Neutron diffraction

About: Neutron diffraction is a research topic. Over the lifetime, 26415 publications have been published within this topic receiving 597194 citations. The topic is also known as: elastic neutron scattering.

A correction for powder diffraction peak asymmetry due to axial divergence

Abstract: Analysis of a crystal structure using the Rietveld profile technique requires a suitable description of the shape of the peaks. In general, modern refinement codes include accurate formulations for most effects; however, the functions used for peak asymmetry are semi-empirical and take very little account of diffraction optics. The deficiencies in these methods are most obvious for high-resolution instruments. This study describes the implementation of powder diffraction peak profile formulations devised by van Laar & Yelon [J. Appl. Cryst. (1984), 17, 47–54]. This formalism, which describes the asymmetry due to axial divergence in terms of finite sample and detector sizes, does not require any free parameters and contains intrinsic corrections for the angular dependence of the peak shape. The method results in an accurate description of the observed profiles for a variety of geometries, including conventional X-ray diffractometers, synchrotron instruments with or without crystal analyzers and neutron diffractometers.

Magnetic order and phase transformation in Ni2MnGa

Abstract: Magnetization, magnetic susceptibility, optical microscopy, X-ray diffraction and neutron diffraction measurements have been made on a quenched sample of Ni2MnGa. Room-temperature neutron diffraction patterns indicate a highly ordered Heusler alloy, L21 type, structure. The alloy is ferromagnetic with a Curie temperature of 376 K, and a magnetic moment of 4·17μB largely confined to the Mn sites, but probably with a small moment <07·3μB associated with the Ni sites. A martensitic phase transition to a complex tetragonal structure occurs on cooling below 202 K. Neutron diffraction oscillation photographs taken using the D12 facility at Institut Laue Langevin, Grenoble, and low-temperature powder neutron diffraction data enabled details of the low temperature crystallographic superlattice and magnetic structure to be determined. Reasons for the structural transformation are discussed.

Structural-electronic relationships in inorganic solids: powder neutron diffraction studies of the rutile and anatase polymorphs of titanium dioxide at 15 and 295 K

Abstract: Rietveld analysis of time-of-flight pulsed neutron diffraction of powders shows a nearly isotropic shrinkage of the structures of both the rutile and anatase polymorphs of TiO/sub 2/ upon cooling from 295 to 15 K and no change in the sense of the distortion of the TiO/sub 6/ octahedra (two long and four short Ti-O distances in both): rutile at 295 (first) and 15 K (second), a/sub 0/ 4.593 08 (4), 4.586 66 (4), c/sub 0/, 2.958 89 (3), 2.954 07 (3), x/sub oxygen/, 0.304 76 (6), 0.304 69 (6), Ti-O(4x), 1.9486 (3), 1.9459 (3), Ti-O(2X), 1.9796 (4), 1.9764 (4); anatase at 295 and 15 K, a/sub 0/, 3.784 79 (3), c/sub 0/, 9.502 26 (12), 0.504 65 (12), x/sub oxygen/, 0.16686 (5), 0.166 75 (4), Ti-O(4x), 1.9338 (1), 1.9322 (1), Ti-O(2X), 1.9799 (5), 1.9788 (4): all distances (A) referenced to silicon (a = 5.430 88 A). Both tight-binding calculations on the crystalline solids and molecular mechanics computations on the oxide lattice alone lead to a model in which the balance of attractive Ti-O and repulsive O-O interactions control the details of the overall structures. The relative bond lengths around metal centers in some other systems are predicted.

Supplement. Tables of bond lengths determined by X-ray and neutron diffraction. Part 2. Organometallic compounds and co-ordination complexes of the d- and f-block metals

Abstract: Average lengths for metal–ligand bonds are reported, together with some intraligand distances, for complexes of the d- and f-block metals. Mean values are presented for 325 different bond types involving metal atoms bonded to H, B, C, N, O, F, Si, P, S, Cl, As, Se, Br, Te, or I atoms of the ligands.