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Showing papers on "Dielectric loss published in 2004"


Journal ArticleDOI
TL;DR: In this paper, a study of the complex permittivity in bismuth titanate was conducted to reveal the nature of an anomaly in the real part of the permittivities, which occurs below the Curie temperature.
Abstract: A study of the complex permittivity in bismuth titanate was conducted to reveal the nature of an anomaly in the real part of the permittivity, which occurs below the Curie temperature. This anomaly is frequency dependent and is caused by a combination of two relaxation phenomena that appear in the imaginary part of the permittivity. One of the relaxations showed classic characteristics of an ion-jump process. Niobium doping suppressed this relaxation and eliminated the nonferroelectric anomaly in permittivity. Niobium is proposed to affect the ion-jump relaxation through a decrease in the concentration and possibly the mobility of oxygen vacancies.

279 citations


Journal ArticleDOI
TL;DR: In this paper, the influence of film thickness on the material properties of aluminum nitride (AlN) thin films deposited on Pt(111) electrodes has been investigated experimentally by means of x-ray diffraction, dielectric response, atomic force microscopy, interferometry measurement of effective d33, and residual stress measurement.
Abstract: The influence of film thickness on the material properties of aluminum nitride (AlN) thin films deposited on Pt(111) electrodes has been investigated experimentally by means of x-ray diffraction, dielectric response, atomic force microscopy, interferometry measurement of effective d33, and residual stress measurement. The thickness was varied between 35 nm and 2 μm. Full width at mid-height of the rocking curve decreased from 2.60 to 1.14°, rms roughness increased from 3.8 to 18.6 A, the effective d33, namely d33,f, from 2.75 to 5.15 pm/V. The permittivity eAlN was stable at 10.2, whereas the dielectric losses decreased from 1% to 0.1%. The breakdown electric field under dc voltages varied between 4.0 and 5.5 MV/cm.

276 citations


Journal ArticleDOI
TL;DR: A technique developed for estimating the complex dielectric constant (CDC) for both the BSW and the free soil water as separate water constituents present in moist soil and a method for deducing the Debye relaxation parameters for both types of soil water was proposed.
Abstract: This paper introduces a new soil dielectric model in the microwave band offering variation over a wide range of soil moisture, texture, mineral content, and wave frequency. The soil dielectric models commonly used in microwave remote sensing algorithms rarely apply intrinsic bound soil water (BSW) dielectric properties. However, models incorporating these properties could offer additional applicability and accuracy. This paper describes a technique developed for estimating the complex dielectric constant (CDC) for both the BSW and the free soil water (FSW) as separate water constituents present in moist soil. For this purpose, it has been shown that there exist two specific soil moisture regions where alteration in soil dielectric property is generated, exclusively, by either BSW or FSW increments, with their CDCs being constant values. The CDCs of the BSW and FSW are derived through straight line fitting with the help of a measured soil complex refractive index (CRI) as a function of moisture. The term CRI is understood here as a square root of the CDC. In order to distinguish between the two moisture regions, the maximum bound water fraction (MBWF) parameter was introduced, which also can be obtained through straight line fitting, using measured CRIs as a function of moisture over both specific moisture regions. Thus, obtained fittings are known in the literature as the refractive mixing dielectric model (RMDM). Finally, a method for deducing the Debye relaxation parameters for both types of soil water was proposed, with their CDCs being input parameters. It was shown that the soil water CDCs measured only at two frequencies are sufficient for deriving the Debye relaxation parameters. A set of equations representing the RMDM, the Debye formula, and the formulas proposed for deriving the Debye relaxation parameters is designated as the generalized refractive mixing dielectric model (GRMDM). In contrast to all previously known soil dielectric models, the GRMDM allows for CDC prediction beyond the frequency range where the initial soil CDC data are acquired.

272 citations


Journal ArticleDOI
TL;DR: By combining the high-dielectric copper phthalocyanine oligomer (PolyCuPc) and conductive polyanline (PANI) within polyurethane (PU) matrix, an all-organic three-component dielectric-percolative composite as mentioned in this paper was demonstrated.
Abstract: By combining the high-dielectric copper phthalocyanine oligomer (PolyCuPc) and conductive polyanline (PANI) within polyurethane (PU) matrix an all-organic three-component dielectric-percolative composite with high dielectric constant is demonstrated. In this three-component composite system, the high-dielectric-constant PolyCuPc particulates enhance the dielectric constant of the PU matrix and this combined two-component dielectric matrix in turn serves as the high-dielectric-constant host for the PANI to realize percolative phenomenon and further enhance the dielectric response. As a result, an electromechanical strain of 9.3% and elastic energy density of 0.4 J/cm(3) under an electric field of 20 V/mum can be induced.

204 citations


Journal ArticleDOI
TL;DR: In this article, the dielectric property complemented by the mechanical measurement (internal friction) in the doped Bi4Ti3O12 [Bi4−xLaxTi3 O12] and Bi4−y/3Ti3−yNbyO12] was systematically investigated from room temperature to 350°C.
Abstract: The dielectric property complemented by the mechanical measurement (internal friction) in the doped Bi4Ti3O12 [Bi4−xLaxTi3O12 (x=0.5,0.75,1) and Bi4−y/3Ti3−yNbyO12 (y=0.015,0.03,0.06)] was systematically investigated from room temperature to 350 °C. In the plot of dielectric loss versus temperature for Bi4Ti3O12 (BiT), a relaxation peak was confirmed to be associated with the motion of the oxygen vacancy. It is found that the La doping at site A is in favor of improvement of the fatigue property, in contrast, the Nb doping at site B can mainly enhance the remanent polarization. Appropriate La doping at site A of perovskite-type unit in BiT enhances the chemical stability of oxygen vacancy by improving the height of the potential barrier for hopping and enhances the mobility of domain by the changing of domain structures. While the Nb doping at site B could induce the distortion of oxygen octahedral and reduce the oxygen vacancy concentration by a compensating effect so that it results in an enhancement of...

179 citations


Journal ArticleDOI
TL;DR: In this paper, the O2 partial pressure during deposition was adjusted to vary the excess Ti incorporation into the films, which influenced the low-field permittivity, loss tangent, and dielectric strength.
Abstract: Large variations in the permittivity of rf magnetron sputtered thin-film barium strontium titanate have been obtained through optimization of growth conditions for maximum dielectric strength and zero-field permittivity in a parallel-plate capacitor structure. Using nominal target compositions of Ba0.5Sr0.5TiO3, and Pt electrodes on c-plane sapphire substrates, adjustment of the O2 partial pressure during deposition was used to vary the excess Ti incorporation into the films, which influenced the low-field permittivity, loss tangent, and dielectric strength. By balancing the benefits of a high permittivity with dielectric strength and loss, we have produced films capable of sustaining short-duration fields greater than 4MV∕cm with over 13:1 (>90%) change in dielectric constant, and greater than 5:1 tunability in bias fields under 1MV∕cm.

175 citations


Journal ArticleDOI
TL;DR: In this paper, the microstructure, dielectric and piezoelectric properties of (Bi 1/2 Na 1/ 2 )TiO 3 -6BaTiO3 doped with Nb 5+, Co 3+ or La 3+ were studied for a candidate as lead-free, lead free, lead-resistant, and lead free ceramics.

172 citations


Journal ArticleDOI
TL;DR: In this article, the microwave dielectric properties of ZnAl2O4 spinels were investigated and their properties were tailored by adding different mole fractions of TiO2, which can be exploited for microwave substrate applications.
Abstract: The microwave dielectric properties of ZnAl2O4 spinels were investigated and their properties were tailored by adding different mole fractions of TiO2. The samples were synthesized using the mixed oxide route. The phase purity and crystal structure were identified using X-ray diffraction technique. The sintered specimens were characterized in the microwave frequency range (3-13 GHz). The ZnAl2O4 ceramics exhibited interesting dielectric properties (dielectric constant ( $\varepsilon_{r}) = 8.5$ , unloaded quality factor (Q u ) = 4590 at 12.27 GHz and temperature coefficient of resonant frequency ( $\tau_{f}) = -79$ ppm/ $^{\circ}$ C). Addition of TiO2 into the spinel improved its properties and the $\tau_{f}$ approached zero for 0.83ZnAl2O4-0.17TiO2. This temperature compensated composition has excellent microwave dielectric properties ( $\varepsilon _{r} = 12.67$ , Q u = 9950 at 10.075 GHz) which can be exploited for microwave substrate applications.

172 citations


Journal ArticleDOI
TL;DR: In this article, the dielectric properties of Ba0.8Sr0.2TiO3 ceramics doped with Mg from 0.5 to 10 mol'% have been investigated systematically.
Abstract: The dielectric properties of Ba0.8Sr0.2TiO3 ceramics doped with Mg from 0.5 to 10 mol % have been investigated systematically. Two effects of Mg doping on the dielectric properties of the Ba0.8Sr0.2TiO3 ceramics have been observed. At low Mg doping concentrations (<2 mol %), Mg mainly acts as an acceptor dopant to replace Ti in the B site of ABO3 perovskite structure, leading to a shift of Curie point (TC) to lower temperatures and a diffused phase transition. The permittivity and dielectric loss are suppressed gradually as the Mg content increases and the grain size decreases drastically. At higher Mg doping concentrations (⩾2 mol %), further suppression of permittivity and losses without further TC shift are observed, which indicates a “composite” mixing effect. The grain size remains almost constant. The solubility limit of Mg in the Ba0.8Sr0.2TiO3 appears to be ∼2 mol %.

171 citations


Journal ArticleDOI
TL;DR: In this paper, a broad phonon spectra and the frequency independent dielectric losses at low temperatures are compatible with the existence of nanoscopic polar regions and disorder to liquid He temperatures similar to relaxor ferroelectrics.
Abstract: Infrared reflectivity, time-domain terahertz transmission, high-frequency dielectric measurements and Raman spectroscopy of Na0.5Bi0.5TiO3 complex ferroelectric perovskite were performed in a broad temperature range. The results were analysed considering the macroscopic symmetry as well as symmetry resulting from local Na–Bi ordering in all three known phases. An overdamped infrared soft mode was revealed in the THz range which, together with central-mode type dispersion in the GHz range, contribute to the strong and broad dielectric permittivity maximum around 600 K. Anharmonic Bi and/or Na vibrations and local hopping, respectively, are suggested to be the main origins of these excitations. The broad phonon spectra and the frequency independent dielectric losses at low temperatures are compatible with the existence of nanoscopic polar regions and disorder to liquid He temperatures similar to relaxor ferroelectrics.

163 citations


Journal ArticleDOI
TL;DR: The structural and electrical properties of magnesium-substituted nickel ferrite having the general formula of Ni1−xMgxFe2O4 have been studied as a function of magnesium ion concentration.

Journal ArticleDOI
TL;DR: In this article, the authors investigated the dielectric properties of three ceramic/epoxy composites, including self-synthesized BaTiO 3 and commercial Pb(Mg 1/3 Nb 2/3 )O 3.

01 Jan 2004
TL;DR: The structural and electrical properties of magnesium-substituted nickel ferrite having the general formula of======Ni1xMgxFe2O4 (x=0, 0.6, 09) has been studied as a function of magnesium ion concentration as discussed by the authors.
Abstract: The structural and electrical properties of magnesium-substituted nickel ferrite having the general formula of Ni1xMgxFe2O4 (x=0, 0.3, 0.6, 0.9) has been studied as a function of magnesium ion concentration. The materials have been prepared by citrate gel process using metal nitrate salts as a cation precursors and citric acid as gelating agent. The powder X-ray diffraction pattern confirms fcc structure for the synthesized compound. The variation of lattice parameter and the tetrahedral radius increases with increase in Mg2+ ion concentration. The AC electrical parameters such as dielectric constant (e0) and loss tangent (tan d) for all the systems have been studied as a function of frequency in the range 50 Hz to 10 kHz at room temperature. A maximum DC electrical conductivity of 3.3 S cm-1 was obtained at a temperature of 1000C and a AC electrical conductivity of 10.94106at 10 kHz was observed in the composition x ¼ 0:6 i.e. for Ni0.4Mg0.6Fe2O4 compound which may be due to the maximum Fe2+ concentration in the octahedral sites. The dielectric constant follows the Maxwell’s–Wagner interfacial polarization and the relaxation peaks were observed in the dielectric loss properties. The FTIR spectra show the characteristic peaks of ferrite sample. The morphological features were studied using scanning electron microscope.

Journal ArticleDOI
TL;DR: In this paper, the dielectric properties of mashed potatoes relevant to microwave and radiofrequency (RF) pasteuriza- tion and sterilization processes were measured over 1 to 1800 MHz and 20 °C to 120 °C.
Abstract: Dielectric properties of mashed potatoes relevant to microwave and radio-frequency (RF) pasteuriza- tion and sterilization processes were measured over 1 to 1800 MHz and 20 °C to 120 °C. Effects of moisture content (81.6% to 87.8%, wb) and salt content (0.8% to 2.8%, wb) were investigated. Dielectric loss factors and constants decreased with frequency. Dielectric loss factors increased with temperature and salt content, but dielectric con- stants were not significantly affected. Ionic conductivity played a dominant role at low frequencies. Power penetra- tion depth increased with moisture content and decreased with temperature, frequency, and salt content. Regression

Journal ArticleDOI
TL;DR: In this paper, the specular absorber method is used in determining the reflection loss (R L ) of the absorber at different thicknesses, which would provide a feasible means of determining the frequency and thickness configuration for minimum reflection from the surface of an absorber.

Journal ArticleDOI
TL;DR: In this article, single-crystal barium titanate capacitors with thickness down to 75nm were measured and the dielectric response typical of large single crystals, rather than conventional thin films.
Abstract: Measurements on 'free-standing' single-crystal barium titanate capacitors with thickness down to 75 nm show a dielectric response typical of large single crystals, rather than conventional thin films. There is a notable absence of any broadening or temperature shift of the dielectric peak or loss tangent. Peak dielectric constants of are observed, and Curie–Weiss analysis demonstrates first order transformation behaviour. This is in dramatic contrast to results on conventionally deposited thin film capacitor heterostructures, which show large dielectric peak broadening and temperature shifts (e.g. Parker et al 2002 Appl. Phys. Lett. 81 340), as well as an apparent change in the nature of the paraelectric–ferroelectric transition from first to second order. Our data are compatible with a recent model by Bratkovsky and Levanyuk (2004 Preprint cond-mat/0402100), which attributes dielectric peak broadening to gradient terms that will exist in any thin film capacitor heterostructure. The observed recovery of first order transformation behaviour is consistent with the absence of significant substrate clamping in our experiment, as modelled by Pertsev et al (1998 Phys. Rev. Lett. 80 1988), and illustrates that the second order behaviour seen in conventionally deposited thin films cannot be attributed to the effects of reduced dimensionality in the system, nor to the influence of an intrinsic universal interfacial capacitance associated with the electrode–ferroelectric interface.

Journal ArticleDOI
TL;DR: The elastic, piezoelectric, and dielectric constants of 0.58Pb(Mg1/3Nb2/3)O3-0.42PbTiO3 were determined experimentally using combined resonance and ultrasonic methods as mentioned in this paper.
Abstract: The elastic, piezoelectric, and dielectric constants of 0.58Pb(Mg1/3Nb2/3)O3-0.42PbTiO3 (PMN-42%PT) were determined experimentally using combined resonance and ultrasonic methods. At room temperature the PMN-42%PT single crystal has tetragonal symmetry. The measured piezoelectric constant d33 is ∼260×10−12 C/N. The electromechanical coefficients k15, k31, k33, and kt are 0.80, 0.39, 0.78, and 0.62, respectively. From the measured material constants the orientational dependence of phase velocities and electromechanical coupling coefficients was calculated. The results showed the tetragonal crystal exhibits isotropy in the X-Y plane and k15, k33, and kt reach their maxima in [001].

Journal ArticleDOI
TL;DR: In this paper, the effects of Sm3+ substitution on the dielectric loss and the mean mean square error (MSE) of Ca1-xSm2x/3TiO3 ceramics were investigated as a function of the amount of Sm 3+ substitution.
Abstract: Microwave dielectric properties of Ca1-xSm2x/3TiO3 ceramics were investigated as a function of the amount of Sm3+ substitution (0.0 ≤x≤ 0.8). The structure was changed from orthorhombic perovskite at x= 0.0 to tetragonal at x= 0.6. As the calcium vacancy concentration increased with increased Sm3+ substitution, the unloaded Q value (similar/congruent 1/tan delta) increased up to the solid-solution limit at x= 0.6 and then decreased because of formation of the secondary phase Sm2Ti2O7. The dielectric constant decreased with increased Sm3+ substitution. The effects of Sm3+ substitution on dielectric loss and dielectric constant of the specimens were analyzed by the infrared reflectivity spectra in the range 50–4000 cm−1, which were evaluated using the Kramers-Kronig analysis and classical oscillator model. The correlations among dielectric constant, dielectric loss, and dispersion parameters were studied.

Journal ArticleDOI
TL;DR: In this paper, the dielectric properties of BaTiO3-based ferroelectric-relaxors were investigated for microwave (MW) tunable applications, and the relative potential for microwave tunability was assessed by the figure of merit (K) defined as K = epsilon(ro) -epilon(rv)/epsilon (ro) (.) tan delta(o), (where er and srv are the relative permittivity at zero and 20 kV cm(-1) at 10 kHz and tan delta (o) is the loss
Abstract: The dielectric properties of BaTi0.09Ga0.05Nb0.05O3 (BTGN) and Ba0.60Sr0.40TiO3 (BST) ceramics prepared by the conventional solid-state route have been investigated. Their relative potential for microwave (MW) tunable applications was assessed by the figure of merit (K) defined as K = epsilon(ro) - epsilon(rv)/epsilon(ro) (.) tan delta(o), (where er and srv are the relative permittivity at zero and 20 kV cm(-1) at 10 kHz and tan delta(o) is the loss at 10 kHz or similar to1 GHz without DC bias). Fine-grained (similar to2-3 mum) BTGN ceramics fired at 1500degreesC in air exhibit dielectric behavior characteristic of relaxor-type materials, with relative permittivity, epsilon(r), decreasing from similar to3082 to similar to2116 and dielectric loss, tan delta, increasing from 0.0035 to 0.0542 at 10 kHz and similar to1 GHz, respectively. In contrast, large-grained (20-100 mum) BST ceramics exhibit a frequency independent epsilon(r) of similar to5000 and show little variation of tan delta with frequency (0.0012 at 10 kHz and similar to0.0048 at 0.6 GHz). At 10 kHz, K-BTGN = 91 and K-BST = 367, whereas at MW frequencies K-BTGN = 6 and K-BST = 92. The large decrease in K-BTGN at MW frequencies is attributed to a substantial increase of tan delta. The applicability of another relaxor-type BaTiO3-based ceramic, Ba(Ti0.70Zr0.30)O-3, which was recently proposed as promising material for tunable MW applications, is also discussed. It is demonstrated that BaTiO3-based ferroelectric-relaxors may exhibit good tunable characteristics at 10 kHz; however, they are not competitive with BST for high K-factor MW applications.

Journal ArticleDOI
TL;DR: In this article, the dielectric properties of Al2O3 doped Ba 0.5Sr0.5TiO3 (BST) thin films were determined with a nondestructive dual resonator near 7.7 GHz.
Abstract: Al2O3 doped Ba0.5Sr0.5TiO3 (BST) thin films, with different Al2O3 contents, were deposited on (100) LaAlO3 substrates by the pulsed laser deposition technique to develop agile thin films for tunable microwave device applications. The dielectric properties of Al2O3 doped BST films were determined with a nondestructive dual resonator near 7.7 GHz. We demonstrated that the Al2O3 doping plays a significant role in improving the dielectric properties of BST thin films. The Al2O3 doping successfully reduced the dielectric loss tangent (tan δ) from 0.03 (pure BST) to 0.011 (Al2O3 doped BST). Reduction in the loss tangent also leads to reduction in the dielectric constant and dielectric tunability. Our results showed that the BSTA4 film remains tunability=15.9%, which is sufficient for tunable microwave devices applications. Consequently, the Al2O3 doping improved the figure of merit (K) for the BST films from K=7.33 (pure BST) to K=14.45 (Al2O3 doped BST).

Journal ArticleDOI
TL;DR: In this paper, the authors discussed the enhanced electrostriction and dielectric constant in an all-polymer percolative composite consisting of poly(vinylidene fluoride-trifluoroethylenechlorotrifluorosethylene) [P(VDF-TrFE-CTFE)] terpolymer matrix and polyaniline (PANI) conductive particles.
Abstract: In this letter, we discuss the enhanced electrostriction and dielectric constant in an all-polymer percolative composite consisting of poly(vinylidene fluoride-trifluoroethylenechlorotrifluoroethylene) [P(VDF–TrFE–CTFE)] terpolymer matrix and polyaniline (PANI) conductive particles. Using a self-consistent approach, we calculate the dielectric constant and dielectric loss tangent of the composite in excellent agreement with experiments, and demonstrate that the electrostriction enhancement is due to the electric field fluctuation in P(VDF–TrFE–CTFE) matrix, which becomes dominant when the dielectric constant of the second phase is much larger than that of the matrix. The inhomogeneous field distribution in the matrix has also been used to estimate the breakdown field of the composite, which agrees well with experimental measurement. The study could be used to design and optimize electrostrictive composites with optimal electromechanical properties.

Journal ArticleDOI
TL;DR: Capacitance and dissipation factor values of polymethyl methacrylate-co-poly 4vinyl pyridine N -oxide (PMMA-CO-P4VPNO) were measured in the frequency range 0.01-100 kHz and temperature range 300-410 K as discussed by the authors.

Journal ArticleDOI
TL;DR: In this paper, an electric circuit model that relates the sensor frequency to the permittivity of the medium and that is able to correct for dielectric losses due to ionic conductivity and relaxation is presented.
Abstract: Capacitance probe sensors are an attractive electromagnetic technique for estimating soil water content. There is concern, however, about the influence of soil salinity and soil temperature on the sensors. We present an electric circuit model that relates the sensor frequency to the permittivity of the medium and that is able to correct for dielectric losses due to ionic conductivity and relaxation. The circuit inductance L is optimized using sensor readings in a modified setup where ceramic capacitors replace the sensor's capacitance plates. The three other parameters in the model are optimized using sensor readings in a range of nonconductive media with different permittivities. The geometric factor for the plastic access tube gp is higher than the geometric factor for the medium gm, indicating that most of the electromagnetic field does not go beyond the access tube. The effect of ionic conductivity on the sensor readings is assessed by mixing salts in three of the media. The influence is profound. The sensor frequency decreases with increasing conductivity. The effect is most pronounced for the medium with the lowest permittivity. The circuit model is able to correct for the conductivity effect on the sensors. However, as the dielectric losses increase, the frequency becomes relatively insensitive to permittivity and small inaccuracies in the measured frequency or in the sensor constants result in large errors in the calculated permittivity. Calibration of the capacitance sensors can be simplified by fixing two of the constants and calculating the other two using sensor readings in air and water.

Journal ArticleDOI
TL;DR: In this article, a basic characterization of several low-temperature-sintered calcium silicates, germanates and tellurates was performed to evaluate their potential as glass-free low-permittivity substrate LTCC materials.
Abstract: To reduce the complexity of LTCC systems, and so accelerate the development of LTCC tapes with new functionalities, it is necessary to reduce the number of phases within a particular tape. This can best be done by using glass-free single-phase ceramic systems. We performed a basic characterization of several low-temperature-sintered calcium silicates, germanates and tellurates in order to evaluate their potential as glass-free low-permittivity substrate LTCC materials. Special attention was focused on their microwave and 1 MHz dielectric properties, their sintering behavior and their compatibility with Ag. Two Ca-germanates, which were found to be the most interesting for LTCC applications exhibit a permittivity of ∼10 and low dielectric losses; however, the temperature dependence of permittivity and the sintering temperature must be further reduced. For CaGeO3 the temperature dependence of permittivity was fully suppressed by the addition of 10 mol% of CaTiO3.

Journal ArticleDOI
TL;DR: In this paper, a series of polycrystalline spinel ferrite with composition CoAl x Fe 2− x O 4, as a function of frequency and temperature, were studied in terms of quantum mechanical tunneling and small polaron tunneling models.

Journal ArticleDOI
TL;DR: In this article, the effect of the Ba/Ti ratio on microstructure, dielectric/ferroelectric properties, and domain width was studied using optical microscopy, ǫ(T) curves, D-E hysteresis, and transmission electron microscopy.
Abstract: The effect of the Ba/Ti ratio on microstructure, dielectric/ferroelectric properties, and domain width was studied using optical microscopy, ɛ(T) curves, D–E hysteresis, and transmission electron microscopy. Although Ti-excess samples showed abnormal grain growth and a decrease of room-temperature permittivity due to a liquid phase at grain boundaries, its ferroelectric properties were similar to those of stoichiometric BaTiO3 ceramics. However, in Ba-excess samples, an increase of permittivity and ferroelectric properties different from those of stoichiometry were found. Changes in domain width and ferroelectric transition behavior indicated that the variation of dielectric properties was related to the internal stress. It is proposed that this internal stress originated from differences in the thermal expansion coefficient between the matrix and the second phase.

Journal ArticleDOI
TL;DR: In this paper, the temperature and frequency dependence of the dielectric losses and tunability of both materials have been compared, and the bias dependent permittivity has been shown to have a hysteresis effect in both materials in the whole investigated temperature range.
Abstract: Thick films have been investigated for application in frequency and phase agile microwave devices. Since Ba0.6Sr0.4TiO3 (BST) and BaZr0.3Ti0.7O3 (BZT) bulk ceramics exhibit high tunability ( τ= e 0 −e E max e 0 ) near room temperature, both compositions have been chosen for preparation of screen printed thick films. Low frequency dielectric properties have been characterized using metal-insulator-metal capacitor structures in a temperature range of −120 °C to +160 °C. Measurements of the bias dependent permittivity show a hysteresis effect in both materials in the whole investigated temperature range. BZT thick films exhibit a more diffuse phase transition than BST and therefore a lower temperature dependence. Permittivity, dielectric loss and tunability have also been determined at microwave frequencies from 4 to 90 GHz. Temperature and frequency dependence of the dielectric losses and tunability of both materials have been compared.

Journal ArticleDOI
TL;DR: In this paper, a dielectric loss peak with the relaxation-type characteristic was observed at about 370K at 100Hz frequency, which was confirmed to be associated with the migration of oxygen vacancies inside ceramics.
Abstract: Pure Bi4Ti3O12 ceramics were prepared using the conventional solid-state reaction method and their dielectric properties were investigated. A dielectric loss peak with the relaxation-type characteristic was observed at about 370K at 100Hz frequency. This peak was confirmed to be associated with the migration of oxygen vacancies inside ceramics. The Cole–Cole fitting to this peak reveals a strong correlation among oxygen vacancies and this strong correlation is considered to commonly exist among oxygen vacancies in ferroelectrics. Therefore, the migration of oxygen vacancies in ferroelectric materials would demonstrate a collective behavior instead of an individual one due to this strong correlation. Furthermore, this correlation is in proportion to the concentration and in inverse proportion to the activation energy of oxygen vacancies. These results could be helpful to the understanding of the fatigue mechanisms in ferroelectric materials.

Proceedings ArticleDOI
13 Dec 2004
TL;DR: In this article, the results of dielectric spectroscopy and space charge measurements on epoxy resin filled with 10% w/w micro-and nano-sized particles of TiO/sub 2, Al/sub 3/O/Sub 2/ and ZnO were presented.
Abstract: This work presents results of dielectric spectroscopy and space charge (PEA) measurements on epoxy resin filled with 10% w/w micro- and nano- sized particles of TiO/sub 2/, Al/sub 3/O/sub 2/ and ZnO The results appear to show that the material from which the nano-particle is made is not highly significant in influencing these results The results support the proposition that the dielectric properties of such nano-filled composites are controlled by Stern-Gouy-Chapman layers ("interaction zones") around the particles

Journal ArticleDOI
TL;DR: In this paper, high-dielectric-constant CaCu3Ti4O12 (CCTO) thin films were prepared on Pt/Ti/SiO2/Si(100) substrates by pulsed-laser deposition (PLD).
Abstract: High-dielectric-constant CaCu3Ti4O12 (CCTO) thin films were prepared on Pt/Ti/SiO2/Si(100) substrates by pulsed-laser deposition (PLD) The 480 nm thick polycrystalline films have preferred orientation and show obvious crystallization on the surface The temperature dependence of dielectric constant and loss of the Pt/CCTO/Pt capacitors is comparable with that obtained in the epitaxial CCTO films grown on oxides substrates We found that the dielectric properties are very sensitive to the postannealing atmosphere and temperature Postannealing in nitrogen atmosphere produces larger low-frequency dielectric relaxation as the annealing temperature increases, while annealing in oxygen atmosphere at high temperature suppresses the relaxation and decreases the dielectric constant of the thin films Such results are attributed to the presence of insulating grain-boundary barrier layers