Abnormal Dielectric Behavior Research Articles

Identifying the Interfacial Polarization in Non‐stoichiometric Lead‐Free Perovskites by Defect Engineering

AbstractRecent advances in perovskite ferroelectrics have fostered a host of exciting sensors and actuators. Defect engineering provides critical control of the performance of ferroelectric materials, especially lead‐free ones. However, it remains a challenge to quantitatively study the concentration of defects due to the complexity of measurement techniques. Here, a feasible approach to analyzing the A‐site defect and electron in alkali metal niobate is demonstrated. The theoretical relationships among defect concentration, conductivity, and oxygen partial pressure can be established based on the defect chemistry equilibria. The type and concentration of defects are reflected through the conductivity variation with oxygen partial pressure. As a result, the variation of defect concentration gives rise to defect‐driven interfacial polarization, which further leads to distinct properties of the ceramics. e.g., abnormal dielectric behavior. Furthermore, this study also suggests a strategy to manipulate defects and charges in perovskite oxides for performance optimization.

Identifying the Interfacial Polarization in Non-stoichiometric Lead-Free Perovskites by Defect Engineering.

Recent advances in perovskite ferroelectrics have fostered a host of exciting sensors and actuators. Defect engineering provides critical control of the performance of ferroelectric materials, especially lead-free ones. However, it remains a challenge to quantitatively study the concentration of defects due to the complexity of measurement techniques. Here, a feasible approach to analyzing the A-site defect and electron in alkali metal niobate is demonstrated. The theoretical relationships among defect concentration, conductivity, and oxygen partial pressure can be established based on the defect chemistry equilibria. The type and concentration of defects are reflected through the conductivity variation with oxygen partial pressure. As a result, the variation of defect concentration gives rise to defect-driven interfacial polarization, which further leads to distinct properties of the ceramics. e.g., abnormal dielectric behavior. Furthermore, this study also suggests a strategy to manipulate defects and charges in perovskite oxides for performance optimization.

Colossal Permittivity and Abnormal Dielectric Behavior in Tio2 Based Ceramics

Colossal Permittivity and Abnormal Dielectric Behavior in Tio2 Based Ceramics

Ferroelectric BT–PVDF Composite Thick Films for Electrical Energy Storage

Hybrid composites have been elaborated by incorporation of BaTiO3 (BT) inorganic nanoparticles into polyvinylidene fluoride (PVDF) polymer. BT–PVDF composite thick films with different volume fractions of BT (0%, 7%, 15%, and 30%) were deposited by spin-coating onto Pt/SiO2/Si substrates. The effects of the BT inorganic content in the PVDF polymeric matrix on the structural, dielectric, ferroelectric, and energy storage properties were investigated at room temperature. The crystal structure of the samples was identified by X-ray diffraction analysis, and their morphology was observed by scanning electron microscopy. Introduction of BT nanoparticles into the PVDF polymer led to a remarkable enhancement of the dielectric constant value and ferroelectric polarization. Additionally, the abnormal dielectric behavior observed for the composite with 30 vol.% BT nanoparticle volume fraction can be explained by the existence of a Debye relaxation domain at low frequency. Moreover, the stored energy density Wc was enhanced from 2.4 J/cm3 for pure PVDF polymer to 9 J/cm3 for the 30 vol.% BT nanoparticle volume fraction. Such BT–PVDF composite thick films are thus promising materials for the manufacture of electrostatic capacitors for electrical energy storage.

Multiresponsive Spin Crossover Driven by Rotation of Tetraphenylborate Anion in an Iron(III) Complex

Dynamic molecular materials, which involve mechanical motions in crystals, usually exhibit tunable properties related to conformational polymorphs. Herein, we describe a solvent-free molecular crys...

Colossal and anomalous dielectric behavior in grain-oriented TiO2

In this work, anatase structure TiO2 particles with a preferential grain growth direction of [002] were synthesized by a facile and modified sol–gel approach. The pellets pressed from the TiO2 particles possess colossal dielectric constant (> 7 × 103 at 100 Hz and room temperature). The colossal dielectric constant behavior can be associated with the Maxwell–Wagner relaxation due to the textured grain structure. This approach is simple and provides an avenue to obtain the excellent dielectric properties of ceramics with oriented grains. Contrary to traditional relaxation behavior, an anomalous dielectric behavior was observed above room temperature. This abnormal dielectric behavior was caused by the positive temperature coefficient of resistance effect resulting from humidity response.

Origin of Abnormal Dielectric Behavior and Chemical States in Amorphous CaCu3Ti4O12 Thin Films on a Flexible Polymer Substrate

High dielectric constant thin films processable at nearly room temperature have been demanded for various flexible electronic devices. Here, we explore the origin of abnormal dielectric behavior of amorphous CaCu3Ti4O12 (CCTO) thin films having an exceptionally high dielectric constant, in conjunction with chemical states and unusual ferroelectricity in the amorphous state. As an optimal example, the amorphous CCTO film sputtered at room temperature under an oxygen partial pressure of 3.6 mTorr exhibits a dielectric constant of ∼192 and a dielectric loss of <0.1 at 100 Hz. The promising dielectric characteristics are unexpectedly found to originate from the evolution of ferroelectric domains, even in the amorphous state. Strong dependence of oxygen partial pressure on chemical states, vacancy formation, and ferroelectric polarization is very critical for the unexpected dielectric behavior. This may be the very first example of exploring the origin of amorphous dielectric behavior for a material that posse...

Normal and abnormal dielectric relaxation behavior in KTaO3 ceramics

KTaO3 ceramic samples were prepared via a conventional solid state reaction route.

Phase transition and dielectric properties of (Pb,La)(Zr,Sn,Ti)O3 ceramics at morphotropic phase boundary

(Pb0.97La0.02)(Zr75Sn0.25-x Tix)O3 (0.08 ≤ x ≤ 0.11) ceramics at morphotropic phase boundary (MPB) were fabricated by the conventional solid–state reactions, and the major phase was changed from tetragonal antiferroelectric phase to rhombohedral ferroelectric phase (AFET-FER) as the increase of Ti/Sn. The dielectric properties in original states and the poled states were systematically studied. Dielectric constant of the electric-induced AFET poled states was greater than the virgin state, then approached and become less as the compositions moved to FER phase. Moreover, there was a dielectric anomaly for FER poled sample on heating, but not observed in cooling cycle and AFET sample, which was a FE-AFE phase transition confirmed by dielectric constant as functions of temperature and electric field, and the abnormal dielectric behavior become more obviously with electric field increasing. This results are useful to understand the dielectric properties and phase transition in AFE and FE materials.

Abnormal dielectric behavior induced by defect dipoles in aged Na0.5Bi0.5(Ti,Zr)O3 thin film

Ferroelectric aging behavior was investigated in Na0.5Bi0.5(Ti0.99Zr0.01)O3 thin film on FTO/glass substrate by the dielectric constant (dissipation factor)-electric field (εr–E and tanδ–E) curves. The aged sample can be gained by keeping the fresh film for two months at room temperature. Compared with the typical single butterfly εr (tanδ)–E of the fresh sample, an abnormal loop has been exhibited in the aged one. Furthermore, with the increase of the measuring electric field or decrease of applied frequency, the aging phenomenon becomes weak and even disappeared. These present results are analyzed based on defect chemistry by the symmetry-conforming principle of defect dipoles.

Structural and dielectric properties of doped ferrite nanomaterials suitable for microwave and biomedical applications

The sol–gel auto-combustion method was adopted to synthesize nanomaterials of single-phase X-type hexagonal ferrites with the composition of Sr2−xGdxNi2Fe28−yCdyO46 (x=0.00, 0.02, 0.04, 0.06, 0.08, 0.10 and y=0, 0.1, 0.2, 0.3, 0.4, 0.5). The structural properties were carried out by XRD analysis and the lattice parameters show variation with the doping of Gd–Cd. The average particle size measured by TEM was in the range of 8–10nm which is beneficial in obtaining suitable signal-to-noise ratio in recording media and biomedical applications. The room temperature resistivity enhanced with the increase of the dopant concentration. The increase in resistivity indicates that the synthesized materials can be considered good for the formation of the multilayer chip inductors (MLCIs) as well as for the reduction of eddy current losses. The dielectric constant decreased with the increase in the frequency which is the general reported trend of the hexagonal ferrites and can be explained on the basis of Koop׳s theory and Maxwell–Wagner polarization-model. The abnormal dielectric behavior indicates the formation of small polarons in the material. The maximum value of tangent loss at low frequencies reflects the application of these materials in medium frequency devices (MF).

Structure, relaxation behaviors and nonlinear dielectric properties of BaTiO3–Bi(Ti0.5Mg0.5)O3 ceramics

(1−x)BaTiO3–xBi(Mg1/2Ti1/2)O3 (BT–BMT, x=0–0.2, abbreviated as BT–BMT100x) ceramics were prepared by using a solid state reaction process. Their crystal structure, microstructure, conduction behavior, dielectric and tunability properties were investigated. It is found that the tetragonal phase and a pseudocubic phase coexist for x≤0.15 and transform to a pseudocubic phase at x=0.20. With the incorporation of BMT, BT–BMT becomes more insulating. The activation energies of the conduction are respectively 1.15(1) and 1.54(1)eV for grain and grain boundary of BT–BMT20. Furthermore, an abnormal nonlinear dielectric tunable behavior is observed. The dielectric permittivity first slightly increases until reaching the threshold electric field, and then suddenly decreases. This abnormal nonlinear dielectric behavior is attributed to the synergetic effects of the clamped oxygen vacancies and excessive aggregation of Bi at the grain boundaries.

Revisiting the low-temperature dielectric properties of ZnO

Electric modulus spectroscopy and impedance analysis were used to investigate the low-temperature (∼100–333 K) dielectric properties of ZnO crystals. Two relaxations were observed. The low-temperature relaxation (R1) features a thermally activated behavior resulting from the bulk response. Our results convincingly demonstrate that this relaxation is a polaronic relaxation. The relaxing species for R1 are localized holes created by zinc vacancies instead of the commonly agreed oxygen vacancies. The high-temperature relaxation (R2) is a Maxwell-Wagner relaxation due to skin-layer effect as it can be eliminated by grinding off the sample surface. The inhomogeneous distribution of zinc interstitials leads to the formation of the skin layer. Interestingly, an abnormal dielectric behavior contrary to the thermally activated behavior was found for the R2 relaxation. This abnormal behavior was confirmed to be related to the positive temperature coefficient of resistance due to the metal-insulator transition occurring within the skin layer.

Dielectric Relaxations and Phase Transition in Laser Crystals Gd2SiO5 and Yb‐Doped Gd2SiO5

The crystals Gd2SiO5 and Yb‐doped Gd2SiO5 were grown by Czochralski method successfully. Dielectric properties of the two crystals were investigated in the temperature range from 100 to 1100 K and the frequency range from 20 Hz to 10 MHz. Our results revealed that these crystals show intrinsic dielectric behavior in the temperature below room temperature, whereas in above room temperature, a relaxor‐like dielectric anomaly and a metal–insulator transition were observed. It was found that the relaxor‐like anomaly contains two dielectric relaxations. Impedance analysis showed that the low‐ and high‐temperature relaxations are dipolar‐ and Maxwell–Wagner‐type relaxation, respectively. The transition was found to be strongly related to oxygen vacancies, which leads to positive temperature coefficient of resistance and an abnormal dielectric behavior contrary to the conventional thermally activated behavior at temperatures near the transition temperature.

HIGH-FREQUENCY DIELECTRIC BEHAVIOR OF INDIUM AND CHROMIUM SUBSTITUTED Mg–Mn FERRITES

Dielectric properties such as DC resistivity (ρ), dielectric constant (ε) and dielectric loss factor ( tan δ) have been measured for Mg 0.9 Mn 0.1 In x Fe 2-x O 4 and Mg 0.9 Mn 0.1 Cr y Fe 2-y O 4 at room temperature. The composition dependence of ρ, ε and tan δ and the frequency dependence of ε and tan δ are presented in this paper. The resistivity increases while the dielectric constant decreases with increasing concentrations of indium and chromium ions. The dielectric loss factor at 100 kHz increases with composition for the samples 0.1 ≤ x ≤ 0.9 and 0.1 ≤ y ≤ 0.7. The dielectric constant for a given sample decreases with increasing frequency showing the normal dielectric behavior. The values of dielectric loss factor have been found to increase with frequency for the samples corresponding to x or y = 0.1 to 0.5; while other samples showed abnormal dielectric behavior. The observed variations in ρ are explained by Verwey's hopping mechanism while the variations in ε and tan δ with composition and frequency are explained by space charge polarization using Koop's theory. Higher values of DC resistivity and low dielectric losses suggest that the prepared materials have great potential for microwave and high-frequency applications.

Effect of iron oxide with Si on the dielectric properties in Mn-Zn ferrite

In this paper, some of the results of dielectric study carried out using locally produced low cost Fe 2 O 3 powder with 0.5 wt% of Si additive are being summarized. The dielectric properties were studied as a function of composition, frequency and temperature for a series of Mn x Zn 1- x Fe 2 O 4 ferrite. The samples were prepared by the usual ceramic technique. It was observed that the values obtained for dielectric constant ∈ ′ and dielectric loss factor tan δ are much lower than those normally obtained for Mn-Zn ferrite prepared by pure Fe 2 O 3 powder. The low values are attributed to the presence of Si, which suppress the ceramic grain growth. The low dielectric loss makes these samples attractive for use at high frequencies. Each of ∈ ′ and tan δ increases on increasing the temperature. Abnormal dielectric behavior observed for x = 0.99 due to forced migration of Fe ions from A sites to B sites at this composition.

Dieletric and magnetic properties of ZnTi substituted M‐type barium hexaferrite

AbstractThe ZnTi substituted barium hexaferrite polycrystalline samples have been synthesized by solid‐state reaction method. The complex permittivity and permeability measurements are carried out on the BaFe12–2xZnxTixO19 (0.2 ≤ x ≤ 0.6) samples in the microwave frequency range of 8–13 GHz by cavity perturbation technique. The observed abnormal dielectric behavior, i.e., an increasing tendency of dielectric constant with frequency has been attributed to the mixed conduction. The effect of ZnTi substitution on the permittivity and dielectric loss has been investigated in the frequency range of 1 kHz–1 MHz as well. The increase in concentration of ZnTi dopants monotonically increases both the permittivity and the permeability in the investigated frequency ranges, which can be attributed to increased polarizability and unpinning of the domain walls, respectively.

Abnormal piezoelectric and dielectric behavior of 0.92Na0.5Bi0.5TiO3-0.08BaTiO3 induced by La doping

Properties and phase structures of lead-free piezoelectric ceramics 0.92Na0.5Bi0.5TiO3-0.08BaTiO3 (NBT-BT) modified with La2O3 have been studied. Because of the different valence and ionic radius between La3+ and the exchangeable A-site ions, the lattice distortion and arrangement in the modified compounds can be expected, which will directly influence the phase composition and electrical characteristics of NBT-BT. Differing from familiar frame of gradual variability going with adulteration, NBT-BT doping 0.2–1.0 at.% La2O3 presents an abnormal increase of dielectric constant and a dramatic vanish of piezoelectricity. Further study on the relaxor property and domain structure implies that it originates from a typical relaxor-to-antiferroelectric crossover phase transition. However, a larger addition of La2O3 could rejuvenate the ferroelectricity and piezoelectricity of NBT-BT, correlating well with the model of competing ferro- and antiferroelectric interactions and metastable intermediate phase behavior in the morphotropic phase boundary region of complex perovskites.

Polarization state-dependent stress effect on the dielectric properties of lead zirconate titanite thin films

We performed a bending experiment on a thin Pb(Zr,Ti)O3 (PZT) film prepared by chemical solution deposition. The changes of dielectric constant under stress were measured upon sweeping the electric field applied across the PZT film. It was found that depending on the strength of the electric field and thereby on the polarization state of the ferroelectric film, stress acts as a promoter as well as an obstructor for the polarization. An explanation for the abnormal dielectric behavior is given based on the domain wall motion and the reorientation of polarization state.

On the Feasibility of Growing Pb[(Zn1/3Nb2/3)0.91Ti0.09]O3 Single Crystals

AbstractPb[(Zn1/3Nb2/3)0.91Ti0.09]O3 (PZNT91/9) single crystals were grown by two methods: from solution using PbO as a self‐fluxing agent (SC method) and directly from the melt without fluxing (MC method). In both growth methods, an allomeric Pb[(Mg1/3‐Nb2/3)0.69Ti0.31]O3 (PMNT69/31) single crystal was used as a seed. X‐ray diffraction patterns of ground crystals showed that phase‐pure perovskite PZNT91/9 single crystals were successfully fabricated by the above two methods. The composition of the crystals obtained by both the SC and MC methods was analyzed using X‐ray fluorescence, which confirmed that the crystal composition is close to the nominal value, although volatilization of PbO and segregation during crystal growth are inevitable. The MC PZNT91/9 crystals exhibit excellent piezoelectric properties, with the piezoelectric constant, d33, in the range of 1800–2200 pC N–1. This value is comparable to that of the SC crystals. However, the MC crystals show an abnormal dielectric behavior. In contrast with the SC crystals, in the MC crystals a much broader dielectric peak appears in the dielectric response curves, accompanied by a much lower peak temperature of around 105 °C. Furthermore, frequency dispersion is apparent over a much wider temperature range (even more apparent than in pure relaxors), where a large, i.e., about 70 °C, full width at half maximum (FWHM) for the dielectric peaks is observed in the dielectric response. It is speculated that such an unusual phenomenon correlates with defects, microinhomogeneities, and polar regions in the as‐grown MC crystals. The origins of this abnormality have not been interpreted in detail until now. However, optical observation of the domain structure confirms that both the SC and MC crystals possess complex structural states.