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.     

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.     

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.     

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.     

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.     

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.     

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.     

The Smallest Correction of an Inconsistent System of Linear Inequalities

The problem of calculating a point x that satisfies a given system of linear inequalities, A x #x2265; b, arises in many applications. Yet often the system to be solved turns out to be inconsistent due to measurement errors in the data vector, b. In such a case it is useful to find the smallest perturbation of b that recovers feasibility. This motivates our interest in the least correction problem and its properties.Let A x #x2265; b be an inconsistent system of linear inequalities. Then it is always possible to find a correction vector y such that the modified system A x #x2265; b #x2212; y is solvable. The smallest correction vector of this type is obtained by solving the least correction problem Let denote the convex cone which consists of all the points for which the system A x #x2265; u is solvable. Let denote the polar cone of . It is shown that the least correction problem has a simple geometric interpretation which is based on the polar decomposition of into and . A further insight into the least correction concept is gained by exploring the duality relations that characterize such problems.     

Growth of aluminium nitride whiskers by sublimation-recrystallization method

Aluminium nitride (AlN) with various morphologies was fabricated through a sublimation-recrystallization method. The influences of type of reactor and temperature gradient were explored, as well as the orientations and growth mechanism of the obtained AlN whiskers. In the early stage of preparation, a vapour-liquid-solid (VLS) mechanism dominated, producing AlN pillars, whiskers and noncrystalline fibres. In the later stage, as the catalyst liquid was removed by volatilization, the pillars and noncrystalline fibres stopped growing, but the growth of AlN whiskers continued through a vapour-solid (VS) mechanism. By Laue method and rotating-crystal method of x-ray diffraction, together with electron diffraction, most of the AlN whiskers were discovered to grow on planes , or , where l=0, 1, 2, 3, along crystal axes , or , where w=0, 1, 2, 3. Oblique grown whiskers also appeared, with a growth direction at an angle of about 54° to the growth plane, .     

On primitive and free roots in a finite field

In this paper them-dimensional extension of the finite field of orderq is investigated from an algebraic point of view. Looking upon the additive group as a cyclic module over the principal ideal domain , we introduce a new family of polynomials over which are the additive analogues of the cyclotomic polynomials. Two methods to calculate these polynomials are proposed. In combination with algorithms to compute cyclotomic polynomials, we obtain, at least theoretically, a method to determine all elements in of a given additive and multiplicative order; especially the generators of both cyclic structures, namely the generators of primitive normal bases in over , are characterized as the set of roots of a certain polynomial over .     

Structural features of Σ = 19, [110] GaAs tilt grain boundaries

= 19, [110] tilt grain boundaries have been observed to facet parallel to particular planes; the facets lie along _A/ _B, ( )_A/ )_B and ( )_A/( )_B. The structural unit of the = 19 ( )_A/( )_B [110] boundaries consists of 5- and 7-member rings, which are similar to the core structure of a/2[110] edge dislocations. The polarities in each grain on either side of the boundaries has been confirmed by CBED methods; a lower number of anti-site type cross-boundary bonds occur along the boundaries compared to when the polarity of one grain is reversed. The presence of 7-member rings and anti-site cross-boundary bonds results in a more open atomic structure at the boundary, shortening the distance between the first and the second {331} atomic planes from the boundary plane by 40%.     

Characteristics of Ba6−3x Nd8+2x Ti18O54 microwave dielectric ceramics derived from ethylenediaminetetraacetic acid precursor

ceramic powders were synthesized by the sol-gel method using ethylenediaminetetraacetic acids as chelating agent. Various techniques were used to characterize the precursors, powders and sintered ceramics. The microwave dielectric properties of ceramics sintered at different temperatures were also measured. Well-crystallized powders with about 80 nm particle size were obtained by calcination of the pulverized resins at 900 °C for 3 h in air. The (x=2/3) ceramics sintered at 1340 °C for 3 h had excellent microwave dielectric characteristics: =87.1, Qf=8710 GHz.     

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.     

Anisotropic flow and fracture in beryl [Be3Al2(SiO3)6]

Flow and fracture resulting from Vickers indentation testing on {0 0 0 1} and {10 0 } planar orientations have been examined. Flow characterized by indent shape differentiation was analysed to belong to the slip system with planes of the types { 10 0} and {11 0}. The ensuing fracture paths were resolved to propagate along {1 0 0} and {1 1 } cleavage planes whileK _c values obtained for them were 0.196 and 0.248 MPam^1/2, respectively.     

Structural, dielectric and electrical properties of Pb(SnTi)O3 ferroelectric system

We have synthesized (PST) with x=0.45, 0.55, 0.65 ferroelectric ceramics by a solid-state reaction technique and performed preliminary X-ray diffraction (XRD) analysis and the temperature and frequency dependence dielectric measurements on them. The a.c. and d.c. conductivities have been investigated over a wide range of temperature and the activation energy have also been calculated. It is observed that: (i) the relative dielectric permittivity () and loss tangent (tan ) are dependent on frequency, (ii) the temperature of dielectric permittivity maximum shifts toward lower temperature side, (iii) permittivity maximum decreases with the increase of Sn content in the (PST) compounds and (iv) no frequency dispersion of the dielectric permittivity reveals the no-relaxor behavior of the materials.     

New approach to isotropic texturing techniques on multicrystalline silicon wafers

Multicrystalline silicon wafers were isotropically textured using two kinds of modified acid texturing methods. One of the modifications is based on the introduction of the spray deposition method into the conventional acid etching of Si wafers. Silicon dioxide or photo-resist was sprayed on the Si wafers and used as masks for following acid etching process. The acid etching solution was modified with and various additives. Short circuit densities of the solar cells fabricated using those modified acid texturing were measured to be in the range between 30.8 and , which were at least higher than those from alkaline textured solar cells.     

Fine SrTiO3 and Sr(Mg0.4Ti0.6)O3–δperovskite ceramic powders prepared by a sol-precipitation process

Fine and Sr(Mg_0.4Ti_0.6)O_3– powders were prepared by a sol-precipitation method. Tetraisopropyl titanate was used as a starting material, which firstly chelated with the acetic acid to form a water-soluble titanyl precursor. This precursor was then precipitated in a strong NaOH solution, to which, a nitrate solution of the required ratio of was also added. By properly controlling reaction conditions, high crystalline undoped and Mg-doped strontium titanates with the dominating perovskite structures could be obtained directly at 80 °C. Owing to the chelating reaction of tetraisopropyl titanate with the acetic acid, the problem of the premature hydrolysis of titanium precursor was circumvented. The rates of the hydrolysis and condensation of titanyl acylate were also diminished. The final powder obtained had a uniform particle size of 40–60 nm. The formation mechanisms of and Sr(Mg_0.4Ti_0.6)O_3– were also discussed. This study indicated that in the entire sol-precipitation process, the mixing of cations was homogeneous and the diffusion of alkaline earth cations into titanium particles occurred all at atomic level, which allowed the realization of the optimized solid-solubility in the complex oxide system. This method could be exploited for the preparation of other doped titanates.     

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.     

Sputter deposition of bismuth and aluminum substituted dysprosium iron garnet films using sol-gel derived targets

Bismuth and aluminum substituted dysprosium iron garnet (Bi, Al:DylG) films were prepared by r.f. sputtering using sol-gel derived targets. The sol-gel derived target was coating on a rigid wafer. The coating was derived from the paste formed by a mixture of powders and viscous sol, which were prepared by the sol-gel process using nitrates as precursors, in appropriate stoichiometric ratios of . X-ray diffraction (XRD) patterns show that the crystallized films sputtered from the sol-gel derived targets are single phase garnet in nature, indicating that the sol-gel derived target is indeed a feasible alternative to a ceramic target. Magneto-optical measurements show that the prepared garnet film exhibits a strongest Faraday rotation of about 4.5°/m at a wavelength of 550 nm. It is believed that this sol-gel method for preparing the sputtering targets comprised of multi-component oxides provides a low cost target preparation process.     

Transmission electron microscope study of a directionally solidified Cu-MgCu2 eutectic

The crystallography and the interface structure of a unidirectionally solidified Cu-MgCu₂ eutectic alloy have been examined by transmission electron microscopy. The microstructure of the eutectic was found to be lamellar and regularly interrupted by faults. The preference of the particular orientation relationship could not be explained by relative atomic densities of the planes comprising the interface. Based on the defect contrast observed and extinction distance calculations, it is suggested that the fine array of defects observed at the interface may be characterized as steps with step vectors parallel to or Dislocations were also observed at the interface but they were rarely regular.