Powder diffraction neutron

There are two types of neutron sources available for powder diffraction. One is the nuclear reactor, which provides a monochromatic beam of wavelength 1.0 A, selected by means of a crystal monochromator from the continuous wavelength spectrum of thermalized neutrons [481. The diffraction experiment uses the Bragg method as in X-ray single crystal diffractometry. 

The other source is the continuous wavelength spectrum of neutrons produced by stopping an accelerated beam of electrons, i.e., the spallation source . Since the electron beam is pulsed, so is the neutron beam [230]. The diffraction experiment uses the Laue method and the wavelengths are measured by their time of flight (TOF). In place of Bragg s law, dhk) = X/2 sin 0hk), the TOF relationship is 

Detectors are usually placed at 26 values of 50°, 90° and 150°. Since air absorption of neutrons is negligible, the flight path can be several meters. 

The 70F method has the advantage that diffraction data can be collected to higher values of sin 6/X than with the monochromatic beam method. However, with larger unit cells there is a resolution problem at short wavelengths, where the powder lines may form a continuum [230, 231]. 

The powder specimens are more easily subjected to controlled temperatures, down to 4 K, and different pressure than single crystals. Relatively large amounts of compound are required, several grams, and sample preparation to obtain a fine powder and avoid preferred orientation is critical. 

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The crystal lattices of a series of ternary alkali metal-silver acetylenediide [M Ag(C=C)] (M1 = Li 161, Na, K 162, Rb, Cs 163) have been analyzed by Ruschewitz and co-workers using X-ray powder diffraction.209 Neutron powder diffraction experiments have also been performed on 161-163 for obtaining precise bond lengths. It has been found that for 161 and 162, the [Ag(C C)] chains were packed parallel to each other, whereas for 163, they were aligned in layers that were rotated by 90° with respect to each other (see Figure 51). 

The crystalline structure of 2-nitroguanidine had already been previously studied by Bryden and coworkers1 (Ref. 29 therein). They there report the existence, but not the position, of hydrogen bonds, which was instead rendered possible through the use of the neutron powder diffraction method5. The skeleton backbone of this molecule consisting of a central C atom and four N atoms is almost coplanar. Both nitramine groups are essentially on the plane of the molecular skeleton. 

The X-ray and neutron powder diffraction methods successfully use two approaches connected to extraction of intensities (see [14]) ... 

Rietveld, H.M. (1967) line profiles of neutron powder-diffraction peaks for structure refinement. Acta Crystallogr.,... 

Figure 16. Neutron powder diffraction pattern of a iayered substituted nickeiate, LiNio.4Mno.4Coo.2O2.

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°). ... 

Tse, J.S. Handa, Y.P. Ratcliffe, C.I. Powell, B.M. (1986). Structure of oxygen clathrate hydrate by neutron powder diffraction. J. Incl. Phen. Microcyclic Chem., 4, 235-240. 

The magnetic properties of iron oxides can be determined using Mossbauer spectroscopy, neutron powder diffraction and magnetometry (see Chap. 7). The characteristic parameters are the magnetic moment, the permeability, the saturation magnetization, the magnetic anisotropy constants and the Bhf (Tab. 6.2). 

The five years since last considering specifically recent developments in X-ray and neutron diffraction methods for zeolites [1] have witnessed substantial progress. Some techniques, such as high resolution powder X-ray diffraction using synchrotron X-rays, have blossomed from earliest demonstrations of feasibility to widespread and productive application. Others, such as neutron powder diffraction, have shown steady progress. For still others, notably microcrystal diffraction, a variety of circumstances have contributed to extended gestation periods. Additionally, opportunities scarcely considered earlier (such as single crystal Laue diffraction, and certain developments in computer simulations that complement diffraction work) now command broad attention and warrant the commitment of substantial further investment. 

Henderson C.M.B., Knight K. S., Redfern S.A.T., and Wood B. J. (1996) High-temperature study of octahedral cation exchange in olivine by neutron powder diffraction. Science 271, 1713-1715. 

Arzi E, Sandor E (1983) A variable temperature sample container for low temperature neutron powder diffraction. J Appl Crystallogr 16 449 52... 

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

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