Frequency Dielectric Properties Research Articles

Enhanced Microwave Magnetic and Attenuation Properties for Barium Ferrite Flaky-Filler Composites

Microwave reflection characteristics as well as high frequency magnetic and dielectric properties have been studied for composites filled with Z-type barium ferrite flakes. Results show that both μ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">'</sup> and μ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">max</sub> <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">''</sup> are enhanced, while ε <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">'</sup> is almost the same, as compared to conventional composites. Therefore, the percentage bandwidth <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">W</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">P</sub> is significantly widened for the flaky-filler composites; <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">W</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">P</sub> achieves 130%-150% for reflection loss <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">RL</i> <; -10 dB. In addition, for all composites, two matching frequencies are found. The first matching frequency is attributed to the quarter-wavelength resonator and the second matching frequency is mainly controlled by the values of both μ <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">'</sup> ( <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">f</i> ) and ε <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">'</sup> ( <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">f</i> ) , where μ <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">'</sup> /ε <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">'</sup> =1/3 .

Experimental and theoretical investigation on the high frequency dielectric properties of Ag/Al2O3 composites

The impedance and dielectric properties of Ag/Al2O3 composites are investigated experimentally in the frequency range from 100 MHz to 1 GHz. Besides, equivalent circuit analysis and numerical simulations were carried out. For the composites with sufficiently high silver loading, current paths were formed and negative permittivity appeared. The negative permittivity can be well described by lossy Drude model. Moreover, the negative permittivity sample manifests inductive characteristic and shunt inductors are added to its equivalent circuit. Numerical simulations show that the interconnection of silver particles results in negative permittivity, hence the serious attenuation of electromagnetic waves.

Large magnetodielectric response in Pr0.6Ca0.4MnO3/polyvinylidene fluoride nanocomposites

We have studied the magnetic field effect on low frequency dielectric properties of Pr0.6Ca0.4MnO3/polyvinylidene fluoride nanocomposite with 22.5% volume fraction of Pr0.6Ca0.4MnO3 nanoparticles. A strong magnetodielectric response was observed below 120 K where Pr0.6Ca0.4MnO3 nanoparticles show the magnetic phase transition indicating a direct correlation between magnetism and dielectric properties. A large change in the dielectric permittivity ∼30% has been observed in a magnetic field of 4.6 T with loss as low as 0.17 at 70 K. The observed magnetodielectric response has been attributed to the decrement of polaron activation barrier of Pr0.6Ca0.4MnO3 nanoparticles with the increase in magnetic field.

Microwave assisted synthesis of barium zirconium titanate nanopowders

The paper reports the synthesis, structural and high frequency dielectric properties of Ba(ZrxTi1−x)O3,BZT, nanopowders where x = 0, 0.1, 0.2, 0.3. These powders were synthesized using both microwave assisted and conventional heating, with the former requiring lower temperature and shorter times compared to the latter, viz., 700 °C for 30 min versus 900 °C for 5 h. The synthesized nanopowders were characterized using X-ray diffraction, micro-Raman spectroscopy, transmission electron microscopy, BET surface area analysis, differential scanning calorimetry and high frequency dielectric measurements. All the microwave synthesized BZT compositions were found to have well crystallized, finer nanoparticles with less agglomeration and higher dielectric permittivity compared to the conventionally prepared powders. The rapidity and less demanding processing conditions associated with the microwave assisted method augers well for the general applicability of the technique for the production of nanocrystalline powders.

Structural, spectroscopic and dielectric investigations on Ba8Zn(Nb6−xSbx)O24 microwave ceramics

Ba 8 Zn(Nb 6− x Sb x )O 24 ( x = 0, 0.3, 0.6, 0.9, 1.2, 1.5, 1.8 and 2.4) ceramics were prepared through the conventional solid-state route. The materials were calcined at 1250 °C and sintered in the range 1400–1425 °C. The structure of the system was analyzed by X-ray diffraction, Fourier transform infrared and Raman spectroscopic methods. The theoretical and experimental densities were calculated. The microstructure of the sintered pellets was analyzed using scanning electron microscopy. The low frequency dielectric properties were studied in the frequency range 50 Hz–2 MHz. The dielectric constant ( ɛ r ), temperature coefficient of resonant frequency ( τ f ) and the unloaded quality factor ( Q u ) are measured in the microwave frequency region using cavity resonator method. The τ f values of the samples reduced considerably with the increase in Sb concentration. The materials have intense emission lines in the visible region. The compositions have good microwave dielectric properties and photoluminescence and hence are suitable for dielectric resonator and ceramic laser applications.

Layered dielectric–magnetic composite structures for Rf-applications

In this paper multilayer magnetic–dielectric composite structures for high frequency applications are introduced. The 0–3 type dielectric and magnetic composites with homogeneously distributed ceramic inclusions were fabricated by mixing extrusion and injection moulding. Magnetic Yttrium Iron Garnet (YIG) and Z-type Hexaferrite (HexaZ) as well as paraelectric Barium Strontium Titanate (BST) powders were used to enhance the permittivity and permeability of the composites. The magnetic–dielectric multilayer composites were constructed by hot-laminating magnetic and dielectric layers in turn to create a solid 2-2 type composite structure. The microstructure, high frequency dielectric and magnetic properties of individual layers and 2-2 composites were investigated and measured. The measurement results indicate that such multimaterial multilayer structures are good candidates for components with reduced dielectric and magnetic losses. Moreover, the observed good frequency stability and the cut-off frequencies above 1 GHz suggested that the composites could be utilized in, e.g., sophisticated functional circuit boards and RF devices.

High frequency dielectric properties distribution of BiFeO3 thin film using near-field microwave microscopy

A near-field scanning microwave microscopy (NSMM) is applied to investigate the local perpendicular dielectric information of single-phase multiferroic BiFeO(3) thin film and single crystal LaAlO(3) material. Our NSMM is composed of a vector network analyzer and a simple open-ended coaxial probe, which is quite different from the commercial probe with a lambda/4 coaxial resonator. The local permittivity is calculated quantitatively according to resonance frequency shift under the quasistatic microwave perturbation theory. We make use of the magnitude of reflection loss S(11) to construct an image reflecting the distribution of dielectric constant of a material. A homogeneous permittivity is observed in LaAlO(3) material and the inhomogeneous permittivity epsilon=215-250 for BiFeO(3) film is depicted from the change of feedback signal S(11) over an area of 100x100 microm(2).

Multilayer BST-COC Composite with Enhanced High Frequency Dielectric Properties

The 0–3 composites with a mixture of randomly dispersed and separated ceramic particles and thermoplastic polymers provide flexible method to fabricate RF devices with adjusted mechanical and electrical properties. However, high ceramic loading levels are required to achieve high relative permittivity which, on the other hand, dramatically degrades the mechanical properties of the composite. In this work vertical and horizontal 2–2 type multilayer structures were fabricated by hot lamination of injection moulded 0–3 BST-COC composite materials with different loading levels of paraelectric ceramic (Ba 0.55 Sr 0.45 Ti 1.01 O 3 ). Each layer and the structures with gradient in permittivity and loss were characterized up to 1 GHz by impedance analyzer. The relative permittivity for the vertical and horizontal gradient structure with identical layer order and average ceramic loading of ∼ 16 vol.% was 6.54 and 10.60 at 1 GHz, respectively. The results showed that especially the horizontal structure is able to provide higher relative permittivity values than a vertical one with similar ceramic loading levels and with competitive dielectric losses. Since the introduced structure is composed of combination of ductile and brittle layers, it also offers a way to fabricate devices with improved mechanical properties.

Growth and high frequency characterization of Mn doped sol-gel PbxSr1−xTiO3 for frequency agile applications

In pursuit of thin film ferroelectric materials for frequency agile applications that are both easily adapted to large area deposition and also high performance, an investigation has been carried out into sol-gel deposition of 3% Mn doped (Pb0.4Sr0.6)TiO3. Large area capability has been demonstrated by growth of films with good crystallinity and grain structure on 4 in. Si wafers. Metal-insulator-metal capacitors have also been fabricated and development of an improved de-embedding technique that takes parasitic impedances fully into account has enabled accurate extraction of the high frequency dielectric properties of the PbxSr1−xTiO3 films. Practically useful values of ε∼1000, tan δ∼0.03, and tunability ∼50% have been obtained in the low gigahertz range (1–5 GHz). Peaks in the dielectric loss due to acoustic resonance have been modeled and tentatively identified as due to an electrostrictive effect with an electromechanical coupling coefficient of ∼0.04 at an electric field of 240 kV/cm which is potentially useful for tunable thin film bulk acoustic wave devices.

Optical and electrical properties of ZnO nanocrystalline textured films prepared by DC reactive magnetron sputtering

ZnO thin films were deposited by DC reactive magnetron sputtering using a metal zinc target. The crystallinity microstructure and surface morphology of ZnO thin films were investigated by X- ray diffraction (XRD) and scanning electron microscopy (SEM). The composition of ZnO thin film was characterized by XPS. The optical properties of ZnO thin film were obtained by spectroscopy ellipsometry and UV-VIS spectrometry. The optical bandgap was found to be 3.29eV of direct-transition type. The low frequency (1kHz- 100kHz) dielectric properties of ZnO thin film were also discussed. The dielectric constant and dielectric loss at 10kHz are 13.4 and 0.03 respectively.

Microwave Dielectric Properties and Low Temperature Sintering of Sm2Si2O7 Ceramic for Substrate Applications

The Sm2Si2O7 ceramics were synthesized by solid‐state ceramic route. The calcination and sintering temperature of Sm2Si2O7 were optimized for the best properties. The crystal structure and microstructure of the ceramic were studied by X‐ray diffraction and scanning electron microscopic methods. The low frequency dielectric properties were studied at 1 MHz. The dielectric properties of the ceramic were measured in the microwave frequency range by the cavity perturbation method. Sm2Si2O7 has ɛr=12.5, tan δ=8 × 10−4, and τɛ=+63 ppm/°C at 1 MHz and a relative permittivity of 10 and tan δ of 6 × 10−3 in the microwave frequency range. The effect of addition of various low loss glasses such as 50ZnO–50B2O3 (ZB), 60ZnO–30B2O3–10SiO2 (ZBS), 27B2O3–35Bi2O3–6SiO2–32ZnO (BBSZ), 22.2MgO–22.2Al2O3–55.5SiO2 (MAS), 35.1Li2O–31.7B2O3–33.2SiO2 (LBS) and 20Li2O–20MgO–20ZnO–20B2O3–20SiO2 (LMZBS) on the microwave dielectric properties of Sm2Si2O7 was also investigated. It was found that the addition of 15 wt% LBS glass reduced the sintering temperature from 1375°C to 975°C with ɛr=9.89 and tan δ=0.024. Fifteen weight percent LMZBS glass ceramic decreased the sintering temperature to 950°C with ɛr=9.09 and tan δ=0.009. The results show that Sm2Si2O7 mixed with suitable amounts of selected glasses is a promising material for microwave substrate applications.

A comparison of the effect of diagnostic X-rays on the radio frequency dielectric properties of bovine liver wint bovine kidney tissues

A comparison of the effect of diagnostic X-rays on the radio frequency dielectric properties of bovine liver wint bovine kidney tissues

Microwave dielectric properties of BiFeO3 thin film prepared by aqueous chemical solution deposition method

We report high frequency dielectric properties of multiferroic BiFeO3 (BFO) thin film deposited by means of aqueous chemical solution deposition on platinized silicon substrate. The structure analysis of the BFO performed by X-ray diffraction and energy dispersive analysis showed pure, single-phase quality of the thin films. The impedance measurements were performed by vector network analyzer in frequency range 100 MHz to 10 GHz at ambient temperature. The film leakage currents dominate dielectric losses at low frequencies. The dielectric constant of the film is around 40. An internal charged defects acting as energy traps for electrons dominate dielectric losses in the frequency region above 4 GHz. .

Dielectric response of BaZrO3/BaTiO3 and SrTiO3/BaZrO3 superlattices

Dielectric materials with high tunability, low loss, and desired range of permittivity are an attractive class of materials for a variety of applications in microwave components such as tunable filters, phase shifters, antennas, etc. In this article, we have investigated the low frequency dielectric properties of BaZrO3/BaTiO3 and SrTiO3/BaZrO3 superlattices of varying modulation periods for the potential application toward electrically tunable devices. The dielectric response of the superlattices as a function of temperature revealed remarkable stability for both types of superlattices, with no observed dielectric anomalies within that range. Dielectric losses were also nominally low with minimal variation within the measured temperature range. Sufficiently high tunability of ∼40% was observed for the BaZrO3/BaTiO3 superlattices at the lowest individual layer thicknesses. In comparison, the SrTiO3/BaZrO3 superlattices showed a minimum tunability for lowest period structures. It showed maximum tunability of ∼20% at 10 kHz and room temperature at an intermediate dimension of 3.85 nm periodicity superlattice. The tunability value degraded with increasing as well as decreasing periodicities for the SrTiO3/BaZrO3 superlattices. The dielectric response has been explained on the basis of size effects, interlayer coupling between dissimilar materials, domain contribution, and depolarizing electric fields.

Li-doped (Ba,Sr)TiO 3 thick film interdigital capacitors for microwave applications

Microwave properties of Li-doped (Ba,Sr)TiO 3 thick film interdigital capacitors have been investigated. According to the reported papers, BaSrTiO 3 materials, paraelectric state at the room temperature, have high dielectric permittivity (>500 @ 1 MHz) and low loss tangent (<0.01 @ 1 MHz) in epitaxial thin film form; however, the sintering temperature of BaSrTiO 3 is over 1350 °C. In order to reduce the sintering temperature, Li (3 wt%) was added to the BaSrTiO 3 materials, and 10 μm thick Li-doped (Ba,Sr)TiO 3 films were screen printed on the alumina (Al 2O 3) substrate and sintered at 900 °C. Interdigital capacitor patterns with five fingers of 200 μm gap and 250 μm length were also designed and fabricated by employing the screen printing method with Ag electrode. The structural feature was analyzed with X-ray diffraction method. Frequency and temperature-dependent dielectric properties were characterized from 1 kHz to 1 MHz and 303–403 K, respectively. Also, current–voltage characteristics were investigated with an elevated temperature. Microwave transmission and reflectance properties of thick film interdigital capacitors will be discussed, and frequency dispersion of dielectric properties will be presented. Specially, designed Au/Li-doped (Ba,Sr)TiO 3/Ag–Pd/Al 2O 3 vertical structure was prepared to measure the tunability. In this sandwich type structure, Li-doped (Ba,Sr)TiO 3 films showed tenability of 7.15% at a bias electric field of 20 kV/cm.

The radio frequency dielectric properties of the stratified UG1–UG2 geological unit in the Bushveld Complex

A new measurement technique enables the complex dielectric properties of the geological strata comprising the UG1–UG2 (Upper Group 1–Upper Group 2) unit of the Bushveld Complex in South Africa to be determined with unprecedented detail at radio frequencies (RF). Results of non-destructive laboratory measurements of representative diamond drill core samples from the UG1–UG2 unit are presented at 25 MHz. These data establish that the UG1 and UG2 chromitite layers are embedded in rock strata (norite, pyroxenite and anorthosite) which are translucent in the HF spectral band, whereas the chromitite layers themselves exhibit significant velocity contrast, making them good radar reflectors. The data presented here is useful for calibration of the radar system, and for predicting the range and resolution performance of borehole radars operating in both the hanging and footwalls of the economically important platiniferous UG2 reef.

The effect of glass addition on the dielectric properties of barium strontium titanate

Ba0.7Sr0.3TiO3 (BST) ceramics were prepared by the conventional solid state ceramic route. Different weight percentages of twelve different glasses were added to the calcined BST ceramics and sintered. The structure and microstructure of the sintered materials were investigated by X-ray diffraction and Scanning Electron Microscopic techniques. The low frequency dielectric properties of the glass-ceramic composites were measured using LCR meter. Some of the glasses improved the dielectric properties and considerably lowered the sintering temperature. The glasses were prepared and characterized under identical conditions. Among the different glasses, 1.5 wt% addition of 71ZnO–29B2O3 lowered the sintering temperature of BST to 975 °C with a dielectric loss of 9 × 10−3 and dielectric constant of 875 at 1 MHz. The curie temperature of BST ceramics was found to shift towards lower temperature with glass addition.

(Ag&lt;sub&gt;1-x&lt;/sub&gt;Na&lt;sub&gt;x&lt;/sub&gt;)(Nb&lt;sub&gt;1-y&lt;/sub&gt;Ta&lt;sub&gt;y&lt;/sub&gt;)O&lt;sub&gt;3&lt;/sub&gt; Dielectric Ceramic Prepared through Citrate Precursor Method

(Ag1-xNax)(Nb1-yTay)O3 (ANNT) dielectric ceramic material with perovskite structure was prepared through a wet chemical synthetic method. The precursor solution for the material was obtained from the citric acid solutions of different metal oxides or nitrates with exact molar ratio by a sol-process. The precursor solution thus prepared was then heated under an infrared lamp to evaporate the solvent. This period showed a self-propagating combustion behavior. Ceramic powder was obtained after the residue was calcined at a certain temperature. It is proved that ANNT sintered at 1040°C was finely grained. The obtained ceramic showed excellent high frequency dielectric properties with considerable high dielectric constant and rather low dissipation factor under 1MHz.

English

The complex perovskite compound CaCu3Ti4O12 (CCTO) is of considerable interest becauseof its anomalously large dielectric response. In this study, the dielectric properties of sol-gel-derived thin films of CCTO prepared at various annealing temperatures; 7000 °C, 7200 °C, and7500 °C have been reported. The frequency and temperature-dependent dielectric properties ofall these samples have been studied in metal-insulator-metal configuration using an impedanceanalyser. Dielectric measurements at room temperature show that the dielectric constant increaseswith the increase in annealing temperature from 700 °C–7500 °C. High dielectric constant (varyingfrom 600 to 3000 with the change in annealing temperature) has been observed at room temperatureat 100 kHz. The dielectric measurements below room temperature do not show any evidence ofstructural relaxation in CCTO except a little additional tilting of the TiO6 octahedra with decreasingtemperature. The dielectric response of Ba-doped CCTO films has also been reported.

Frequency and temperature-dependent dielectric properties of BaTiO 3 thin film capacitors studied by complex impedance spectroscopy

Thin film capacitors with BaTiO 3 as dielectric and RuO 2 as electrode material have been prepared by rf-magnetron sputtering at temperatures up to 750 °C and under various oxygen partial pressures. They have been analyzed by complex impedance spectroscopy in the temperature range 20–200 °C. At about 10 kHz, the grain effect is dominant and the electrical and dielectric properties of the bulk grains can be extracted. The activation energies of the conductivity are in the range 30–100 meV, characteristic for hopping of electrons. The dielectric constant at room temperature ranges from 60 to 1500, depending on the preparation conditions. There is a maximum in the temperature dependence of ε r that shifts to lower temperatures when the capacitors have been prepared with more oxygen. Above that temperature, Curie–Weiss behavior is observed with characteristic temperatures in the range 250–400 K. Biggest dielectric permittivity and lowest dielectric loss are obtained for films prepared at 750 °C at medium oxygen partial pressures. With increasing oxygen content the low-frequency semicircle and the effective dielectric permittivity, attributed to grain boundaries or an electrode interface layer, increases for the films prepared at all deposition temperatures. The films prepared with high oxygen partial pressure show increased crystallinity and dense columnar structure.