Neutron powder diffraction data

Deep pink polycrystalline solid Rup4 has been prepared by treatment of AsFs with [Ru(F)g] in anhydrous HF solution." A combination of X-ray synchrotron and neutron powder diffraction data reveal that each Ru-atom has six F ligands with an octahedral framework, four in the same plane, each shared with another Ru-atom, to form a puckered-sheet array (Ru—F (bridge) = 2.00 A and 2.00 A, Ru—F—Ru 133°). ... 

Table 8 Structural parameters of La, 0Ca,, Cu,Oc. (Neutron powder diffraction data) (Ref. 27). ...

The program just described, for Rietveld analyses using generalized coordinates, has been used in the structural analysis of isotactic polypropylene recently undertaken both with x-ray and with neutron powder diffraction data. We believe this analysis (Immirzi, in preparation) to be the first Rietveld analysis of a polymer done from x-ray data. Rietveld analyses of polymers from neutron data have been done but, at least in the polyethylene case reported by Willis and co-workers (15), there was no use of generalized coordinates. 

A complete understanding of the structure of the material under study or application is a sine qua non condition for the successful research or use of the material. In the case of powders, the best way to decipher the structure of new materials is the Rietveld method. This methodology was initially developed by Hugo M. Rietveld in 1969 [23] as a procedure for refining crystal structures using neutron powder diffraction data. To implement the method in practice, certain information about the estimated crystal structure of the phase or phases of interest in the diffraction profile under test is necessary. 

Recently, Wu [37] reported the crystal structure of the ternary imide Li2Ca(NH)2 which was determined using neutron powder diffraction data on a deuterated sample. In his paper, the reaction, Li2Ca(NH)2 + H2 LiNH2 + LiH + CaNH, was indicated. However, with respect to the reaction mechanism of the Li-Mg-N-H system [38], the reaction process in this report was thought to be stopped halfway. 

Table 7.2. Experimental and calculated unit-cell parameters and atom positions for a-cristobalite, and their percent difference. The numbers in parentheses are the standard deviations of the last significant digit for the time-of-flight neutron powder diffraction data. The atom locations are given in units of the primitive translation lengths a = b and c...

Neutron powder diffraction data were collected at 2 and 295 K, in addition to several temperatures in the 30-60 K range. The 2 K data are shown in figure I. The nickel atoms were placed in positions a (0, 0, 0) and b ( A, ki, Vi), and theJluorine atoms in Gf x,y, z) of space group R3. The final refined values of structural parameters for the 2 and 295 K refinements are given in table III. 

Hill, R. J., and Howard, C. J. Quantitative ph2ise analysis from neutron powder diffraction data using the Rietveld method. J. Appl. Cryst. 20, 467-474 (1987). Franklin, R. E., and Gosling, R. G. Molecular configuration in sodium thymonu-cleate. Nature (London) 171, 740-741 (1953). 

Figure 2.59. The electron (left) and nuclear (right) density distributions in the xOz plane of the unit cell of CeRhGcs calculated from x-ray and neutron powder diffraction data, respectively Figure 2.58). The contour of the unit cell is shown schematically as the rectangle under each Fourier map. The peaks correspond to various atoms located in this plane and are so marked on the figure. The volumes of the peaks are proportional to the scattering ability of atoms for x-rays the scattering power decreases in the series Ce(58 e) Rh(45 e) Ge(32 e) for neutrons, the coherent scattering lengths decrease in the reverse order Ge(8.19 fm)...

Table 6.23. The list of Bragg reflections and observed structure factors squared determined after Le Bail s full pattern decomposition of the neutron powder diffraction data of CeRhGe3. ...

This crystal structure was solved earlier (see sections 6.10 and 6.11), first using x-ray and then using neutron powder diffraction data. The x-ray data (Mo Ka radiation) were collected at room temperature, while the neutron scattering experiment (K = 1.494 A) was conducted at 200 K. Hence, combined Rietveld refinement is not feasible because of the differences in the lattice and structural parameters of the alloy due to thermal expansion, and we will use the two sets of data independently. 

Table 7.12. The progress of Rietveld refinement of the crystal structure of CeRhGes using neutron powder diffraction data collected at T = 200 K. The wavelength used X = 1.494 A.

The results of the last refinement can be considered final if the location of a single independent hydrogen atom in the unit is not of concern. Not surprisingly, it was impossible to locate hydrogen from the x-ray data unambiguously. Therefore, we will also employ neutron powder diffraction data collected on a powder diffractometer at the McMaster University nuclear reactor using thermal neutrons with X = 1.3920 A. 

Table 7.18. Atomic parameters and interatomic distances (in A) after the completion of the combined Rietveld refinement based on both the x-ray and neutron powder diffraction data collected from NiMn02(0H) powder. The refined chemical composition is NiMnOs (OH)j where 8 = 0.62(5). The unit cell parameters are a = 2.86112(4), b = 14.6516(1), c =...

MODELLING ICE Ic OE DIFFERENT ORIGIN AND STACKING-FAULTED HEXAGONAL ICE USING NEUTRON POWDER DIFFRACTION DATA... 

It is shown that both the Bragg and the diffuse scattering parts of neutron powder diffraction data on ice Ih can be interpreted simultaneously by constructing large models of the structure that are consistent with the measured total scattering functions within errors. The RMCPOW algorithm proved to be readily applicable for the purpose. 

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