[en] The integrated intensities measured in X-ray single-crystal high-pressure structural studies using a diamond-anvil cell are shown to be reduced substantially when the diamonds diffract at the same setting as the sample - by as much as 50% in some cases. The pressure and wavelength dependence of this process have been studied and also the effect of changing the beam divergence by the use of a synchrotron beam. The consequences for the accuracy of structural information derived from data sets collected at high pressure are considered and a data-collection strategy for detecting and avoiding the effects of diamond diffraction is proposed. (orig.)

[en] The accuracy of structural parameters obtainable from measurements carried out with a Merrill-Bassett diamond-anvil high-pressure cell has been tested in an X-ray diffraction study of cubic CaF₂. The measurements were performed at 0.0001, 0.70, 1.70, 2.60, 2.90, 3.66 and 4.42 GPa. It was found that a simple modification of the shape of the gasket can eliminate the problem of partly obscured reflections and yield reliable values for the Ca and F thermal parameters - the only variables in this simple structure, and hence particularly sensitive to any systematic errors in the data. (orig.)

No abstract available

[en] The analysis of neutron-diffraction data collected at room temperature from a single crystal of RB(Hsub(0.45)Dsub(0.55))₂PO₄ is shown to require a model of the partially deuterated structure that treats the H and D atoms separately. From the refined structural parameters the length of the symmetric O-(D,D)-O bond in (fully deuterated) RbD₂PO₄ is estimated as 2.522(4)A, with a D-site separation of 0.466(8)A. (author)

[en] The crystal structure has been determined for NH₄H₂PO₄ and ND₄D₂PO₄ at atmospheric pressure, and for NH₄H₂PO₄ at a hydrostatic pressure of 8.9 kbar. In each case the temperature was set to just above the antiferroelectric-to-paraelectric phase transition. The relationship between the transition temperature and the O-H-O and O-D-O bond dimensions is discussed in comparison to the isomorphous but ferroelectrically ordering KH₂PO₄ and KD₂PO₄. (orig.)

[en] The sample volume in diamond-anvil pressure cells suitable for X-ray powder diffraction studies is very small (≤ 100 μm across). The resulting low signal-to-noise ratio has made it very difficult to obtain useful results with monochromatic angle-dispersive techniques, and the alternative white-beam energy-dispersive techniques have limited resolution and generally give unreliable peak intensities. The situation has been transformed recently by the introduction of the image-plate two-dimensional detector, which allows angle-dispersive methods to be used with a greatly increased signal and improved powder averaging. A short review is given of this development, the experimental techniques, and the principal advantages, particularly as found in results obtained at SRS Daresbury over the past two or three years. (au) (18 refs.)

[en] The monoclinic crystal structure of NaH₂PO₄ at room temperature has been refined from neutron-diffraction measurements on a single-crystal sample and compared with the closely related structure of monoclinic KD₂PO₄. Attention is paid to the information obtained from these two structures about the geometry of hydrogen (deuterium) bonds approx. < 2.6 A. (orig.)

[en] Short communication

[en] The phases of cerium above 5GPa have been studied using angle-dispersive powder diffraction techniques. The phase obtained between 5 and 12GPa at room temperature with filings of Ce has a monoclinic, distorted-fcc structure with four atoms in a C-face-centered unit cell. Heating to 373K for many hours yields the known α-U phase. With a single cut piece as a sample, the α-U phase is obtained at room temperature. copyright 1997 The American Physical Society

[en] An analysis of the intensity data and the derived crystal structure parameters from neutron diffraction experiments on a DKDP (deuterated KH₂PO₄) crystal are presented. The ILL D19A diffractometer equipped with a PSD and the D8 diffractometer equipped with a conventional monodetector were used. The experiments were performed at room temperature. The study shows that data collected with the D19A 'fly's-eye' PSD gives structural parameters as reliable and accurate as conventional techniques under similar conditions. (U.K.)