Efficient data reduction for time-of-flight neutron scattering experiments on single crystals.

Event-mode data collection presents remarkable new opportunities for time-of-flight neutron scattering studies of collective excitations, diffuse scattering from short-range atomic and magnetic structures, and neutron crystallography. In these experiments, large volumes of the reciprocal space are surveyed, often using different wavelengths and counting times. These data then have to be added together, with accurate propagation of the counting errors. This paper presents a statistically correct way of adding and histogramming the data for single-crystal time-of-flight neutron scattering measurements. In order to gain a broader community acceptance, particular attention is given to improving the efficiency of calculations.

Total scattering and pair distribution function analysis in modelling disorder in PZN (PbZn1/3Nb2/3O3).

The ability of the pair distribution function (PDF) analysis of total scattering (TS) from a powder to determine the local ordering in ferroelectric PZN (PbZn1/3Nb2/3O3) has been explored by comparison with a model established using single-crystal diffuse scattering (SCDS). While X-ray PDF analysis is discussed, the focus is on neutron diffraction results because of the greater extent of the data and the sensitivity of the neutron to oxygen atoms, the behaviour of which is important in PZN. The PDF was shown to be sensitive to many effects not apparent in the average crystal structure, including variations in the B-site-O separation distances and the fact that 〈110〉 Pb(2+) displacements are most likely. A qualitative comparison between SCDS and the PDF shows that some features apparent in SCDS were not apparent in the PDF. These tended to pertain to short-range correlations in the structure, rather than to interatomic separations. For example, in SCDS the short-range alternation of the B-site cations was quite apparent in diffuse scattering at (½ ½ ½), whereas it was not apparent in the PDF.

In situ synchrotron high-energy X-ray diffraction analysis on phase transformations in Ti-Al alloys processed by equal-channel angular pressing.

Mixtures of 47-Al and 53-Ti powders (atomic %) have been consolidated using back pressure equal-channel angular pressing starting with both raw and ball-milled powders. In situ synchrotron high-energy X-ray diffraction studies are presented with continuous Rietveld analysis obtained upon a heating ramp from 300 K to 1075 K performed after the consolidation process. Initial phase distributions contain all intermetallic compounds of this system except Al, with distribution maxima in the outer regions of the concentrations (alpha-Ti, TiAl(3)). Upon annealing, the phase evolution and lattice parameter changes owing to chemical segregation, which is in favour for the more equilibrated phases such as gamma-TiAl, alpha(2)-Ti(3)Al and TiAl(2), were followed unprecedentedly in detail. An initial delta-TiH(2) content with a phase transition at about 625 K upon heating created an intermediate beta-Ti phase which played an important role in the reaction chain and gradually transformed into the final products.