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In this work, Ba 1 − x Ca x Ti 0. 8 8 Zr 0. 1 2 O3 (x = 0.00–0.25) ceramics were prepared by a solid-state reaction method, and the variation of dielectric, ferroelectric and piezoelectric characteristics has been investigated together with the structure evolution. The crystal structure varies from rhombohedral to tetragonal at room-temperature and the morphotropic phase boundary (MPB) is determined around x = 0.10, where the significantly enhanced ferroelectric and piezoelectric properties are achieved. With the increase of Ca content, the system gradually evolves into a relaxor ferroelectric. This work provides useful guidance for future research on lead-free piezoelectric materials. [ABSTRACT FROM AUTHOR]

Magnetotransport properties of La1-xCaxMnO3 (x=0.33, 0.5) thin films on different substrates are systematically studied. Due to the different lattice-substrate mismatch between films and substrates, compressive, and tensile epitaxial strain can be induced, respectively. The structure distortion induced by the strain with different sign influences the transport property and magnetoresistance. The tensile strain induces an increase of resistivity and magnetoresistance, while the resistivity peak temperature decreases. Compressive strain leads to a contrary behavior. The microstructure of films is also dominated by the lattice-substrate mismatch strongly. The inhomogeneities and different mixed domain structure induce the broadening of magnetic transition in films on SrTiO3 and NdGaO3, and a sharp increase in magnetoresistance in La0.67Ca0.33MnO3 films with increasing field. In addition, the low temperature metal–insulator transition in the resistivity of La0.5Ca0.5MnO3 film on LaAlO3 also indicates the sample inhomogeneities. The suppression of the charge-ordering state in La0.5Ca0.5MnO3 films is mainly dominated by the magnetic field, whereas the effect of the lattice-substrate mismatch is weak. It is due to the origin of the charge-ordering state. When the charge-ordering state is completely suppressed, the effect of lattice-substrate mismatch on charge transport and magnetoresistance shows up obviously. [ABSTRACT FROM AUTHOR]

We report structural, caloric, and dielectric properties in the blends of relaxor poly(vinylidene fluoride-trifluoroethylene-chlorofluoroethylene) terpolymer with small amount of poly(vinylidene fluoride-chlorotrifluoroethylene) copolymer, developed on aluminum surface. X-ray diffraction and differential scanning calorimetry results indicate that the copolymer additive disturbs the crystallizing process of the terpolymer. Consequently, relatively high values of the dielectric constant of ≈80, detected in terpolymer films around room temperature, decrease to ≈60 in blends. We show that addition of the copolymer does not influence the relaxor dielectric dynamics of the terpolymer and we explain the detected dielectric response by calculations that take into account the fact that in these heterogeneous systems two similar dynamic processes superimpose in the same temperature range, i.e., relaxor dynamics in the crystalline regions and a glassy transition in the amorphous matrix. [ABSTRACT FROM AUTHOR]

In the present work, the effects of Ti-substitution for Mn upon the structure, magnetic and dielectric properties in La2NiMnO6 ceramics have been investigated. Ti-substitution for Mn strongly affects the crystallographic, magnetic, and dielectric properties of La2NiMnO6 double perovskite ceramics. Refinements of the x-ray diffraction data show that all compositions investigated here have the monoclinic perovskite structure in space group P21/n with a partially ordered arrangement of Ni and Mn/Ti cations. The magnetic nature of the present ceramics with x up to 0.8 is ferromagnetic (FM), while that is antiferromagnetic for La2NiTiO6. The Curie temperature and the spontaneous magnetization, or FM component, decrease with increasing x. These ferromagnetic states are attributed to the Ni2+-O-Mn4+ superexchange interaction. The dielectric constant monotonically decreases and the relaxor-like behavior is suppressed with x. The similar variation tendency of magnetic and dielectric properties with increasing x can be explained simply by the dilution effect. [ABSTRACT FROM AUTHOR]

A room temperature multiferroic compound Ba4Bi2Fe2Nb8O30 was synthesized using a solid state reaction technique. Rietveld analysis of x-ray diffraction data shows that Ba4Bi2Fe2Nb8O30 has a tetragonal (space group P4bm) tungsten bronze structure. In this structure, the Fe3+ and Nb5+ statistically occupy the octahedral center while the Ba2+ ions and the Bi3+ ions occupy the pentagonal channels and the square channels, respectively. Diffuse dielectric peaks with strong frequency dispersion in the temperature range from 150 to 300 K can be attributed to the random distribution of Fe3+ and Nb5+ at B sites. Magnetic hysteresis loop at room temperature is also obtained, which suggests that Ba4Bi2Fe2Nb8O30 is a room temperature multiferroic compound. The coupling between the relaxor behavior and magnetic ordering is verified by observing an increase of magnetization near the maximum dielectric constant temperature. [ABSTRACT FROM AUTHOR]

Dielectric properties of La2CuTiO6 ceramics were investigated in a broad frequency and temperature range. There is only one dielectric relaxation in the curve of temperature dependence of dielectric properties for La2CuTiO6 ceramics. This dielectric relaxation is a thermal activated process. The bulk and grain boundary resistances can be obtained from results of the least-mean-square fitting on impedance spectra. The conduction mechanism of the present ceramics is also a thermal activated process. The activation energy of dielectric relaxation is almost same as that of electrical conductivity and this indicates the closely correlation between the dielectric relaxation and electrical conductivity. The dielectric relaxation in the present ceramics should be attributed to the mixed-valent structure (Cu+/Cu2+ and Ti3+/Ti4+), which is induced from the oxygen vacancy. [ABSTRACT FROM AUTHOR]

Dielectric characteristics of Ba6CoNb9O30 tetragonal tungsten bronze ceramics have been evaluated over a broad temperature and frequency range. A broad dielectric peak with strong frequency dispersion is observed at 140–225 K, which well follows the Vogel–Fulcher relationship and indicates the relaxor ferroelectric nature in the present ceramics. The P-E hysteresis loops varying with temperature are consistent with this dielectric relaxation process and provide the further evidence on the relaxor ferroelectric nature. The nonlinear magnetic hysteresis curve is observed in Ba6CoNb9O30 ceramics at 5 K, indicating the soft magnetic behavior which is related to the tetragonal tungsten bronze crystal structure containing magnetic ions of Co3+. [ABSTRACT FROM AUTHOR]

Dielectric characteristics of Ba4Nd2Ti4Nb6O30 tungsten bronze ceramics have been investigated over a broad range of temperature and frequency. The real part of the dielectric constant ([variant_greek_epsilon]′) shows a sharp peak at 417 K indicating the ferroelectric phase transition. Two dielectric relaxations are observed in the lower temperature range, which are very obvious in the dielectric loss (tan δ) and the imaginary part of the dielectric constant ([variant_greek_epsilon]″). The differential scanning calorimetry (DSC), Raman scattering, and ultrasonic studies of the present ceramics have also been conducted in a broad temperature range covering the ferroelectric transition and/or the dielectric relaxation temperatures. The endothermal peak in the DSC curve around the ferroelectric transition temperature confirms the first-order structural transition with the transition enthalpy of 5.72 kJ/mol. Steplike anomalies in the wave number of the Raman vibrations and abnormal drop of the intensity of the Raman spectra are observed accompanying the ferroelectric phase transition. The dielectric relaxations in the temperature range below Tc are attributed to the structure fluctuations associated with the coupling between the polarizability in the ab plane and the c axis displacement, as well as the remaining random field effects, which are suggested as the possible origin of the anomalous reduction of the Raman intensity below Tc as well as the anomalies in the ultrasonic velocity and attenuation measurements. Freezing of these structure fluctuations are detected by the ultrasonic anomaly at about 120 K and the increasing Raman intensity below 150 K. [ABSTRACT FROM AUTHOR]

Structure and dielectric characteristics of Ba[(Fe0.9Al0.1)0.5Ta0.5]O3 solid solution were investigated. The cubic crystal structure in space group Pm3m(221) was confirmed in the Al-substituted Ba(Fe0.5Ta0.5)O3 ceramics. The extended giant dielectric constant step and the significantly reduced room-temperature dielectric loss were obtained in the Al-substituted Ba(Fe0.5Ta0.5)O3 ceramics. These improvements of dielectric characteristics have great scientific significance for potential application of giant dielectric constant materials. XPS analysis results confirmed that the low-temperature dielectric relaxation originated from the mixed-valent structure of Fe2+/Fe3+ and the hopping of the charge carriers between them, and the improvements of dielectric characteristics in the Al-substituted Ba(Fe0.5Ta0.5)O3 ceramics were attributed to the modification of such mixed-valent structure of Fe2+/Fe3+. [ABSTRACT FROM AUTHOR]

We report the effects of the Mg doping on the dielectric properties of CaCu3Ti4O12 in the frequency range of 200 Hz–200 kHz and in the temperature range of 58–473 K. It is found that the incorporations of Mg2+ result in increases in the dielectric constant by 12%–20% and decreases in the dielectric loss by 41%–64% (with the minimum of 0.042 for CaCu2.7Mg0.3Ti4O12) at room temperature and at 1 kHz. The x-ray photoemission spectroscopy measurements reveal that the content of Cu3+ increases with the increasing concentration of Mg2+. The enhanced dielectric response may be related to the influence of Cu3+ and/or Mg2+. In other words, Mg2+ is an effective ion to optimize the dielectric properties of CaCu3Ti4O12. [ABSTRACT FROM AUTHOR]

Dielectric characteristics of YFeO3 antiferromagnetic ceramics were evaluated over broad temperature and frequency ranges. Two dielectric relaxations were observed at low and high temperatures, respectively, and a dielectric constant step was detected between them. The low temperature dielectric relaxation was an intrinsic thermally activated process following the Arrhenius law with the activation energy very close to that for electronic ferroelectrics, while the high temperature dielectric relaxation was related to the point defect since it could be significantly suppressed by O2 annealing. M-H hysteresis loop was detected at room temperature, and this indicated the weak ferromagnetism in YFeO3 ceramics. [ABSTRACT FROM AUTHOR]

Undoped GaN-based metal-oxide-semiconductor high-electron-mobility-transistors (MOS-HEMTs) with atomic-layer-deposited Al2O3 gate dielectrics are fabricated with gate lengths from 1 μm up to 40 μm. With a two-dimensional numerical simulator, we report simulation results of the GaN-based MOS-HEMTs using field-dependent drift velocity model. A developed model, taking into account polarization-induced charges and defect-induced traps at all of the interfaces and process-related trap levels of bulk traps measured from experiments, is built. The simulated output characteristics are in good agreement with reported experimental data. The effect of the high field at the drain-side gate edge and bulk trap density of GaN on the output performance is discussed in detail for the device optimization. AlGaN/GaN/AlN quantum-well (QW) MOS-HEMTs have been proposed and demonstrated based on numerical simulations. The simulation results also link the current collapse with electrons spreading into the bulk, and confirm that a better electron localization can dramatically reduce the current collapse for the QW-MOS-HEMTs. Due to the large band edge discontinuity and effective quantum confinement of the AlGaN/GaN/AlN quantum well, the parasitic conduction in the bulk is completely eliminated. [ABSTRACT FROM AUTHOR]

The microstructure, ferroelectric, and dielectric properties of vanadium-doped Bi4Ti3O12 ceramics have been investigated. V substitution is found to cause a transition from an orthorhombic phase to a tetragonal phase at x∼0.03, and again to an orthorhombic phase at higher V content. The ferroelectric properties of Bi4Ti3O12 were significantly improved by V doping. The 2Pr of Bi4Ti3O12 is 16 μC/cm2, and it reaches a maximum value of 26.4 μC/cm2 when the V content is 0.03. The two relaxation peaks (PI, PII) are observed in the dielectric loss (D) curves for all of the samples. The PI and PII peaks related to oxygen vacancies tend to decrease with V doping, which implies the decreasing of the oxygen vacancy concentration caused by V doping and favors the improvement of 2Pr and 2Ec. On the contrary, Raman spectra reveal the occurrence of Ti vacancies when V content is more than x=0.01, which may be responsible for the variation of the microstructure and the deterioration of 2Pr and 2Ec. The ferroelectricity of V doping Bi4-x/3Ti3-xVxO12 ceramics is therefore likely dominated by these two competing mechanisms, with the optimal ferroelectric properties appearing at V content x=0.03. [ABSTRACT FROM AUTHOR]

Dense Bi3.15Nd0.85Ti3O12 (BNdT) ceramics of a layered perovskite structure were sintered at 1100 °C by solid state reaction. Ferroelectric domains were probably observed in plate-shaped grains. The BNdT ceramics exhibit saturated ferroelectric hysteresis loops with a remanent polarization (2Pr) of 45 μC/cm2 and a coercive field of 67.6 kV/cm. The dielectric constant and dissipation factor of the ceramics at 100 kHz are 221 and 0.0064, respectively. A broad dielectric peak was observed around 408 °C, and it might come from the oxygen-vacancy-related dielectric relaxation. The leakage current density of the ceramics is less than 7.5×10-7 A/cm2 under an applied field below 239 kV/cm. The BNdT ceramics show Schottky emission behavior under low electric field below 75 kV/cm. [ABSTRACT FROM AUTHOR]

We have synthesized ferroelectrics of M6Ti2Nb8O30 (M=Ba, Sr) with filled tungsten-bronze structure. The microstructures and dielectric properties of the present materials have been investigated as well as the behavior and features of the ferroelectric phase transition. Similar to perovskite ABO3, tungsten-bronze structure consists of several BO6 octahedra. The close distortion of BO6 octahedra concluded from the √10 c/a ratios is observed in Ba6Ti2Nb8O30 and Sr6Ti2Nb8O30, and two ferroelectrics have the close Curie temperature (155 °C for the former and 160 °C for the latter at 1 MHz). Deducing from Raman spectra at different temperatures around phase transition and the modified Curie-Weiss law, the ferroelectric phase transition of Ba6Ti2Nb8O30 and Sr6Ti2Nb8O30 may belong to the displacive transition. The obvious diffuse characteristics of the ferroelectric transition may be attributed to the disordered distributions of octahedra, as two kinds of BO6, i.e., TiO6 and NbO6, exist in one cell. The weak ferroelectric of the present materials are indicated from the P-E hysteresis loops, both with 2Pr of 4 μC/cm². [ABSTRACT FROM AUTHOR]

The dielectrics of Ba6Ti2Ta8O30 and Sr6Ti2Ta8O30 were prepared and characterized. These compounds have the tetragonal tungsten–bronze structure and paraelectric nature at room temperature. Very low dielectric loss was determined at 1 MHz in both dielectrics together with a relatively small temperature coefficient. The dielectric constant was 174 and 180 for Ba6Ti2Ta8O30 and Sr6Ti2Ta8O30, respectively. [ABSTRACT FROM AUTHOR]

The dielectric behavior and the features of the diffused phase transition of the SrpSm6-pTi8-pNb2+pO30 (p=4,5) ceramics were investigated together with their structure. Both Sr5SmTi3Nb7O30 and Sr4Sm2Ti4Nb6O30 had tungsten bronze structure and weak ferroelectric nature. Though Sr5SmTi3Nb7O30 showed the diffused ferroelectrics phase transition, it was concluded that the transition was mainly the displacive ferroelectric phase transition. In Sr4Sm2Ti4Nb6O30, the Sr2+ ions and Sm3+ ions did not form an order structure and it showed a typical displacive ferroelectric phase transition. The dielectric anomaly was attributed to the different BO6 octahedral distortion. [ABSTRACT FROM AUTHOR]

(1-x)Pb(Mg[sub 1/3]Nb[sub 2/3])O[sub 3]–xLa(Mg[sub 1/2]Ti[sub 1/2])O[sub 3] dielectrics were prepared by a solid-state reaction process and the structures were evaluated together with the dielectric characterization. The pyrochlore-free dielectrics were obtained with increasing La(Mg[sub 1/2]Ti[sub 1/2])O[sub 3] content due to the increased electronegativity difference. The 1/2(111) superlattice reflection showed 1:1 ordering on the B site in all compositions. Antiphase tilting of oxygen octahedra and B-site cation displacing appeared at x=0.9. Low loss (tan δ∼10[sup -4]) dielectrics with high dielectric constant (36–900) were obtained in the present system, and the good microwave dielectric properties were achieved in the compositions with x>=0.7. The best combination of microwave dielectric properties was obtained for x=0.9: ε=34, Qf=21 280 GHz, and τ[sub f]=-60 ppm/°C. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Presents information on a study which conducted microstructure analysis and dielectric characterization of a lead-based complex perovskite dielectric. Dielectric properties of perovskites; How the samples were prepared for the experiment; Results and discussion.

The dielectric properties of SmSrNiO ceramics with different concentrations of oxygen vacancies were characterized. The ceramics with lower concentration of oxygen vacancies were prepared by directly sintering the sol-gel derived powders in air, while the higher one could be obtained by annealing the as-sintered ceramics in the flow of nitrogen. The post-densification annealing in the flow of nitrogen decreased the dielectric constant at low temperature and increased it at high temperature, while the dielectric loss increased in overall temperature range. The activation energy of low-temperature dielectric relaxation decreased with increasing the concentration of oxygen vacancies, and so did that of bulk electrical resistances although the values of resistances increased, while the activation energy of electrical resistances for grain boundary increased though the values of resistances decreased. The giant dielectric response in the as-sintered SmSrNiO ceramics should be mainly attributed to the small polaronic hopping process, while that of annealed ceramics should be directly linked to the oxygen vacancies. [ABSTRACT FROM AUTHOR]

The novel (Ba0.96Sr0.04)(Zr0.04Y0.005Ti0.955)O2.9975Ceramics with giant dielectric constant were sintered at different temperatures for different dwell time. The effects of sintering temperature and dwell time on the microstructure and dielectric properties were studied in detail. All ceramics have a single tetragonal phase with no second phase. The size and shape of ceramic grains varied with the sintering temperatures and dwell times. The ceramics exhibit satisfied dielectric property (ϵr∼200066.8, tanδ ∼0.30023, at 0.1 kHz, 25°C) when the ceramics are sintered at 1350°C for 24 hour, which presenting a high potential to be used in applications of energy storage. [ABSTRACT FROM PUBLISHER]

The dielectric properties of Sr2 TiMnO6 ceramic samples were investigated as functions of temperature (100 K ≤ T ≤ 320 K) and frequency (100 Hz ≤ f ≤ 10 MHz). Two thermally activated dielectric relaxations were observed. The sample was confirmed to possess multivalent states of Mn and Ti ions and the coexistence of electron holes and electrons. Our results revealed that both relaxations are bulk effect related to localized carriers hopping inside grains. It was suggested that the low-temperature relaxation ( LTR) can be related to dipolar effect due to electron holes, and the high-temperature relaxation ( HTR) was associated with the electrons hopping between Ti3+ and Ti4+ ions. [ABSTRACT FROM AUTHOR]

Nanoparticles of (Zr0.8Sn0.2)TiO4 ( ZST) ceramics were prepared by ball milling. Different concentrations of (1, 2 and 3 wt%) nanoparticles of size about 60 nm were introduced into the sub micron-sized (0.8 μm) powder of the ZST ceramics to study the effect of their inclusion on densification, microstructure, and microwave dielectric properties of the ZST ceramics. It is found that the addition of nanoparticles to the ZST ceramics significantly improved the density with reduction in sintering temperature. In the present case, it is believed that the surface energy of fine powders and their defect energy are the driving force for sintering and increase in uniform grain size, which are activated at the sintering temperature. The microwave dielectric properties of ZST ceramics were also heavily influenced by the addition of nanoparticles of ZST. The maximum dielectric constant of 39.2 and Q × fo value of 72 900 were found to be for the samples added with 2 wt% of the nanoparticles and sintered at 1300°C for 3 h. However, it is observed that samples made with nanopowder alone exhibited poor sinterability. [ABSTRACT FROM AUTHOR]

La0.5Bi0.5MnO3 ceramics with a single phase were prepared by a solid-state reaction method, and their dielectric properties were characterized. Two dielectric relaxations with a giant dielectric constant were identified in the temperature range from 125 to 350 K. The electron hopping between Mn3+ and Mn4+ was found to be the origin of the dielectric relaxation at low temperatures (125–200 K) with an activation energy of 0.18 eV. The high temperature (200–350 K) dielectric relaxation can be attributed to the conduction. [ABSTRACT FROM AUTHOR]

Temperature-stable high dielectric constant was observed in magnetoelectric (1-x) Sr0.5Ba0.5Nb2O6/xNi0.8Cu0.2Fe2O4 composite ceramics. The related dielectric relaxation and the formation of the dielectric platform were discussed in detail with various compositions. The high dielectric constant observed at low frequencies for composite ceramics was interpreted within the Maxwell-Wagner polarization model. Similar to that in CaCu3Ti4O12 a dielectric constant step in a broad temperature interval (323-623 K) was also observed in 0.8Sr0.5Ba0.5Nb2O6/0.2Ni0.8Cu0.2Fe2O4, and it was originated from the compromise between the dielectric relaxations caused by ferroelectric phase transition and thermally activated Maxwell-Wagner polarization process. [ABSTRACT FROM AUTHOR]

The dielectric properties and conductivity of semiconducting Bi-substituted LaMnO3 ceramics were investigated. It was found that the electron hopping between Mn3 + and Mn4 + contributed to the colossal dielectric response of Bi-substituted LaMnO3 ceramics. A dielectric relaxation with the same activation energy of conductivity was observed in the temperature range from 120 K to 240 K. Due to the effects of the lone-pair electron of Bi3 +, the activation energy of the dielectric relaxation in La1 - xBixMnO3 ceramics increased with increasing amount of Bi3 +. [ABSTRACT FROM AUTHOR]

This paper presents a novel harmonic-suppressed microstrip open loop resonator bandpass filter with defected ground structure (DGS) for wireless local area network (WLAN) application. To improve the stopband rejection of the filter, DGSs are applied under the feed lines to suppress the harmonics. The bandpass filter with center frequency of 2.44 GHz is designed and fabricated on a TLX substrate with thickness of 1 mm and dielectric constant of 2.55. By using two dumbbell-shape DGSs the filter has a wide stopband characteristic with attenuation -25 dB up to 8 GHz and has an -1.25 dB insertion loss while it demonstrates a little larger than the conventional one. The measured results agree well with the simulation results. The proposed filter is found to possess low in-band insertion loss and high out-band suppression, making it suitable in WLAN application. [ABSTRACT FROM AUTHOR]

Lead Strontium Titanate ((Pb, Sr)TiO3, PST) thin films were epitaxially grown on (001) magnesium oxide (MgO), (001) lanthanum aluminate (LaAlO3, LAO), and (110) neodymium gallate (NdGaO3, NGO) substrates by pulsed laser deposition. Microstructural studies revealed that the as-grown PST films are with excellent epitaxial quality. PST films on MgO and LAO substrates exhibit a tetragonal distortion whereas the films on NGO substrates show an orthorhombic distortion. Dielectric property measurements at 1.0 MHz revealed that the room temperature dielectric constant is about 1500 with an extra large dielectric tunability value of 65% at 50 kV/cm for the PST film on the MgO substrate, and dielectric constant of 3100 with a dielectric tunability value of 48% at 50 kV/cm for the PST film on the LAO substrate. PST films on NGO substrates show anisotropic in-plane dielectric properties due to the anisotropic in-plane strain. A high zero-field dielectric constant of 4220 with a dielectric tunability value of 59% at 50 KV/cm was achieved along the a-axis of the PST film on the NGO substrate. All the films show dielectric losses smaller than 0.01. These excellent results suggest the highly epitaxial PST thin films can be a good candidate for developing room temperature tunable microwave device applications. [ABSTRACT FROM AUTHOR]

Dense (1− x)Ca(Mg1/3Ta2/3)O3/ xCaTiO3 ceramics (0.1≤ x≤0.9) were prepared by a solid-state reaction process. The crystal structures and microstructures were characterized by X-ray diffraction, scanning electron microscopy, and transmission electron microscopy. Single-phase solid solutions were obtained in the entire composition range. Long-range 1:2 ordering of B-site cations and oxygen octahedra tilting lead to the monoclinic symmetry with space group P21/ c for x=0.1. For x above 0.1, the long-range ordering was destroyed and the crystal structure became the orthorhombic with space group Pbnm. The microwave dielectric properties showed a strong dependence on the composition and microstructure. The dielectric constant and temperature coefficient of resonant frequency increased nonlinearly as the CaTiO3 content increased while the Qf values decreased approximately linearly. Good combination of microwave dielectric properties was obtained at x=0.45, where ℇr=45.1, Qf=34 800 GHz, and τf=17.4 ppm/°C. [ABSTRACT FROM AUTHOR]

This article presents a study on a dielectric-loaded folded monopole antenna operating at ultra high frequency band for Digital Video Broadcasting-Handheld terminals. It is an optimization of the folded monopole antenna in our previous work. The proposed antenna has a 43% reduction in volume when compared with the previous design. Because of the ground plane independency of the antenna, the proposed antenna can be mounted on any type of ground plate, thus improving the adaptability to different terminal designs. © 2007 Wiley Periodicals, Inc. Microwave Opt Technol Lett 50: 487–490, 2008; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.23111 [ABSTRACT FROM AUTHOR]

Nonstoichiometric Mg2SiO4 forsterite dielectric ceramics with various Mg/Si ratios ( R=2.025, 2.05, and 2.2) were prepared and characterized. The appearance of a MgSiO3 secondary phase could be effectively suppressed by adjusting the nonstoichiometry, and a single-phase forsterite structure was obtained in the present ceramics with Mg/Si ratios of 2.025 and 2.05. The microwave dielectric characteristics were significantly improved in the nonstoichiometric Mg2SiO4 ceramics on eliminating the MgSiO3 secondary phase, where an enhanced Q× f value and a suppressed temperature coefficient of resonant frequency λ f were obtained. The best microwave characteristics were achieved in the nonstoichiometric forsterite ceramics with an Mg/Si ratio of 2.05: ℇ r=7.5, Q× f=114 730 GHz, and λ f=−59 ppm/°C. [ABSTRACT FROM AUTHOR]

The dielectric characteristics of BaBi2Nb2O9, BaBi4Ti4O15, BaBi8Ti7O27, and La-substituted SrBi4Ti4O4 were investigated to discuss their ferroelectric phase transition and relaxor behaviors. BaBi2Nb2O9 showed typical relaxor behaviors, and a shift of Tm with increasing frequency was observed in BaBi4Ti4O15 and SrBi4− xLa xTi4O15 ( x=0.8, 1.0) but they underwent a real paraelectric–ferroelectric phase transition on zero-field cooling, while BaBi8Ti7O27 showed a normal ferroelectric nature. The reduced concentration and weakened coupling of the dipoles related to A-site bismuth are believed to be responsible for the appearance of short-range electric ordering and the relaxor behaviors in these bismuth layer-structured compounds. [ABSTRACT FROM AUTHOR]

The dielectric characteristics of BaBi2Nb2O9, BaBi4Ti4O15, BaBi8Ti7O27, and La-substituted SrBi4Ti4O4 were investigated to discuss their ferroelectric phase transition and relaxor behaviors. BaBi2Nb2O9 showed typical relaxor behaviors, and a shift of Tm with increasing frequency was observed in BaBi4Ti4O15 and SrBi4− xLa xTi4O15 ( x=0.8, 1.0) but they underwent a real paraelectric–ferroelectric phase transition on zero-field cooling, while BaBi8Ti7O27 showed a normal ferroelectric nature. The reduced concentration and weakened coupling of the dipoles related to A-site bismuth are believed to be responsible for the appearance of short-range electric ordering and the relaxor behaviors in these bismuth layer-structured compounds. [ABSTRACT FROM AUTHOR]

We report on the results of a comparative study in which the mechanical response of both fully dense and porous low-κ dielectric thin films was evaluated using two different techniques: nanoindentation and the plane-strain bulge test. Stiffness values measured by nanoindentation are systematically higher than those obtained using the bulge test technique. The difference between the measurements is caused by the Si substrate, which adds significantly to the contact stiffness in the indentation measurements. Depending on the properties of the coatings, the effect can be as large as 20%, even if the indentation depth is less than 5% of the film thickness. After correction of the nanoindentation results for the substrate effect using existing models, good agreement is achieved between both techniques. The results further show that densification of porous material under the indenter does not affect stiffness measurements significantly. By contrast, nanoindentation hardness values of porous thin films are affected by both substrate and densification effects. It is possible to eliminate the effect of densification and to extract the yield stress of the film using a model for the indentation of porous materials proposed by the authors. After correcting for substrate and densification effects, the nanoindentation results are in close agreement with the bulge test measurements. The results of this comparative study validate the numerical models proposed by Chen and Vlassak for the substrate effect and by Chen et al. for the densification effect. [ABSTRACT FROM AUTHOR]

A piezoelectric composite has been prepared with highly aligned BaTiO3 whiskers as the active phase and polyvinylidene fluoride (PVDF) as the matrix. Its dielectric and electromechanical properties are characterized. It is found that the dielectric constant (ε), piezoelectric constant (d33) and remnant polarization (Pr) are considerably higher in the whisker composite than in the corresponding composite containing BaTiO3 powders as the active phase, while the loss factors follow the opposite trend. For the whisker composite, ε, d33 and Pr along the direction of the whisker orientation are much higher than the values normal to the whisker orientation. The reasons for the observed differences are discussed. [ABSTRACT FROM AUTHOR]

We have very recently prepared perovskite high-K dielectric thin films in the CaZrO3-SrZrO3 solid solution system using the sol-gel wet chemical technology for CMOS gate and nanoelectronics applications. Such sol-gel prepared (Ca, Sr)ZrO3 thin films with various compositional ratios of Ca/Sr on Pt coated (001) Si substrates are annealed in flowing O2 at different temperatures from 550 to 700°C. Based on our best knowledge, it is the first time in the literature to successfully prepare the (Ca, Sr)ZrO3 thin films using wet chemical methods, including sol-gel and metallo-organic decomposition (MOD) technique. These thin films have been systematically characterized using differential thermal analysis (DTA), thermogravimetric analysis (TGA), X-ray diffraction (XRD), scanning electron microscopy (SEM), Auger spectra (AES), and electrical and dielectric measurements. Using these techniques, the different reactions in various processing steps have been clarified. The values of dielectric constant in a range of 20–30 in (Ca, Sr)ZrO3 thin films have been obtained, and these sol-gel derived (Ca, Sr)ZrO3 thin films exhibit stable dielectric properties nearly independent on the applied electrical field and frequency at room temperature. The leakage current density of a CaZrO3 thin film annealed at 650°C for 1 hour is approximately of 9.5 × 10-8 A/cm2 at a very high applied electrical field of 2.6 MV/cm. The high dielectric constant, low leakage current density and high breakdown strength suggest that the (Ca, Sr)ZrO3 thin films are promising for CMOS gate and nanoelectronics applications. [ABSTRACT FROM AUTHOR]

Presents a study that investigated a model for predicting direct current arc behavior and critical flashover voltage of ice-covered insulating surfaces. Theoretical background; Methodology; Results and discussion.

TiO2 ceramics doped with 1.0 mol% Ca and different concentrations of Ta were obtained by sintering processing at 1450°C. The microstructures, nonlinear electrical behavior and dielectric properties of the ceramics were investigated. The samples have nonlinear coefficients of α = 2.0–5.0 and ultrahigh relative dielectric constants which is up to 105. Especially, the effects of Ta dopant on the nonlinear electrical characteristics and dielectric properties of the (Ca, Ta)-doped TiO2 ceramics were studied in detail. When the concentration of Ta is 2.0 mol%, the sample exhibits the highest nonlinear coefficient and a comparatively lower dielectric constant. By analogy to a grain-boundary atomic defect model, the effects of Ta and the nonlinear electrical behavior of the TiO2 system were explained. [ABSTRACT FROM AUTHOR]

Modification of BaBi8Ti7O27 ceramics was investigated by La substitution for Bi, and the dielectric properties were determined together with the microstructures. Ba(Bi1−xLax)8Ti7O27 solid solution was observed for x≤0.25, and Ba(Bi,La)2Ti4O12 secondary phase appeared for x>0.25. The dielectric constant, the dielectric loss and the temperature coefficient of dielectric constant increased first and reached their maximums at x=0.15 then decreased together. Ceramics with good dielectric properties: ϵ=102, tan δ=0.0006 and τϵ=−152 ppm/°C at 1 MHz were obtained at x=0.5 where the ceramics were not single phase. [Copyright &y& Elsevier]

The ferroelectric and dielectric properties of ferroelectromagnet Pb(Fe1/2Nb1/2)O3 (PFN) ceramics and thin films prepared by pulsed laser deposition (PLD) have been investigated systematically. PFN ceramics experienced a para-ferroelectric transition and a para-antiferromagnetic transition at 380 K and 145 K, respectively. At room temperature, it has an electrical remnant polarization of 11.5 μC/cm2 and a coercive field of 4.04 kV/cm. The dielectric behaviors show characteristics of diffusive phase transition at a wide temperature range around 380 K. Anomalies in the dielectric constant and loss tangent have been observed near the Neel temperature of 145 K, indicating a coupling between the ferroelectric and antiferromagnetic orders in PFN ceramics. At room temperature, the PFN films exhibited a remnant electric polarization of 7.4 μC/cm2, a coercive field of 10.5 kV/cm, and a dielectric constant of 486 at frequency of 10 kHz, indicating their potential applications in memory devices. [ABSTRACT FROM AUTHOR]

Dielectric response of tetragonal tungsten bronze dielectrics (BaxSr1-x)4Nd2Ti4Nb6O30 was investigated over a broad temperature and frequency range, and the obvious composition-dependent dielectric anomalies with respect to x value were discussed in detail in association with the radius differences between A1- and A2-site ions. With decreasing the magnitude of radius difference between A1- and A2-site ions, the normal ferroelectric peak above 400 K became weaker, and two relaxor peaks at lower temperatures became obvious. The low- and high-temperature relaxor behaviors, which followed well the Vogel-Fulcher relationship, were associated with the polar clusters caused by the off-center Nb/Ti displacements and the incommensurate tilting modulation, respectively. [ABSTRACT FROM AUTHOR]

Dielectric response of Y3Fe5O12 ceramics was investigated over broad temperature and frequency ranges. Three dielectric relaxations were identified in the temperature range from 125 to 620 K. A Debye-type dielectric relaxation at low temperatures (125–320 K) with an activation energy of 0.29 eV is shown to originate from the carrier hopping process between Fe2+ and Fe3+. In a higher temperature range (320–620 K), a low frequency (f≤10 kHz) dielectric relaxation with an activation energy of 0.84 eV most likely arises from the inhomogeneous structure, such as grain boundaries. Another dielectric relaxation in a wider frequency range has a similar activation energy with conduction (Ea=1.00 eV) suggests that it can be attributed to the conduction [ABSTRACT FROM AUTHOR]

Dielectric relaxations of Ba(Fe1/2Ta1/2)O3 ceramics were investigated and discussed over a broad temperature and frequency range. Two dielectric relaxations following Arrhenius law were observed at 153–382 and 440–623 K, where there was a giant dielectric constant step between them. The frequency dependent rapid drop of dielectric constant at 153–382 K was nearly a Debye relaxation with the intrinsic nature, while the high temperature dielectric relaxation with an extremely high dielectric constant peak and very strong frequency dispersion was attributed to the defect ordering but not a typical relaxor ferroelectric behavior. The O2 annealing almost completely suppressed the dielectric peak and subsequently extended the giant dielectric step, while the low temperature dielectric relaxation and the magnitude of such step were not obviously affected. [ABSTRACT FROM AUTHOR]

Ferroelectric single crystal of Na1/2Bi1/2TiO3-BaTiO3 (NBT-BT) and Ce doped NBT-BT have been grown by flux technique. It is found that the addition of Ce plays a significant role in improving the ferroelectric properties of NBT-BT crystals, (i) by improving the value of the dielectric constant at room temperature and at Tm (the phase transition temperature between antiferroelectric and paraelectric phases with dielectric maximum), (ii) by increasing the depolarization temperature (Td) and Tm, (iii) by increasing the degree of diffuseness, and (iv) by increasing the remnant polarization (Pr) and coercive field (Ec). The reasons behind these enhancements of ferroelectric properties are discussed in detail. [ABSTRACT FROM AUTHOR]

Dielectric characteristics of Ba(Fe1/2Nb1/2)O3 ceramics were investigated over a broad temperature and a frequency range. Two dielectric relaxations following Arrhenius law were observed at 150–400 and 406–650 K. An extremely high relaxorlike dielectric peak (202 270 at 5 Hz, 91 930 at 1 kHz, and 37 030 at 100 kHz) with very strong frequency dispersion was observed at 406–650 K, and it was not relaxor ferroelectric but an oxygen defect induced dielectric abnormity. The significant drop of dielectric constant at 146–400 K was also frequency dependent, and it was nearly a Debye relaxation. Between these two dielectric relaxations, there was a frequency dependent dielectric constant plateau over a wide temperature interval. [ABSTRACT FROM AUTHOR]

We report the direct microscale resistance profile measurements on a symmetric thin-film electrical pulse induced resistance change (EPIR) device composed of a Pa0.7Ca0.3MnO3 (PCMO) active layer, using surface scanning Kelvin probe microscopy. The resistance switching is found to be an integration of the resistance changes from three parts of the device: the two interface regions within ∼1–3 μm of the electrical contacts, and the bulk PCMO material. Such a symmetric EPIR device showed a “table leg” resistance switching hysteresis loop under electric pulsing at room temperature. The symmetric EPIR device may be used as a resistive random access memory nonvolatile memory device with different operation modes by controlling electric pulse voltage. [ABSTRACT FROM AUTHOR]

For Cu/ultralow κ application, understanding of interfacial interaction between Ta and pore-sealing layer over porous dielectric is very important in order to achieve a good barrier performance. However, characterizing the effect of pore-sealing layer on barrier performance poses a big challenge. Most studies monitored degradation of the electrical performance of the Ta barrier after integration process with little discussions on interfacial interaction. In this letter, the interaction at the interface between Ta and pore-sealing layer deposited over porous SiLK (κ ∼ 2.2) film is investigated. The barrier performance is improved significantly by nitrogen incorporation during liner growth. This methodology is very effective for improving metal barrier and pore-sealing performance for Cu/ultralow κ interconnects. [ABSTRACT FROM AUTHOR]

Large Ca0.28Ba0.72Nb2O6 (CBN-28) single crystals exhibit saturated ferroelectric hysteresis loops under an electric field of 115 kV/cm along the [001] direction. Their spontaneous polarization, remanent polarization and coercive field are 35.3 μC/cm2, 32.2 μC/cm2, and 38.1 kV/cm, respectively. The dielectric constant and dielectric loss tan δ of the crystals are 195 and 0.32 at 10 kHz, respectively. A diffused dielectric anomaly with relaxor characteristic was observed in the range of 325-500 °C at low frequencies, while the CBN-28 crystals experienced a first-order normal-relaxor ferroelectric phase transition around 252 °C on heating. A broad dielectric loss peak appears around 120 °C and it is interpreted in terms of the migration of oxygen vacancies. The conductance activation energy was determined to be 1.33 eV in the high temperature regime (500–560 °C). [ABSTRACT FROM AUTHOR]

Epitaxial behavior of (Pb,Sr)TiO3 thin films on (110) NdGaO3 substrates fabricated in different conditions have been investigated using high resolution x-ray diffraction and characterized with interdigital dielectric measurement. A slow cooling results in films with a-axis normal to the surface (a-axis growth), whereas a fast cooling leads to growth of c-axis oriented films. The dielectric properties of the films prepared under different cooling rates are closely related to the crystalline structure of the films. [ABSTRACT FROM AUTHOR]

Ferroelectric (Pb,Sr)TiO3 (PSTO) thin films were epitaxially grown on (001) LaAlO3 (LAO) by using pulsed laser deposition. Microstructural characterizations with x-ray diffraction and transmission electron microscopy indicate that the as-grown films have excellent single crystalline quality and a (001)PSTO//(001)LAO and [100]PSTO//[100]LAO interface relationship. Dielectric property measurements reveal that the as-grow films have a very high dielectric constant value of 3100 and very large dielectric tunability of 48% at 40 V/cm at room temperature. These excellent results suggest that the highly epitaxial ferroelectric (Pb,Sr)TiO3 thin films can be developed for room-temperature tunable microwave elements in wireless communication applications. [ABSTRACT FROM AUTHOR]