Robert J. Cernik

A new high-flux chemical and materials crystallography station at the SRS Daresbury. 1. Design, construction and test results

The scattering efficiencies of four test samples given in Table 1 of the original report [Cernik et al. (1997). J. Synchrotron Rad. 4, 279–286] were calculated incorrectly. Corrected values are provided; these are two to three orders of magnitude lower.

A two-circle powder diffractometer for synchrotron radiation with a closed loop encoder feedback system

A high-angular-resolution two-circle powder diffractometer equipped with long diffracted-beam collimators has been built at Daresbury Laboratory. The diffractometer has encoders mounted directly on the 2θ and ω axes. These give a nominal angular resolution of 0.1 and 1.0 mdeg respectively. Repeated scans of single powder peaks have demonstrated a reproducibility of 0.1 mdeg 2θ. Measurements on five independent peaks of tungsten give a self consistency of 1(1) × 10−5 A. An example data set from synthetic olivine Mg2SiO4 has been refined using the Rietveld method and the results compare very well with single-crystal structure refinements.

Pixellated Cd(Zn)Te high-energy X-ray instrument

We have developed a pixellated high energy X-ray detector instrument to be used in a variety of imaging applications. The instrument consists of either a Cadmium Zinc Telluride or Cadmium Telluride (Cd(Zn)Te) detector bump-bonded to a large area ASIC and packaged with a high performance data acquisition system. The 80 by 80 pixels each of 250 μm by 250 μm give better than 1 keV FWHM energy resolution at 59.5 keV and 1.5 keV FWHM at 141 keV, at the same time providing a high speed imaging performance. This system uses a relatively simple wire-bonded interconnection scheme but this is being upgraded to allow multiple modules to be used with very small dead space. The readout system and the novel interconnect technology is described and how the system is performing in several target applications.

Electrostatically driven charge-ordering in Fe2OBO3

Charge-ordering is an important phenomenon in conducting metal oxides: it leads to metal–insulator transitions in manganite perovskites (which show ‘colossal’ magnetoresistances), and the Verwey transition in magnetite (in which the material becomes insulating at low temperatures when the conduction electrons freeze into a regular array). Charge-ordered ‘stripes’ are found in some manganites, and copper oxide superconductors; in the latter case, dynamic fluctuations of the stripes have been proposed as a mechanism of high-temperature superconductivity. But an important unresolved issue is whether the charge-ordering in oxides is driven by electrostatic repulsions between the charges (Wigner crystallization), or by the strains arising from electron–lattice interactions (such as Jahn–Teller distortions) involving different localized electronic states. Here we report measurements on iron oxoborate, Fe2OBO3, that support the electrostatic repulsion charge-ordering mechanism: the system adopts a charge-ordered state below 317 K, in which Fe2+ and Fe3+ ions are equally distributed over structurally distinct Fesites. In contrast, the isostructural manganese oxoborate, Mn2OBO3, has been previously shown to undergo charge-ordering through Jahn–Teller distortions. We therefore conclude that both mechanisms occur within the same structural arrangement.

A two‐circle powder diffractometer for synchrotron radiation on Station 2.3 at the SRS

The two-circle powder diffractometer on Station 8.3 at the SRS has recently been relocated to station 2.3, some half the distance from a dipole radiation source with the same nominal 1.2T field. The purpose of this paper is to detail the changes and modifications to the diffractometer operation.

X-ray diffraction study of hafnia under high pressure using synchrotron radiation

Abstract Hafnia, HfO 2 , has been studied to 20 GPa at ambient temperature using synchrotron energy-dispersive X-ray powder diffraction methods. Traces of the initial monoclinic (baddeleyite) phase could still be identified at 20 GPa, but a phase transition begins at 2.6 GPa to HfO 2 II, the lines of which can be indexed on an orthorhombic cell ( Pbcm , Z = 4). The relative intensities of the (111) and (−111) monoclinic reflections suggests that a further phase change may begin near 10 GPa but work at high temperatures is needed to establish this. The bulk compressibility of hafnia is 1.2 × 10 −4 kbar −1 . A Rietveld analysis of the baddeleyite phase gave results in close agreement with earlier work but showed the sample to be internally strained.

The breadth and shape of instrumental line profiles in high-resolution powder diffraction

The instrumental resolution function for the Daresbury 9.1 high-resolution powder diffractometer has been measured as a function of wavelength, slit width and specimen geometry. It has been demonstrated that the effects of size and strain from the sample of annealed barium fluoride used as a reference material were negligible, and that it is a suitable standard for studying instrumental broadening. The results of considering the angular dependence of the Lorentzian and Gaussian components of the integral breadths of instrumental line profiles are in excellent agreement with those predicted by the receiving-slit width and the known wavelength spread in the incident beam. The measured instrumental resolution function was found to be dependent on the slit dimensions at low and intermediate angles, and to be dominated by the effects of angular dispersion at higher angles. The line shapes are predominantly Gaussian at low angles and for a flat sample tend to a pure Lorentzian shape at 180 ~. The line profiles for a capillary sample are similar at low and intermediate angles and tend to an intermediate Gaussian/ Lorentzian form at high angles.

Pair distribution function computed tomography

An emerging theme of modern composites and devices is the coupling of nanostructural properties of materials with their targeted arrangement at the microscale. Of the imaging techniques developed that provide insight into such designer materials and devices, those based on diffraction are particularly useful. However, to date, these have been heavily restrictive, providing information only on materials that exhibit high crystallographic ordering. Here we describe a method that uses a combination of X-ray atomic pair distribution function analysis and computed tomography to overcome this limitation. It allows the structure of nanocrystalline and amorphous materials to be identified, quantified and mapped. We demonstrate the method with a phantom object and subsequently apply it to resolving, in situ, the physicochemical states of a heterogeneous catalyst system. The method may have potential impact across a range of disciplines from materials science, biomaterials, geology, environmental science, palaeontology and cultural heritage to health.

The new materials processing beamline at the SRS Daresbury, MPW6.2

A new beamline (MPW6.2) has been designed and built for the study of materials during processing where three synchrotron techniques, SAXS, WAXS and XAS, are available simultaneously. It has been demonstrated that Rietveld refinable data can be collected from silicon SRM 640b over a 60 degrees range in a time scale of 1 s. The data have been refined to a chi(2) of 2.4, the peaks fitting best to a Pearson VII function or with fundamental parameters. The peak halfwidths have been found to be approximately constant at 0.06 degrees over a 120 degrees angular range indicating that the instrumental resolution function has matched its design specification. A quantitative comparison of data sets collected on the same isotactic polypropylene system on MPW6.2 and DUBBLE at the ESRF shows a 17% improvement in angular resolution and a 1.8 improvement in peak-to-background ratio with the RAPID2 system; the ESRF data vary more smoothly across detector channels. The time-dependent wide-angle XRD was tested by comparing a hydration reaction of gypsum-bassanite-anhydrite with energy-dispersive data collected on the same system on the same time scale. Three sample data sets from the reaction were selected for analysis and gave an average chi(2) of 3.8. The Rietveld-refined lattice parameters are a good match with published values and the corresponding errors show a mean value of 3.3 x 10(-4). The data have also been analysed by the Pawley decomposition phase-modelling technique demonstrating the ability of the station to quickly and accurately identify new phases. The combined SAXS/WAXS capability of the station was tested with the crystallization and spinodal decomposition of a very dilute polymer system. Our measurements show that the crystallization of a high-density co-polymer (E76B38) as low as 0.5% by weight can be observed in solution in hexane. The WAXS and SAXS data sets were collected on the same time scale. The SAXS detector was calibrated using a collagen sample that gave 30 orders of diffraction in 1 s of data collection. The combined XRD and XAS measurement capability of the station was tested by observing the collapse and re-crystallization of zinc-exchanged zeolite A (zeolite Zn/Na-A). Previous studies of this material on station 9.3 at the SRS were compared with those from the new station. A time improvement of 38 was observed with better quality counting statistics. The improved angular resolution from the WAXS detector enabled new peaks to be identified.

The crystal and molecular structure of cis-diammine-1,1-cyclobutanedicarboxoplatinum(II) [cis-Pt(NH3)2CBDCA]. Dynamic puckering of the cyclobutane ring

Abstract C6H12N2O4Pt, Mr = 371.27, orthorhombic, Pnma, a = 7.724(2), b = 10.464(3), c = 11.176(2) A, V = 903.29 A3, Z = 4, DX = 2.73 Mg m−3, μ (Mo Kα) = 16.32 mm−1, λ = 0.71069 A. Final R = 0.029 for 856 reflexions. A mirror plane containing the platinum and average cyclobutane ring bisects the molecule. One of the cyclobutane carbon atoms shows excessive thermal motion, which is interpreted in terms of a dynamically puckering ring.