A compact high-resolution X-ray powder diffractometer

Abstract

A new powder diffractometer operating in transmission mode is described. It can work as a rapid very compact instrument or as a high-resolution instrument, and the sample preparation is simplified. The incident beam optics create pure Cu K 1 radiation, giving rise to peak widths of $0.1 in 2 in compact form with a sample-to-detector minimum radius of 55 mm, reducing to peak widths of <0.05 in high-resolution mode by increasing the detector radius to 240 mm. The resolution of the diffractometer is shown to be governed by a complex mixture of angular divergence, sample size, diffraction effects and the dimensions of the detector pixels. The data can be collected instantaneously, which combined with trivial sample preparation and no sample alignment, makes it a suitable method for very rapid phase identification. As the detector is moved further from the sample, the angular step from the pixel dimension is reduced and the resolution improves significantly for very detailed studies, including structure determination and analysis of the microstructure. The advantage of this geometry is that the resolution of the diffractometer can be calculated precisely and the instrumental artefacts can be analysed easily without a sample present. The performance is demonstrated with LaB 6 and paracetamol, and a critical appraisal of the uncertainties in the measurements is presented. The instantaneous data collection offers possibilities in dynamic experiments.

A new theory for X-ray diffraction

“…It suggests that the degree of texture could well be underestimated or biased because of the distribution of scattering in and X. Based on this new theory, it has been possible to build and operate a small, high-resolution powder diffractometer, using a highly parallel beam of pure Cu K 1 and very small sample sizes and achieve reliable intensities (Fewster & Trout, 2013). It is hoped that this theory will help free-up the development of ideas in this area of research.…”

“…This is clearly outside the range of probability for capture. This experiment used a pure Cu K 1 incident beam (3.5 mm FWHM Â 1000 mm) with an angular divergence of 0.01 and a Soller slit acceptance of 2.3 (0.04 radian) (Fewster & Trout, 2013). The sample consisted of a single layer of crystallites; if the crystallites covered the adhesive mounting tape used, with no gaps, then the crystallite number would be $300.…”

Estimating the structure factors in X-ray diffraction

“…If we assumed that the crystals were imperfect and that the conventional theory was correct then we would require 100 000 mosaic blocks in each 3.5 mm crystal, and the blocks would be $0.075 mm in size with an intrinsic diffraction width of $0.11 . This width is 4Â that measured for this standard sample (Fewster & Trout, 2013). 3 These requirements make the conventional theory explanation very unlikely.…”

Development of a laboratory-based transmission diffraction technique forin situdeformation studies of Mg alloys

“…A prerequisite for transmission-based measurements is a parallel or semi-parallel incident beam of X-rays. This is generally achieved by application of a high-efficiency incident beam X-ray mirror (Shanak et al, 2009;Fewster & Trout, 2013) or polycapillary optic (Kumakhov, 1990). On the laboratory level, literature on the application of transmissionbased experiments, in particular dynamic experiments, is somewhat limited owing to the reduced incident beam intensity and penetration capabilities of the sealed-tube X-ray source.…”

“…For these polymer-based studies the X-ray transmission geometry was not problematic because of the nature of the sample: the sample/capillary thickness was in general limited to less than 1 mm to minimize the geometrical broadening and to reduce the absorption of X-rays (Klug & Alexander, 1974). Most recently, Fewster & Trout (2013) reported on a new compact transmission X-ray diffraction (XRD) setup using an X-ray mirror for microstructure and phase identification for powder samples. The X-ray polycapillary optic can also be used for transmission studies owing to the limited beam divergence and high incident X-ray intensity.…”