Dielectric Constant Curve Research Articles

Micromachined microstrip patch antenna with controlled mutual coupling and surface waves

Silicon micromachining has been used to demonstrate the possibility of building high performance microwave and millimeter-wave antennas. To suppress higher order substrate modes and increase the bandwidth of a patch antenna, silicon substrate has been used and material has been selectively removed under the patch area. In addition, the effect of etched grooves around a patch element has been studied for performance improvement, it has been shown that micromachined substrate structure can effectively suppress unwanted surface wave modes resulting in improved radiation efficiency. Moreover, effective dielectric constant curves for the shielded micromachined substrates are provided for accurate design of patch antennas. We have demonstrated that mutual coupling between the radiating patch elements due to surface waves can be controlled using various micromachined substrate configurations.

Temperature dependence of elastic and dielectric properties of (Bi2O3)1 − x(CuO)x oxide glasses

Oxide glasses with the general formula (Bi2O3)1 - x(CuO)x have been prepared by quick quenching technique. Their longitudinal and shear elastic moduli have been determined by measuring the corresponding ultrasonic wave velocities between 300 and 470 K, which are well below the glass transition temperature of this system. Temperature variation of ultrasonic velocity and attenuation exhibit anomalies around 435 K in glasses with x ≥ 0.3. A nonlinear behaviour is also reflected in the CuO concentration dependent dielectric constant curve around x = 0.3. These anomalies are interpreted in terms of a structural softening (or transformation) taking place in samples having CuO concentration above the critical value. The high dielectric constant of these glasses show very little increase with increase of temperature. Anomalies are also found in the temperature dependence of dielectric constant around 435 K. This behaviour is again considered to be associated with the softening of the glass network.

Composites of 0.9Pb(Mg1/3Nb2/3)O3-0.1PbTiO3 prepared by a sol-gel method: effect of atmosphere powders

Dielectric and electrical properties of relaxor ferroelectric 0.9PMN-0.1PT ceramics prepared by a sol-gel method were investigated as a function of PbZrO3 atmosphere powders. The proper amount of atmosphere powders led to better properties of dielectric constant, polarization, and strain by preventing PbO volatilization from ceramics. Excessive amount of atmosphere powder, however, resulted in aging characteristics such as decreases in dielectric constant and loss exhibiting saddle-shaped dielectric constant and loss vs. temperature curves. A propeller-shaped P-E hysteresis curve indicating aging characteristics was also observed when an excessive amount of atmosphere powder was used during sintering. The aging of ceramics caused by absorption of PbO into the ceramics resulted in decreased polarization and strain. These aging characteristics associated with defects by excessive PbO absorption could not be reversed even though the aged ceramics underwent a heat-treatment above the dielectric maximum temperature.

Diffuse phase transitions in the (PbxBa1-x)TiO3 system

Diffuse phase transitions were observed in the solid solution (PbxBa1-x)TiO3. By measuring the diffuseness of the paraelectric to ferroelectric transition as a function of composition in the solid solution (PbxBa1-x)TiO3 the average size of the ferroelectric nuclei may be determined. Dielectric constant versus temperature curves were measured over the temperature range where the ferroelectric transition occurs. From these curves, the diffuseness of the transition was determined. The size of the microregions (Kanzig regions), which are responsible for the diffuse behaviour, was estimated to be between 2.5 and 4.0 nm. These microregions are the ferroelectric nuclei and hence this allows the measurement of the ferroelectric nuclei size. © 1998 Kluwer Academic Publishers

Particle-size-induced diffuse phase transition in the fine-particle barium titanate porcelains

The effect of particle size on the ferroelectric transition in fine-particle porcelain produced by the inorganic sol - gel method was investigated. The phase transition was measured by dielectric properties, variable temperature x-ray diffraction, and differential scanning calorimetry (DSC). The tetragonal distortion of the unit cell decreases with size and vanishes at . The decreases gradually but the transition becomes diffuse with a decrease in the size of 0.081 to , below which there is no peak in the dielectric constant or DSC curve, though ferroelectric distortion (c/a) persists down to .

Dielectric study on Rb1−x(NH4)xH2PO4 powder system in ferroelectric phase boundary region

Complex dielectric constants have been measured on the microcrystalline Rb1−x(NH4)xH2PO4 powder system in the concentration range, 0.15 ≤ x ≤ 0.19. Rounded peak in the real dielectric constant curve and the glassy dispersion at low temperature are observed. Dielectric behavior is largely affected by small change of ammonium concentration x near the phase boundary. More asymmetric dielectric loss behaviors are shown in the ferroelectric phase boundary region than in the pure proton glass region. The broad and asymmetric loss dispersion curves observed for x = 0.15 are believed to be related with the remaining ferroelectric clusters.

Electron spectra calculations of Sn2P2S6 family crystals

The main parameters of energy zones dispersions in k-space calculations were carried out by the strong bond semiempirical method. On the basis of obtained results the imaginary part of dielectric constant curve is evaluated. Comparison of theoretical curve and experimental curve of the imaginary part of dielectric constant, which was obtained from reflection spectra by the use of Kramers-Kronig relations, shows good correlation. The simplification of calculation process is achieved by taking into account only one formula unit of Sn2P2S(Se)6.

Correlation of microwave and conduction calorimeter measurements on the hydration of cement

Ordinary Portland cement (OPC) is one of the most widely used construction materials. The hydration of cement involves very complicated chemical and physical processes. A better understanding of the mechanisms of hydration and microstructural development in the cement paste is important for improving its mechanical strength. There are two methods to study cement hydration in situ. One is conduction calorimetry [1] which is a well-established method, and the other is electrical measurement [2±7] which is not yet well established because of the dif®culty in directly relating the results of the electric measurement to the chemical and physical changes which occur during cement hydration. We have successfully developed a microwave technique to study the early hydration of OPC [8, 9], slag cement [8, 9], mortar [10] and OPC±high-alumina cement (HAC) blend [11] by measuring the change in dielectric constant during cement hydration. The heat evolution rate of OPC in the ®rst 30 h of hydration measured using conduction calorimetry is shown in Fig. 1. There is a large broad peak in the heat evolution rate curve, which corresponds to the chemical reactions that have occurred during cement hydration. At the same time the rate of change in dielectric constant, -da=dt, was monitored using the microwave technique and the result is also plotted in Fig. 1. It is interesting to see that the two curves have similar shapes and features, showing that there is a correlation between them for OPC. Since the traditional de®nition of the four periods of cement hydration is based on the heat evolution rate curve, if we can correlate the rate of change in dielectric constant curve with the heat evolution rate curve for any cement system, then we can apply this welldeveloped de®nition of the four periods of cement hydration to the rate of change in dielectric constant curve and hence provide an accurate interpretation of the dielectric constant results. This paves the way for a novel method in studying the cement hydration process in situ. In this letter, we explore the correlation between the results measured by microwave technique and the results measured by conduction calorimetry. Several samples, namely, OPC, OPC±HAC, OPC± silica fume, OPC±pulverized fuel ash (PFA) and slag cement, have been measured in this study (Fig. 2). We used the water cement ratio, w=c, of 0.4 and measured samples at a microwave frequency of 9.5 GHz. The details of the measurement have been given in [8±11]. For the OPC±30% HAC blend, there are two different peaks in the heat evolution

High-temperature X-ray structural, thermal and dielectric characteristics of ferroelectric Bi2VO5.5

The X-ray powder diffraction, dielectric and thermal studies of bismuth vanadate (Bi2VO5.5) ceramic have been carried out as a function of temperature (300–900 K). The hightemperature X-ray studies, supported by differential scanning calorimetry, clearly demonstrate that Bi2VO5.5 undergoes two major phase transitions at ∼730 and ∼835 K. It was found that the one at 730 K is associated with both the ferroelectric and the crystallographic transition, while at 835 K, Bi2VO5.5 undergoes only the crystallographic transition. Anomalies in both the dielectric constant and specific heat curves have been observed at ∼ 730 and ∼ 835 K. The total heat, ΔQ, and entropy, ΔS, associated with the transition at 730 K were found to be higher than those at 835 K.

Critical phenomena and phase transition in SOL-GEL derived ferroelectric PLZT thin films

Abstract Lanthanum doped Pb(Zr, Ti)O3 thin films have been fabricated by the solgel deposition technique. The small-signal dielectric constant ϵ has been investigated in the temperature range of 25°C to 550°C. The maximum value in the dielectric constant occurs at certain temperature for each particular composition. The apparent critical temperature is close to the Curie temperature reported in literature for the bulk material with similar composition. Lanthanum modified PbTiO3 and PbZrTiO3 have shown lower and broaden peaks. Ferroelectric hysteresis loops have been observed. The shape of the loop, the amplitude of the remnant polarization, and the coercive field significantly changed when the films were heated across the critical temperature that appeared in the dielectric constant curve. The critical temperature is assumed to be associated to the phase boundaries between the paraelectric-cubic and the ferroelectric tetragonal phases. A diffuse phase transition region were observed in lanthanum doped films.

Stress induced modifications in ferroelectric films

Stresses in rf sputtered polycrystalline BaTiO3 thin films, deposited at 300 to 700°C and at pressures from 0.1 to 100 Pa, on both Si and sapphire single crystals, are investigated. From the measured total stress values at room temperature, both the intrinsic stresses in the film and biaxial modulus of the film, Ef/(1–νf), are calculated. At lower deposition temperatures and pressures compressive intrinsic stresses are obtained, whereas at high deposition temperatures and pressures intrinsic stresses are tensile in nature. The biaxial modulus value approaches the single crystal value for films deposited at low pressures and decreases significantly with increasing deposition pressure. BaTiO3 films with high compressive stresses (≧ 400 MPa) show higher refractive indices, higher extinction coefficients, and lower optical band gaps compared to those for films with low compressive stresses (≈ 40 MPa). Furthermore, Curie point and coercive fields are increased, while remanant polarization decreases with increasing compressive stress. In addition, films in a state of high compression show a broad peak in the dielectric constant versus temperature curve which indicates a diffuse transition from ferroelectric to paraelectric state. By a judicious choice of deposition conditions, BaTiO3 films having low intrinsic stresses and properties close to those of single crystals are obtained. For example, some of the properties of BaTiO3 films deposited at 650°C and at 2 Pa pressure on silicon substrate are: n = 2.37 at 700 nm, Eg = 3.13 eV, Pr = 15.9 μC/cm2, Ec = 10.2kV/cm, Cure point 129°C, and σi = −47 MPa.

Influence of Stresses on the Properties of Ferroelectric BaTiO3 Thin Films

Stresses in rf sputtered polycrystalline thin films, deposited at 300°–700°C and at pressures from 0.1 to 100 Pa, on both Si and sapphire single crystals, were investigated. From the measured total stress values at room temperature, both the intrinsic stresses in the film and biaxial modulus of the film, , were calculated. At lower deposition temperatures and pressures compressive intrinsic stresses were obtained whereas, at high deposition temperatures and pressures intrinsic stresses were tensile in nature. The biaxial modulus value approached the single crystal value for films deposited at low pressures and decreased significantly with increasing deposition pressure. films with high compressive stresses (≥400 MPa) showed higher refractive indexes, higher extinction coefficients and lower optical bandgaps compared to those for films with low compressive stresses (≃40 MPa). Furthermore, Curie point and coercive fields were increased while remanent polarization decreased with increasing compressive stress. In addition, films in a state of high compression showed a broad peak in dielectric constant vs. temperature curve which indicates a diffuse transition from ferroelectric to paraelectric state. By a judicious choice of deposition conditions, films having low intrinsic stresses and properties close to those of single crystals were obtained. For example, some of the properties of films deposited at 650°C and at 2 Pa pressure on silicon substrate are: at 700 nm, , , , and .

Effects of annealing conditions on the properties of tantalum oxide films on silicon substrates

The formation of a SiO2 layer at the Ta2O5/Si interface is observed by annealing in dry O2 or N2 and the thickness of this layer increases with an increase in annealing temperature. Leakage current of thin (less than 40 nm thick) Ta2O5 films decreases as the annealing temperature increases when annealed in dry O2 or N2. The dielectric constant vs annealing temperature curve shows a maximum peak at 750 or 800° C resulting from the crystallization of Ta2O5. The effect is larger in thicker Ta2O5 films. But the dielectric constant decreases when annealed at higher temperature due to the formation and growth of a SiO2 layer at the interface. The flat band voltage and gate voltage instability as a function of annealing temperature can be explained in terms of the growth of interfacial SiO2. The electrical properties of Ta2O5 as a function of annealing conditions do not depend on the fabrication method of Ta2O5 but strongly depend on the thickness of Ta2O5 layer.

Structural and electrical properties of Dy-doped barium sodium niobate ceramics

Abstract It is proposed to discuss the experimental results concerning the influence of the Dy3+ amount of Barium Sodium Niobate (BNN) ceramics on their structural and electrical properties in this paper. X-ray diffraction, SEM, electrical (dielectric and resistivity), and piezoelectric measurements were carried out for ceramics of composition Ba4-2xNa2 + xDyx 3+Nb10O30 with x = 0.3, 0.5 and 0.7 processed by the usual ceramic method. X-ray diffraction studies showed a single phase in all the compositions with a tetragonal tungsten bronze (TB) symmetry. SEM micrographs reveal an inhibition of grain growth with Dy and is in the range 1 ∼ 3 μm. The room temperature dielectric constant, broadening of the dielectric constant versus temperature curves are observed to increase and the ferroelectric curie temperature (Tc ) decreases with the Dy concentration. It is interesting to note that a PTC effect has been observed in all the compositions and the region of the section of PTC shifted to higher temperatures wi...

Dynamic mechanical and dielectric properties of epoxidized SBS triblock copolymer

AbstractThe morphological and dynamic properties of epoxidized styrene–butadiene–styrene block copolymers were studied and compared with their parent styrene–butadiene–styrene block copolymer (SBS). Two peaks were observed in the mechanical loss (tan δ) curve which can be attributed to segmental motion of epoxidized polybutadiene (EPPB) and polystyrene. Analysis by DSC thermograms also showed the linear increase of glass transition temperature for EPPB domain with the epoxy group content. Phase separated structures of epoxidized SBS as observed by TEM suggests a considerable degree of mixing occurred between phases after 80 mol % of the double bonds in SBS were epoxidized. The interfacial region displays a third peak and causes much steeper drop in modulus at higher temperature than Tg of EPPB. Parallel dielectric relaxation measurements were also made in the frequency range of 30 Hz–1 KHz as a function of temperature. In each dielectric constant (ϵ′) curve, there is a maximum near the Tg of EPPB determined from the dielectric loss tangent curve. The shift in Tg of EPPB versus epoxy group content was consistent with that measured by the thermal and dynamic mechanic analysis. These findings indicated an 8°C shift in glass transition temperature as the epoxy group content in EPPB increased 10%.

ELECTRICAL PROPERTIES OF CRYSTALLINE-NONCRYSTAL-LINE COMPOSITE Li IONIC CONDUCTOR

In the paper, the electrical properties of crystalline LiCl-noncrystalline Li2O·3B2O3 composite Li ionic conductor are studied. Some new phenomena of changes in electrical properties of this composite ionic conductor have been found, i.e. a "two-peak" effect of conductivity enhancement appears on macroscopic conductivity σm versus composition curve. Correspondingly, "two-valley" appears on apparent activation energy Em versus composition and dielectric constant εm versus composition curve. These experimental phenomena have been discussed in detail, and the results are consistent with conduction theory.

Dielectric-Properties of Ceramics in the System Pb(Mg1/2W1/2)O3–Pb(Ti1-xZrx)O3–ZnO

Dielectric properties of the relaxor ferroelectric ceramics in the system Pb(Mg1/2W1/2)O3–PbTiO3–PbZrO3–ZnO were investigated. The dielectric constant vs temperature curve for these dielectrics exhibited dual peaks with increasing zinc oxide up to 8 mol%. This resulted in a small capacitance change over widely extended temperature ranges. A double hysteresis loop and the dual peaks of dielectric constant curve were explained as a result of dielectric aging phenomenon associated with nonstoichiometry of the compositions caused by the addition of zinc oxide.

Infra-red spectra and optical constants of polytetrafluoroethylene films

Transmission and reflection infra-red spectroscopy were used to determine refractive indices in thin films of poly(tetrafluoroethylene) and poly(tetrafluoroethylene-hexafluoropropylene) over the range 2200 to 800 cm −1. The results showed the expected pattern over the strong absorption region but they also showed that film anisotropy exhibits a significant effect on the measurements. In addition, a calculation of the real and imaginary dielectric constants was performed on one of the thin films of poly(tetrafluoroethylene) to validate the refractive index measurements. The real dielectric constant curve showed an unexpected dip below zero on the high frequency sides of the two strong absorption bands. This suggests that surface excited waves may be observed under restricted conditions for films of poly(tetrafluoroethylene) and its copolymers.

Dielectric properties of poly(α‐methyl α‐n‐propyl‐β‐propiolactone)/poly(vinyl chloride) blends

AbstractThe dielectric properties of miscible blends of poly(vinyl chloride) (PVC) and poly(α‐methyl‐α‐n‐propy‐β‐propiolae‐tone) (PMPPL) have been investigated at different temperatures above and below Tg. The results were analyzed using the Cole‐Cole representation and lead to the conclusion that this mixture does not exhibit micro‐scale heterogeneities. Dielectric constant and dielectric loss master curves were constructed using the stress relaxation shift factors determined previously; the same shift factors could be used for the homopolymers and their blends. Similarities between the dielectric master curves and the stress relaxation master curves of PVC, PMPPL, and their blends, are also discussed.

Thermodynamic and physical properties of binary mixtures involving nitrobenzene + the first term of the aliphatic and aromatic nitrile series

Jannelli, L., Pansini, M. and Lopez, A., 1983. Thermodynamic and physical properties of binary mixtures involving nitrobenzene + the first term of the aliphatic and aromatic nitrile series. Fluid Phase Equilibria, 15: 219–229. Enthalpies of mixing at 298.16 K, and excess volumes and dielectric constants at temperatures ranging between 293.16 and 333.16 K, have been measured for the binary systems nitrobenzene + acetonitrile and + benzonitrile, over the entire composition range. The benzonitrile and nitrobenzene molecules have very nearly equal volumes and approximately similar shapes; acetonitrile and nitrobenzene are isodielectric. The excess volumes on mixing are negative and the excess enthalpies are positive for both systems; the excess dielectric constants are negative in the case of benzonitrile + nitrobenzene, and positive in the case of acetonitrile + nitrobenzene. Both systems, however, exhibit only small deviations from ideality, extremely small in the case of the benzonitrile + nitrobenzene system. These deviations may be interpreted in terms of only moderate interactions of any kind. nevertheless, the presence of a flat maximum in the excess dielectric constant versus composition curve for acetonitrile + nitrobenzene indicates that interactions between unlike molecules may not be excluded entirely. On the whole, the data collected supply evidence for the supposition that differences in the properties of the pure components should be regarded as the factors which play the most important role in determining deviations from ideality for both systems.