X-ray diffraction poling

STEREOPOLE software for the analysis of X ray diffraction pole figures with IDL, I. Salzmann and R. Resel, J. Appl. 

X-ray diffraction pole figure measurements on a poly(vinyl fluoride) film [91]. 

The value of the approach using dichroic ratios coupled with a knowledge of the assignments of peaks is further illustrated by measurements on plain polyethylene films [2]. The production process leads to a rather complex orientation pattern. The molten polymer is extruded as a thin, hollow cylinder, in what may be termed the machine direction. It is simultaneously expanded in a plane perpendicular to the machine direction by the application of internal pressure. Additional variables are the extrusion temperature and the rate at which the blown film has been cooled. The resulting orientation behaviour is best studied by x-ray diffraction pole figure measurements [3,4,5] but the infrared approach provides a relatively simple means for obtaining a useful amount of information, particularly for the behaviour of chains in amorphous regions. 

Small-angle X-ray diffraction pole figures can be collected by a method analogous to conventional wide-angle X-ray diffraction pole figures [50]. 

In more recent work, talc-filled polystyrene compounds, with various filler volume fractions, have been processed by compression moulding and through a variety of slit, capillary, rectangular and annular dies [37]. Particle orientation has been characterised using wide angle X-ray diffraction, then expressed in the form of pole figures, and by scanning electron microscopy. It was concluded that... 

To assess about the quality and purity of the synthesized membranes, several experimental techniques and procedures are available many of those are commonly employed in catalyst characterization. Thus, XRD (x-ray diffraction) analysis of the supported samples is conventionally used to identify the type of zeolite, the proportion of amorphous material and impurities, and the preferential orientation of the crystals (XRD-pole figure). However, for the vast majority of the synthesis procedures described, the XRD spectra of the scrapped membrane or the resulting powder from the liquid phase is supplied to avoid the support contribution. 

Figure 26. (102) X-ray pole figure of the (Tl, Bi)-1223 film used for the X-ray diffraction d-26 spectrum measurement shown in Fig. 25. The four well-developed diffraction positions indicate that a and b axes are aligned.

Abstract. Structural properties of rubrene thin films on cleaved mica (001) surfaces were investigated by optical microscopy and x-ray diffraction. Optical microscopy shows, that the crystallization of rubrene results in formation of spherulites. X-ray specular diffraction reveals polycrystalline and polymorphic nature of rubrene. The pole figure measurements of films prepared at low deposition rates reveal orthorhombic structure and indicate fiber textures with crystallographic planes (121), (131) and (141) preferentially oriented parallel to the substrate surface. High deposition rate thin films in addition show polymorphism, corroborating the existence of the orthorhombic and the triclinic phase. 

For thin specimens it is also possible to perform pole figure measurements in transmission mode [2]. Because of the difficulty of preparing thin specimens with a constant thickness this last mode is not often used today for x ray diffraction. 

There are today standard computer controlled x ray diffraction equipments for pole figure measurements as well as software packages for ODF calculation so that only a general knowledge about texture analysis is usually required of researchers who intend to study the anisotropic behavior of materials. Moreover, many papers have demonstrated how physical or mechanical properties can be calculated in textured materials. This is especially true for cubic metals and alloys and, to a lesser extent, for hexagonal alloys. There remain, therefore, many studies to be undertaken, particularly for non-metallic polycrystalline materials. 

Fig. 5.1 A set-up for a study of X-ray diffraction on liquid crystals X-ray tube (X), beam collimators (C), mirrors (M), a detector (D) and a data acquisition system (PC). A sample is represented by a stack of parallel layers placed in a camera with controllable temperature installed between the poles of a magnet...

According to the theory developed by Wada and Hayakawa the piezoelectric activity in PVDF depends strongly on the magnitude of persistent polarization Ps which originates from a dipole orientation. The piezoelectric eai constant increases proportionally with the Ps. In order to orient the dipoles in form I crystals, it is necessary that the dipoles should be rotated in a main chain by the applied electric field. From this view point, it may be easily understandable that the internal rotation of dipoles more preferentially occurs in the roughly packed crystal lattice than in the closely and thermodynamically stable lattice. This is confirmed by the effect of poling on the intensity of X-ray diffraction. 

X-ray diffraction peaks for unpoled, partially poled, and poled composites. The relative intensities of the (001) and (100) peaks are reversed in the unpoled and poled samples, which indicates near-saturation poling of the composites. Hence, a simple XRD technique can yield information about the electronic properties of... 

Shortly afterward, the same authors also developed a palladium(II) catalyst [Pd(2-PyCH=NPh)(OCOC6F5)2] for the hydroarylation of fullerene with boronic acids, which presents good catalytic activity (reaction generally occurring at room temperature), bench stability in the solid state, and efficiency under air conditions. Single-crystal X-ray diffraction analysis confirmed unequivocally the addition of the aryl moiety and hydrogen in a 1,2-fashion at the a double bond of Cjq, with the phenyl group attached at the position close to the pole of the C70 unit [31]. 

In the as-mechanically stretched PVDF film, the polar axis, i.e., the dipole moment axis, is randomly oriented to the stretching direction. An electrical poling treatment is needed to make the dipole axis reorient to align predominantly along the poling z-axis, that is, perpendicular to the film s plane. The field-induced dipole alignment in phase (I) crystals has been investigated by Raman spectroscopy, x-ray diffraction, and infrared dichroism (Wada and Hayakawa 1981). 

Tbe most convincing evidence for dipole reorientation and the 60 increment model was provided by Bur et aL [17], They measured the intensity of X rays diffracted from a l>mm-diameler cylinder machined from a PVDF l>mm-thick film sriiicb had been stretched by rolling and poled at the same time. Films produced by rolling have a phase, single-crystal-like texture. The chain axis (c) it oriented in ik rolling direction. 

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