Computer-aided design of small patch antenna using (Al, Mg)TaO2 ceramics

The microwave dielectric properties of (AMT) ceramics and the design of small coplanar waveguide fed antenna (CPWFA) have been investigated. ( and ( have orthorhombic and tetragonal structure, respectively. As ( concentration increased, AMT ceramics transformed into the tetragonal structure. Specimens having tetragonal single phase could be obtained above x=0.6. As ( concentration increased, the grain size, dielectric constant and quality factor (Q) significantly increased and the temperature coefficient of resonant frequency changed from negative to positive. The of was realized at x=0.65 and the Q · f _O value and for this composition were 112 470 GHz and 26.1, respectively. Newly developed dielectric materials were used for 1.5 GHz band CPWFA design and fabrication. The size of the CPWFA can be reduced by using high dielectric constant AMT ceramics, insetting slits into the patch, and fabricating CPW feed line in the ground plane. The slits play a role in not only lowering a center frequency but also fine tuning for the proposed antenna together with the open stub of CPW feed line. The CPWFA with slits has a lower center frequency than the conventional CPWFA, which suggests that the antenna size can be reduced by as much as 16.3%. The structure simulations of the CPWFAs have been performed to obtain impedance matching and to investigate the effects of slits. Experimental results of the fabricated device were in good agreement with the simulation.     

Electrical and magnetic properties of BaTiO3−(Ni0.3Zn0.7)Fe2.1O4 composites

Ceramic composites consisting of ferroelectric and ferrite ( were synthesized by the mixed oxide route. The phase assemblage, electrical and magnetic properties of the samples were investigated. The results indicates that the phase is compatible with ( phase, and dense diphasic composite ceramics were obtained. Electrical resistivity of composites varies with increasing amounts of ( phase, and shows a percolation-like drop. Magnetic hysteresis loops were observed in the composites.     

Fabrication and electrical properties of lead zirconate titanate thick films using a new sol-gel processing technique

Lead zirconate titanate (Pb ( , PZT) ferroelectric films 2–60 m in thickness have been successfully fabricated on Pt-coated oxidized Si substrates by a new sol-gel-based process. The films are a 0-3 ceramic–ceramic composite formed by dispersing ceramic powders in a sol-gel solution. The precursor solution for spin coating was prepared from lead acetate, tetrabutyl titanate, and zirconium nitrate. The microstructure and morphology of the prepared PZT thick films were investigated via X-ray diffractometry (XRD) and scanning electron microscopy techniques. XRD analysis shows that the thick films possess single-phase perovskite-type structure, no pyrochlore phase exists in thick films, and SEM micrographs suggest that the PZT thick films were uniform, dense, and crack free. A dielectric constant of 860, loss tangent of 0.03, remanent polarization of , and a coercive field of were measured on 50 m thick films.     

Electrical properties of Pd–Au/(In x –Sn1 – x ) Oxide/Si(p)/Al heterojunction diodes

Current–voltage (I–V ) and capacitance–voltage – characteristics of [Pd–Au/( – ) Oxide/Si(p)/Al] semiconductor oxide semiconductor (SOS) solar cells were measured in the temperature range between 300 and 500 K. The dark forward current–voltage curves were found to be independent of temperature. Consequently, the diode quality factor was temperature dependent. Analysis of the data indicated that the predominant carrier transport mechanism of the samples in the intermediate bias voltage region was thermionic field emission and recombination tunneling. From the experimental data it was found that, the open circuit voltage – , the short circuit current – and the fill factor 0.28–0.32, under illumination of 1124 lux.     

Effect of PFT substitution on dielectric properties of PFW-PFN perovskite ceramics

Perovskite phase formation and dielectric characteristics of ceramic system with addition of were investigated in order to examine the influence of . The ceramic system powders were synthesized via a B-site precursor route. Peculiar behaviors of frequency dispersion in dielectric constant spectra in the paraelectric region were observed due to increasing conductivity. Lattice parameters, dielectric maximum temperatures, and maximum dielectric constants increased with increasing content.     

Preparation and properties of PTCR ceramics with low resistivity sintered at low temperature

Two types of positive temperature coefficient of resistance (PTCR) ceramics with relatively low room-temperature resistivity were prepared using the four-component system (Ba, Sr, Ca, Pb)TiO₃ with lanthanum oxide (La₂O₃) as the donor dopant and boron nitride (BN) as the sintering aid. The first type of materials was sintered at 1080 °C for 2 h. It has a Curie point , a room-temperature resistivity of 58 cm and a resistivity jump of around . For the second type of materials that were sintered at 1100 °C for 20 min, , and . These PTCR ceramics are considered to be suitable materials for fabricating multilayer PTCR devices by the co-firing process. Factors associated with the composition that influence the PTCR property of the materials are discussed.     

Effect of the addition of Y2O3 on the structure, microstructure and piezoelectric properties of PZT(53/47)

In this work, an attempt is made to study system with x=0.0125, 0.025, 0.050, 0.075 and 0.1. It was shown that there is limited solid solubility (0.625 mol %) of or 1.25 mol % of in PZT(53/47). For higher levels of dopant, mainly two other extra second phases were detected. The first was a Zr-rich phase in which some and small amounts of was dissolved. The second one was a Pb solid solution composed of mainly PbO, and which was initially also seen in calcined samples. The formation of Zr-rich phase is thought possibly to originate due to the sublimation of Pb from source during the sintering process. For higher x values, a structural shift towards Ti-rich region of PZT's phase diagram is seen. All piezoelectric parameters of the doped samples such as , are seen to decline sharply compared to that of undoped samples. Increasing the level of dopant gave rise to the increase of conductivity and dielectric loss of sintered samples. The formation of non-ferroelectric extra phases, and the Zr/Ti change of the main formed phase is believed to be responsible for this behavior.     

Anisotropic lattice coherency of GaAs nanocrystals deposited on Si(100) surface by molecular beam epitaxy

Lattice coherency and morphology of GaAs nanocrystals grown on Si(100) substrate have been studied by transmission electron microscope in order to see growth mechanism of the nanocrystals. GaAs nanocrystals consisting of four {111} facet planes and a rectangular basal plane with four sides along [01 ] and [011] directions have grown on the Si surface. Either (011) or (01) lattice planes along the minor axis on the rectangular basal plane in the GaAs nanocrystal are completely-coherent with {011} lattice planes in the Si substrate. On the other hand, another (01) or (011) lattice planes along the major axis are partially-coherent with those in the Si substrate. When the lattice planes of the either (011) or (01), which is randomly determined by local atomic structures, become partially-coherent with those in the Si substrate to relax accumulated lattice strain, the growth rate of nanocrystal is remarkably increased along the direction parallel to unstrained (011) or (01) planes which prevents from each area of the strained {011} planes in the nanocrystals increasing. The anisotropic lattice coherency between the GaAs nanocrystals and the Si substrate causes the anisotropic morphology of the GaAs nanocrystals which is elongated the directions parallel to the strained {011} planes.     

Highly conductive and transparent In-doped zinc oxide thin films deposited by chemical spray using Zn(C5H7O2)2

Highly conductive and transparent indium-doped zinc oxide, ZnO, thin films were deposited on sodocalcic glass substrates by chemical spray, using zinc acetylacetonate, Zn(C₅H₇O₂)₂, and doped with indium chloride. Substrate temperature, dopant concentration in the starting solution and the kind of alcohol used as a solvent (methanol, ethanol and isopropanol) were varied in order to optimize deposition conditions. The lowest resistivity value of was obtained with ethanol at a substrate temperature of 475 °C and a [In]/[Zn]=2.5 at % ratio in the starting solution. The mobility and the carrier concentration values were in the order of and , respectively. For optimal deposition conditions no preferential growth was found. Surface morphology was altered depending on the kind of alcohol used, producing a rough surface with isopropanol than with methanol or ethanol. Transmittance average was of the order of 85%, at 550 nm.     

Hole Density in Charge Stripes and Effect of Next-Nearest-Neighbor Transfer

By applying a variational Monte Carlo method to the two-dimensional t-J model, a couple of properties of striped states are studied. In the charge domain walls vertical (or horizontal) to the lattice (VDW), the hole density is favorable in energy similarly for 0.5 , whereas in the diagonal domain walls (DDW) the stable hole density is limited to = 1. Negative next-nearest-neighbor transfer (t/t < 0) further stabilizes VDW with = 0.5 and DDW with = 1 against the -wave superconducting state.     

Growth and characterization of Zn1 – x Mg x S thin films for electroluminescent applications

:Mn thin films (x=0–0.30) were prepared by thermal co-evaporation of ZnS, Mg and Mn. The structural investigation shows the solid solution is formed in the Mg composition range x=0–0.25 and phase segregation occurs at higher Mg composition (x > 0.25). The optical band gap shows an increase with increase of Mg composition. The electroluminescent emission corresponding to the transition ion shows a blue shift with increase of Mg composition in the film. :Mn films could be used as an active layer in a.c. thin film electroluminescent (ACTFEL) devices for obtaining green emission color.     

Cu3Ge Schottky contacts on n-GaN

The electrical properties and thermal stability of (hereafter referred to as ) Schottky contacts to n-GaN as a function of the Ge concentration and annealing temperature are studied. Upon rapid thermal annealing the /n-GaN Schottky diode is formed at 300 °C and is stable up to 650 °C. At 700 °C the agglomeration occurs in the films. For the Cu-25 at % Ge films the ideality factor, n, barrier height, , and flat band barrier height, , of the /n-GaN diodes are in the ranges of 1.22–1.36, 0.53–0.72 eV, and 0.65–0.97 eV, respectively, being decreased with the annealing temperature. Higher Ge concentration in the Cu-35 at % Ge films results in larger n, , and of /n-GaN Schottky diodes. The film is expected to be a suitable candidate for stable Schottky contacts to n-GaN at elevated temperatures.     

Higher approximations for supersonic flow past slowly oscillating bodies of revolution

Summary Supersonic flow past slowly oscillating pointed bodies of revolution is studied. Starting from the complete nonlinear potential equation an elementary linearized solution is discussed and it is shown how this solution together with the method of matched asymptotic expansions can be used to derive an elementary second-order slender body theory. This approach is further demonstrated for the oscillating cone and its range of validity is evaluated by comparison with other theoretical methods.

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Zusammenfassung Es wird die Überschallströmung um langsam schwingende spitze Rotationskörper untersucht. Ausgehend von der vollständigen nichtlinearen Potentialgleichung wird zuerst eine elementare linearisierte Lösung besprochen und gezeigt, wie diese Lösung im Verein mit der Method of matched asymptotic expansions zur Herleitung einer elementaren Schlankkörpertheorie zweiter Ordnung verwendet werden kann. Die Theorie wird am Beispiel des schwingenden Kegels näher erläutert und mit anderen Methoden verglichen.

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Symbols a Velocity of sound - c _N Normal force coefficient - Damping coefficient - F _(x) Dipole distribution - k Reduced frequency - M Mach number - R (x) Meridian profile - t Time - x, r, Cylindrical coordinates - - Ratio of specific heats - Amplitude of oscillation - Thickness ratio - Perturbation potential - Zero angle of attack potential - æ - Velocity potential - Out-of-phase potential - - In-phase potential - - Source coordinate With 4 Figures     

Combined effect of partial calcination and sintering condition on low loss Mn-Zn ferrite

In order to achieve highly densified lower loss Mn-Zn ferrite materials, various powder processing routes have been under investigation. In this report, a lower sintering temperature with lower oxygen partial pressure and proper attrition milling duration are suggested. From the previous study, a partial calcination procedure was studied and an optimum partial calcination level was found. Accordingly, Mn_0.71Zn_0.22Fe_2.07O₄ ferrite was prepared by calcination with small amounts of CaCO₃, SiO₂, Nb₂O₅ and SnO₂. The partially calcined ferrites were made by calcining the mixture of the whole amount of ZnO and amount of Fe₂O₃ and Mn₃O₄ and sintering the mixture of the calcined powders and the remaining of Fe₂O₃ and Mn₃O₄. Initially, from the 40 min secondary milling and the partial calcination, lower temperature (1300°C) sintered samples showed a power loss of 340 mW cm^–3 at 90°C. Secondly, several milling durations showed secondary milling had a more profound effect on magnetic properties than primary milling. The 20 min primary and 90 min secondary milling showed lower core loss around 320 mW cm^–3 at 1300°C and 1250°C, suggesting the sintering temperature could be reduced to 1250°C. Thus, the proper sintering condition of lower oxygen partial pressure at 1250°C was studied. As a result, lower loss with higher density was realized.     

Microstructure studies of ZnO nanoneedles

ZnO nanoneedles with uniform diameter and length have been synthesized using thermal evaporation approach. Their microstructure and anisotropic growth mechanism have been studied by means of scanning electron microscopy, high-resolution electron microscopy and convergent-beam electron diffraction. The ZnO polarity induces fast [0001] axial growth of the ZnO nanoneedles which are directed either by high index and planes or by ZnO nanoparticle nuclei formed at the (0001)-Zn growth fronts. Moreover, the {0002} stacking faults are believed to assist the ZnO nanoneedle growth. The slope surfaces at the inactive -O bottom geometrically favor ZnO nanorods growth through twinnings.     

The effect of temperature on the electric conductivity property of Bi3Zn2Sb3O14 pyrochlore type phase

The electric conductivity characteristic of ceramics was investigated by impedance spectroscopy in the frequency range from 5 Hz to 13 MHz. Electric measurements were performed at temperatures in the range from 25 to 700 °C. The phase type pyrochlore was synthesized by the polimeric precursors method. Ceramic presenting a relative density of 98% of the theoretical density was prepared. The data were presented in Nyquist diagrams form, from which the electric resistivity was determined. The electric conductivity followed the Arrhenius law with an apparent activation energy of the conduction process equal to 1.37 eV. The electric conductivity at room temperature was determined by extrapolation being equal to . Between 400 and 700 °C, the conductivity values were and , respectively.     

A model of non-Ohmic conduction in ZnO varistors

A simple phenomenological approach to non-Ohmic conduction in zinc oxide based varistors is suggested. The decrease of the barrier height on voltage is considered as a reason of varistor effect. This model gives the relationship between the current density j and the average electric field E in the form , where the nonlinearity factor α is proportional to the rate of change of the barrier height on voltage . The nonlinearity factor α or the normalized nonlinearity coefficient (E ₁ is the electric field at fixed current density) can be used instead of the traditional but empirical nonlinearity coefficient . Fairly reasonable agreement between suggested model and experimental results is found. On leave from Dniepropetrovsk National University, Dniepropetrovsk, Ukraine; Fax: +52-953-5320214, ext. 106     

Temperature-dependent current–voltage and capacitance–voltage characteristics of the Ag/n-InP/In Schottky diodes

The current–voltage (I–V) and capacitance–voltage (C–V) characteristics of Ag/n-InP/In Schottky diodes have been studied in a wide temperature range by steps of 10 K. A decrease in the apparent barrier height (BH), , an increase in the ideality factor, and a nonlinearity in the activation energy plot with a decrease in temperature have been seen. The experimental values of BH and ideality factor for the devices were calculated as 0.61 eV and 1.18 at 320 K, 0.48 eV and 1.52 at 200 K, and 0.20 eV and 3.89 at 70 K, respectively. An abnormal decrease in the experimental BH and an increase in the ideality factor n with a decrease in temperature have been explained by the barrier inhomogeneities at the metal–semiconductor (MS) interface. From the temperature dependent I–V characteristics of the Ag/n-InP contact, that is, and A* as 0.79 and 0.55 eV, and 7.96 and , respectively, have been calculated from a modified vs. 1/T plot for the two temperature regions. The Richardson constant values are in close agreement with the value of known for n-type InP. Moreover, the difference between the apparent BHs obtained from the I–V and C–V characteristics has been attributed to the existence of Schottky BH inhomogeneity.     

Etch characteristics of Pt by using BCl3/Cl2-gas mixtures

The inductively coupled plasma etching of platinum with -gas chemistries was examined. Plasma characteristics were investigated with increasing ratios using a Langmuir probe and optical emission spectroscopy. The chemical reaction during the Pt etching was also examined via the chemical binding states of the etched surface, by X-ray photoelectron spectroscopy. The relationship between plasma and etch characteristics with various gas mixing ratios is discussed. On the basis of the relationship, the Pt etching mechanism with -gas chemistries is described.     

Theory of dielectric polarization of a substance. Calculation of dielectric permittivity of water,ammonia, and chlorine

A theory of dielectric polarization of a substance is developed. The theory is verified by experiment and by phenomenological relations that follow from the determination of polarization, molar polarization, and dielectric permittivity.Notation _s static dielectric permittivity - high-frequency dielectric permittivity - _s permittivity perpendicular to the acisC - _s permittivity in the direction of the axisC - a average molecular polarizability - dielectric susceptibility - _i molecular hyperpolarizability - p ⁰ constant dipole moment of a molecule - p dipole moment of a molecule in condensed state - p _add additional dipole moment of a molecule - P polarization of a substance - P _m molar polarization - k Boltzmann constant - T Kelvin temperature - t Celsius temperature - angle between the vectors and - F internal electric field strength - Û internal interaction energy, J·mol^–1 - û internal interaction energy per molecule - N ₀ Avogacro number - V ₀ molar volume - a _t total molecular polarizability - H ⁰ (H) enthalpy as a function of temperature - l(x) Langevin function - n molecular concentration Murmansk State Academy of Fish Fleet. Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 68, No. 5, pp. 767–773, September–October, 1995.