Dielectric Properties Of Ceramics Research Articles

Effects of Ti<sup>4+</sup> Substitution on Microstructure and Microwave Dielectric Properties of ZnNb<sub>2(1-x)</sub>TixO<sub>(6-3x)</sub> Ceramics

The microstructure and microwave dielectric properties of dielectric ceramics comprised of ZnNb2(1-x)TixO(6-3x) (x = 0 ~ 1) were investigated systematically using X-ray powder diffraction, SEM and a network analyzer in this study. The results showed that four phases were observed in this system. The dielectric properties at microwave frequencies exhibit a significant dependence on the composition and crystal structure of the ceramics. The dielectric constant ( er) of ZnNb2(1-x)TixO(6-3x)ceramics increases with increasing Ti content and the quality factors (Q ×f) significantly decreased. However, the temperature coefficient of resonant frequency ( t f ) changes from –59.08 ppm/oC at x = 0 to + 25.1 ppm/oC at x = 1, and a zero temperature coefficient of resonant frequency ( t f ) for this ceramics system was obtained at x = 0.84.

Dielectric properties of (1 − x)Pb(Zr 0.52Ti 0.48)O 3–( x)BaTiO 3 ceramics under uniaxial compressive pre-stress

Effects of uniaxial compressive pre-stress on the dielectric properties of ceramics in PZT–BT solid-solution system are investigated. The physical properties measurements reveal that the addition of BT into PZT results in the increase of grain size and microstructural heterogeneity, except for the density which sees the opposite trend. The dielectric properties measured under stress-free condition show a gradual increase of the dielectric constant with increasing BT content, while the dielectric loss tangent is not considerably different. The dielectric properties under the uniaxial compressive pre-stress of the PZT–BT ceramics are observed at stress levels up to 15 MPa using a uniaxial compressometer. The results clearly show that both the dielectric constant and the dielectric loss tangent of the PZT–BT ceramics increase significantly with increasing applied stress. Larger changes in the dielectric properties with the applied stress are observed in the PZT-rich compositions. The experimental observations have been attributed to the increase of the domain wall motions from the application of the compressive pre-stress.

Preparation of BaTiO3-based ceramics by nanocomposite doping process

BaTiO3-based ultrafine nonreducible dielectrics for multilayer ceramic capacitors were prepared by a newly developed nanocomposite doping process. According to TG-DTA, XRD and TEM analysis, the nanocomposite dopants via sol–gel method were uniform and well dispersive. The micromechanism was investigated based on comparing conventional process with nano-doping process. It indicated that due to the special nano-effect, doping effect of additives became more effective and the microstructure and dielectric properties of ceramics were improved. The results showed that high performance dielectrics satisfying X8R specification were achieved, with high dielectric constant of 2,900, low dielectric loss of 0.6% and large insulation resistivity of 1012 Ω cm.

Effects of sintering condition on phase formation, microstructure and dielectric properties of lead titanate ceramics

Lead titanate ceramics have been prepared by two different processing methods: conventional (or single-stage) and two-stage sintering. Effects of designed sintering conditions on phase formation, densification, microstructure and dielectric properties of the ceramics were characterized via X-ray diffraction, Archimedes density measurement, scanning electron microscopy and dielectric measurement, respectively. The potentiality of a two-stage sintering technique as a simple ceramic fabrication method to obtain highly dense and pure lead titanate ceramics was demonstrated. It has been found that, under suitable two-stage sintering conditions, dense perovskite lead titanate ceramics can be successfully achieved with better dielectric properties than those of ceramics from a single-stage sintering technique.

Effect of milling time on the properties of Pb(Mg1/3Nb2/3)O3 ceramics using the starting precursors PbO and MgNb2O6

Abstract Lead magnesium niobate, Pb(Mg 1/3 Nb 2/3 )O 3 (PMN) ceramics were prepared from the columbite method using calcined powders of various milling time (24–96 h). The effects on the grain size and dielectric properties of the ceramics were investigated. The results show that dielectric properties of ceramics are strongly influenced by the milling time of the starting precursors. Higher percentage of perovskite phase was found in the ceramics that was milled longer and thus the dielectric constant was found to increase when compared to the conventional 24 h milled results. Moreover, milling time also affected the particle size of the starting precursors and that of PMN powders. Therefore, milling time did not only affect the particle size of PMN powders but also the resultant grain size and the formation of perovskite phase, consequently affecting the dielectric constant of the ceramics.

Low-temperature sintering and phase transition of zinc titanate ceramics with V 2O 5 and B 2O 3 addition

V 2O 5 and B 2O 3-doped (abbreviated to V–B) zinc titanate ceramics were prepared by a conventional mixed-oxide method combined with a chemical processing. Fine particle powders were prepared by chemical processing to activate the formation of ZnTiO 3 and to improve the sinterability. The effects of V–B addition on the low-temperature sintering behavior, the phase-structure and dielectric properties of ceramics were investigated, and phase transition mechanism and low-temperature sintering mechanism were discussed. The results show that the densification temperature of zinc titanate ceramics could be reduced from 1100 to 875 °C by V–B addition. The complete phase transition temperature of hexagonal ZnTiO 3 to cubic Zn 2TiO 4 was lowered from 945 to 930 °C by substituting V 5+ for Ti 4+. Exaggerated grain growth was found in high-V content samples and disappeared with B 2O 3 content increasing. At the same time, the grains became uniform. The dielectric properties of V–B additions-doped zinc titanate ceramics were measured at different frequencies. The results showed the decreasing tendency with the increasing measuring frequencies for both the dielectric constants and the loss tangents, and there existed the best dielectric properties for 3VB-doped ceramics.

Effects of uniaxial stress on dielectric properties of ferroelectric ceramics

The effects of uniaxial stress on the dielectric properties of ceramics in PMN–PZT system are investigated. Ceramics with the formula ( x )Pb(Mg 1/3 Nb 2/3 )O 3 –(1 − x )Pb(Zr 0.52 Ti 0.48 )O 3 when x = 0.0, 0.1, 0.3, 0.5, 0.7, 0.9 and 1.0 are prepared by a conventional mixed-oxides method. The sintered ceramics are perovskite materials with their physical properties proportionally depending on the PMN and PZT contents. The dielectric properties under the uniaxial stress of the unpoled and poled PMN–PZT ceramics are observed at stress levels up to 5 MPa. For the unpoled ceramics, the dielectric properties do not change significantly with the applied stress and the changes are independent of the ceramic compositions. For the poled ceramics, on the other hand, the dielectric constant of the PZT-rich compositions increases slightly, while that of the PMN-rich compositions decreases with increasing applied stress. In addition, changes in the dielectric loss tangent with stress are found to be composition independent. This study clearly shows the influences of the domain re-orientation, domain wall motion, degradation and depoling mechanisms on the variation of the dielectric properties of PMN–PZT ceramics under the uniaxial stress.

DIELECTRIC RELAXOR BEHAVIOR OF Pb(Mn1/3Sb2/3)O3-Pb(Zr0.52Ti0.48)O3 CERAMICS

ABSTRACT In this paper, xPb(Mn1/3Sb2/3)O3-(1−x)Pb(Zr0.52Ti0.48)O3 (PMS-PZT) ceramics were fabricated by using conventional ceramics technique. Temperature and frequency dependence of the dielectric properties of ceramics were investigated. For PMS-PZT ceramics with 0.08 ≤ x ≤ 0.15, the maximum dielectric constant decrease as the measurement frequency increases and its permittivity maximum temperature (T m) is shifted towards higher temperatures as well, these behavior show ‘relaxor-like’ ferroelectric behavior. While for x = 0.05, there is no shift in transition temperature which shows normal ferroelectric behavior. The mechanism of dielectric relaxor behavior for high PMS content is discussed in the paper.

The ferroelectric transition temperature as an intrinsic probe for sintered nanocrystallineBaTiO3 synthesized under supercritical conditions

We have investigated the sintering behaviour of cubicBaTiO3 nanoparticles obtained under supercritical conditions. The ferroelectric properties of samples sintered between950 and 1300 °C were measured from room temperature up to200 °C and in the frequency range 100 Hz–10 kHz. The influence of the initial powder characteristicson the microstructure and dielectric properties of ceramics have been investigated. Theferroelectric transition temperature was used as an intrinsic probe for the ceramiccharacterization and was then found to be dependent on the Ba:Ti ratio of the initialpowder. Understanding the role of the key parameters at different scales (bulk andnanoscale composition, tetragonal distortion, microstructure) on the permittivity, lossesand transition temperature would lead to a possible modulation of ferroelectricproperties.

Low Temperature Sintering of Ca[(Li1/3Nb2/3)1-xTix]O3-δ Based Microwave Dielectric Ceramics with Glass Frit

The microstructures and the microwave dielectric properties of Ca[(Li1/3Nb2/3)1-xTix]O3-δ (CLNT) ceramics with different amount of glass frit additions were investigated. Addition of glass frit(B2O3–ZnO–SiO2–PbO system) improved the densification and decreased the sintering temperature from 1150°C to 900°C of Ca[(Li1/3Nb2/3)1-xTix]O3-δ microwave dielectric ceramics. The dielectric constants (εr) and bulk density were increased, as increasing glass contents from 10 wt% to 15 wt%. The quality factor (Q·f0), however, was decreased slightly. The temperature coefficients of the resonant frequency (τf) shifted positive value as glass contents were increased. The dielectric properties of Ca[(Li1/3Nb2/3)0.8Ti0.2]O3-δ with 12 wt% glass sintered at 900°C for 3 h were εr=40, Q·f0=12,500, τf=-8 ppm/°C, respectively. The relationship between the microstructure and dielectric properties of ceramics was studied by X-ray diffraction (XRD), energy dispersive spectroscopy (EDS) and scanning electron microscopy (SEM).

Dielectric properties of BaTiO 3-based ceramics sintered in reducing atmospheres prepared from nano-powders

In this paper, high purity BaTiO 3 (BT) nano-powders with various grain sizes of 30–85 nm synthesized by chemical method were used to fabricate temperature-stable BT-based ceramic materials for application in base metal electrode (BME) multilayer ceramic capacitors (MLCC). The effects of the initial grain sizes of BT nano-powders on the phase structures, microstructures and dielectric properties of the ceramics were investigated. The BT based MLCC ceramics with the average grain size less than 200 nm were achieved in reducing atmospheres, showing high dielectric constant up to 2000, low dielectric loss less than 1%, which could satisfy the X7R characteristics prescribed by EIA standard.

Effects of uniaxial stress on dielectric properties lead magnesium niobate–lead zirconate titanate ceramics

Effects of uniaxial stress on the dielectric properties of ceramics in lead magnesium niobate–lead zirconate titanate (PMN–PZT) system are investigated. The ceramics with a formula (x)Pb(Mg1/3Nb2/3)O3–(1−x)Pb(Zr0.52Ti0.48)O3 or (x)PMN–(1 − x)PZT when x = 0.0, 0.1, 0.3, 0.5, 0.7, 0.9, and 1.0 are prepared by a conventional mixed-oxide method. Phase formation behaviour and microstructural features of these ceramics are studied by x-ray diffraction and scanning electron microscopy methods, respectively. The dielectric properties under the uniaxial stress of the PMN–PZT ceramics are observed at stress levels up to 5 MPa using a uniaxial compressometer. It is found that with increasing applied stress the dielectric constant of the PZT-rich compositions increases slightly, while that of the PMN-rich compositions decreases. On the other hand, the dielectric loss tangent for most of the compositions first rises and then drops with increasing applied stress.

Gyrotron-traveling wave-tube circuits based on lossy ceramics

The gyro-traveling wave tube (gyro-TWT) is a microwave amplifier with simultaneous high power, high frequency, and broad bandwidth capabilities. Techniques for providing a controlled loading of the TE/sub 01/ cylindrical-guide operating mode of a 35 GHz gyro-TWT using monolithic, lossy ceramic structures are presented. The loading scheme, which also suppresses spurious backward-wave oscillations in the TE/sub 11/, TE/sub 21/, and TE/sub 02/ modes, is based on a sequence of alternating ceramic cylindrical shells and metal rings to form the electron beam tunnel. Design techniques for achieving optimal performance and methods for reducing the sensitivity to temperature-induced variations in ceramic dielectric properties are presented.

Preparation and microwave characterization of PbTiO3 ceramic andpowder

The ceramics of PbTiO3 and its powders have been prepared bya sol-gel process. The constitution of its phase and structure wasexamined by x-ray diffraction and Fourier transform infrared spectroscopy.Characterization studies were performed to determine the effects ofparticle size and degree of tetragonality. The dielectric properties ofceramics and powders of PbTiO3, composited with paraffin, were measuredfrom 1 MHz to 18 GHz. All samples exhibited evidence of relaxationphenomena in their dielectric spectra. The relaxation frequenciesincreased with decreasing particle size.

Effects of ceramic processing parameters on the microstructure and dielectric properties of (Ba1-xCax)(Ti0.99-y, ZryMn0.01)O3 sintered in a reducing atmosphere

The effect of A/B ratio, sintering temperature, and oxygen partial pressure on microstructure and ceramic dielectric properties of 1 mol % MnO2 doped (Ba,Ca)(Ti,Zr,)O3 sintered in a reducing atmosphere were investigated. Microstructure is found to be closely related to processing parameters. With decreasing A/B ratio, decreasing oxygen partial pressure and increasing sintering temperature, grain growth is enhanced. Concurrent with the grain size reduction, the crystal structure transformed from tetragonal to pseudocubic at room temperature and the dielectric constant, the dissipation factor and Curie point all decreased. However, the effects of grain size give a marked discrepancy on breakdown. The effect of A/B ratio and sintering temperature both suggest that breakdown voltage is decreased with increasing grain size. However, the breakdown voltage in relation to grain size by changing the oxygen partial pressure seems to show no significant difference.

Phase analysis and dielectric properties of ceramics in PbO-MgO-ZnO-Nb2O5 system: A comparative study of materials obtained by ceramic and molten salt synthesis routes

Compositions of the type 3PbO-MgO/ZnO-Nb2O5 were synthesized by the ceramic route at 1000°C and sintered at 1200°C. Powder X-ray diffraction studies of the 1000°C heated products show the presence of the cubic pyrochlore and the columbite (Mg/ZnNb2O6) type phase in the ratio of 3 : 1 for all possible combinations of MgO and ZnO. Further heating at 1200°C led to a decrease in the cubic pyrochlore phase and an increase in the columbite phase by around 10%. Compacted pellets sintered further showed the appearance of the perovskite phase. Similar compositions synthesized using the KCl-NaCl molten salt method at 900°C for 6 h gave a significant amount of the cubic perovskite related phase of the type Pb(Mg/Zn)1/3Nb2/3O3 for all compositions containing MgO. The amount of the perovskite phase was nearly 55% for the Mg rich compositions and decreased with increase in Zn content, the pure Zn composition yielding mainly the cubic pyrochlore phase. On sintering these phases at 1000°C the perovskite phase content decreased. The dielectric constant of the composite materials formed by the ceramic route was in the region of 14 to 20 and varied little with frequency. The composites obtained by the molten salt method, however, showed much larger dielectric constants in the region 40–150 at 500 kHz for various compositions. The dielectric loss tangent of these composites were lower by an order (0.005–0.03 at 500 kHz) compared to the ceramic route.

Preparation and dielectric properties of ceramics in the SrBi 2(Ta 1− xNb x) 2O 9 solid solution system

Ceramics in the SrBi 2(Ta 1− x Nb x ) 2O 9 solid solution system were prepared by a solid state reaction process, and the dielectric characteristics were determined together with the microstructures. An increased dielectric constant and improved temperature coefficient of permittivity were achieved in this solid solution system, while the dielectric loss remained at the same level as that of SrBi 2Ta 2O 9.

Optical and Electrical Properties of Microwave Dielectric Thin Films

The dielectric properties of ceramics and thin films of Bi2(Zn1/3Nb2/3)2O7, BiZN, materials were examined in low frequency (1 kHz – 3 MHz), microwave frequency (0.5 – 10 GHz) and optical frequency (4×1011–7×1011 kHz) regimes. The dielectric properties in the optical frequency regime, (εr)op\\cong4.9–6.5, are insensitive to the material characteristics, implying that only the electronic polarization is functioning in this frequency regime. By contrast, the properties in the low frequency regime, (εr)lf\\cong160–300, are markedly influenced by the synthesis parameters, indicating that the dielectric properties in this regime are predominated by the ionic polarization process. Therefore, these properties vary with the crystallinity of the materials.

Microstructural and dielectric properties of ceramics based on tetragonal tungsten bronze

Studied ceramics have been sintered from mixtures of powders including a tetragonal tungsten bronze (TTB) phase K0.2Sr0.4NbO3 (KSN), two perovskite phases, Pb(Mg1/3Nb2/3)O3 (PMN) and Pb(Fe½Nb½)O3 (PFN), and a lithium salt in a small amount. We studied the whole relaxor/TTB composition diagram. We had shown in previous studies that these ceramics could exhibit either type I or type II dielectric behaviors, depending on both the composition and the sintering schedule. We present here our last results in the perovskite side of the diagram with regard to a fine analysis of such ceramics sintered at 1240°C in an oxygen flow. In particular, results obtained with X-ray Photoemission Spectroscopy (XPS), Scanning Electron Microscopy (SEM) associated with EDS analysis and X-ray diffraction have been correlated with 1 kHz dielectric measurements from-50°C to 150°C and ferroelectric characterizations.

Barium titanate powders synthesis from solvothermal reaction and supercritical treatment

A new semi-continuous process is reported for BaTiO 3 powders synthesis under high pressure (10 MPa). The first step is the hydrolysis of the alkoxide BaTi(O– iC 3H 7) 6 in isopropanol at temperatures between 100°C and 200°C in tubular flow reactor. The second one is a thermal treatment of the formed solids, under the supercritical state of the solvent. Particle size of the dried crystalline recovered powders is around 10 nm. Powder sintering and ceramic dielectric properties have been tested.