Dielectric properties of BaTiO3-based ceramics measured up to GHz region

A new measuring method and analyzing procedure were proposed to determine the complex dielectric constant of materials with relatively high dielectric constant by a lumped impedance measurement using impedance analyzer. Samples used for the measurement were (Ba_0.6Sr_0.4)TiO₃ (BST) and Ba(Zr_0.25Ti_0.75)O₃ (BZT) ceramics. Micro planar electrodes were formed on the surface of samples by electron beam lithography followed by lift-off method. Complex admittances of these samples were measured up to 3 GHz at different temperatures. Electromagnetic simulations were performed for determining the relative dielectric constant and dielectric loss. The complex dielectric constant vs frequency curves of Ba(Zr_0.25Ti_0.75)O₃ showed a broad dielectric relaxation, while that of (Ba_0.6Sr_0.4)TiO₃ was almost flat up to 3 GHz on high-temperature side of T _m at which dielectric constant shows maximum value. Dielectric dispersion properties were discussed from the viewpoint of diffuse phase transition in ferroelectrics.     

Influence of Space Charge Layers on the Dielectric Properties of Ba0.6 Sr0.4TiO3 Nanostructured Thin Films

Barium strontium titanate (Ba_0.6Sr_0.4TiO₃) nanostructured thin films have been deposited on platinized silicon substrates by the sol-gel method. The as-fired films were found to be amorphous, which crystallize to cubic phase after annealing at 550°C in air for one hour. The low-frequency dielectric responses of the BST films were measured as functions of frequency range from 1 kHz to 1MHz. The thickness dependence dielectric constant of the BST thin films were measured in the temperature range from ?150°C to 150°C at 100 kHz and discussed in the light of an interfacial dead layer. All the samples showed a diffuse type phase transitions. Both the dielectric constant and loss tangent showed anomaly peaks at about 10°C, which corresponds to a tetragonal ferroelectric-to-cubic paraelectric phase transition.     

Effect of BaTiO3 size on dielectric property of BaTiO3/PVDF composites

The BaTiO₃/polyvinylidene fluoride (BaTiO₃/PVDF) polymer-based composites with different size and concentration of BaTiO₃ particles were fabricated via a simple physical mixing and subsequently hot-press processing. Effect of the filler size and frequency on the dielectric properties of the BaTiO₃/PVDF binary composites was discussed. The result shows that the BaTiO₃ size has an effect on the morphology of the BaTiO₃/PVDF composites. The composites with 0.2 and 0.3 μm BaTiO₃ exhibit high dielectric permittivity than those with 0.4 and 0.5 μm BaTiO₃. The composite with 0.4 μm BaTiO₃ has a minimum dielectric permittivity except one with 0.1 μm BaTiO₃. Dielectric loss of the BaTiO₃/PVDF binary composites changes slightly with the BaTiO₃ sizes. The ternary BaTiO₃/PVDF composites with 0.1 and 0.7 μm BaTiO₃ in coexistence exhibit good dielectric properties. As a result, the BaTiO₃/PVDF ternary composites in this study may have a promising application as dielectric material in embedded capacitor.     

Relaxor-like behavior of bismuth-based pyrochlores containing Sn

Dielectric relaxation studies have been made in pyrochlore (Bi_1.5Zn_0.5)(Zn_0.5?x/3Sn _x Nb_1.5?2x/3)O₇ ceramics where 0?≤?x?≤?1.5. The measurements of dielectric constant (?) and dielectric loss (tanδ) are made in the frequency range from 1 to 1,000 kHz at low temperatures from 100 to 450K. Frequency dispersion associated with dielectric relaxation phenomena in polycrystalline cubic pyrochlore is analyzed. The effect of Sn on the dielectric relaxation behavior and the physical mechanism giving polarization is briefly discussed.     

Phase transition,microstructure and properties of (Na<Subscript>0.5</Subscript>Bi<Subscript>0.5</Subscript>)<Subscript>1-x</Subscript>Ba<Subscript>x</Subscript>TiO<Subscript>3</Subscript> lead-free piezoelectric ceramics

In this article, (Na_0.5Bi_0.5)_1-xBa_xTiO₃ lead-free piezoelectric ceramics were prepared by solid-state reaction. The influence of Ba contents on phase structures, compositional distribution and electrical properties of (Na_0.5Bi_0.5)_1-xBa_xTiO₃ ceramics were systematically investigated to further understand the nature of phase transition. It was found that the phase structure of (Na_0.5Bi_0.5)_1-xBa_xTiO₃ transforms from rhombohedral to tetragonal symmetry at x = 0.06 ~ 0.07 and Ba²⁺ segregation forms the coexistence of Ba-rich tetragonal and Ba-deficient rhombohedral phases close to MPB. The electrical properties of prepared samples regularly changed with Ba content, which is closely related to the distribution of rhombohedral and tetragonal phases. The prepared sample near MPB exhibited the largest dielectric constant and the excellent piezoelectric properties (the maximal measuring field reached 78 kV/cm and the piezoelectric constant d ₃₃ = 151pC/N).     

Effect of Fe – substitution on phase transformation,optical, electrical and dielectrical properties of BaTiO<Subscript>3</Subscript> nanoceramics synthesized by sol-gel auto combustion method

The structural, microstructural, optical, electrical and dielectrical properties of nanocrystalline Fe substituted BaTiO₃ synthesized by sol-gel auto combustion have been investigated. The X-ray diffraction (XRD) analysis revealed the existence of the tetragonal phase for lower Fe content (x = 0.0–0.3) whereas, coexistence of the tetragonal and hexagonal structure of higher Fe content (x = 0.4 and 0.5). The lattice constant (a and c) and unit cell volume (V) increases with increase in Fe content; and an average crystallite size (t) was recorded in the range of ~14–20 nm. The surface morphology as examined using field emission scanning electron microscopy (FESEM) and the compositional stoichiometry was confirmed by energy dispersive spectrum (EDS) analysis. The UV-Vis spectra showed that the band gap energy sensitively depends on the Fe concentration x. DC-electrical conductivity (σ) was recorded in the temperature range of 333–714 K which was found to be increases with increasing temperature and Fe concentration; indicating that an electrical conduction was a thermally activated process. The type of temperature dependent DC conductivity indicates that the electrical conduction in the material is a thermally activated process. The dependencies of the conductivity contributions were predicted from the simple defect model presented, in which oxygen vacancies charge compensate Fe substitution of Ti. Dielectrical property was measured as a function of frequency in the range 50 Hz - 5 MHz at room temperature which was found to be higher at lower frequencies. Dielectric constant (ε’) and loss tangent (tan δ) shows strong compositional as well as frequency dependences.     

Synthesis and characterizations of SrTiO<Subscript>3</Subscript> modified BNT-KNN ceramics for energy storage applications

Lead-free (1-x) [0.934BNT-0.07KNN]-x SrTiO₃/BNT-KNN-ST ceramics with x = 0, 0.04, 0.08, 0.12 and 0.16 were synthesized in single perovskite phase by conventional solid state reaction route. Effect of SrTiO₃ modification on phase, microstructure, dielectric, electric field induced polarization, electric field induced strain and energy-storage properties were investigated and discussed in detail. Dielectric study confirmed relaxor nature with a drastic decrease of T _c with the increase of SrTiO₃ content in BNT-KNN-ST system. Saturation polarization, remnant polarization, coercive field (E _c ) and maximum induced strain decreased with the increase of SrTiO₃ content in BNT-KNN-ST system. High recoverable energy storage density of ~0.59 J/cm ³ with energy storage efficiency of ~64% were obtained in x = 0.16 ceramic samples, which suggested its usefulness for energy-storage capacitor applications.     

Thermal Expansion Behavior of (Bi0.5Na0.5)Zr1-x Ti x O3 Ceramics

(Bi_0.5Na_0.5)Zr_1-xTi_xO₃ with x = 0, 0.1, 0.2, 0.3, 0.4, 0.5 and 0.6 ceramics were fabricated by a conventional sintering technique at 850–950°C for 2 h. From X-ray diffraction study, three regions of different phases were observed in the ceramic system; i.e., orthorhombic phase region (0 ≤ x ≤ 0.2), mixed-phase region (0.3 ≤ x ≤ 0.4), and rhombohedral phase region (0.5 ≤ x ≤ 0.6). The thermal expansion coefficient data indicated the phase transition in the temperature range from 100°C–150°C of the ceramics. The thermal strain curve of all compositions suggested a decrease of local polarization with temperature increment up to the Burns temperature.     

Dielectric properties and defect mechanisms of (1-<Emphasis Type="Italic">x</Emphasis>)Ba(Fe<Subscript>0.5</Subscript>Nb<Subscript>0.5</Subscript>)O<Subscript>3</Subscript> -<Emphasis Type="Italic">x</Emphasis>BiYbO<Subscript>3</Subscript> ceramics

(1-x)Ba(Fe_0.5Nb_0.5)O₃ -xBiYbO₃ (BFN-xBY) ceramics were prepared by a conventional solid-state reaction method. The dielectric properties and relaxation behavior of BFN-xBY ceramics were analyzed according to dielectric and impedance spectroscopy. Dielectric permittivity of the ceramics increases with increasing temperature below 500 K then remains unchanged up to 700 K, while corresponding loss factor decreases with the increase of temperature below 500 K then increase slowly. Defect compensation mechanism of this system was analyzed in detail. The giant dielectric behavior of the ceramics arises from the internal barrier layer capacitor (IBLC) effect. Polarization effect at insulating grain boundaries between semiconducting grains accompanied by a strong Maxwell-Wagner (MW) relaxation mode. The characteristic of grain boundaries was revealed using impedance spectroscope and the universal dielectric response law.     

Dielectric and piezoelectric properties of KCT added (Li0.02(Na0.56 K0.46)0.98(Nb0.81Ta0.15Sb0.04)O3 ceramics

In this study, [Li_0.02(Na_0.56 K_0.46)_0.98](Nb_0.81Ta_0.15Sb_0.04)O₃ + x mol% K_5.4Cu_1.3Ta₁₀O₂₉ ceramics were fabricated by conventional solid-state solution processes. Then, their dielectric and piezoelectric properties were investigated. Sinterability of all samples was enhanced because K_5.4Cu_1.3Ta₁₀O₂₉ (abbreviated as KCT) acted as sintering aids. As the result of XRD, phase structure showed orthorhombic symmetry when KCT ≤ 0.2 mol%. Whereas, the phase structure changed from orthorhombic symmetry to tetragonal symmetry when KCT?≥?0.4 mol%. The results suggest that the orthorhombic and tetragonal phases co-exist in the composition ceramics with 0.2 mol% < KCT < 0.4 mol% at room temperature. The effects of the addition of KCT on the dielectric and piezoelectric properties were investigated. As the result, excellent properties of density=4.81[g/cm³], electromechanical coupling factor (k_p)=0.48 and piezoelectric constant(d₃₃)=252[pC/N] were obtained in the composition ceramics with 0.4 mol%KCT.     

Structural and electrical properties of SrBi2VxNb2?xO9 ferroelectric ceramics: Effect of temperature and frequency

Aurivillius type bismuth layered materials have received a lot of attention because of their application in ferroelectric non-volatile random access memories. Among bismuth layer structured ferroelectric ceramics SrBi₂Ta₂O₉ (SBT)/SrBi₂Nb₂O₉ (SBN) are of great interest for researchers because of their fatigue resistance and less distorted structure. Recently vanadium substitution in SBN/SBT has shown interesting electric and dielectric properties. In the present work, processing conditions, microstructure and electrical studies of vanadium doped SBN ferroelectric ceramics have been performed. Samples of compositions SrBi₂V _x Nb_2-x O₉, x = 0.0, 0.1, 0.3, 0.5 were prepared by solid-state reaction technique using high purity oxides / carbonates. The samples were calcined at 700 °C and sintered at 800 °C. X-ray diffractograms show that a single phase layered perovskite structure is formed in all the samples. Effect of partial substitution of pentavalent niobium ion (0.68 ?) by smaller pentavalent vanadium ion (0.59 ?) at B site on the microstructure, Curie temperature, Dielectric constant, Dielectric loss and electrical conductivity have been investigated. Dielectric properties of SBVN have been investigated from room temperature to 500 °C and frequency of 100 Hz to 1 MHz. Dielectric constant values at their respective Curie points are observed to increase with increasing vanadium concentration. Curie temperature is observed to be maximum in x = 0.1 vanadium doped sample. Strong relaxor like dielectric relaxation at the transition temperatures have been observed. With increasing vanadium concentration the dielectric loss is observed to increase significantly. It is also observed that dielectric loss increases with increase in temperature. The variation of conductivities in these samples is also reported.     

Effect of Bi3+ ion on piezoelectric properties of K x Na1−x NbO3

This paper describes the material preparation and characteristics of potassium sodium niobate, K _x Na_{1? x} NbO₃ (KNN), with Bi³⁺ doping. Some physical properties including density, dielectric constant, loss tangent and ferroelectric hysteresis, were examined. The samples were characterized by using X-ray diffraction method and the grain size was measured by using SEM micrographs. Dielectric constant, loss tangent, and electromechanical coupling coefficient of samples were measured at different frequencies. The changes in physical properties are remarkable when KNN is doped with Bi³⁺ ions.     

Crystal structure and the effect of annealing atmosphere on the dielectric properties of the spinels MgAl2O4, NiFe2O4, and NiAlFeO4

The non-transition metal spinel MgAl₂O₄ and the transition metal spinels (NiFe₂O₄, NiAlFeO₄) have been prepared by standard ceramic processing method in the air. The effect of annealing atmosphere on the dielectric properties after sintering has been studied. The annealing atmospheres were N₂, O₂, and N₂–H₂ mixture. Dielectric constant ? _r and tangent loss tanδ have been characterized by varying the measuring temperature and frequency (5 Hz–5 MHz) using the impedance analyzer. The ? _r and tanδ of the non-transition metal spinel MgAl₂O₄ remained unchanged even with varying the annealing atmosphere. While the dielectric properties of the transition metal spinels, NiFe₂O₄ and NiAlFeO₄ were critically dependent on the annealing atmosphere. Crystal structural models for the samples manufactured in air have been tested by the Rietveld refinement method for both the centrosymmetric Fd-3m and the noncentrosymmetric F-43m. The electron density distributions were determined by the whole pattern fitting based on the maximum entropy method (MEM). The dielectric properties of the samples have been also discussed in terms of the structure and electron distribution analysis results.     

Chemical synthesis,structural characterization and electrical studies of nanoceria for CMOS applications

Cerium oxide nanoparticles were synthesized using cerium nitrate hexa hydrate and ammonium carbonate as precursors. Structural characterizations were done using X-ray diffraction (XRD) and transmission electron microscopy (TEM). The crystallite size and lattice strain on the peak broadening of CeO₂ nanoparticles were studied using Williamson-Hall (W-H) analysis. The dielectric properties of nanocrystalline CeO₂ samples with different calcination temperatures, and frequencies have been studied over a temperature range from 303 to 423 K. It is found that the dielectric constant and dielectric loss for all temperatures have high values at low frequencies, which decreases rapidly as frequency is increased and attains a constant value at higher frequencies. The room temperature dielectric constant ε′ obtained for the as prepared CeO₂ nanoparticle sample is 61, which constitutes the highest value ever reported at low frequency. A.C. conductivity, which was derived from dielectric constant and loss tangent data, has a low value at smaller frequencies that increases as the frequency is increased. The dielectric constant and a.c. conductivity values are shifted upwards as the temperature is raised. However, these values are decreased as the annealing temperature is increased. The desired structural properties and high dielectric constant of nanophase CeO₂ make it as a promising material for the high dielectric constant dielectric gate in complementary metal oxide semiconducting (CMOS) devices.     

High-temperature stable dielectrics in Mn-modified (1-x) Bi0.5Na0.5TiO3-xCaTiO3 ceramics

In the current work, the bulk (1-x) Bi_0.5Na_0.5TiO₃-xCaTiO₃ [BNCT100x] system was synthesized via solid-state route. CaTiO₃ in solid solution with Bi_0.5Na_0.5TiO₃ was observed to decrease the dielectric constant at higher temperature and raise the dielectric constant at lower temperature. Polarization hysteresis measurements indicated that the ferroelectricity of Bi_0.5Na_0.5TiO₃ was weakened with an increase of CaTiO₃, resulted in the shift of the depolarization temperature (T _d) toward lower temperatures. X-ray diffraction analysis revealed that TiO₂ was produced as a secondary phase due to the losses of Bi and Na during milling and sintering processes. Moreover, the addition of Ca promoted the segregation of Ti out of BNT grains. Dielectric properties of BNCT12 ceramics with different dopant levels of Mn were characterized as a function of temperature for potential use of high-temperature capacitors. Modification of BNCT12 materials with Mn improved the temperature characteristic of capacitance (?55°C to 250°C, △C/C_25°C ≤ ±15%). Finally, by doping 1.5 wt% Mn, the dielectric constant at room temperature could reach over 900, with a low dielectric loss below 1% and a high insulation resistivity about 10¹² Ω?cm. Furthermore, a small amount of Mn influenced the microstructure in the way to inhibit the long grains and grain growth of BNCT solution ceramics. However, excess Mn caused abnormal grain growth, and therefore, rectangle grains appeared again.     

Dielectric Properties of Yttrium Vanadate Crystals from 15 K to 295 K

Yttrium Vanadate (YVO₄) is a birefringent crystal, which has similar dielectric constant as that of Sapphire. In this paper we have reported the measurement of the real part of permittivity and loss tangent of YVO₄ crystal in the temperature range 15–295 K at a frequency of 16.3 GHz. We have used the dielectric post resonator technique for the microwave characterisation of the YVO₄ dielectric rod. The multifrequency Transmission Mode Q-Factor (TMQF) technique has been used for data processing and hence precise values of permittivity and loss tangent are achieved. Easily machineable YVO₄ is characterized by low losses at microwave frequencies. At temperature of 15 K and frequency of 16.3 GHz the permittivity was 9.23 and loss tangent was 2 × 10^{− 5}. YVO₄ is identified as a potential candidate to replace expensive Sapphire in many microwave applications.     

Piezoelectric properties of MnO2 doped low temperature sintering Pb(Mn1/3Nb2/3)O3–Pb(Ni1/3Nb2/3)O3–Pb(Zr0.50Ti0.50)O3 ceramics

In this study, in order to develop the composition ceramics for low loss and low temperature sintering multilayer piezoelectric actuator, Pb(Mn_1/3Nb_2/3)O₃–Pb(Ni_1/3Nb_2/3)O₃–Pb(Zr_0.50Ti_0.50)O₃ (abbreviated as PMN-PNN-PZT) ceramics were fabricated using Li₂CO₃ and Na₂CO₃ as sintering aids, and their piezoelectric and dielectric characteristics were investigated according to the amount of MnO₂ addition. At the 0.2 wt% MnO₂ doped specimen sintered at 900 °C, density and mechanical quality factor (Q _m) showed the maximum values of 7.81[g/cm³]and 1186, respectively. And also, at 0.1 wt% MnO₂ doped specimen, electromechanical coupling factor (k _p), piezoelectric constant (d ₃₃) of specimen showed the maximum values of 0.608 and 377[pC/N], respectively. Dielectric constant (? _r) slightly decreased with increasing MnO₂. Taking into consideration the density of 7.81[g/cm³], electromechanical coupling factor (k _p)of 0.597 the mechanical quality factor (Q _m) of 1,186, and piezoelectric constant (d ₃₃) of 356[pC/N], it could be concluded that 0.2 wt% MnO₂ doped composition ceramics sintered at 900 °C was best for low loss and low temperature sintering multilayer piezoelectric actuator application.     

CHARACTERIZATION OF FERROELECTRIC FILMS UP TO 60 Ghz: APPLICATION TO PHASE SHIFTERS

ABSTRACT

Paraelectric Ba_0.5Sr_0.5TiO₃ films 0.3 μm thick have been deposited by sol-gel on c-axis sapphire substrates. They have been investigated from 1 kHz to 60 GHz using coplanar waveguide transmission lines and interdigitated capacitors. The dielectric constant ε_r is around 300 and the loss tangent is 0.16 at 50 GHz. The tunability is constant with frequency with a mean value of 42%. Analog phase shifters were subsequently fabricated. A 180° phase shift was obtained at 60 GHz with a 17 V bias. The maximum value of phase shift per decibel of insertion losses (at 0 V) is 13°/dB at 30 GHz with a bias of 30 V.     

Fabrication and dielectric properties of Na0.5Bi0.5Cu3Ti4O12 from co-precipitation method

High dielectric Na_0.5Bi_0.5Cu₃Ti₄O₁₂ (NBCTO) ceramics were firstly prepared by co-precipitation method at low temperature. X-ray diffraction results revealed that pure phase of NBCTO was achieved by calcination at 950 °C for 2 h. Thermo-gravimetric analysis on a dried NBCTO precursor was carried out to study the thermal decomposition process. The microstructure and dielectric properties of NBCTO ceramics sintered at different temperatures were investigated. The results indicate that the sintering temperature has a sensitive influence on the microstructure and dielectric properties. Higher sintering temperature gave rise to increased dielectric constant and dielectric loss of NBCTO samples, and the sample sintered at 975 °C for 8 h exhibits high dielectric constant of 8.3?×?10³ and low dielectric loss of 0.069 at 10 kHz. The dielectric properties were further discussed by the impedance spectroscopy.     

Ferroelectric phase transition and electrical properties of Ba(Bi0.5Ta0.5)O3

A lead free polycrystalline material Ba(Bi_0.5Ta_0.5)O₃ was prepared by a standard high-temperature solid-state technique (calcination temperature?=?1180 °C and sintering temperature?=?1200 °C) using high-purity ingredients. The room temperature X-rays diffraction analysis of the material has confirmed its formation in the monoclinic crystal system. The study of microstructure using scanning electron microscopy (SEM) shows that the compound has well-defined grains uniformly distributed throughout the surface of the sample. Detailed studies of dielectric and impedance properties of the material were carried out in a wide frequency range (1 kHz ?1 MHz) at different temperatures (30 °C to 490 °C). Dielectric study shows that the material has ferroelectric properties with diffuse-phase transition around 315 °C. Complex impedance spectroscopic analysis establishes some correlation between the microstructure and electrical properties of the material. The frequency dependence of ac conductivity follows the Jonscher’s power law. The dc conductivity, calculated from the ac conductivity spectrum, shows the negative temperature coefficient of resistance behavior similar to that of a semiconductor. The temperature dependent pre-exponential factor shows peak, and frequency exponent possesses a minimum at transition temperature.