X-ray diffraction line profile analysis for defect study in Zr-2.5% Nb material

The “state of the art” of the diffraction analysis of crystallite size and lattice strain.

Abstract: This paper addresses both old, but "renovated" methods and new methods for diffraction line-profile analysis. Classical and even extremely simple single-line methods for separating "size" and "strain" broadening effects have merit for characterization of the material im- perfectness, but it is generally very difficult to interpret the data obtained in terms of microstructure parameters as used in materials science. Developments of recent years, focusing on distinct anisotropic line-broadening effects, as due to the type, orientation and distribution of dislocations and minute compositional variation, will be touched upon. The most promising development may be the synthesis of line profiles on the basis of a microstructure model and application of the (kinematical) diffraction theory without any further assumption, which contrasts with the other methods. This approach can in principle be applied in sin- gle-line and multiple-line variants and also in analyses of the whole diffraction pattern. The advantage is the direct evaluation of microstructure parameters as used in materi- als science. The challenge is to develop microstructure models which are flexible enough to be applicable in more than one case ...

The effect of Ti doping on the growth of Mg nanostructures by oblique angle codeposition

Abstract: Using an oblique angle codeposition technique, 0–8at.% Ti has been doped into Mg and aligned nanostructure arrays, composed of hexagonal Mg single crystals with preferred orientations, are formed. Ti doping produces nanorod structures instead of the nanoblade structures that are formed from pure Mg deposition. This is due to the pinning effect of Ti for Mg adatom diffusion. There is a linear shift of the Mg diffraction peaks toward the higher 2θ angles with the Ti dopant concentration. This is possibly caused by the partial substitution of large Mg atoms by small Ti atoms.

Crystal imperfections and Mott parameters of sprayed nanostructure IrO2 thin films

Abstract: Nano-crystalline iridium oxide thin films were obtained by a spray pyrolysis technique onto preheated glass substrates. X-ray diffraction reveals that IrO2 thin films were polycrystalline in the rutile structure with primitive tetragonal lattice and its preferential orientation were along the 〈110〉 and 〈101〉 directions. X-ray diffraction line profile analysis (XRDLPA) was used to assign microstructure and crystal imperfections of IrO2 thin films. Some important parameters such as crystallite size, microstrain, average residual stress, number of crystallite/cm2 and dislocation density were studied. The effects of deposition temperatures and solution concentrations on the microstructural and crystal defects were discussed. All estimated values were found to be dependent upon the growth parameters. Mott parameters, trapping state energy and potential barrier were investigated and studied for a defined thin film sample. This sample was selected because it has the suitable conditions for electrochromic applications.

Influence of lattice distortion and oxygen vacancies on the UV-driven/microwave-assisted TiO2 photocatalysis

Abstract: The influence of lattice distortions on TiO 2 photocatalysis produced by subjecting commercially available P25 titania samples to a heat treatment in the temperature range 645–800 °C was examined; it caused the initial anatase-to-rutile ratio of 81/19 to decrease to 1/99 at the highest temperature. The photoactivities of these heat-treated samples were established through the photodegradation of 4-chlorophenol (4-CP) exposed to UV irradiation alone, UV/microwave irradiation (2.45 GHz), and to UV irradiation accompanied with conventional heating at a temperature otherwise identical to that under UV/MW irradiation. Raman band intensities of pure anatase (143 cm −1 ), pure rutile (446 cm −1 ) and of the heat-treated P25 specimens were examined in situ after being exposed to microwave irradiation for about 4 min. Changes are attributed to a microwave non-thermal effect involving oxygen vacancies that affect the specimens’ photoactivities as determined by subjecting samples of Evonik P25 titania (AEROXIDE ® TiO 2 P25) and Ishihara ST-01 TiO 2 to a heat treatment in the presence of molecular hydrogen. Such treatment caused lattice distortions of both systems that affected the kinetics of degradation of the chlorophenol under various irradiation conditions. UV/visible absorption spectra of the heat/H 2 -treated specimens displayed a broad unresolved absorption envelope at wavelengths above 400 nm that has been attributed to oxygen vacancies and thus to F -type color centers in accord with an earlier study by Kuznetsov and Serpone. The presence of such defects, particularly in the heat/H 2 -treated samples, and the influence of the microwaves caused the photodegradation kinetics for the 4-CP to be enhanced significantly.

Studies of dielectric characteristics of BaBi2Nb2O9 ferroelectrics prepared by chemical precursor decomposition method

Abstract: BaBiNb2O9 (BBN) powders in the nanometer range were prepared by chemical precursor decomposition method (CPD). TG–DTA showed that precursor sample got freed from organic contaminants at 575 °C. XRD showed that a single phase with the layered perovskite structure of BBN was formed after calcining at 600 °C. No intermediate phase was found during heat treatment at and above 600 °C. The crystallite size (D) and the effective strain (η) were found to be 26 nm and 0.000867, respectively, while the particle size obtained from TEM was 28 ± 2 nm. SEM revealed that the average grain size after sintering at 900 °C for 4 h was ∼1.67 μm. A relative density of ∼93% was obtained using a two-step sintering process at moderate pressure. Dielectric and ferroelectric properties were investigated in the temperature range 50–500 °C and frequencies from 1 kHz to 5 MHz. Strong dispersion of the complex relative dielectric constant was observed including typical relaxor features such as shift of permittivity maximum with frequency and broadening of the peak maximum. The high dielectric constant of 545 measured at 100 kHz and other properties of BBN ceramics were compared to that of BBN prepared by other conventional methods and found to be superior.

Use of the Voigt function in a single-line method for the analysis of X-ray diffraction line broadening

Abstract: The use of the Voigt function for the analysis of the integral breadths of broadened X-ray diffraction line profiles forms the basis of a rapid and powerful single-line method of crystallite-size and strain determination which is easy to apply. To avoid graphical methods or interpolation from tables, empirical formulae of high accuracy are used and an estimation of errors is presented, including the influence of line-profile asymmetry. The method is applied to four practical cases of size-strain broadening: (i) cold-worked nickel, (ii) a nitrided steel, (iii) an electrodeposited nickel layer and (iv) a liquid-quenched AlSi alloy.

Choice of collimators for a crystal spectrometer for neutron diffraction

Abstract: In this paper we establish some criteria for the choice of the collimators for a crystal spectrometer for neutron diffraction in order to achieve a good compromise between luminosity and resolution. General expressions for the full width at half maximum and for the luminosity of the diffraction peaks are developed for powder sample. The advantage of the parallel arrangement is also computed.

A Numerical Fourier-analysis Method for the Correction of Widths and Shapes of Lines on X-ray Powder Photographs

Abstract: A method is derived, using Fourier analysis, for finding the corrected distribution of intensity across an x-ray diffraction line, and the procedure is illustrated by a numerical example. The method may also be of use in spectrum analysis and statistical problems.

On Variance as a Measure of Line Broadening in Diffractometry General Theory and Small Particle Size

Abstract: The mean-square breadth of a deliberately truncated portion of a diffraction line has been suggested as a measure of particle size by Tournarie. Tournarie's theory is generalized to include other causes of line broadening. For small particle size it is shown that the mean-square breadth in 2θ can be expressed in the form W26 = (Kλδ(2θ)/2π2p cosθ) - (Lλ2/4π2p2cos2θ) where p is the cube root of the particle volume, Δ(2θ) is the range of 2θ used in evaluating W2θ, K is a quantity analogous to the Scherrer constant, and L is a quantity, for which the name taper parameter. is proposed, depending on the rate of decrease of the area of cross section of the crystallites in the hkl direction. For non-spherical crystals both K and L are functions of hkl; they are evaluated in terms of hkl for certain simple crystal shapes and Tournarie's numerical values of K are confirmed.