Showing papers on "Texture (crystalline) published in 2003"

{1 0 0}-Textured, piezoelectric Pb(Zrx, Ti1−x)O3 thin films for MEMS: integration, deposition and properties

Abstract: Pb(Zr-x, Ti1-x)O-3 (PZT) piezoelectric thin films are of major interest in MEMS technology for their ability to provide electro-mechanical coupling. In this work, the effective transverse piezoelectric coefficient e(31,f) of sol-gel processed films was investigated as a function of composition, film texture and film thickness. Dense, textured and crack-free PZT films have been obtained on silicon substrates up to a thickness of 4 mum. Crystallization anneals have been performed for every 0.25 mum. Nucleation on the previous perovskite layer combined with directional growth leads to a gradient of the compositional parameter x of +/-20% (at x = 0.53 average composition). Best properties have been achieved with {100}-textured film of x = 0.53 composition. Large remanent e(31,f) values of -11 to -12 C/m(2) have been obtained in the whole thickness range of 1-4 mum. These values are superior to values of undoped bulk ceramics, but smaller than in current, optimized (doped) bulk PZT. (C) 2003 Elsevier Science B.V. All rights reserved.

Magnetically aligned single wall carbon nanotube films: preferred orientation and anisotropic transport properties

Abstract: Thick films of single wall carbon nanotubes (SWNT) exhibiting in-plane preferred orientation have been produced by filter deposition from suspension in strong magnetic fields. We characterize the field-induced alignment with x-ray fiber diagrams and polarized Raman scattering, using a model which includes a completely unaligned fraction. We correlate the texture parameters with resistivity and thermal conductivity measured parallel and perpendicular to the alignment direction. Results obtained with 7 and 26 T fields are compared. We find no significant field dependence of the distribution width, while the aligned fraction is slightly greater at the higher field. Anisotropy in both transport properties is modest, with ratios in the range 5–9, consistent with the measured texture parameters assuming a simple model of rigid rod conductors. We suggest that further enhancements in anisotropic properties will require optimizing the filter deposition process rather than larger magnetic fields. We show that both ...

Combined XRD, EXAFS, and Mössbauer Studies of the Reduction by Lithium of α ­ Fe2 O 3 with Various Particle Sizes

Abstract: The electrochemical reduction of hematite with various particle sizes by metallic lithium has been studied by means of X-ray diffraction (XRD) Mossbauer and extended X-ray absorption fine structure (EXAFS) spectroscopy. Previous in situ XRD analysis coupled with electrochemical data showed that lithium can be inserted in the nanosized sample up to 1 Li per Fe2O3 whereas bulk material undergoes an irreversible Li-driven transformation from an hexagonal anionic packing to a close cubic packed framework as soon as 0.03 Li is inserted in the corundum structure. The present data show that only 0.6 Li per formula unit are actually inserted in the structure of small particles. The remaining lithium (0.4) is engaged in irreversible reduction of surface groups, or capacitive behavior. Beyond the solid solution domains, both samples are multiphase, and consist of Li2Fe2O3, Fe0 clusters (10-15 A) and inserted -Fe2O3, which proportions are used to calculate the mean iron oxidation state in the electrode as the reaction proceeds. From these data, we found that electrolyte decomposition can occur at very different steps of the reduction depending on the texture of the active materials. In addition, during the reduction process, we evidenced a reaction of disproportionation (3Fe2+2Fe3+ + Fe0), an intense electrochemical grinding of the hematite particles and the formation of extremely fine metallic surface clusters. For the first time, the EXAFS/X-ray absorption near-edge structure signature of the divalent intermediate Li2Fe2O3 phase is obtained.

Basal plane texture and flow pattern in friction stir weld of a magnesium alloy

Abstract: The microtextures in a friction-stir-welded magnesium (Mg) alloy, AZ61, with a nugget-shaped stir zone were analyzed by orientation imaging microscopy (OIM). The base material had a (0002) 〈uvi0〉 texture ((0002) parallel to the sheet plane, 〈uvi0〉 parallel to the welding direction). Friction stir welding produced texture components different from those of the base material in the stir zone. Except for the upper surface of the plate, most of the stir zone had a texture with a strong tendency for the (0002) basal plane to align with the surface of the hard pin of the welding tool. Formation of this texture component was attributable to shear deformation arising from the rotation of the hard pin. The (0002) planes tended to align with an ellipsoidal surface in the nugget-shaped stir zone. The present study suggests that the nugget shape, which is a characteristic feature of the stir zone, is strongly related to formation of the ellipsoidal surface described by the (0002) basal plane.

Scanning X-ray microdiffraction with submicrometer white beam for strain/stress and orientation mapping in thin films.

Abstract: Scanning X-ray microdiffraction (µSXRD) combines the use of high-brilliance synchrotron sources with the latest achromatic X-ray focusing optics and fast large-area two-dimensional-detector technology. Using white beams or a combination of white and monochromatic beams, this technique allows for the orientation and strain/stress mapping of polycrystalline thin films with submicrometer spatial resolution. The technique is described in detail as applied to the study of thin aluminium and copper blanket films and lines following electromigration testing and/or thermal cycling experiments. It is shown that there are significant orientation and strain/stress variations between grains and inside individual grains. A polycrystalline film when investigated at the granular (micrometer) level shows a highly mechanically inhomogeneous medium that allows insight into its mesoscopic properties. If the µSXRD data are averaged over a macroscopic range, results show good agreement with direct macroscopic texture and stress measurements.

Nematic Elastomer Fiber Actuator

Abstract: We report the synthesis and physical studies of a liquid crystalline elastomer fiber consisting of two side-chain liquid crystalline acrylates and a nonmesogennic comonomer side group that acts as a reactive site for cross-linking. The terpolymer was synthesized by radical polymerization, and the cross-linking of the network was achieved by using a diisocyanate unit. The fiber formed shows good liquid crystal alignment texture under a cross-polarizer microscope. Thermoelastic response shows strain changes through the nematic−isotropic phase transition of about 30−35%. A retractive force of nearly 300 kPa was measured in the isotropic phase. Static work loop studies show the viscoelastic losses in these materials to be very small. We also present preliminary studies on the effect of doping carbon nanotubes on the induced strain at the nematic−isotropic transition.

Angular dependent vortex pinning mechanisms in YBCO coated conductors and thin films

Abstract: We present a comparative study of the angular dependent critical current density in YBa2Cu3O7 films deposited on IBAD MgO and on single crystal MgO and SrTiO3 substrates. We identify three angular regimes where pinning is dominated by different types of correlated and uncorrelated defects. We show that those regimes are present in all cases, indicating that the pinning mechanisms are the same, but their extension and characteristics are sample dependent, reflecting the quantitative differences in texture and defect density. In particular, the more defective nature of the films on IBAD turns into an advantage as it results in stronger vortex pinning, demonstrating that the critical current density of the films on single crystals is not an upper limit for the performance of the IBAD coated conductors.

Mesoscopic Texture in Manganites

Abstract: From atom-scale stripes to micron-scale patches, manganites exhibit a wealth of fascinating phase-separated behavior.

An off-normal fibre-like texture in thin films on single-crystal substrates

Abstract: In the context of materials science, texture describes the statistical distribution of grain orientations. It is an important characteristic of the microstructure of polycrystalline films1,2,3,4,5, determining various electrical, magnetic and mechanical properties. Three types of texture component are usually distinguished in thin films: random texture, when grains have no preferred orientation; fibre texture6,7,8,9,10, for which one crystallographic axis of the film is parallel to the substrate normal, while there is a rotational degree of freedom around the fibre axis; and epitaxial alignment (or in-plane texture) on single-crystal substrates11,12,13,14,15, where an in-plane alignment fixes all three axes of the grain with respect to the substrate. Here we report a fourth type of texture—which we call axiotaxy—identified from complex but symmetrical patterns of lines on diffraction pole figures for thin films formed by solid-state reactions. The texture is characterized by the alignment of planes in the film and substrate that share the same d-spacing. This preferred alignment of planes across the interface manifests itself as a fibre texture lying off-normal to the sample surface, with the fibre axis perpendicular to certain planes in the substrate. This texture forms because it results in an interface, which is periodic in one dimension, preserved independently of interfacial curvature. This new type of preferred orientation may be the dominant type of texture for a wide class of materials and crystal structures.

Pulse electrodeposition of nanocrystalline nickel using ultra narrow pulse width and high peak current density

Abstract: The synthesis of nanocrystalline nickel by electrodeposition has been studied for more than 10 years. However, most attention has been on the adjustment of bath composition or development of new chemical additives. In this paper, a new method was developed to synthesize bulk nanocrystalline nickel without using any additives. Pulse plating with ultra narrow pulse width and high peak current density was employed to increase the deposition current density and the nucleation rate. At an on-time of 10 μs and an off-time of 90 μs, it was found that different surface morphologies, grain sizes, textures, and hardness were obtained at different current densities. Grain sizes ranging from 50 to 200 nm were obtained when the current density varied from 300 to 60 A dm −2 . The preferred orientation of the nickel deposit changed from a weak (2 0 0) fiber texture to a strong (2 0 0) fiber texture when the peak current density increased from 40 to 100 A dm −2 . It was obtained however that the intensity of the (2 0 0) fiber orientation decreased when there was a further increase in the current density. The hardness of the nickel deposit was also found to increase with increasing peak current density when it changed from 20 to 150 A dm −2 , but the hardness tended to decrease when the current density was above 150 A dm −2 . These experimental findings are considered to relate to the change in cathodic overpotential which affects both the grain size, the internal stress, the porosity, and the preferred orientation.

Dielectric and piezoelectric properties of 〈001〉 fiber-textured 0.675Pb(Mg1/3Nb2/3)O3–0.325PbTiO3 ceramics

Abstract: The 0.675Pb(Mg1/3Nb2/3)O3–0.325PbTiO3 (PMN–32.5PT) ceramic composition (with 1 wt. % excess PbO) was fiber textured in the 〈001〉 direction by the templated grain growth process using 5 vol % oriented {001}-BaTiO3 platelet crystals as the templates. The templated ceramics annealed at 1150 °C for 5 h attained texture fractions as high as 0.9. The fiber-textured samples showed an increase in the piezoelectric, electromechanical coupling, and compliance coefficients when poled and measured in the 〈001〉-textured direction. The low drive field (<5 kV/cm) d33 coefficients in the 〈001〉, measured directly from unipolar strain-field measurements, were ∼1150 pC/N. This d33 coefficient is 1.2–1.5 times greater than randomly oriented samples. The poled emax and ert for a 0.9-textured PMN–32.5PT ceramic were 21 500 and 2450, respectively. Factors limiting further property improvements are discussed.

(Reactive) Templated Grain Growth of Textured Sodium Bismuth Titanate (Na1/2Bi1/2TiO3-BaTiO3) Ceramics—I Processing

Abstract: Textured (Na1/2Bi1/2)TiO3-BaTiO3 (5.5 mol% BaTiO3) ceramics with pc (where pc denotes the pseudocubic perovskite cell) orientation were fabricated by Templated Grain Growth (TGG) and Reactive Templated Grain Growth (RTGG) using anisotropically shaped template particles. In the case of TGG, molten salt synthesized SrTiO3 platelets were tape cast with a (Na1/2Bi1/2)TiO3-5.5 mol%BaTiO3 powder and sintered at 1200°C for up to 12 h. In the RTGG approach, Bi4Ti3O12 (BiT) platelets were tape cast with a Na2CO3, Bi2O3, TiO2, and BaCO3 powder mixture and reactively sintered. The TGG approach using SrTiO3 templates resulted in >90% texture along [001] whereas the RTGG approach using BiT templates resulted in 80% texture. The grain orientation distribution along the textured direction, as measured by X-ray rocking curve, showed a full width at half maximum of ∼8° and a texture fraction of 80%.

Microstructure and texture of EB-PVD TBCs grown under different rotation modes

Abstract: The role of vapor incidence pattern (VIP) on the microstructure and texture of thermal barrier coatings (TBCs) produced by electron-beam physical vapor deposition (EB-PVD) is examined. Two distinct VIPs are induced by proper design of the substrate rotation mode. One is the sunrise–sunset pattern typical of conventional deposition on the curved face of a rotating cylinder (mode A), and the other is a conical pattern resulting when deposition is done on the cylinder base at an offset distance from the plume axis (mode P). These geometries afford fundamental insight on the processes of microstructure and texture evolution and also have practical implications to the variability of properties that may be expected between the body and platform regions of a turbine airfoil. Comparable deposition rates and thickness uniformity can be achieved by proper selection of the experimental geometry. Both coatings exhibit the typical 〈100〉 texture normal to the substrate, but mode A also yields a preferred in-plane orientation which is absent in mode P. The ensuing differences in column packing and tip shadowing yield lower densities and larger pipe-like inter-columnar voids in mode P. The absence of an in-plane evolutionary selection mechanism in the latter also leads to narrower columns than in mode A.

Strongly coupled critical current density values achieved in Y1Ba2Cu3O7−δ coated conductors with near-single-crystal texture

Abstract: One of the most intensely researched subjects in the development of YBa2Cu3O7−δ (YBCO)-based coated conductors is the methodology for achieving ever-sharper film texture on flexible metal substrates. This is a critical issue due to the intrinsic weak-link behavior that results in depressed critical current density (Jc) in polycrystalline YBCO. Using ion-beam-assisted deposition of magnesium oxide, we have achieved YBCO texture on superalloy substrates approaching that on single-crystal oxide substrates. This advance has allowed us to fabricate coated conductor samples with Jcs that are as high as for films on oxide crystals; for example, >2 MA/cm2 (75 K, self-field) at a YBCO thickness of ∼1.5 μm.

Synthesis of a Li−Mn-oxide with Disordered Layer Stacking through Flocculation of Exfoliated MnO2 Nanosheets, and Its Electrochemical Properties

Abstract: A new type of layered Li−Mn-oxide with heavy stacking faults has been synthesized via flocculation of delaminated MnO2 nanosheets with Li ions. Flocculated products were characterized by powder X-ray diffraction, thermal analysis, scanning electron microscopy, transmission electron microscopy, chemical analysis, N2 adsorption, and electrochemical measurements. Chemical analysis and X-ray diffraction results indicated that the colloidal MnO2 nanosheets were restacked to produce a lamellar material Li0.36MnO2·1.15H2O with a basal distance of 0.72 nm. Simulation of the X-ray diffraction profile suggested that the sheet-to-sheet registry was nearly random with partial order (20−40%) involving a shift vector of (1/3, 2/3, 1). A disordered mesoporous texture was resulted via the stacking of a limited number of the sheets and irregular aggregation of the resulting restacked crystallites. The structure proved to be stable during low-temperature soft-chemical synthetic processes while thermo-metastable upon heat t...

X-ray microdiffraction study of growth modes and crystallographic tilts in oxide films on metal substrates

Abstract: The crystallographic texture of thin-film coatings plays an essential role in determining such diverse materials properties as wear resistance, recording density in magnetic media and electrical transport in superconductors. Typically, X-ray pole figures provide a macroscopically averaged description of texture, and electron backscattering provides spatially resolved surface measurements. In this study, we have used focused, polychromatic synchrotron X-ray microbeams to penetrate multilayer materials and simultaneously characterize the local structure, orientation and strain tensor of different heteroepitaxial layers with submicrometre resolution. Grain-by-grain microstructural studies of cerium oxide films grown on textured nickel foils reveal two distinct kinetic growth regimes on vicinal surfaces: ledge growth at elevated temperatures and island growth at lower temperatures. In addition, a combinatorial approach reveals that crystallographic tilting associated with these complex interfaces is qualitatively described by a simple geometrical model applicable to brittle films on ductile substrates. The sensitivity of conducting percolation paths to tilt-induced texture improvement is demonstrated.

Magnetic properties of aligned Fe-filled carbon nanotubes

Abstract: We report on the magnetic properties of Fe-filled multiwalled carbon nanotubes (MWNTs) grown by chemical vapor deposition (CVD) on Si substrates with ferrocene as precursor. The MWNTs are aligned perpendicularly to the substrate plane. X-ray diffraction analyses indicate the presence of both bcc and fcc iron with a relatively strong texture. Magnetometry measurements show a pronounced magnetic anisotropy with the easy axis perpendicular to the substrate plane and parallel to the axis of the aligned MWNTs, respectively. The low-temperature behavior suggests a negligible coupling between the two iron phases. We accessed the magnetic properties of individual Fe-filled MWNTs by electron holography using a transmission electron microscope (TEM).

Strain and texture analysis of coatings using high-energy x-rays

Abstract: We investigate the internal strain and crystallographic orientation (texture) in physical-vapor deposited metal nitride coatings of TiN and CrN. A high-energy diffraction technique is presented tha ...

Anisotropy and non-uniformity in plastic behavior of AZ31 magnesium alloy plates : Special issue on platform science and technology for advanced magnesium alloys, II

Abstract: On the AZ31-O magnesium alloy plates of 20 mm in thickness, basal plane texture was studied for the samples taken from different layers. Compression tests were carried out in the rolling, width and thickness directions at room temperature. Tensile tests were conducted for the specimens taken from the different layers of the plates in different planar directions. The formability in deep drawing and stretch forming was evaluated for the thin sheet specimens taken from different layers of the plates and the results were discussed in relation to the texture and mechanical properties. The severity of the basal plane texture is higher at the surface layer than the inner layers. In tensile tests at room temperature, proof stress is higher for the surface layer than the inner layers, whereas elongation is lower and r-value is higher at the surface layer. In compression tests at room temperature, yield stress in the rolling and width directions is appreciably lower than in the thickness direction. At 573 K, anisotropic and non-uniform deformation behavior disappeared. Thin sheet specimens taken from inner layers of the plates showed higher formability than those from the surface layer in deep drawing and stretch forming. It is concluded that the formability of magnesium alloy sheets can be improved by decreasing the severity of the basal plane texture.

Polymer-induced microstructure variation in zinc oxide crystals precipitated from aqueous solution

Abstract: The microstructure of zinc oxide particles precipitated in the presence of a poly(ethylene oxide-block-methacrylic acid) (P(EO-b-MAA)) and a poly(ethylene oxide-block-styrene sulfonic acid) (P(EO-b-SSH)) diblock copolymer was investigated. The crystals precipitated with the P(EO-b-MAA) copolymer consist of a region with a lower but still relatively high order close to a central grain boundary and regions of very high order further away from the central grain boundary. Selected area diffraction (SAD) found single crystalline particles in the control sample, confirmed the formation of single crystalline domains with slightly different orientations with the P(EO-b-MAA) copolymer, and confirmed the formation of a mosaic texture with the P(EO-b-SSH) copolymer. High-resolution transmission electron microscopy images exhibit little defects in the control sample. More defects are found close to the central grain boundary in the sample precipitated with P(EO-b-MAA). With the P(EO-b-SSH) copolymer, a single crystal...

Physicochemical Surface Properties of Fe, Co, Ni, and Cu-Doped Monolithic Organic Aerogels

Abstract: Fe, Co, Ni, and Cu-doped monolithic organic aerogels were prepared by the sol−gel method through the polymerization of a resorcinol formaldehyde mixture containing the metal acetates as polymerization catalysts. The aerogels were supercritically dried with carbon dioxide, and their surface morphology and pore texture were characterized by means of scanning electron microscopy, N2 adsorption at −196 °C, and mercury porosimetry. The dispersion, distribution, and chemical nature of the metal-containing phase were analyzed by X-ray diffraction, backscattering electron imaging, energy-dispersive X-ray, high-resolution transmission electron microscopy, and X-ray photoelectron spectroscopy. According to these analyses, the surface morphology and pore texture were influenced by the metal acetate present because of its different catalytic activity and pH of the initial mixtures. The metal-containing phase was very highly dispersed in Co and Ni-doped monolithic organic aerogels, and it was homogeneously distributed...