Powder XRD pattern

The first analytical tool to assess tire quality of a zeolite is powder x-ray diffraction. A collection of simulated powder XRD patterns of zeolites and some disordered intergrowths togetlier witli crystallographic data is available from tlie IZA [4o]. Phase purity and x-ray crystallinity, which is arbitrarily defined as tlie ratio of tlie intensity of... 

Figure 1. (left) Powder XRD pattern of 700 °C-calcined sample cubic M112O3 (right) SEM images of the hexagonal nanoplates of (a) as-synthesized and (b) 700 °C-calcined samples. 

HnZSM-5 were obtained by calcination procedure under 02 at 673 K during 24 h of NH4+-exchanged zeolites from VAW aluminium (Schwandorf, Germany) and from Zeolyst International (Valley Forge, USA). The chemical analysis, powder XRD patterns, 29Si, 27A1 MAS-NMR, IR, Raman, Diffuse reflectance UV-visible (DRUVv)... 

The powder XRD patterns of calcined and ion-exchanged MAPO-36 are shown in Fig.l. The XRD patterns of calcined MAPO-36 coincided with already reported data [7]. The XRD patterns of ion-exchanged MAPO-36 revealed absence of structural degradation. Further, there are no patterns corresponding to non-framework metal oxide. 

Nanosized anatase (< 10 nm) and brookite ( 70 run) particles have been successfully synthesized via sonication and hydrothermal methods. Figure 5.1 shows the powder XRD patterns of as-synthesized anatase and brookite nanoparticles. The particle sizes were characterized by XRD and scanning electron microscopy (SEM) (Fig. 5.2). 

The identity of the polytype present in a given LDH sample may, in principle at least, be determined from the powder XRD pattern, although as we shall see for many LDHs this is not possible, as the amoimt of useful information therein is limited. By convention, the indexing of powder patterns for rhombohedral polytypes is based on a triple hexagonal unit cell (see Fig. 3). 

Fig. 13 Experimental, calculated and difference powder XRD patterns for [Zn4Al2(OH)i2] Cl2-nH20 at ambient temperature. Reprinted with permission from [106]. Copyright Academic Press...

It has been suggested that powder XRD patterns of some mineral samples of LDH minerals show evidence of superlattice reflections [7,113] but there is no clear consensus [100]. It should also be borne is mind that, as discussed in Sect. 3.5, superlattice reflections may be due to anion, rather than cation, ordering although the latter may be an indication of the former. 

Fig.1 Model for alignment of PAE No. 19 in Table 2 on the surface of a Pt plate. The powder XRD pattern indicates both and 2 peaks, whereas the XRD pattern of a cast film, measured with a reflection mode, gives only the di peak di= l.lS n+lO) A (n=number of carbon atoms in the OR group) [93,95]...

T together in the sohd state for 20 min produced a material which had the same powder XRD pattern as that calculated from the known crystal structure AT. By comparison, however, an interesting distinction exists with an analogous base pair involving 9-ethylguanine G and 1-methylcytosine C, which had also... 

Fig. 1 Low-angle powder XRD pattern of cubic mesostructured germanium. The Bragg diffraction peaks consistent with the body-centered Ia-3d unit cell with a = 8.4 nm...

XRD and TEM analysis on template-removed MSU-Ge-2 evidenced the presence of a well-defined, long-range periodicity of the hexagonal pore structure (Fig. 3). The low-angle powder XRD pattern of as-prepared and template-removed mesoporous MSU-Ge-2 indicates a pore periodicity of 4.8 and 4.0 nm, respectively. The pore-to-pore distance (4.0 nm) determined from XRD... 

The traditional approach for structure solution follows a close analogy to the analysis of single-crystal XRD data, in that the intensities 1(H) of individual reflections are extracted directly from the powder XRD pattern and are then used in the types of structure solution calculation (e.g. direct methods, Patterson methods or the recently developed charge-flipping methodology [32-34]) that are used for single-crystal XRD data. As discussed above, however, peak overlap in the powder XRD pattern can limit the reliability of the extracted intensities, and uncertainties in the intensities can lead to difficulties in subsequent attempts to solve the structure. As noted above, such problems may be particularly severe in cases of large unit cells and low symmetry, as encountered for most molecular solids. In spite of these intrinsic difficulties, however, there have been several reported successes in the application of traditional techniques for structure solution of molecular solids from powder XRD data. 

Fig. 3 A typical result from Rietveld refinement (specifically for the material TDMM discussed in Sect. 6.3). The experimental powder XRD pattern is shown as red plus marks and the calculated powder XRD pattern for the structural model is shown as the green line. The tick marks indicate peak positions. The difference between the experimental and calculated powder XRD profiles is shown as the purple line at the bottom. Clearly, for a good quality Rietveld refinement, this difference profile should be as flat as possible, and should ideally reflect only the noise level in the experimental data...

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