Composites single-crystal textures

Applications The general applications of XRD comprise routine phase identification, quantitative analysis, compositional studies of crystalline solid compounds, texture and residual stress analysis, high-and low-temperature studies, low-angle analysis, films, etc. Single-crystal X-ray diffraction has been used for detailed structural analysis of many pure polymer additives (antioxidants, flame retardants, plasticisers, fillers, pigments and dyes, etc.) and for conformational analysis. A variety of analytical techniques are used to identify and classify different crystal polymorphs, notably XRD, microscopy, DSC, FTIR and NIRS. A comprehensive review of the analytical techniques employed for the analysis of polymorphs has been compiled [324]. The Rietveld method has been used to model a mineral-filled PPS compound [325]. 

Impressive theoretical progress has been made in the prediction of fundamental modifications of catalyst surface structures and compositions as a function of the chemical potential of the environment in relatively simple cases (N0rskov et al., 2006 Reuter and Scheffler, 2002 Stampfl et al., 2002). This level of dynamic analysis with either single crystals or realistic polycrystalline catalyst materials has not yet been attained experimentally and certainly not in experiments with XRD under reaction conditions. There are no investigations that provide quantitative links between the phases and texture of a catalyst with its performance. All investigations discussed here can at best provide evidence relating the catalytic activity with a phase or a defect structure of a phase. 

Reactant characterization also includes determination of any changes, such as loss of water of crystallization and/or phase transformations, prior to decomposition. Such processes may cause changes in composition (e.g. water loss) and/or surface textures, and in the numbers and distributions of imperfections. Some dehydrations yield an anhydrous salt, or lower hydrate, that is amorphous to X-rays, and a single crystal reactant is converted to an assemblage of fine crystalhtes. The consequences of annealing on defect concentrations and the decomposition of surface material of low stability may also require consideration. 

Figure 18.10 Comparison of the high-field strain response of textured (001) PMN-PT with single crystals of similar composition. From Ref [49].

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