Absorption corrections for neutron diffraction
01 Nov 1970-Acta Crystallographica Section A (International Union of Crystallography)-Vol. 26, Iss: 6, pp 682-691
TL;DR: In this paper, the transmission factor Ahkl is computed as a function of μRand sin2θ, where R is the radius of the crystal and δ is the mean linear absorption coefficient.
Abstract: Absorption corrections for cylindrical and spherical crystals have been evaluated by numerical integration for values of μR in the range 0 to 1.0, where μ is the mean linear absorption coefficient and R is the radius of the crystal. For this range of μR, which is that normally required for neutron diffraction data, interpolation from existing tables is unsatisfactory. The transmission factor Ahkl is tabulated as a function of μRand sin2θ, accurate to four decimal places. The intervals chosen for the tabulation are such that linear interpolation may be used for intermediate values. Analytical expressions, which may be used for calculating the transmission factor when a lower accuracy is acceptable, are also given.
Citations
More filters
[...]
25 Apr 1992
TL;DR: The Rietveld method is described in this article, where structure and lattice parameters are directly refined from powder diffraction data and several functions such as extinction correction, preferred orientation, and profile shape function have been improved to give physical meanings to parameters contained in them.
Abstract: The outline of the Rietveld method is described where structure and lattice parameters are directly refined from powder diffraction data. Several functions such as extinction correction, preferred-orientation function, and profile-shape function, which are contained in the model function, have been improved to give physical meanings to parameters contained in them. Structure-refinement strategy is introduced which may be useful for beginners. Combined refinement of X-ray and neutron diffraction data is now being used more and more widely to extract structural information from powder patterns as much as possible.
502 citations
21 Feb 2009-Nuclear Instruments & Methods in Physics Research Section A-accelerators Spectrometers Detectors and Associated Equipment
TL;DR: Z-Code as discussed by the authors is a software suite for powder diffraction data analysis in the Materials and Life Science Facility (MLF) of the Japan Proton Accelerator Research Complex (J-PARC).
Abstract: A new analysis software suite, Z-Code, is under development for powder diffraction data analyses in the Materials and Life Science Facility (MLF) of the Japan Proton Accelerator Research Complex (J-PARC). This software suite comprises data processing, data analyses, graphical user interface and visualization software. As a part of Z-Code, a Rietveld analysis program for neutron (TOF and angle dispersive) and X-ray data, Z-Rietveld, has been developed. Here we report the basic traits and some significant features of Z-Rietveld.
360 citations
TL;DR: In this paper, the absolute coherent distinct differential cross section was separated into intermolecular and intramolecular contributions, and the variation of molecular structure in passing from the gas phase to the liquid was obtained from this intra-olecular contribution.
Abstract: Neutron-diffraction studies on liquid deuterated acetonitrile at 20°C were carried out at neutron wavelengths of 0·5 A and 0·7 A. For the latter wavelength samples of two different diameters were measured. The data were corrected for background, absorption, multiple scattering and inelastic effects (Placzek correction) and then were normalized to absolute differential cross section by comparison with vanadium standard. The different steps in the correction procedure were experimentally verified. The absolute coherent distinct differential cross section was separated into intermolecular and intramolecular contributions. The variation of molecular structure in passing from the gas phase to the liquid was obtained from this intramolecular contribution.
164 citations
TL;DR: In this article, the irreducible representations of the distortions from the possible high-temperature symmetry (P6}_{3}/mmc$ to the low-tem temperature symmetry were calculated.
Abstract: Reports about the ferroelectric ordering temperatures in the multiferroic hexagonal $R{\mathrm{MnO}}_{3}$ system are controversial: transition temperatures varying between $\ensuremath{\approx}900\mathrm{K}$ and $\ensuremath{\approx}1300\mathrm{K}$ are reported for the same material. To elucidate the structural changes leading to ferroelectric distortions in hexagonal manganites, we calculate the irreducible representations of the distortions from the possible high-temperature symmetry ${P6}_{3}/mmc$ to the low-temperature symmetry ${P6}_{3}\mathrm{cm}.$ There are four different orthogonal modes, of which only one allows a spontaneous electric polarization. Structure refinements and an accurate statistical analysis of neutron powder-diffraction data of ${\mathrm{TmMnO}}_{3},$ based on this group-theoretical analysis, reveal two phase transitions: We extrapolate a polar to nonpolar transition temperature of ${T}_{\mathrm{npt}}=1433(27)\mathrm{K},$ where the hexagonal bitetrahedra start to tilt, while the ferroelectric distortion appears at ${T}_{\mathrm{FE}}=1050(50)\mathrm{K}.$ For $R=\mathrm{Lu},$ Yb the tilt of the bitetrahedra and the buckling of the R layers as well as the ferroelectric distortion were extrapolated to comparable temperatures.
155 citations
TL;DR: In this article, twin-axis neutron diffraction data have been obtained for vitreous silica at five incident wavelengths and analyzed to give the total correlation function T(r).
Abstract: Reactor twin-axis neutron diffraction data have been obtained for vitreous silica at five incident wavelengths and analysed to give the total correlation function T(r). A fit to the first SiO and OO peaks in the Gaussian approximation yields distances of 1.61 and 2.63 A respectively. The peaks are, however, asymmetric, the form of the asymmetry being qualitatively as predicted for anharmonicity in the SiO bond stretching modes. The results show that, in order to avoid significant static approximation distortions of the distinct scattering, measurements on vitreous silica must be limited to scattering angles less than 80°. The effect of temperature on the interference function is demonstrated by an additional measurement at liquid nitrogen temperature.
138 citations