Polycrystalline X-ray Diffraction Research Articles

COMPUTER DEPTH PROFILING ANALYSIS METHOD FOR X-RAY DIFFRACTION POLYCRYSTALLINE PATTERNS

A new method to extract X-ray polycrystalline diffraction patterns diffracted from different depth in real scale is pnesented. In this method the X-ray polycrystalline diffraction data of surface layer are collected at different incident angles, and then the X-ray diffraction patters diffracted from thin sheets at different depth are extracted directly by some special mathematical method. So the depth profiles of peak intensity, peak position and line profile can be obtained quantitatively and nondestrnctively. The algorithm was deduced in theory, and the feasibility of this method was primarily tested with a Ni/Mo film sample with prefered orientation. This method has the prospective application in the area of the thin films and its reactions, interface and surface processing studies.

Structural Characterization of Thin Films by X-Ray Diffraction and Reflectivity

X-ray polycrystalline diffraction was used to track progress toward improving the structural properties of SrS:(Eu,Sm) thin films. These thin films are used as the active layer of the ETOM (Electron Trapping Optical Memory) media. In this study conventional x-ray diffraction and x-ray reflectivity were used to evaluate the effect of two deposition parameters on film structures. Line broadening analysis performed using the Warren-Averbach technique showed the beneficial effects of a hydrogen sulfide reactive atmosphere and the RF magnetron sputtering technique on crystallite size and microstrain. A factor of five improvement in crystallite size and a factor of two reduction in microstrain was observed. Film thickness, density, and interfacial and surface roughnesses were determined for two SrS thin films. The sin2Ψ technique was used to determine the in-plane biaxial stress for two films prepared by different deposition techniques. These films exhibit inhomogeneous stress states with an average stress of less than IMPa.

High-pressure X-ray diffraction study of diaspore

Effects of pressure on lattice parameters and molar volume of diaspore were studied to 25.5 GPa at 300 K by polycrystalline X-ray diffraction techniques. The pressure-volume data fit with a second-order Birch-Murnaghan equation of state give a bulk modulus K 0 = 167.5 GPa by Ruoff and previously reported, but unsubstantiated, value of K 0 = 85 GPa by Ruoff and Vanderborgh [ Phys. Rev. Lett. 66, 754 (1991)]. Thermodynamic calculation indicates that hydrogen and ruby are stable relative to diaspore and aluminum to pressures above 200 GPa.

Hydrotalcite formation on aluminum sheet and powder

We have observed the formation of the hydrotalcite-like phase of lithium dialuminate, LiAl2(OH)6OH · 2H2O, and also the carbonate analog, by the oxidation of aluminum sheet and also aluminum powder in aqueous lithium hydroxide or lithium carbonate solutions. A secondary phase, bayerite, was also observed following the oxidation process, except when the aluminum was treated with lithium oxalate solutions where it is the principal phase. Results have been obtained for the time required to form a passivating film to hydrogen formation as a function of temperature and oxidizing solution. Grazing incidence x-ray diffraction of aluminum sheet samples, combined with polycrystalline x-ray diffraction on similarly treated aluminum powder, were used to evaluate the formation of the films. Both transmission and reflectance infrared absorption spectra on powder and sheet samples were used to support the x-ray observations. Scanning and transmission electron microscopies show morphological differences between preparations, film thicknesses of 10–20 μm, and also film defects. Additional SIMS analysis determined the relative lithium and aluminum concentrations in the films, suggesting that a higher concentration of lithium occurs when lithium carbonate is present in the reacting solutions.

Growth of c-axis-oriented films of YbBa 2Cu 3O 7− δ on single and polycrystalline MgO substrates by oxidation of a liquid alloy precursor

Textured superconducting films of YbBa 2Cu 3O 7–δ supported on both single and polycrystalline MgO substrates were prepared by oxidation of a liquid precursor alloy. The substrates were coated by dipping them into the molten alloy (YbBa 2Cu 3, melting point ≈870°C). After withdrawal from the melt, the adhering metal was oxidized to the corresponding oxide phase, i.e., Y YbBa 2Cu 3O 7−δ, which exhibited a superconducting transition at ≈80 K following annealing in pure O 2 at 500°C. With MgO(1 0 0) substrates, evidence was seen for the epitaxial growth of YbBa 2Cu 3O 7−δ crystals having their c-axis parallel to the [1 0 0] direction of the substrate. For polycrystalline MgO, X-ray diffraction and microstructural examination showed that the high- T c crystallites in the films were also oriented with their c-axis perpendicular to the substrate surface, but the directions of the a and b axes were disordered rather than epitaxial. The superconducting properties of as-prepared films are discussed together with the effects of key processing parameters on composition and microstructure.

Synthesis of C-oriented YbBa2Cu3O7-δ Films on Single and Polycrystalline Substrates by Oxidation of Liquid Alloys

ABSTRACTTextured superconducting films of YbBa2Cu3O7-δ supported on single and polycrystalline substrates were prepared by oxidation of a liquid precursor alloy. The substrates were coated by dipping them into a molten alloy (YbBa2Cu3, m.p. ∼870°C), withdrawing them from the melt, then oxidizing the adhering liquid alloy layer to the corresponding oxide phase, i.e., YbBa2Cu3O7-δ. Samples prepared in this way exhibited a superconducting transition at ∼80 K following annealing in pure O2 at 500°C. With SrTiO3 (100) and MgO (100) substrates, evidence was seen for the epitaxial growth of YbBa2Cu3O7-δ crystals having their c-axis parallel to the [100] direction of the substrate. For polycrystalline MgO, x-ray diffraction and microstructural examination showed that the high-Tc crystallites in the films were also oriented with their c-axis perpendicular to the substrate surface, but the a and b axes directions were randomly oriented rather than epitaxial.

Powder X-Ray Diffraction Characterization of Laser Deposited Ferroelectric Thin Films

AbstractThin films of BaTiO3and Pb(Zr53Ti47)O3(PZT) have been deposited on Pt and Pt-coated silicon substrates using both Nd-YAG and excimer lasers. The BaTiO3films were prepared using heated substrates and were crystalline. The PZT films were deposited at room temperature and were amorphous; on annealing, they crystallized and gave rise to well-defined powder x-ray diffraction patterns.To compare and correlate the properties and processing conditions of these thin films, characterizations were performed using a variety of analytical techniques including x-ray diffraction, TEM, SEM/EDX and ferroelectric and dielectric property measurements. The x-ray diffraction technique was used for identifying the various phases formed and also for analyzing the profiles of the diffraction peaks. Both the PZT films annealed below 800°C and the BaTiO3 films typically show polycrystalline x-ray diffraction patterns corresponding to a pseudo-cubic structure (i.e no peak splitting) instead of the tetragonal patterns characteristic of the target materials. It was found that for the BaTiO3films the pseudosymmetry was due to crystallographic alignment of the longer c-axis In the substrate surface to relieve strain. In the FZT films annealed below 900°C, it is suggested that the residual surface strain and/or small crystallite size of these materials may have precluded the peak splitting; at higher annealing temperatures, the tetragonal symmetry was recovered.

Inhomogeneity and Microstructure in e-Beam Evaporated ZrO2 Films

ABSTRACTThin films of zirconium dioxide are deposited by e-beam evaporation on optically polished borosilicate crown glass. Two different oxygen partial pressures in the chamber are used. The optical properties of the films are characterized by ellipsometry. The influence of oxygen stoichiometry on the composition and microstructure of the material is investigated by polycrystalline X-ray diffraction for different film thicknesses. The films are found to be inhomogeneous, and a composition gradient (i.e. amorphous ⇔ tetragonal ⇔ monoclinic) is observed from the substrate to the surface. The oxygen partial pressure influences the growth of the films.

Effect of structural instability between 80 and 300 K on superconductivity of YBa2Cu

The lattice parameters of ${\mathrm{YBa}}_{2}$${\mathrm{Cu}}_{3}$${\mathrm{O}}_{\mathrm{x}}$ have been carefully measured by x-ray polycrystalline diffraction between 80 and 300 K. As a function of temperature, they reveal a large variation above ${T}_{c}$, which is mainly attributed to a few abrupt changes near certain temperatures rather than thermal expansion. Such structure instability, accompanied with the appearance of internal friction peaks and elastic softening, is related to oxygen content x. The instability near 120 K was found to be related to the superconductivity at 90 K.

ANOMALOUS BEHAVIOR ABOVE Tc AND 90K SUPERCONDUCTIVITY IN YBa2Cu3Ox

Internal friction and lattice parameter were measured by Marx’s three components oscillator and X-ray polycrystalline diffraction respectively. As a function of temperature, there exist a few anomalies above Tc, of which the 110K-130K anomaly is found to be closely connected with 90K superconducting transition, but no obvious relation was observed for the 210K anomaly. In addition, a relaxation type internal friction peak was measured at about 100K.

Advances in Synchrotron X-ray Polycrystalline Diffraction

The advantages of synchrotron radiation for X-ray polycrystalline diffraction are illustrated by a number of examples. The plane wave parallel-beam X-ray optics uses a Si(lll) channel monochromator for easy wavelength selection and a set of long parallel slits to define the diffracted beam. The constant simple instrument function and the high resolution symmetrical profiles (FWHM 0.05") greatly simplify the data analysis and add a new dimension to profile broadening studies. The geometry permits uncoupling the 6-26 sample-detector relationship without changing the profile shape and makes possible new applications such as grazing angle incidence depth analysis of thin films. The same instrumentation is used for high resolution energy dispersive diffraction (BOD) by step-scanning the monochromator. The resolution is two orders of magnitude better than conventional BOD and can be used at high count rates. The easy wavelength selection yields diffraction patterns with the highest PI B and permits anomalous scattering studies.

Polycrystalline Diffraction and Synchrotron Radiation

AbstractSynchrotron radiation sources allow a new generation of parallel beam instruments to be developed for polycrystalline xray diffraction. Spectroscopy can be combined with diffraction in either angle or energy scanning modes. The high intensity narrow instrument profile and freedom from aberrations make possible a wide range of measurements; of anomalous dispersion, of peak-shape analysis to determine particle size and strain, of preferred orientation and structure as a function of depth and of lattice parameters with a precision approaching 1 part per million. The parallel beam instrument which we have developed is now to be installed on a regular basis at SSRL and at Daresbury.

Accuracy and Precision of Intensities in X-Ray Polycrystalline Diffraction

AbstractThe integrated and peak intensities of a series of silicon powder samples of various crystallite sizes were measured with a computer automated diffractometer and a profile fitting method (PFM). The accuracy of the PFM was better than 0.003% in computing the integrated intensities. The PFM gave more precise values than would be expected from counting statistics of the peak intensity. The average difference between each measurement and the average intensity was 0.5% with little dependence oo the absolute intensity. Crystallite sizes have a large effect and it is essential to rotate the specimen around the diffraction vector. The best results were obtained with <10 μm particles. Larger sizes decrease the absolute intensities and change the relative intensities. Structure refinement using the POWLS (powder least squares refinement) program showed the presence of (111) preferred orientation even in the <10 μm specimens. R(Bragg) decreased from 4.3% to 0.7% by including the preferred orientation correction in the refinement.

Polymorphism and the crystal structures of InSb at elevated temperature and pressure

Polycrystalline x-ray diffraction data are reported for three high-pressure phases of InSb. InSb-II patterns are indexed on the basis of a body-centered tetragonal lattice with unit cell parameters a=5.810 Å and c=3.136 Å at P∼4.3 GPa and T≳100 °C; a unique space group has not been assigned. Possible space groups and structures have been determined for the other high-pressure phases. Contrary to published results, InSb-III is orthorhombic with a=5.712 Å, b=5.357 Å, c=3.063 Å at 11.5 GPa and room temperature, the space group is either Pmmm or Pmmn, and Z=2. InSb-IV is also orthorhombic with a=2.919 Å, b=5.618 Å, and c=3.066 Å at P=4.4 GPa and room temperature; the space group is Pmm2, and Z=1. Atomic coordinates and appropriate bond angles are also reported.

New Orthorhombic Phase in the Ru–B and Os–B Systems

By the use of single crystal and polycrystalline x-ray diffraction techniques, isomorphous orthorhombic lattices (space group No. 59) have been found in the Ru-B and Os-B systems having lattice parameters of a0=4.6443±0.0003 Å, b0=2.8668±0.0008 Å, c0=4.0449±0.0004 Å and a0=4.6832±0.0001 Å, b0=2.8717±0.0002 Å, c0=4.0761±0.0001 Å, respectively. The probable empirical formulas are RuB2 and OsB2, with two formula weights per unit cell.