Energy-dispersive diffraction

Fig. 7. Energy-dispersive diffraction profile of TNT with 500 counts total.

Beale AM, Jacques SDM, Bergwerff JA, Barnes P, Weckhuysen BM. Tomographic energy dispersive diffraction imaging as a tool to profile in three dimensions the distribution and composition of metal oxide species in catalyst bodies. Angew Chem Int Ed. 2007 46 8832. 

High time-resolution is afforded with energy dispersive diffraction (see above). While systematic errors are problematic, reliable structural refinements are possible for a limited class of experiment. The software and method to enable structure refinement using the Rietveld method and ED powder diffraction data are now well-established (Chen and Weidner 1997, Larson and von Dreele 1986). In a recent study of the partitioning of iron between the olivine and ringwoodite polymorphs of (Mg,Fe)2Si04, energy dispersive data were sufficiently accurate to allow derivation of unit cell volumes... 

The reader may wonder why an energy-dispersed spectrum as shown in Fig. 15-12 does not also contain the various hkl diffraction lines of the specimen, like the energy-dispersive diffraction pattern of Fig. 7-23. After all, the experimental arrangements for diffraction and spectroscopy are similar. Spectra sometimes do contain diffraction lines. Ordinarily, however, they are not observed because spectrometers do not contain collimators. The resulting crossfire of diffracted beams means that the angle 6 is not defined the diffracted radiation is therefore not peaked at particular energies but is merely spread over the background. 

Figure 2.17 Schematic representation of the energy dispersive diffraction (EDD) technique. The energy discriminating detector at fixed scattering angle determines the wavelength of each detected photon and hence the d spacing of the diffracting lattice planes.

Disadvantages of energy dispersive powder diffraction are the low resolution obtained due to the limited energy resolution of the detectors, making it difficult to determine accurate unit cell parameters. Fluorescence lines and absorption edges will also influence the collected spectrum and it is generally difficult to obtain structural information, e.g. from Rietveld refinement, from energy dispersive diffraction data. 

Another approach to studies of hydrothermal and solvothermal reactions is to use energy dispersive diffraction. A normal size laboratory autoclave is used with a thinning of a small part to allow X-rays to penetrate the wall. Collimated slits are used to obtain diffraction from only a small volume element inside the autoclave. Stirring is necessary to prevent sedimentation of the materials. 

Fig. 17. The krypton lattice parameter as measured by EXAFS and energy dispersive diffraction...

IR microspectroscopy [12], and UV-Vis-NIR DR microspectroscopy [9,12-15] as invasive techniques and tomographic energy-dispersive diffraction imaging (TEDDI) [16] and magnetic resonance imaging (MRI) [17-25] as noninvasive techniques. In what follows, we will discuss the application of these methods for catalyst preparation studies, illustrating their possibilities and limitations. 

TEDDI tomographic energy-dispersive diffraction imaging... 

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