STRUCTURAL CHARACTERIZATION OF CD(SE, S)-DOPED GLASSES

Two Cd(Se, S)-doped glasses, one richer in selenium and the other richer in sulphur, were examined by X-ray scattering (at high and at small angles) in order to determine with high precision the stoichiometry of the microcrystalline phase as well as the crystallite/particle average size and size distribution. The peak profile broadening analysis, carried out by best-fitting methods, has shown the presence of microstrains inside the dispersed crystalline particles. This result agrees with very recent HRTEM observations. Particle sizes, as determined by SAXS, are shown to agree very well with the corresponding ones determined by SANS. © 1992 Elsevier Science Publishers B.V. All rights reserved

A PROFILE-FITTING PROCEDURE FOR ANALYSIS OF BROADENED X-RAY-DIFFRACTION PEAKS .1. METHODOLOGY

A convolutive profile-fitting procedure is described for analysing X-ray diffraction peak profiles broadened by microstructural factors (crystallite size and lattice disorder). The method requires, in a first stage, an accurate determination of the instrumental function, which is subsequently convoluted with a parametric function adjusted to fit the diffraction profile intensities of the specimen investigated. In the calibration of the instrument function throughout the angular range 20-145° in 2θ, 58 peaks of a well crystallized a-quartz specimen are examined. Provision is made to include in the instrument function an exponential function containing an angle-dependent asymmetry parameter. In the present methodology, a pseudo-Voigt function is suggested to obtain the shape factors (integral breadth, peak width at half maximum, Gaussian content) that contain useful information related to the microstructural properties in the frame of the so-called 'simplified methods' of line broadening analysis. Furthermore, if the optimized profile functions in the Fourier analysis of the broadened peaks are used directly, many relationships follow straightforwardly in the real-space domain. In this way it is easy to apply the formalisms currently used to derive physical information (e.g. the Warren & Averbach and Vogel, Haase & Hosemann methods)

PHASE CHARACTERIZATION OF ION-BEAM-MIXED AND THERMALLY REACTED FE/PD THIN-FILM BILAYERS

The structure of mixed layers resulting from thermal treatments or Kr ion bombardment and post-thermal annealings of thin film Fe/Pd bilayers has been investigated using X-ray diffraction and transmission electron microscopy. Ion mixing experiments were performed using 200 keV Kr2+ ions at a dose of 2.5 × 1016 cm-2. Thermal treatments were carried on in flux of formings gas at 350 and 550°C. In the ion-mixed samples the dominant phase is FePd3 and the part of the iron film which is not mixed with palladium is heavily structurally modified. Annealings induce compositional changes both in as-deposited and ion-mixed samples: at the highest temperature we detected the formation of the FePd compound in the as-deposited sample, while the composition of the ion-mixed sample moves towards the same phase but without reaching it yet. © 1990

Crystallinity of polymers by x-ray diffraction: a new fitting approach

A new method for determining the crystallinity fraction of semi-crystalline polymers from X-ray powder diffraction measurements is presented. Using the scattering of an amorphous sample of the same material and a convenient expression for the disorder factor, the method can lead to precise separation of the crystalline and amorphous contributions by a fitting procedure. In this way, the crystallinity fraction and the disorder factor are automatically obtained. The method is applied to polyethylene terephthalate. © 1991

SHORT-RANGE STRUCTURE OF ZIRCONIA XEROGEL AND AEROGEL, DETERMINED BY WIDE-ANGLE X-RAY-SCATTERING

The short-range structure of amorphous zirconia, investigated by X-ray diffraction, has been found to bear more resemblance to the monoclinic ZrO2 structure than it does to the tetragonal structure. This result was achieved in two zirconia samples (xerogel and aerogel) by analyzing both the positions of the maxima of the experimental (Fourier-transformed) 'reduced' radial correlation function, G(r), and the experimental radial atom (number) density distribution, p(r). This latter function was simulated as a weighted sum of three partial atom density distributions, ρ{variant}′ZrO, ρ{variant}′ZrZr, and τ′OO, based on the monoclinic or the tetragonal coordination frame and limited inside a sphere of 9 Å in radius. The coordination statistics are described in terms of sums of Gaussian functions into which distortion effects (first-type and second-type disorder) were introduced. © 1993

FRACTAL PROPERTIES OF A PARTIALLY CRYSTALLINE ZIRCONIUM-OXIDE AEROGEL

A zirconium oxide aerogel with a 70% by weight degree of crystallinity was prepared from zirconium n-propoxide with an excess of water being used in the hydrolysis process. The small-angle X-ray scattering (SAXS) technique revealed that this system had a mass-fractal character. The elementary building blocks had a size of about 50 angstrom and displayed a nonfractal (smooth) boundary surface. The mass-fractal dimension, Dm, was found by SAXS to be equal to 1.95 (5). The novelty of this fractal system lies in the fact that the elementary blocks are made up of zirconium oxide particles with a high degree of crystallinity (preponderantly tetragonal in form). The crystalline nature of this system has allowed an interesting comparison to be made between the particle size determined by the crossover in the log I(h) versus log h SAXS plot and the crystallite size determined by the line-broadening X-ray diffraction analysis