Neutron diffractometry

Brown, PJ. and I orsylh, J.B. (1964) The determination of beam polarisation and flipping efficiency in polarised neutron diffractometry, Brit. J. Appl. Phys., 14, 1529-1532. 

Techniques used in the research examined In the period examined the most widely used technique was X-ray diffraction, even though neutron diffractometry has recently become popular. 

The kinetics of the retiction appears not be diffusion controlled. A halftime of reaction Ti/2 of 340 s was derived while a further much slower process with 240 min w is determined by real time neutron diffractometry. 

Bastie, P., Vallade, M., Vettur, C., Zeyen, C.M.E. Meister, H. (1981). Neutron diffractometry investigation of ttie tricritical point of KH2PO4. J. Phys. Paris 42, 445 58. 

Neutron diffractometry on U2N3+J, has shown that the excess nitrogen atoms are located at the 16 (c) position and regular nitrogen atoms at the 48(e) position of the space group la3 (237). 

Quantitative measurements of oxygen exchange between solid or liquid substances and the gas phase for scientific investigations, in different processes of the chemical and biochemical industry, in metallurgy, at semiconductor fabrication, and production of ceramics, etc. This method can be applied alternatively to thermogravimetiy and can support the results of chemical analysis, spectroscopy. X-ray, or neutron diffractometry. 

Of particular interest to the study of liquids is the use of neutron diffraction to obtain experimental measurements of the pair correlation function (Eq. 12.6). Because neutrons respond to the nuclei in the sample rather than the electron clouds, neutron diffractometry produces higher resolution maps of the distribution of the atoms than can be obtained using x-rays. This feature becomes especially valuable when studying liquids, where the distances between the molecules are comparable to the distances within the molecules, and where there is no regular pattern to the orientations of the molecules. 

Another characteristic point is the special attention that in intermetallic science, as in several fields of chemistry, needs to be dedicated to the structural aspects and to the description of the phases. The structure of intermetallic alloys in their different states, liquid, amorphous (glassy), quasi-crystalline and fully, three-dimensionally (3D) periodic crystalline are closely related to the different properties shown by these substances. Two chapters are therefore dedicated to selected aspects of intermetallic structural chemistry. Particular attention is dedicated to the solid state, in which a very large variety of properties and structures can be found. Solid intermetallic phases, generally non-molecular by nature, are characterized by their 3D crystal (or quasicrystal) structure. A great many crystal structures (often complex or very complex) have been elucidated, and intermetallic crystallochemistry is a fundamental topic of reference. A great number of papers have been published containing results obtained by powder and single crystal X-ray diffractometry and by neutron and electron diffraction methods. A characteristic nomenclature and several symbols and representations have been developed for the description, classification and identification of these phases. 

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 techniques of single-crystal diffractometry have been discussed by Arndt and WUlis (51). We should note that extinction is a very serious problem in the determination of accurate magnetic intensity data from single crystals. Although extinction must always be accounted for in conventional crystallographic studies, it is particularly important to make proper correction in polarized neutron experiments where the ratio of magnetic to nuclear structure factors is determined. 

T.M. Sabine, R.B. Von Dreele, and J.E. Jorgensen, Extinction in time-of-flight neutron powder diffractometry, Acta Cryst. A44, 374 (1988) T.M. Sabine, A reconciliation of extinction theories, Acta Cryst. A44,368 (1988). 

Vol. 1 Modulation Spectrometry of Neutrons with Diffractometry Applications by Pekka Hiismaki... 

Single-crystal diffractometry under high pressure presents several experimental problems, which generally produce low-quality intensity data, and hence, inferior structural refinement results (Zanazzi 1996, Angel et al. 2001). Generally, diffractometry studies were performed with sealed-source X-ray tubes, synchrotron, or neutron radiation. 

Selection of the crystal is the crucial step of the whole study and the time spent on it is well spent. During data collection the crystal should remain within that inner part of the incident beam which has a uniform intensity distribution. Its diameter is smaller (80% at best) than the nominal diameter of the collimator. Thus in X-ray diffractometry a good working norm is for all dimensions of the crystal to be <0.5 mm, and preferably as uniform as possible. For neutron experiments. 

The direct method includes direct observation by electron microscope and field emission technique structural analysis using X-ray, neutron and electron diffractometry, or channelling technique and also resonance techniques such as ESR, NMR, and Mossbauer absorption. The techniques used in the indirect method include the measurement of a property sensitive to the nonstoichiometric composition, such as lattice constant, density, equilibrium partial pressure, and electric conductivity. The defect structure is estimated from the correspondence between the defect model assumed and the measured change of the property. With the indirect method, it is rather difficult to estimate defect structures more complex than the simple point defect. 

This peculiar phenomenon is interpreted to indicate that at the transition, the arrangement of valence electrons becomes disordered, while the interstial oxygen atoms remain in order or become more ordered. Ishii et al. (275) have shown from neutron and X-ray diffractometry that in substoichiometric U409 y, the oxygen atoms in the normal lattice sites enter the interstitial sites by the thermal energy at the transition temperature, and contribute to intensification of the superlattice reflections. 

Niimura. N. Minezaki. Y. Nonaka. T. Castagna. J.C. Cipriani, E. Hoghoj, P. Eehmann. M.S. Wilkinson. C. Neutron Eaue diffractometry with an imaging plate provides an effective data collection regime for neutron protein crystallography. Nat. Struct. Biol. 1997. 4. 909-914. 

B. Buras Time-of-flight diffractometry. Reactor Centrum Netherland Report -234 New methods and techniques in neutron diffraction (1975) pp. 307-346. 

Some 4503, 5 perovskite-structured materials, where A and B represent larger and smaller cations, are ionic conductors, while some other 503 s perovskite-type compounds are mixed conductors. Heavy elements such as La and Ba occupy the A site, but because the mobile O anion is a light element, conventional X-ray powder diffractometry is not sensitive to positional and occupational disordering of oxide ions. To investigate the diffusion path of mobile oxide ions, and structural disorder and crystal structure in perovskite-structured ionic and mixed conductors [5, 6, 8, 10-14], we applied a high-temperature neutron powder diffraction method. Our reasons for choosing this method were as follows [24] ... 

---