X-ray powder

X-ray powder diffraction studies are perfonned both with films and with counter diffractometers. The powder photograph was developed by P Debye and P Scherrer and, independently, by A W Hull. The Debye-Scherrer camera has a cylindrical specimen surrounded by a cylindrical film. In another commonly used powder... 

Karfunkel H R, B Rohde, F J J Leusen, R J Gdanitz, emd G Rihs 1993. Continuous Similarity Measure Between Nonoverlapping X-ray Powder Diagrams of Different Crystal Modifications. Journal oj Computational Chemistry 14 1125-1135. 

The formation of such materials may be monitored by several techniques. One of the most useful methods is and C-nmr spectroscopy where stable complexes in solution may give rise to characteristic shifts of signals relative to the uncomplexed species (43). Solution nmr spectroscopy has also been used to detect the presence of soHd inclusion compound (after dissolution) and to determine composition (host guest ratio) of the material. Infrared spectroscopy (126) and combustion analysis are further methods to study inclusion formation. For general screening purposes of soHd inclusion stmctures, the x-ray powder diffraction method is suitable (123). However, if detailed stmctures are requited, the single crystal x-ray diffraction method (127) has to be used. 

Analysis. Excellent reviews of phosphate analysis are available (28). SoHds characterization methods such as x-ray powder diffraction (xrd) and thermal gravimetric analysis (tga) are used for the identification of individual crystalline phosphates, either alone or in mixtures. These techniques, along with elemental analysis and phosphate species deterrnination, are used to identify unknown phosphates and their mixtures. Particle size analysis, surface area, microscopy, and other standard soHds characterizations are useful in relating soHds properties to performance. SoHd-state nmr is used with increasing frequency. 

Many of the procedures used for technical analysis of aluminum hydroxides are readily available from the major producers of aluminum hydroxides. Phase Composition. Weight loss on ignition (110°—1200°C) can differentiate between pure (34.5% Al(OH)2) ttihydroxides and oxide—hydroxides (15% Al(OH)2). However, distinction between individual ttihydroxides and oxide —hydroxides is not possible and the method is not useful when several phases are present together. X-ray powder diffraction is the most useful method for identifying and roughly quantifying the phase composition of hydroxide products. 

R. Jenkins and R. L. Snyder, Introduction to X-ray Powder Diffractometry, John Wiley Sons, Inc., New York, 1996. 

Doping of alkali-metals into CNTs has been examined [11]. The X-ray powder diffraction (XRD) patterns of the K- or Rb-doped CNTs show that alkali-metals are intercalated between the CNT layers. The hexagonal unit cell is essentially the same as that of the stage-1 alkali-metal intercalated graphite ACg (A=K, Rb). For a sample doped with Rb, the observed lattice parameter of the perpendicular... 

IF7 has been shown to act as a weak Lewis acid towards CsF and NOF, and the compounds CsIFg and NOIFg have been characterized by X-ray powder patterns and by Raman spectroscopy they are believed to contain the IFg anion. 

According to X-ray powder diffraction data, compounds RF NbOFs, Cs2NbOF5 [174] and Cs2TaOF5 [176] have similar type structure and are similar to K2GeF6, whereas (NFL,)2NbOF5 crystal structure is similar with Rb2Mo02F4 [184]. The above-mentioned compounds contain isolated NbOF52" complex ions [185]. 

Lastochkina et al. [216] reported on the preparation of KTaOi.5F3-H20, but the X-ray powder diffraction pattern obtained for the anhydrous product, KTaOi.5F3, does not correspond with the pattern given for K2Ta203F6 in [215]. 

The compounds characterized by X Me = 3.5 have a common formula of M2Me205F2 and crystallize either in a pyrochlore [192] or a veberite [229] type structure. According to X-ray powder diffraction patterns, the structure of Na2Nb205F2 can be regarded as a super-structure of pyrochlore, which is made up of octahedrons connected in layers and arranged in the (111) direction. The layers are linked via octahedrons so that each octahedron in one layer shares three vertexes with an octahedron in the adjacent layer. 

Fig. 43 shows fragments of X-ray powder diffraction patterns of compounds with rock-salt-type structures. 

Fig. 43. Fragments of X-ray powder diffraction patterns of compounds with rock-salt structures that underwent modification to a state of disordered ionic arrangement. 1 - Li3Ta04 2 - LiflbO 3 - Li4Ta04F 4 - Li3Ti03F 5 -LiiFeOiF 6 - LiNiOF (Reflections attributed to LiF are marked by an asterisk).

In all cases, broad diffuse reflections are observed in the high interface distance range of X-ray powder diffraction patterns. The presence of such diffuse reflection is related to a high-order distortion in the crystal structure. The intensity of the diffuse reflections drops, the closer the valencies of the cations contained in the compound are. Such compounds characterizing by similar type of crystal structure also have approximately the same type of IR absorption spectra [261]. Compounds with rock-salt-type structures with disordered ion distributions display a practically continuous absorption in the range of 900-400 cm 1 (see Fig. 44, curves 1 - 4). However, the transition into a tetragonal phase or cubic modification, characterized by the entry of the ions into certain positions in the compound, generates discrete bands in the IR absorption spectra (see Fig. 44, curves 5 - 8). 

X - Ray powder diffraction data of some important tantalum and niobium fluoride compounds (CuKa radiation)... 

Crystalline material will diffract a beam of X-rays, and X-ray powder diffractometry can be used to identify components of mixtures. These X-ray procedures are examples of non-destructive methods of analysis. 

Structural Studies. X-ray powder diffraction patterns for I indicate that the crystal structure is isomorphous to Zr2(0H)2-(SOO3 (H20)>. Figure 1 depicts the structure of the zirconium compound (5). The structure of I is identical to that of the zirconium analog except for variations in bond distances and angles which do not affect the overall structure. We have as yet been unable to obtain single crystals of I which are suitable for X-ray diffraction studies. 

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