Preparation and dielectric properties of Pb(Zn1/3Nb2/3)O3-based ferroelectric ceramics

The sintering behavior of mechanochemically prepared 0.9Pb(Zn_1/3Nb_2/3)O₃-0.1ABO₃ (ABO₃ = BaBiO₃, BaMnO₃, BaTiO₃) powders is studied. PbO and Bi₂O₃ are shown to volatilize at relatively low temperatures owing to partial reduction of these oxides during the mechanochemical synthesis. Dense (97% of theoretical density) ceramics are obtained under mild sintering conditions, and their dielectric properties are studied at different frequencies. The observed variations of their dielectric permittivity and loss tangent with frequency are typical of relaxor ferroelectrics, but the ceramics have a reduced dielectric permittivity, which is attributable to nanostructuring.     

Locating the normal to relaxor phase boundary in Ba(Ti1−xHfx)O3 ceramics

In this article, we report our studies on the relaxor behavior of Ba(Ti_1−xHf_x)O₃ ceramics, made with close compositions between 0.20 ≤ x ≤ 0.30, to locate the hafnium concentration boundary for the normal to relaxor crossover. X-ray diffraction followed by Rietveld refinement shows the occurrence of single-phase cubic structure for the synthesized Ba(Ti_1−xHf_x)O₃ ceramics. Temperature and frequency dependence of the real (?′) and imaginary (?″) parts of the dielectric permittivity has been studied in the temperature range of 90-350 K at frequencies of 0.1, 1, 10, and 100 kHz. A diffuse phase transition accompanying frequency dispersion is observed in the permittivity versus temperature plots revealing the occurrence of relaxor ferroelectric behavior. The T_m verses Hf concentration plot shows a discontinuous jump and change in the slope at x = 0.23. Quantitative characterization based on phenomenological models has also been presented. The plausible mechanism of the relaxor behavior has been discussed. Substitution of Hf⁴⁺ for Ti⁴⁺ in BaTiO₃ reduces the long-range polar ordering yielding a diffuse ferroelectric phase transition.     

Crystal structure and dielectric properties of (1 ? x)(NaBi)1/2TiO3 · xBi(ZnTi)1/2O3 perovskite solid solutions

(1 ? x)(NaBi)_1/2TiO₃ · xBi(ZnTi)_1/2O₃ ceramics have been prepared by solid-state reactions. In the composition range x < 0.2, we obtained (NaBi)_1/2TiO₃-based solid solutions with a rhombohedrally distorted perovskite structure. With increasing x, the degree of rhombohedral distortion, the angle of antiphase tilts of oxygen octahedra about the hexagonal axis in the unit cell, and the octahedral strain decrease systematically and the unit-cell parameters a _H and c _H increase. We have studied the dielectric properties of the solid solutions using ceramic samples. The results demonstrate that the ceramics undergo a high-temperature diffuse ferroelectric phase transition. Near the temperature of the maximum in the real part of the dielectric permittivity (510?C610 K), the ceramics have low ??? dispersion and low dielectric losses. At low temperatures (below 500 K), the dielectric response of the materials exhibits ferroelectric relaxor behavior.     

Effect of sintering temperature on phase structure, microstructure, and electrical properties of (K0.5Na0.5)NbO3–(Ba0.6Sr0.4)0.7Bi0.2TiO3 lead-free ceramics

Lead-free 0.98(K_0.5Na_0.5)NbO₃–0.02(Ba_0.6Sr_0.4)_0.7Bi_0.2TiO₃ (abbreviated as 0.98KNN–0.02BSBT) ceramics were prepared by the conventional solid-state sintering method. Effect of sintering temperature on 0.98KNN–0.02BSBT ceramics was systematically investigated. The frequency dependent dielectric permittivities show that the ceramics sintered at different temperatures are indeed “relaxor-like” ferroelectric ceramics, which possess a diffuse phase transition without a strong frequency dispersion of dielectric permittivity. The diffuseness parameter γ, the comparison of the relaxor behavior based on empirical parameters (ΔT _diffuse) and the slimmer P–E hysteresis loops confirm that the “relaxor-like” characteristics of the ceramics are strengthened with increasing sintering temperature. At the optimum sintering temperature, the dielectric permittivity maximum (? _max) has a value of approximately 2795 (at 1 KHz), $ \tan \delta $ is lower than 2.5 % and the diffuseness parameter γ = 1.68 at a broad usage temperature range (150–350 °C), which indicate its potential application in high temperature multilayer ceramics capacitor field.     

Structural and dielectric properties of Bi doped Ba<Subscript>0.6</Subscript>Sr<Subscript>0.4</Subscript>TiO<Subscript>3</Subscript> ceramics

The dielectric properties of 0.1–15% mol bismuth doped Ba_0.6Sr_0.4TiO₃ (BST) ceramics have been investigated systematically. The solubility limit of bismuth is determined as about 10 mol% by means of both X-ray diffraction and scanning electron microscopy, which is further verified by the fact that the lattice constant of the samples above 10 mol% is almost invariable. The temperature dependence of the dielectric permittivity suggest that the ferroelectric behavior transit to relaxor ferroelectric type when impurity concentration reaches 5 mol%, and further to relaxor behavior for samples above 10 mol% Bi content, which is verified by the absence of a hysteresis loop. Thermal expansion results show differences between 5 and 10 mol% doped samples. Dielectric tunability at room temperature decreases with bismuth content increasing. The variation of properties was attributed to the impurity induced polar regions and former long-order structure.     

Dielectric properties of Sr3CuNb2O9 perovskite ceramics

The dielectric constant ? and loss tangent tanδ of Sr₃CuNb₂O₉ perovskite ceramics prepared by solid-state reactions have been measured at temperatures from 300 to 900 K and frequencies from 25 to 1 × 10⁶ Hz. The results demonstrate that the samples slowly cooled from the temperature of the final, high-temperature firing (1200°C) have relatively low permittivity (? ? 10) and dielectric losses (tanδ ? 0.005 at 1 kHz) at room temperature, with no strong dielectric dispersion and no prominent maxima in the temperature dependences of their permittivity and dielectric loss. The ceramics quenched from 1300°C exhibit a pronounced Debye-type low-frequency relaxation and strong dielectric dispersion in conjunction with high permittivity ? ? 2000 at low frequencies and/or high temperatures. The observed dielectric anomalies in the Sr₃CuNb₂O₉ ceramics can be understood in terms of Maxwell-Wagner relaxation at dielectric inhomogeneities associated with the quenching-induced difference in oxygen-vacancy concentration between the grain bulk and surface layer.     

Orientation dependence of dielectric and relaxor behaviour in Aurivillius phase BaBi2Nb2O9 ceramics prepared by spark plasma sintering

Grain-oriented Aurivillius phase BaBi₂Nb₂ O₉ ceramics were fabricated using Spark Plasma Sintering (SPS). Their relaxor behaviour was confirmed by a strong frequency dispersion of the dielectric response. The dielectric behaviour has been fitted using different relaxor models. The relaxor parameters are isotropic, while the dielectric constants are highly anisotropic. The piezoelectric constant d ₃₃ is zero perpendicular and parallel to the hot pressing direction, and the P–E response is dominated by losses. The inability to pole the samples at room temperature is consistent with the T _f temperature (∼ ∼115 K) estimated from fitting the experimental data to the Vogel–Fulcher model. This suggests that it may be possible to observe piezoelectric and ferroelectric properties at very low temperatures.     

Dielectric characterization of (1-x)PMN-xPT (x = 0.07 and 0.10) ceramics synthesized by an ethylene glycol-based soft chemical route

Materials based on relaxor ferroelectrics have become one of the most important families of functional materials being explored for such applications as sensors/actuators, micro-electromechanical systems (MEMS), non-volatile random access memories, and high-energy-density capacitors. Fabrication of high-quality relaxor-based ceramics remains, however, a challenging task. In this work, a new soft chemical synthetic method for the preparation of the complex perovskite-based relaxor ferroelectric solid solutions, (1-x)Pb(Mg(1/3)Nb(2/3))O(3)-xPbTiO(3) was developed using ethylene glycol as the solvent. Ceramics with compositions of x = 0.07 and 0.10 were prepared and it was found that a 10% stoichiometric excess of Pb(2+) was required to compensate for lead oxide volatility at the high temperatures used for sintering. The ceramics produced by this method show excellent dielectric properties at room temperature, such as a high dielectric constant (~20 000) and low loss over a large temperatures range (tan δ < 0.01 between 20 and 200°C). The temperature dependence of the dielectric constant exhibits typical relaxor ferroelectric behavior, fitting a quadratic law which describes the high-temperature slope of ε'(T) peak. The frequency dispersion of the temperature of maximum permittivity satisfies the Vogel-Fulcher law.     

复相弛豫铁电陶瓷的相组成与介电性能

采用两相混合烧结法在Ｐｂ（Ｚｎ１／３Ｎｂ２／３）Ｏ３－ＢａＴｉＯ３－ＰｂＴｉＯ３系统中制备了弛豫铁电陶瓷材料，相组成研究表明，该陶瓷具有两相共存的复相结构，对复相陶瓷的介电性能进行了研究，结果表明，复相结构可有效地改善弛豫铁电陶瓷的介温特性、频率特性和介质老化性能。     

弛豫铁电体的弛豫性结构研究

利用特殊的陶瓷烧结方法制备了铅基弛豫铁电体0．9Pb(Mg1／3Nb2／3)O3-0．1PbTiO3和Pb(Zn1／3Nb2／3)O3基陶瓷。铅基弛豫铁电体PMNT、PZN的弛豫过程可用修正的玻璃局域冻结模型描述。在微畴一宏畴转变过程中,铁电体的结构起伏引起弛豫性;弛豫铁电体结构起伏程度越大,弛豫性越低;随微畴增大,铁电体的弛豫特性减弱直至消失。     

Structural and dielectric relaxor properties of A-site deficient samarium-doped (Ba1−x Sm2x/3)(Zr0.3Ti0.7O3) ceramics

Rare earth samarium (Sm)-doped barium zirconate titanate (Ba_1?x Sm_2x/3)(Zr_0.3Ti_0.7)O₃ (x = 0.00, 0.02, 0.04, 0.06, 0.08, 0.10) ceramics were prepared using solid state reaction (SSR) route. The structural and microstructural characterizations of the materials were done by using X-ray diffraction and SEM analysis, respectively. Rietveld refinement technique employed to investigate the details of crystal structure revealed single-phase cubic perovskite structure belonging to space group Pm-3m. Microstructure of the doped ceramics were found to be porous and of irregular shape and size along with aggregative characteristic. FTIR technique was employed to study the influence of additives in ceramics compositions and to investigate the displacement of M–O bonds. Raman spectroscopic study revealed that the substitution of Ba²⁺ ions by Sm³⁺ ions shifted the Raman-active modes toward higher energy, which indicated that these materials undergo an increase in average cubicity with increase in Sm³⁺ ion concentration. The temperature dependence of dielectric properties was investigated in the frequency range from 1 kHz to 1 MHz. The dielectric measurement indicated a diffuse type of phase transition (DPT). The broadening in the dielectric permittivity and frequency dependence behavior with increase in frequency indicated a relaxor behavior of these materials. The relaxation strength of these materials was well adjusted by using the Vogel–Fulcher relation.     

Effect of annealing conditions and concentration of oxygen vacancies on vanadium doped SrBi2Ta2O9

This paper studied the annealing effects on the dielectric characteristics of vanadium doped SrBi₂Ta₂O₉ (SBT). SBT was synthesized at 1000 °C and vanadium doped SBT at 900 °C by solid-state reaction. Crystallization structure and phase purity of the prepared ceramic samples was observed by X-ray diffraction analysis. XRD analysis indicated a single layered perovskite structure without any secondary phases up to 15% of vanadium doping in SBT ceramics. Detailed dielectric study on vanadium doped SBT ceramics indicated that post-sinter annealing enhances the peak dielectric permittivity, which is attributed to the increased homogeneity in the system at atomic scale upon annealing. Annealing for larger time interval suppresses the permittivity growth beyond transition temperature which gives a direct evidence for the existence of lower valance state of vanadium (V⁺⁴) in as-sintered SBTV ceramics and also the permittivity growth is related to the oxygen ions or oxygen vacancies created during sintering. UV–Vis spectroscopy was also performed to confirm the lower valance state of the vanadium ions in the ceramics.     

Investigation of density of states and electrical properties of Ba<Subscript>0.5</Subscript>Co<Subscript>0.5</Subscript>Bi<Subscript>2</Subscript>Nb<Subscript>2</Subscript>O<Subscript>9</Subscript> nanoceramics prepared by chemical route

Barium-cobalt-bismuth-niobate, Ba_0.5Co_0.5Bi₂Nb₂O₉ (BCoBN) nanocrystalline ferroelectric ceramic was prepared through chemical route. XRD analysis showed single phase layered perovskite structure of BCoBN when calcined at 650 °C, 2 h. The average crystallite size was found to be 18 nm. The microstructure was studied through scanning electron microscopy. The dielectric and ferroelectric properties were investigated in the temperature range 50–500 °C. The dielectric constant and dielectric loss plot with respect to temperature both indicated strong relaxor behavior. Frequency versus complex impedance plot also supported the relaxor properties of the material. The impedance spectroscopy study showed only grain conductivity. Variation of ac conductivity study exhibited Arrhenius type of electrical conductivity where the hopping frequency shifted towards higher frequency region with increasing temperature. The ac conductivity values were used to evaluate the density of state at the Fermi level. The minimum hopping distance was found to be decreased with increasing temperature.     

Phase transition and dielectric study in Ba<Subscript>0·95</Subscript>Dy<Subscript>0·05</Subscript>TiO<Subscript>3</Subscript> ceramic

Temperature and frequency dependence dielectric permittivity of Ba0·95Dy0·05TiO₃ ceramic has been studied in the temperature range of 100–350 K at the frequencies, 1 kHz, 10 kHz, 100 kHz and 1 mHz. Diffuse phase transition and frequency dispersion is observed in the permittivity-vs-temperature plots. This has been attributed to the occurrence of relaxor ferroelectric behaviour. The observed relaxor behaviour has been quantitatively characterized based on phenomenological parameters. A comparison with the Zr doped BaTiO₃ has also been presented. The microstructure of as-sintered samples shows a dense and almost uniform micrograph without any impurity phases; the grains are almost spherical with random orientation.     

Relaxor ferroelectric-like behavior in 10PbTiO3–10Fe2O3–30V2O5–50B2O3 glass for energy storage applications

Recently, demand increased for dielectric materials used in energy storage devices at high voltage applications. Appearance of polar clusters in glass matrix could promote its use in energy storage applications. Conventional quenched glass sample of composition 10PbTiO₃–10Fe₂O₃–30V₂O₅–50B₂O₃ were successfully developed. The glassy nature was confirmed by XRD and DSC measurements. Boson peak observed at low frequency from the Raman spectra confirms polar cluster formation. Dielectric properties of prepared glass were investigated in a wide range of frequency and temperature. Broad and diffuse peak of dielectric permittivity shifted to the higher temperatures, denoting the typical relaxor ferroelectrics like behavior. Sample shows energy storage density of about 164.7 mJ/cm³ at room temperature. Quenched glass sample shows typical anti-ferromagnetic behavior.

     

Electrical properties of Nb<Subscript>2(1–<Emphasis Type="Italic">y</Emphasis>)</Subscript>Ta<Subscript>2y</Subscript>O<Subscript>5</Subscript>-based ceramics

We have studied the electrical properties of ceramic Nb_2(1–y)Ta_2yO₅ samples, examined the dispersion of the real part of their dielectric permittivity ε′ at room temperature, and assessed their lattice dielectric permittivity ε′_∞ The temperature dependences ε′(T) have been obtained at different frequencies, and the dielectric loss tan δ has been evaluated as a function of measuring electric field frequency and temperature. The direct-current conductivity (σ_dc) of the solid solutions has been determined at room temperature. Using impedance spectroscopy data, we have obtained temperature dependences of σ_dc for the Nb_2(1–y)Ta_2yO₅ ceramics and evaluated the activation enthalpy for charge transport in these materials in different temperature ranges.     

The electrostrictive effect and dielectric properties of lead-free 0.5Ba(ZrxTi1−x)O3–0.5(Ba0.75Ca0.25)TiO3 ceramics

Lead-free 0.5Ba(Zr_xTi_1?x)O₃–0.5(Ba_0.75Ca_0.25)TiO₃ (x = 0.25, 0.30, 0.35, 0.40) ceramics have been synthesized by a conventional solid state sintering method. The room temperature ferroelectric and electrostrictive properties of these ceramics were studied. Based on the measured properties, these ceramics showed a typical relaxor behavior. The Curie temperature of BZT–BCT ceramics decreases with increasing the Zr content. The largest electrostrictive strain and electrostrictive coefficient are founded in BZT–BCT ceramic with x = 0.25, the value is 0.16 % and 0.079 m⁴ C^?2, respectively. The polarization, electrostrictive strain and electrostrictive coefficient (Q ₁₁) decrease with increase in Zr concentration. For samples with low Curie temperature, which have large room temperature dielectric constant (ε), electrostrictive coefficient increases (Q ₁₁) is smaller. Because doping can disrupt the long range cation order, and electrostrictive (Q ₁₁) coefficient increases with cation order from disordered, through partially-ordered, simple relaxor and then ordered perovskites, ferroelectrics with a disordered structure have a huge permittivity, but a small electrostrictive coefficient (Q ₁₁).     

Investigation into the dielectric behavior of ferroelectric superlattices formed by pulsed laser deposition

In an attempt to reproduce the functional properties associated with relaxor electroceramics, pulsed laser deposition has been used to fabricate thin-film capacitor structures in which the dielectric layer is composed of a superlattice of Ba_0.8Sr_0.2TiO₃ and Ba_0.2Sr_0.8TiO₃. The properties of the capacitors were investigated as a function of superlattice periodicity. The dielectric constant was enhanced at stacking periodicities of a few unit cells, consistent with relaxor behavior. However, enhancement of the dielectric constant was found to be associated with high dielectric loss. Analysis of the imaginary permittivity as a function of frequency shows that fine-scale superlattices conform to Maxwell–Wagner behavior. This suggests that the observed enhancement of the real part of the dielectric constant is an artefact produced by carrier migration. A comparison of this data with that already published on dielectric superlattices suggests that previous claims of an enhancement in dielectric constant may also be due to the Maxwell–Wagner effect. The onset of Maxwell–Wagner behavior was attributed to increasing density of defect zones associated with discontinuities in the superlattice structures. In an attempt to exaggerate the influence of such zones, deliberate delays between deposition of successive dielectric layers were introduced. This resulted in reproduction of several features normally associated with relaxors: enhancement of dielectric constants by over an order of magnitude; strong frequency dispersion around and below T_m; migration of T_m with frequency. However, these features were again associated with relatively high loss.     

Investigation on dielectric response of PMN ceramics around paraelectric–ferroelectric diffuse phase transition

Abstract

The dielectric properties of relaxor ferroelectric lead magnesium niobate Pb(Mg_1/3Nb_2/3)O₃ (PMN) ceramics have been investigated. These studies were conducted taking into account the characterisations of the complex dielectric permittivity (real and imaginary parts) as a function of temperature and frequency in a wide interval. On the other hand, the dc 'bias' electrical field dependence of the real dielectric permittivity (C–V characterisations) has been analysed around the paraelectric–ferroelectric diffuse phase transition. Results obtained at room temperature (paraelectric phase) showed a typical behaviour of conventional dielectric materials, while measurements performed at 200 K (ferroelectric phase) evidenced an anomalous behaviour for frequencies up to 100 kHz. Such observed anomalies were characterised by two asymmetrical peaks on sweep-up and sweep-down, at ? 15 and + 18 kV cm^?1 respectively.     

Structural and dielectric studies of Li2SiO3 ceramic

Lithium metasilicate (Li₂SiO₃) ceramic was prepared via solid-state reaction technique. X-ray diffraction pattern showed that Li₂SiO₃ ceramic is orthorhombic. Microstructural analysis by field emission scanning electron microscopy (FE-SEM) shows that the compound has well defined grains separated by grain boundaries. Dielectric studies of the compound shows a strong frequency dispersion of permittivity in the low frequency region followed by a nearly frequency independent behavior in the high frequency region. The dielectric permittivity and dielectric loss at 5 MHz are 25.66 and 0.033 at room temperature. The activation energy (E_a) of the sample calculated from the plot of ac conductivity versus inverse of absolute temperature was found to be less than 1 eV. The smaller activation energy of the compound within moderate temperature range suggests the presence of singly ionized oxygen vacancies in the conduction process.