Temperature-diffuse scattering

Temperature diffuse scattering patterns are of three main types. Hard materials such as diamond and tungsten show only small. 

A dynamic transition in the internal motions of proteins is seen with increasing temperamre [22]. The basic elements of this transition are reproduced by MD simulation [23]. As the temperature is increased, a transition from harmonic to anharmonic motion is seen, evidenced by a rapid increase in the atomic mean-square displacements. Comparison of simulation with quasielastic neutron scattering experiment has led to an interpretation of the dynamics involved in terms of rigid-body motions of the side chain atoms, in a way analogous to that shown above for the X-ray diffuse scattering [24]. 

For local deviations from random atomic distribution electrical resistivity is affected just by the diffuse scattering of conduction electrons LRO in addition will contribute to resistivity by superlattice Bragg scattering, thus changing the effective number of conduction electrons. When measuring resistivity at a low and constant temperature no phonon scattering need be considered ar a rather simple formula results ... 

Early studies, which did not include many high-order reflections, revealed systematic differences between spherical-atom X-ray- and neutron-temperature factors (Coppens 1968). Though the spherical-atom approximation of the X-ray treatment is an important contributor to such discrepancies, differences in data-collection temperature (for studies at nonambient temperatures) and systematic errors due to other effects cannot be ignored. For instance, thermal diffuse scattering (TDS) is different for neutrons and X-rays. As the effect of TDS on the Bragg intensities can be mimicked by adjustment of the thermal parameters, systematic differences may occur. Furthermore, since neutron samples must be... 

The X-N technique is sensitive to systematic errors in either data set. As discussed in chapter 4, thermal parameters from X-ray and neutron diffraction frequently differ by more than can be accounted for by inadequacies in the X-ray scattering model. In particular, in room-temperature studies of molecular crystals, differences in thermal diffuse scattering can lead to artificial discrepancies between the X-ray and neutron temperature parameters. Since the neutron parameters tend to be systematically lower, lack of correction for the effect leads to sharper atoms being subtracted, and therefore to larger holes at the atoms, but increases in peak height elsewhere in the X-N deformation maps (Scheringer et al. 1978). 

Another reason why high angle reflections are better measured at low temperature is the decreased thermal diffuse scattering (see Sect. 2.2) which allows a more accurate integration of those intensities. 

Rebscher and Pyell [62, 63] were the first to report the use of fluorescence detection. The baseline noise with ICFD was about twice that of OCFD. This could be attributed to the minute motions of the packed bed in the applied electric field and the diffuse scattering in the bed that increased the level of background fluorescence. R.S.D. s found for the retention times of polyaromatic hydrocarbons were less than 1.1 and < 0.4 % for ICFD and OCFD, respectively. Variations in the peak areas were about twice as high in ICFD (2.6-5.1%) compared to OCFD (1.4-2.3%). According to the authors, this could be due to variations in the temperature within the capillary. 

A preliminary knowledge of the crystal structure is important prior to a detailed charge density analysis. Direct methods are commonly used to solve structures in the spherical atom approximation. The most popular code is the Shelx from Sheldrick [26] which provides excellent graphical tools for visualization. The refinement of the atom positional parameters and anisotropic temperature factors are carried out by applying the full-matrix least-squares method on a data corrected if found necessary, for absorption and diffuse scattering. Hydrogen atoms are either fixed at idealized positions or located using the difference Fourier technique. 

If one looks between diffraction peaks at high resolution, one finds "streaks" due to lattice phonons, which sharpen gradually at low temperatures this is called thermal diffuse scattering. 

Salient experimental features exhibited by RADP/D-RADP type mixed systems are (1) diffuse scattered intensities at temperatures less than 100 K, (2) a broad rather than a sharp Cusp in the dielectric susceptibility experiment at the PG transition temperature (unlike in spin glasses), (3) deviation of the temperature... 

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