. The rate of removal of the water by-product from the reaction solution was precisely measured under equivalent reaction conditions (i.e., time and temperature) using both microwave and conventional heating methods. Microwave heating selectively activated and removed the water from the reaction solution more rapidly and to a greater extent than oil bath heating. Measurement of the temperature-dependent dielectric properties of the reactants revealed that the dielectric loss factor (eʹʹ) of BD increased with increasing temperature, peaking at 80 °C. In contrast, the eʹʹ of the mixture of BD and SA was significantly lower than that of BD alone from 70–140 °C. These results indicate that the principal effect of microwave irradiation in the synthesis of PBS was the accelerated removal of the water by-product. The origin of the reaction rate acceleration in the microwave-assisted synthesis of poly(butylene succinate) (PBS) was investigated by measuring the rate of removal of the water by-product from the reaction solution under equivalent reaction conditions using both microwave and conventional heating methods. Microwave heating selectively activated and removed the water from the reaction solution more rapidly and to a greater extent than oil bath heating. These results indicate that the principal effect of microwave irradiation in the synthesis of PBS was the accelerated removal of the water by-product.

Correlation between the dielectric and electrochemical properties of TiO2-V2O5 nanocomposite for energy storage application

The structural and morphological analysis of TiO2-V2O5 nanocomposite has been performed using FTIR, XRD and FESEM. Temperature (300 K-500 K) and frequency dependent dielectric properties and complex impedance analysis have been carried out to investigate the effect of grain and grain boundary of the synthesized sample. The electrochemical properties like cyclic voltammetry (CV), galvanostatic charge/discharge (GCD) rate and electrochemical impedance (EIS) of the electrode material have also been investigated. The maximum specific capacitance (Cm) obtained from cyclic voltammetry (CV) and GCD measurement are 262 Fg-1 at scan rate 2 mV s−1 and 251.5 Fg-1 at current density 0.09 mA cm−2 respectively. The stability of the electrode material is measured up to 1000 cycles. The correlation between the dielectric properties and electrochemical properties is successfully demonstrated for the first time. Large grain boundary resistance played an important role for low specific capacitance value at room temperature.

Frequency and temperature dependent electrical and dielectric properties of LaCrO3 and Ir doped LaCrO3 perovskite compounds

Perovskite oxide materials, especially perovskite lanthanum chromium oxide, LaCrO3 (LCO) have taken considerable attention among the scientists due to the changing optical, electrical, dielectric and magnetic properties depending on doping via various elements. In this study, the LCO and iridium (Ir) doped LCO (LaCr1-xIrxO3) (x = 0.10) compounds were synthesized using solid-state reaction method. Scanning electron microscope (SEM) and X-ray photoelectron spectroscopy (XPS) have been employed to study particle morphologies and oxidation states of synthesized powders, respectively. Frequency-depended electrical/dielectric properties of perovskite oxide samples were performed in wide range frequency (1Hz-10 MHz) and temperature (−100 °C to +100 °C) using dielectric/impedance spectrometer. Electrical measurements have underscored that the dielectric constant of LCO compound dramatically decreased after doped with Ir. Furthermore, it was observed that ac conductivity and capacitance value of LCO decreased while impedance increased after Ir doping due to i) Ir occupation in Cr sites and ii) lattice distortion owing to doping larger ion Ir4+ into smaller Cr3+ ion in the LCO lattice. Finally, overlapping large polaron tunneling (OLPT) and quantum mechanical tunneling (QMT) conduction mechanisms were suggested for LCO while the correlated barrier hopping (CBH) and QMT conduction mechanisms were observed for Ir doped LCO compound. Moreover, the activation energy values have been calculated by employing both fmaxvs. 1/T and σdcvs. 1/T plots. It has been shown those energy values are in good agreement with each other for LCO and Ir doped LCO samples at various temperature ranges.

Influence of K0.5Bi0.5TiO3 on the structure, dielectric and ferroelectric properties of (Ba,Ca)(Zr,Ti)O3 ceramics

A new lead-free ferroelectric solid solution between (Ba,Ca)(Zr,Ti)O3 (BCZT) and K0.5Bi0.5TiO3 (KBT) has been systematically investigated in terms of its phase transformations, microstructure, dielectric and ferroelectric properties. The incorporation of KBT into BCZT was found to enhance the sintering behavior, although secondary phases of K4Ti3O8 and BaBi4Ti4O15 were detected at high KBT contents. Chemical heterogeneity was also observed in the form of core-shell grain structures comprising tetragonal ferroelectric BCZT-rich cores with pseudo-cubic relaxor ferroelectric KBT-rich shell regions. Temperature-dependent dielectric property measurements revealed that the BCZT-KBT ceramics exhibited both normal and relaxor ferroelectric behaviour simultaneously, associated directly with the core-shell structure. Ferroelectric hysteresis measurements indicated that the remanent polarisation and coercive field were strongly dependent on KBT content. In common with other lead-free relaxor ferroelectrics, increasing temperature led to the formation of constricted polarisation-electric field hysteresis loops, indicating the occurrence of a reversible electric field-induced nanopolar to long-range ordered ferroelectric state.

Microwave Characterization of Activated Carbons

Microwave complex permittivity measurements of activated carbons were investigated using two different microwave measurement techniques, microwave cavity perturbation at 2.5 GHz and broadband coaxial probe in the frequency range between 10 MHz and 10 GHz. Such measurements demonstrate the ability of these materials to interact with the microwave electric field, both in terms of strong polarization and absorption. We have thus used complex permittivity to quantify the variability of different forms of activated carbon produced from different sources and different treatments, such as thermal treatments or impregnation. In addition, the cylindrical cavity at 2.5 GHz was used for temperature-dependent dielectric properties measurements of activated carbons to investigate their susceptibility to microwave heating as function of temperature. Microwave complex permittivity of activated carbons was measured in the temperature range from 30?C up to 150?C.