High Degree Of Texture Research Articles

Defect Chalcopyrite Cu(In1-x, Gax)3Se5 Polycrystalline Thin-Film Materials

AbstractThe defect chalcopyrite material CuIn3Se5 has been identified as playing an essential role in efficient photovoltaic action in CuInSe2-based devices; it has been reported to be of n-type conductivity, forming a p-n junction with its p-type counterpart CuInSe2. Because the most efficient cells consist of the Cu(In1-xGax)Se2 quaternary, knowledge of some physical properties of the Ga-containing defect chalcopyrite Cu(In1-xGax)3Se5 may help us better understand the junction phenomena in such devices.Polycrystalline Cu(Inl-xGax)3Se5 (with O<x<l) thin films have been grown on 7059 Coming glass, soda-lime silica glass, n-type (100)Si, and Mo-coated soda-lime glass by coevaporation from elemental sources. In general, optical data show direct optical bandgaps that range from 1.20 eV for x=0 to ∼1.85 eV for x=l (this represents ∼200 meV higher bandgaps than the Cu(In, Ga)Se2 counterparts). Micrographs of the thin films show a substantial change in morphology as the Ga content is increased—for identical conditions of growth rate and substrate temperature. X-ray diffraction patterns agree with previously publish data for the ternary case (x=0), where these materials have been referred to as ordered vacancy compounds. Pole figures confirm a high degree of texturing in the films and a change in preferred orientation as Ga content is increased.

Deformation-induced texture in cold-rolled Ag sheathed bi(2223) tapes

We have found that the Bi(2212) grains in unreacted Ag/Bi(2223) tapes at the end of the cold-rolling process show already a high degree of texture. X-ray diffraction analysis and current transport measurements at 77 K in magnetic fields up to 0.5 T have been performed before and after reaction on tapes with thicknesses in the range from 75 to 286 μm (filament thickness between 30 and 115 μm). The critical current density j c increases for smaller tape thicknesses, a maximum being found for a tape thickness of about 90 μm, below which sausaging effects are observed. The mean misalignment angles of Bi(2223) grains in these tapes have been determined by angle-dependent transport critical curent data at 77 K. We have found that the mamin reason for the enhancem,ent of j c for thin tapes in due to the higher average texture of the Bi(2223) grains when compared to thick tapes. This is a direct consequence of the high degree of texture of Bi(2212) grains after the cold-rolling process, which has been observed here on 90 μm thick tapes with j c(77 K, 0 T) reaching between 25 and 30 kA/cm 2.

Nanophase precursors for high-Jc Ag-clad superconducting BiPbSrCaCuO tapes

A controlled coprecipitation technique has been used to synthesize precursors of superconducting BiPbSrCaCuO ceramics. The oxalate precursors were nano-sized powders with high homogeneity, low crystallinity, and well-defined stoichiometry. These precursors have been used to fabricate superconducting tapes by the powder-in-tube technique, which involves the use of Ag sheaths. The nano-sized homogeneous powders require considerably reduced tape-processing (sintering) times for Bi-2223 formation, and provide 'clean' intergrain boundaries within the sintered tapes. As a result, high critical transport current density, Jc, can be obtained even in multiphase composites that do not necessarily exhibit a high degree of texture. To gain further insight into the role of microstructural details at each step of the tape fabrication, extensive X-ray diffraction analyses and scanning electron microscopy measurements have been made. The influence of homogeneity and grain size distribution on the superconducting properties of the Ag-clad tapes is discussed. We have reproducibly achieved, within 60 h of the thermal processing, Jc values as high as 4.4*104 A cm-2 at 77 K in zero applied magnetic field.

Ion-beam-assisted deposition of molybdenum nitride films

A series of molybdenum nitride films was synthesized by electron beam evaporative deposition of molybdenum, with simultaneous bombardment by nitrogen ions from a Kaufman ion source. The nitrogen ions were accelerated to 500 or 1000 eV. The film compositions and structures were determined using Rutherford backscattering spectrometry and X-ray diffraction respectively. Effective reflection and sputtering coefficients for nitrogen incident on the molybdenum nitride surfaces were extracted from the data. These coefficients were used to calibrate the deposition system and allowed the deposition of molybdenum nitride films with control of the nitrogen atom concentration to ±2.3 at.%. In general, the films were polycrystalline with a high degree of texturing. The phases found in order of increasing measured nitrogen content were as follows: γ-Mo2N (f.c.c.), β-Mo16N7 (b.c.t.), B1-MoN (f.c.c.) then δ-MoN (h.c.p.).

High temperature superconductors for power cables

Six major European electrical companies have been collaborating together in a precompetitive BRITE/EURAM research project targetting the application of high T c superconductors in power cables and other high-current applications. The main objectives that have been addressed are: (1) identifying new superconducting phases with superior properties for the intended applications, including improved flux pinning at liquid nitrogen temperature; and (2) devising and improving techniques for fabricating experimental conductors with a high degree of texturing. The results obtained to date include the discovery of a new (Pb,Cd)-1212 superconducting phase and the fabrication and assessment of experimental conductors incorporating YBCO and BSCCO phases. Some of these samples provide encouragement for high-current applications.

Microstructural characterization of Ag-sheathed Tl-Ba-Ca-Cu-O and Bi-Sr-Ca-Cu-O superconducting tapes by analytical electron microscopy

The microstructures of Tl(1223) and Pb-doped Bi(2223) silver tapes produced by the powder-in-tube (PIT) method have been examined by scanning electron microscopy (SEM), transmission electron microscopy (TEM) and energy dispersive spectrometry (EDS). The Tl tapes annealed below the melting point exhibited fine grains and a high density of pores while tapes subjected to partial melting prior to solid state annealing were fully dense with large grains. However, these tapes also showed an increase in the size and density of impurity particles, particularly CaO and a Ba-Cu rich phase. Silver powders added to the precursors tended to promote the growth of Tl(1223) at lower temperatures but also interfered with the development of texture by providing nucleation sites of random orientations. In contrast, the Bi(2223) tape exhibited a high degree of texture and alignment. The incorporation of silver within the superconducting phase was found to be negligible for both the Tl(1223) and Bi(2223) tapes. >

Effect of low temperatures on the wear mechanism of solid lubricant coatings in vacuum

The conditions of transition to mild wear and the regularities of secondary structure formation in solid lubricant coatings of various compositions were studied using a variety of methods. It was found that the fatigue mechanism of fracture of these coatings is realized in the case of a high degree of texturing of the lamellar lubricant component within the active layer, owing to plasticization of the binder during sliding. The parameters of transition to a mild mode of wear are defined by the testing temperature and by the nature of the polymer binder.

Texture study of two molybdenum shaped charge liners by neutron diffraction

The textures of two different conical shaped liners, fabricated by the same forging processes from arc-cast and powder-sintered ingots, were investigated by using neutron-diffraction measurements and three-dimensional orientation-distribution-function (ODF) analysis. The major textures of both liners could be described by the (1 1 1) 〈uv w〉 and (1 0 0) 〈u v w 〉 type. The two liners had essentially identical texture at the 8 cm position (measured from the base of the cone) with strong sheet-type texture components, i.e. (1 1 1) 〈¯1 0 1〉, (1 1 1) 〈¯1 1 0〉 and (1 0 0) 〈0 1 1〉. However, the dominant textures at the 3 cm positions were 〈1 1 1〉 and 〈1 0 0〉 fibre textures with the fibre axes oriented parallel to the normal direction in both liners. A strong cube texture was observed at the 3 cm position of the arc-cast liner but it was not observed for the powder-sintered liner. The arc-cast liner had a generally higher degree of texture than the powder-sintered liner.

Textured BSCCO/Ag superconducting microcomposites with improved critical current density through mechanical deformation

Mechanical deformation has been used to produce BSCCO/Ag superconducting microcomposite ribbons with a c-axis-oriented texture and greatly improved critical current density, Jc. Melt-spun precursor ribbons were oxidized and annealed to produce a well developed '2223' phase, then subjected to mechanical deformation and annealing to produce a textured microstructure. Superconducting BSCCO/Ag ribbons with TR=0=104-110 K and Jc(77) of 4000-10000 A cm-2 have been produced by this method. The Lotgering factor, F, was measured by X-ray diffraction to determine the degree of c-direction texture of the '2223' phase. Jc in a magnetic field was measured to study the effect of microstructural texturing on the field dependence of Jc. This study concentrated on the interrelations between the deformation processes, the degree of c-axis texturing and Jc. Microstructural observation and electron probe microanalysis were also performed to study the relationships between the processing parameters, microstructure and transport properties. The chemical composition and annealing conditions were optimized to maximize the quantity of the '2223' phase, to reduce the amount of the non-superconducting Ca- and Cu-rich phases, and to produce a high degree of texture.

High critical current densities in Bi(2223)/Ag tapes

Bi(2223)/Ag monofilamentary tapes have been characterized by measurements of jc vs. B and vs. theta , the angle between the applied magnetic field and the c axis. High degree of texturing, high density and Bi(2223) single phase conditions were found to be the major effects leading to high jc values. A further condition for reaching the highest jc values is a very low overall carbon content, the presence of carbon at the grain boundaries acting as a strong limiting factor. The highest value of jc in the present work is 4.104 A/cm2 at 77K,0T, corresponding to more than 2.105 A/cm2 at 4.2K,0T.

Critical currents and processing of wound coils of Ag-sheathed Bi-2223 high T c tape: Microstructural and pinning effects

Using a ‘‘powder-in-tube’’ process long lengths of high Tc prototype tape have been fabricated with high critical currents at liquid-nitrogen temperature and excellent high field properties at liquid-helium temperature. A Pb-doped bismuth-based 2223 powder was initially prepared then packed into silver tubes. Using a combination of cold work and heat treatment, a high degree of texture and good compaction with uniform properties was achieved. Current densities exceeding 10 000 A/cm2 at 77 K and 50 000 A/cm2 at 4.2 K in zero field were measured. At the 4.2 K temperature, the material still carried approximately 14 000 A/cm2 at 8 T. Tests on spirally wound and reacted coils, 52 cm long, have also demonstrated high current carrying capability. Effects of process variations and observed microstructure on superconducting properties are described.

Critical currents in Ag sheathed tapes of the 2223-phase in (Bi,Pb)-Sr-Ca-Cu-O

The critical current density of Ag-sheathed (Bi,Pb)-Sr-Ca-Cu-O tapes with thicknesses below 0.2 mm exhibiting the 2223 phase has been systematically studied for various compositions and oxygen contents of the surrounding atmosphere. Various sequences of the final thermochemical treatment leading to a textured structure were also examined. Conditions for obtaining a high degree of texturing in Ag-sheathed tapes were found, yielding J/sub c/ values up to 17.500 A/cm/sup 2/ at 77 K, 0 T. A major factor for the improvement of J/sub c/ by the present cold deformation approach was the thickness of the 2223 layer, which should be smaller than 20 mu m. Due to the large number of parameters involved in the optimization of this system and to the complex formation conditions, a substantial further increase of J/sub c/ in the 2223 phase is still expected. This is particularly important in view of the use of 2223 tapes at 4.2 K and at high magnetic fields.

Texture processing of bulk YBa 2Cu 3O 6+ x by zone melting

Zone melting has been used to produce texture in bulk YBa 2Cu 3O 6+ x . By controlling the directional solidification of the molten zone, oriented structures are produced that consist of domains of aligned grains, with some misalignment between domains. Scanning electron microscopy and optical microscopy show a high degree of texture produced by this technique. Magnetization measurements show a large increase in hysteresis at 77 K compared to unaligned polycrystalline YBa 2Cu 3O 6+ x . The use of BaCuO 2 as a solvent to aid the texturing process is discussed.

Orientation dependence of grain-boundary critical currents in YBa2Cu3O7- delta bicrystals.

The critical current densities across grain boundaries have been measured as a function of misorientation angle in the basal plane of bicrystals of $\mathrm{Y}{\mathrm{Ba}}_{2}{\mathrm{Cu}}_{3}{\mathrm{O}}_{7\ensuremath{-}\ensuremath{\delta}}$. For small misorientation angles, the ratio of the grain-boundary critical current density to the bulk critical current density is roughly proportional to the inverse of the misorientation angle; for large angles, this ratio saturates to a value of about $\frac{1}{50}$. These results imply that achieving a high degree of texture both normal to and within the basal plane is important for the obtaining of very high critical currents in pure polycrystalline samples.

Preferred orientation of calcite in the Aepyornis eggshell

Using X‐ray diffractometry, the development of preferred orientation of the calcite was studied in the Aepyornis eggshell. As in the shells of the extant ratite species, a high degree of texture develops in which the (001) plane lies parallel to the shell surface. This texture then decreases gradually throughout the outer half of the shell.

Relation between the optical and metallurgical properties of polished molybdenum mirrors

A study has been performed to determine the correlation among the microstructure, metallurgical processing, and optical surface finish of commercially available types of molybdenum (Mo) bar and plate and 0.5-mm thick Mo sheet. Specimens of bar and plate stock produced from low-carbon vacuum-arc-cast Mo or powder-metallurgy-processed Mo, as well as TZM (Ti-Zr-Mo) Mo alloy, were in the form of 3.86-cm diam disks. In addition, typical cross-rolled sheet specimens were produced from powder-metallurgy-processed Mo that had a very fine grain structure and a high degree of texture. Specimens were extensively characterized both optically and metallurgically. It was found that well-polished surfaces have surface topographies directly related to the microstructure and hence to the processing of the material. In sheet material having a well-developed texture, the polishability appeared to be independent of texture, and the grain size did not result in a lower scatter surface. It was concluded that the optimum type of Mo to use for smooth low-scatter mirrors is low-carbon vacuum-arc-cast plate or sheet material.

Magnetic properties of a new high permeability oriented silicon steel

A cube-on-edge oriented silicon steel with a higher degree of texture was discovered by H. Grenoble and H. Fiedler of the General Electric Co. This new steel contains a small amount of boron plus a controlled amount of manganese and sulfur to provide the necessary inhibition for developing a permeability at 10 oersteds as high as 1950 gauss/oersted. This paper discusses the adaptation of the new chemistry to full scale mill processing and describes the magnetic properties of the steel as it is produced at Allegheny Ludlum Steel Corporation.

On the texture of aluminum rods extruded under various conditions

The texture of aluminum rods developed by the extrusion under various conditions was studied. The tests were conducted by varying extruding temperature, position of rod, and angle of dying. The results obtained were as follows.(1) Extruded aluminum rod showed cyclic fibrous structure, and the planes having high degree of texture were (112) [111], (213) [111], (178) [111], (001) [100], and (012) [100].(2) The amount of structure component was larger with the rise of extruding temperature, and that at the middle part of the rod (250mm from the tip) was greater than that at its front end (60mm from the tip), which showed that the amount gradually increased from the end to the middle owing to the recrystallization during extrusion.(3) In the position adjacent to the angle of dying, the amount of component was larger with the increase of angle.