Dielectric Dispersion Research Articles

Dielectric analysis of unpolymerized and photopolymerized NOA65 in a parallel-plate cell

The flourishing development of liquid crystal research in recent decades has highlighted the importance of polymer materials in enhancing liquid–crystal material and device properties, demonstrating tremendous potential in a wide range of industries. One of the polymer materials widely used in polymer-dispersed liquid crystal is Norland UV-curable optical adhesive (NOA65). This study focuses on the dielectric behavior of the optical adhesive in a parallel-plate cell. Given the broadness and asymmetry of the dielectric dispersion curve, the two-relaxation Havriliak–Negami model was employed to analyze the complex dielectric spectra of NOA65 before and after photocuring. Experimental results indicate that as temperature rises, the dielectric relaxation of NOA65 undergoes a blue shift, leading to an eventual overlap with pseudo-dielectric relaxation at a higher frequency. This brings about an increase in the obtained signal in the dielectric loss spectrum, implying that the observed feature of pseudo-dielectric relaxation is actually superposed or contributed by the intrinsic relaxation signal. Furthermore, as temperature continues to rise, the intrinsic dielectric loss signal of NOA65 becomes untraceable beyond the frequency span within which the pseudo-dielectric relaxation signal lies.

Dielectric relaxation and electrical conduction mechanism via hopping of polarons in (Pb0.3Bi0.7)(Zn0.1Nb0.2Fe0.7)O3 perovskite compound: A study based on CBH model

This work analyses the dielectric and conducting properties of the PZN-modified BF solid solution (0.3PZN-0.7BF) synthesized at 850 °C by solid-state reaction. The Rietveld refinement of 0.3PZN-0.7BF solid solution displays three phases: tetragonal Pb(Fe0.5Nb0.5)O3 (76.68 %), α-BZN (21 %), and Bi2Fe4O9 (2.32 %). Dielectric parameter frequency dispersion implies normal ferroelectricity. Thermal relaxation shifts dielectric loss, imaginary impedance (Z''), and loss modulus (M'') peaks to higher frequencies. Electrical investigation indicates electrode polarization, dipole orientation, charge ordering, oxygen vacancies, and defects. Investigations suggest p-type polarons dominate conductivity. At room temperature and 1 MHz, the compound has 117 dielectric constant and 0.009 tangent loss. Conductivity and impedance testing show semi-conductivity. UV–Vis spectrum investigation shows a 1.97 eV energy band gap, supporting its semiconductor properties. Photovoltaic and optoelectronic device applications benefit from 0.3PZN-0.7BF solid solution optical and electrical property studies.

Low-temperature sintering BCZT-Dy ceramics with low strain hysteresis for actuator application

Ba(Cu0.5W0.5)O3 (BCuW)-doped [(Ba0.85Ca0.15)1-xDyx](Zr0.1Ti0.9)O3 (BCZT-xDy, x = 0.001, 0.03) ceramics were prepared by conventional ceramic processing via low-temperature sintering technique. Rather pure perovskite structure and densified morphology with irregular nearly spherical-shape grains are achieved in all ceramics due to liquid-phase sintering. All BCuW-doped BCZT-xDy ceramics present apparent dielectric frequency dispersion and relaxor ferroelectric characteristic due to ion substitution and adding BCuW. The ceramics prepared at optimized sintering temperatures have rather large strain and small strain hysteresis, showing prospect application in piezoelectric high-precision actuators.

Polaron-assisted dielectric relaxation processes in donor-doped BaTiO3-based ceramics

Ceramic samples based on the Ba1-xGdxTiO3 system, where x = 0.001, 0.002, 0.003, 0.004 and 0.005, were prepared via the Pechini’s chemical synthesis route. Structural properties, analyzed from X-ray diffraction and Rietveld refinement, revealed the formation of the pure ABO3 perovskite structure with tetragonal symmetry (P4mm) for all the studied compositions. Doping with Gd3+ promoted a reduction in the unit-cell volume, confirming the preferential substitution of the rare-earth cation at the A-site. The dielectric properties have been analyzed over a wide temperature and frequency range, revealing a significant contribution of the conduction mechanisms in the dielectric response of the studied ceramics. In fact, by using the Davidson-Cole formalism, the observed electrical behavior was found to be associated with relaxation processes related to intrinsic defects mobility promoted by a thermally-activated polaronic mechanism. The obtained values of the activation energy for the relaxation processes, estimated from the Arrhenius’ law for the mean relaxation time, revealed a decrease from 0.29 up to 0.21 eV as the Gd-doping concentration increases, which suggests the conduction process to be associated with the polaronic effects due to the coexistence of Ti4+ and Ti3+ ions in the structure. Analysis from the conductivity formalism, by using the Jonscher’s universal power-law, confirmed the polaron-type conduction mechanism for the dielectric dispersion, as suggested by the dielectric analysis, being the nature of the hopping mechanism governed by small polaron hopping (SPH) charge transport in the studied Ba1–xGdxTiO3 ceramics.

Ex vivo electrical bioimpedance measurements and Cole modelling on the porcine colon and rectum

Different pathological changes in the large intestine wall, associated with the development of different chronic diseases, including colorectal cancer, could be reflected in electrical bioimpedance readings. Thickness and composition of the mucus bilayer covering it in the luminal side, abundance of bacteria of the intestinal microbiota, the permeability of the epithelium and inflammation are some of these. However, scientific literature on electrical passive properties of the large intestine is scarce. In this study, complex impedance measurements at 8 frequencies were carried out on 6 specimens of porcine colorectal tissue, within half ab hour post-mortem, obtained from a local abattoir. For 5 different distances, measured proximally from the border of the anus, 3 readings were taken at 3 different points with a tetrapolar probe. The results show 2 different dielectric dispersions in the α and β regions and it seems that there is a relationship between the values of resistivities and the thickness of the wall. Also, parameter values both for the Cole and the geometrical models are given. Another set of electrical bioimpedance readings was carried out in order to assess the effect of the mucus layer on electrical properties of the tissue. It seems that these layers are related to the low frequency dispersion. Finally, electrical passive properties of porcine colorectal tissue, reported in this work, give reference values and behaviour patterns that could be applied for further research in human medicine, based on bioimpedance measurements.

Unveiling the Terahertz Nano-Fingerprint Spectrum of Single Artificial Metallic Resonator.

As artificially engineered subwavelength periodic structures, terahertz (THz) metasurface devices exhibit an equivalent dielectric constant and dispersion relation akin to those of natural materials with specific THz absorption peaks, describable using the Lorentz model. Traditional verification methods typically involve testing structural arrays using reflected and transmitted optical paths. However, directly detecting the dielectric constant of individual units has remained a significant challenge. In this study, we employed a THz time-domain spectrometer-based scattering-type scanning near-field optical microscope (THz-TDS s-SNOM) to investigate the near-field nanoscale spectrum and resonant mode distribution of a single-metal double-gap split-ring resonator (DSRR) and rectangular antenna. The findings reveal that they exhibit a dispersion relation similar to that of natural materials in specific polarization directions, indicating that units of THz metasurface can be analogous to those of molecular structures in materials. This microscopic analysis of the dispersion relation of artificial structures offers new insights into the working mechanisms of THz metasurfaces.

Structural distortion-induced low-temperature dielectric dispersion in lanthanide titanate pyrochlores

Rare-earth titanate pyrochlores have attracted significant attention for their unique magnetic frustration; however, research on the origin of low-temperature dielectric dispersion and the relationship between dielectric properties and structure lags far behind. Here, by systematically investigating the dielectric properties of representative rare-earth titanates R2Ti2O7 (R = La, Nd, Sm, Er, Yb, and Lu), we demonstrate that R2Ti2O7 with a cubic pyrochlore structure exhibits low-temperature dielectric dispersion behavior, while the other compounds with a monoclinic perovskite-like layered structure possess no dispersion behavior but excellent temperature-stable dielectric property. The dielectric dispersion in cubic pyrochlores arises from the structural distortion. Furthermore, the existence of structural distortion is affirmed by the anomalous phonon softening of A1g Raman mode around the dielectric dispersion temperature, and the origin of the structural distortion is attributed to anharmonic phonon–phonon interactions induced by intrinsic vacant oxygen at Wyckoff 8a sites. In addition, with increasing ionic radius from R = Lu to Sm, the increased lattice parameter leads to varied bond length and bond angle of Ti-O(1)-Ti, which strengthens the local lattice distortion of TiO(1)6 octahedra and thus enhances diffusion degree of dielectric dispersion. On the other hand, the absence of intrinsic vacant oxygen site hardly gives rise to the local structural distortion and thus no dielectric dispersion in monoclinic R2Ti2O7. Our work not only clarifies the mechanism of dielectric dispersion but also gives a comprehensive perspective on the structure–property relationship of rare-earth titanates R2Ti2O7, and thus lays a solid foundation for further work on related materials.

Electrical and electrochemical properties of A-site non-stoichiometry Ca0.67La0.22□0.11Ti(1−x)CrxO3−δ electrolyte materials for solid oxide fuel cells

Due to increasing global energy demands and environmental concerns, the search for alternative and environmentally friendly energy sources is of paramount importance. Solid oxide fuel cells (SOFCs) have emerged as a promising solution thanks to their high efficiency and minimal environmental impact. In this regard, perovskite oxides, with their unique properties, have attracted significant attention. This study investigates the dielectric dispersion, electrical features, scaling behavior, and optical defects of Ca0.67La0.22Ti0.85Cr0.15O3 with x = 0.15, CLT0.85Cr0.15. The presence of a vacancy in the A-site is denoted by the square in the formula. Relaxation phenomena were analysed using dielectric and modulus formalism, while the conductivity mechanism was explored through electrical conductivity measurements. The optical defects of CLT0.85Cr0.15 were analysed using electron paramagnetic resonance (EPR) spectroscopy. The findings revealed the formation of Cr3+–VO center defects. These defects serve as sources of in-gap electron traps, thereby enhancing the optical properties of CLT0.85Cr0.15, making it as a compelling material for various optical applications. The power density increased with temperature, reaching 0.73 W/cm2 at 850 °C, suggesting that CLT0.85Cr0.15 could be a promising electrolyte for IT-SOFCs. The peak in power density correlated with temperature due to thermal effects on ion motion. However, the open circuit voltage decreased with temperature increase, due to increased oxygen vacancies and electron/hole conduction in CLT0.85Cr0.15. The findings suggest that perovskite materials could revolutionize SOFCs technology, paving the way for more efficient and environmentally friendly energy solutions.

Direct Calculations of the Dielectric and Optical Parameters of Some Compound Semiconductors: A Study Using the Lorentz Oscillator and Wemple-DiDomenico Models

The Lorentz single oscillator model is widely utilized to describe the electron-phonon interaction in solids. The use of this model to calculate the dielectric function and optical parameters of compound semiconductors represents a novel approach in materials science which may lead to develop new materials with tailored optical properties and consequently can offer vast applications in areas such as quantum computing and quantum information processing. This work presents direct calculations of the complex dielectric function and some optical parameters, such as refractive index, extinction coefficient, and reflectivity for some selected III-V and II-VI compound semiconductors using Lorentz oscillator model. The dielectric and optical dispersion parameters among the infrared and visible electromagnetic spectra follows the so-called Transmission-Absorption-Reflection-Transmission (TART) trend. The TART curve provides information about how a material interacts with light at different wavelengths, which is crucial for understanding and optimizing various optoelectronic devices. Moreover, dielectric loss functions such as loss tangent, surface energy loss function and volume energy loss function are investigated. The refractive index dispersion is analyzed using Wemple–DiDomenico single effective oscillator model and Sellmeier equation. The energy of the effective single oscillator (Eo) and the dispersion energy (Ed) are estimated.

Electrical transport characteristics of rare earth ions (Er³⁺, Sm³⁺) exchanged cobalt-manganese ferrite using impedance spectroscopy

This study presents findings on the AC impedance characteristics of rare earth-doped Co0.5Mn0.5RExFe2-xO4 ferrites (where RE = Er and Sm, and 0.0 ≤ x ≤ 0.1), synthesized utilizing the citrate auto-combustion process. Employing impedance spectroscopy at frequencies ranging from (100 −1 MHz) and temperatures between 30°C and 120°C, we distinguished the impact of grains (Gs) and grain boundaries (GBs) in these compositions. The Jonscher power law was applied to characterize the AC conductivity results. The dielectric constant έ and dielectric loss ε” decline as the frequency rises and reach a stable state at higher frequencies, indicating the characteristic dielectric dispersion. This phenomenon manifests the Maxwell-Wagner polarization, as described by Koop's hypothesis. The modified Debye formula provides a good match for the frequency-dependent dielectric permittivity fluctuation. The Cole-Cole plots revealed a single semicircle for the unaltered sample and lower Er³⁺ concentrations (up to x=0.02), but two semicircles appeared at higher Er³⁺ concentrations and in the Sm³⁺ doped samples. The G and GB resistances increased with higher concentrations of Er³⁺/ Sm³⁺ but showed a decrease at x=0.1 in Sm³⁺-doped samples. The data examination designates that the resistive and capacitive possessions are predominantly affected by G and GB processes. A relaxation phenomenon in the existing samples is shown by the frequency-dependent of the imaginary portion of impedance (Z"). Remarkably, the relaxation time (τz) showed linear temperature dependence. Additionally, studies of the electrical modulus (M’ and M”) highlighted non-Debye sort dielectric relaxation in all compositions, with peaks in the imaginary modulus indicating a shift in charge carrier mobility from long-range toward short-range. The investigation focused on the non-Debye relaxation, which was analyzed by determining the stretching exponential parameter (β). This factor was obtained by fitting the modified Kohlrausch-Williams-Watts (KWW) formula to the graph of the imaginary electric modulus. The substitution of Fe3+ by Er3+ and Sm3+ ions substantially enhanced the dielectric properties, particularly Co-Mn-Sm ferrite series, suggesting their potential use in high-frequency devices.

Intrinsic and extrinsic dielectric response of Sr0.95Nd0.05Fe12O19 nanoceramics doped with Sc3+ and Al3+ ions

ABSTRACT The dielectric response of M-hexaferrite nanoceramics is complex since it is determined by crystal structure and microstructure. We studied the dielectric behavior of Nd3+ modified Sr2 + Fe12O19 nanoceramics with ferric ions, responsible for magnetic properties, substituted by Sc3+ and Al3+. To compare the effect of different ionic radii we discussed the dielectric response of Sr0.95Nd0.05Fe12-xScxO19 and Sr0.95Nd0.05Fe12-xAlxO19 at the doping level of x = 1.08. The dielectric response was found to consist of four contributions: (i) Low-temperature dispersion of dielectric polarization created by doping-induced spin-canting. The polarization, described by the inverse Dzyaloshinskii-Moriya model, is in nanoceramics limited by the shape and size of the crystallites. (ii) Changes in relaxation modes of polar vacancies due to interaction with electric dipole moments modified by deformation of oxygen octahedra. (iii) Dielectric dispersion in room temperature range related to space charge relaxation in grain boundaries. (iv) High-temperature electric conductivity of the grain interiors.

Enhanced multiferroic properties of NZCFO-BNFSO composites: Synthesis, characterization, and performance analysis

The structural and multiferroic properties of xNi0.24Zn0.58Cu0.18Fe2O4(NZCFO)-(1-x)Bi0.9Nd0.1Fe0.95 Sc0.05O3(BNFSO) are explored in this paper. Bi2O3 additives significantly lower the sintering temperature of the composites. The XRD analysis validates the coexistence of hexagonal perovskite BNFSO and spinel NZCFO phases. The FESEM images illustrate an almost homogeneous amalgamation of the BNFSO and NZCFO grains. The real part of initial permeability and the relative quality factor increases with NZCFO contents in the composites. The maximum permeability is observed for the composite with 80 % ferrite content. The ferroelectric BNFSO exhibits antiferromagnetic behavior and with the increase in NZCFO the saturation magnetization increases significantly. The dielectric constant confirms typical dielectric dispersion at low frequencies because of Maxwell–Wagner space charge polarization. The P-E hysteresis measurement reveals that the composite with 40 % ferrite content exhibits the highest loop area and hence a large energy storage capacity. Incorporating BNFSO and NZCFO into the composite boosts the multiferroic properties, which might be a suitable alternative to single-phase multiferroics.

Development of Lead‐Free Defect Brownmillerite Perovskite Ceramic LiBiFeMnO5 Solid Solution for Electronic Devices

This article reports the fabrication (synthesis) and characterizations (structural, microstructural topographic surface, dielectric, transport, impedance, current–voltage, and resistive properties) of a complex lead‐free defect perovskite material of composition LiBiFeMnO5. A preliminary structural investigation of the X‐ray diffraction pattern using N‐TREOR09 methods shows monoclinic symmetry. The scanning electron microscopic spectrum examines the sample's microstructural topographic surface, fractal study, and roughness (using the standard ISO25178). The analysis of Maxwell–Wagner dielectric dispersion, relaxation, and transport mechanisms is investigated utilizing dielectric, impedance, and conductivity spectrum accumulated within the experimental frequency of (1 kHz–1 MHz) at different temperatures (30–500 °C). A nonoverlapping small polaron tunneling conduction mechanism and correlated barrier hopping mechanism in the material have helped to understand its conduction phenomena. The Ohmic and space–charge limited conduction mechanisms are investigated by the slope of the logarithmic electric field (E) and current density (J). The thermistor constant (β) is determined to be 1982.87. The temperature coefficient of resistance is found to be −0.00419, which may be suitable for negative temperature coefficient thermistors, sensors, and other related devices.

Investigations on structural and opto-electrical characterization of Ag-TCNQ (metal-organic frameworks) as complex thin films for potential device applications

The silver- (7, 7, 8, 8-tetracyanoquinodimethane (Ag-TCNQ) organometallic complex was synthesized chemically as a nano-powder and thereafter deposited as a thin film by thermal evaporation. The monoclinic, needle-like, polycrystalline structure of the Ag-TCNQ complex was analyzed employing x-ray diffraction (XRD) and a scanning electron microscope (SEM). Whereas their chemical structure and stability were explored using Fourier transformation infrared (FTIR) techniques. The findings imply a charge transfer of degree −0.5 between TCNQ° and TCNQ−, as revealed by the shift of the bands of the C≡N stretching and the (C═C-H) bond positioned at 2198 and 824 cm−1, respectively. As well as the optical properties of Ag-TCNQ thin film were studied using spectrophotometric measuring in the wavelength ranging 200 to 2500 nm. The measurement of transmittance and reflectance spectra were employed to calculate the refractive index (n), dielectric constant, absorption index (k), surface and volume energy loss functions, and optical conductivity. In the normal dispersion zone, optical characteristics such free charge carrier concentration, infinity dielectric constant (ε ∞), lattice dielectric constant (ε L), oscillator energy (Eo), and dispersion energy (Ed) were estimated. Furthermore, the optoelectronic nonlinear optical features and electronic transitions for the Ag-TCNQ thin film were assessed. Finally, these findings are promising milestones on the path to providing convincing evidence for the synthesis of stoichiometric thermally stable Ag-TCNQ thin film by conventional thermal evaporation technique that is potential to be utilized in optoelectronic devices applications.

Polarization-Dependent Formation of Extremely Compressed Femtosecond Wave Packets and Supercontinuum Generation in Fused Silica

Previous studies of formation of extremely compressed wave packets during femtosecond filamentation in the region of anomalous group velocity dispersion in solid dielectrics mostly considered the case of linearly polarized laser pulses. However, recent results suggest potential applications of polarization state manipulation for ultrafast laser writing of optical structures in bulk solid-state media. In the present work, evolution of radiation polarization parameters during formation of such extreme wave packets at the pump wavelength of 1900 nm in fused silica is studied numerically on the basis of the carrier-resolved unidirectional pulse propagation equation (UPPE). It was revealed that initial close-to-circular polarization leads to higher intensity of the anti-Stokes wing in the spectrum of the generated supercontinuum. Numerical simulations indicate a complex, space–time variant polarization state, and the resulting spatiotemporal electric field distribution exhibits a strong dependence on the initial polarization of the femtosecond pulse. At the same time, electric field polarization tends to linear one in the region with the highest field strength regardless of the initial parameters. The origin of this behavior is attributed to the properties of the supercontinuum components generation during filament-induced plasma formation.

Correlation of relaxation processes by BDS: Calorimetric, spectral findings and molecular dynamics of active side chain amino acids in hydrated medium

The dielectric dispersion behavior of amino acids (L-arginine and L-glutamic acid) was studied in the aqueous state by Broadband Dielectric Spectroscopy (BDS). The complex permittivity spectra of the solutions were recorded for the frequency regime 10 MHz – 50 GHz at a temperature range of 283 K to 303 K for various mole fractions. The interaction of polarized side chains of the solute (positive in L-arginine and negative in L-glutamic acid) with hydrated polar media is the significance of the work. The hydration effect of the amino acid modifies the dielectric and physicochemical properties of the solution. The study of Differential Scanning Calorimetry (DSC) analysis and thermal parameters specifies that the L-glutamic acid has super strong nature than L-arginine. The formation of hydrogen bond, nature and strength of the interaction through side chain are confirmed by spectral analysis (FT-Raman, FT-IR and NMR). The geometrical properties were computed with DFT/B3LYP −6-31G(d,p) basis set. The obtained spectral signals were compared with experimental data. The experimental and quantum mechanical calculations are used to identify the hydrodynamic coupling of the solution. The present study correlate the dielectric, thermal parameters, spectral inferences with molecular structure, dynamics is a novel approach which confirms the nature and strength of the complex formation.

Effect of zinc substitution on structural, electrical, dielectric and magnetic properties of magnesium nano-ferrites prepared by co-precipitation route

Zinc substituted Magnesium ferrites synthesized by using Co-precipitation method. The structural characterisations of samples are carried out and formation of single-phase nickel ferrite was substantiated through powder X-ray diffraction. The lattice parameters were calculated that are in the range 8.323–8.361 Å.Surface morphology of samples were also investigated through Scanning electron microscopic (SEM) analysis. SEM images revealed clear grain structures of synthesised samples. Magnetic measurements showed the ferromagnetic behaviour, analysed through vibrating sample magnetometer (VSM) while magnetic parameters obtained using VSM measurementat room temperature. MS and HC were found to decrease with increases in the Zn concentration due to non-magnetic behaviour of zinc. The dielectric dispersion for the Mg–Zn ferrites were determined as a function of frequency (50 Hz to 5 MHz). The dielectric constant and the loss tangent decrease expeditiously with incrementing frequency, and then reaches a constant value. The semiconducting behaviour of Mg-Zn ferrites proved by measuring resistivity as a function of temperature and materials are showing thermistor relatively good thermistor constants, they can be utilized as thermistors. The results were discussed in detail in this research article.

Structural, Dielectric and Magnetic studies of Mixed Ferrites of Co-Zn using combustion method

Using auto-combustion approach, cobalt ferrite nanoparticles doped with Zn+2 with the basic chemical composition ZnxCo1-xFe2O4 (x = 0 to 1: in steps of 0.25) were prepared. Phase confirmation of the proposed samples was confirmed through XRD studies. XRD pattern of the calcined ferrites revealed single phase spinel cubic structure. At room temperature, using HIOKI LCR meter (Model no: 3520-50) the dielectric measurements in the frequency range 102 Hz–106 Hz were performed. Dielectric constant (ε′) and dielectric loss tangent (tan δ) of synthesized nano-materials were investigated as a function of frequency and Zn+2 concentration at ambient temperature and all the samples exhibited dielectric dispersion. Magnetic measurements for ZnxCo1-xFe2O4 nano-ferrites were carried out at room temperature using a vibrating sample magnetometer (VSM), and all the samples of the system CoZnFe2O4 exhibited ferromagnetic behavior.

Envisioning the structural and room temperature impedance spectroscopy study of praseodymium modified lanthanum ferrites

Praseodymium-modified lanthanum ferrites with general formula La1-xPrxFeO3 [x = 0.0, 0.1, 0.3, 0.5] were prepared using the sol-gel auto combustion technique. The X-ray diffraction patterns of all samples supported the orthorhombic crystal structure with the Pbnm space group. With increasing Pr concentration, it was discovered that the average crystallite size dropped from 44.29 to 29.83 nm. An LCR metre was used to evaluate the frequency-dependent dielectric characteristics between 100 Hz and 1 MHz at room temperature. A single semicircle on the Nyquist plots highlights the impact of grain resistance on electrical behaviour. The depressed semicircles at intermediate frequencies might be created by the grain boundary effect, while semicircles depressed at high frequencies imply grain conduction. The dielectric behaviour of lanthanum ferrites is explained based on Koop’s theory. The loss factor resulting from domain wall resonance displayed the same dielectric constant dispersion behaviour. At high frequencies, orthoferrites were shown to have lower dielectric losses. This is due to the constrained motion of the domain wall, which suggests that magnetically tunable filters and oscillators are possible practical uses.

Broadband dielectric spectroscopy of Nb-doped 0.7BiFeO3–0.3BaTiO3 ceramics

Bismuth ferrite-barium titanate (BF-BT) solid solutions are lead-free ferroelectrics that show great promise as the basis for high temperature piezoelectric transducers. This article investigates the dielectric properties of such materials using broadband dielectric spectroscopy. The study focuses on the re-entrant relaxor ferroelectric behaviour of Nb-doped BF-BT ceramics, exploring a wide frequency range from approximately 20 Hz to 30 GHz and temperature from 200 to 500 K. The results reveal the presence of thermally induced transitions between ordered and disordered states. Quantitative analysis of the dielectric dispersion is accomplished using the Cole-Cole model, modified to account for the contribution from conduction losses at low frequencies/high temperatures. This analysis revealed that the freezing temperature of the polar nanoregions is around 158 K, with an activation energy of 0.194 eV. The findings contribute to understanding the dielectric relaxation mechanisms and thermal evolution of functional properties in BiFeO3-BaTiO3 ceramics.