Diffuse streaks

Metallic cobalt exhibits this phenomenon, and so do layered silicates and layered halides like Cdl2 or Bil3. In X-ray diffraction, stacking faults cause the appearance of diffuse streaks (continuous lines in the diffraction pattern). 

The chemical stabilization of the structure is thus characterized by the absence of faults or discernible defect structures, confirmed by sample tilting experiments in diffraction contrast and by HRTEM. The corresponding electron diffraction in the (101) orientation, however, shows diffuse streaks (figure 3.38(b)). The streaks are mainly along the (111) and (010) directions. Some weak diffuse streaking along (101) is also observed. The streaks are indicative of considerable disorder in the structure. These results are consistent with the NMR data. 

Dynamic smdies of the alloy system in CO and H2 demonstrate that the morphology and chemical surfaces differ in the different gases and they influence chemisorption properties. Subnanometre layers of Pd observed in CO and in the synthesis gas have been confirmed by EDX analyses. The surfaces are primarily Pd-rich (100) surfaces generated during the syngas reaction and may be active structures in the methanol synthesis. Diffuse scattering is observed in perfect B2 catalyst particles. This is attributed to directional lattice vibrations, with the diffuse streaks resulting primarily from the intersections of 111 reciprocal lattice (rel) walls and (110) rel rods with the Ewald sphere. 

Among the most common surface X-ray scattering techniques used to probe mineral-fluid interface structure is the measurement of crystal truncation rods (CTRs). CTRs are diffuse streaks of intensity connecting bulk reciprocal lattice (Bragg) points in the direction perpendicular to a surface, and arise as a natural... 

At Mf temperature for TiNi, the magnitude of the shear movements initiated at Ms temperature now reached their maximum. The structure thereby assumes a new crystallographic symmetry that differs from that of the structure above Ms temperature. The theoretical X-ray photographs reflecting these physical changes in TiNi can be described qualitatively in three separate temperature regions (a) at and above the Ms temperature - discrete spot reflections, (b) between Ms and Mr temperatures - diffuse streaks and spot reflections, where the degree of diffuseness is dependent on temperature, and finally (c) at and below the Mr temperature - new set of discrete spot reflections. 

In the metallic state below about 150 K a set of diffuse streaks was found in X-ray studies as shown in Fig. 18 which suggests the onset of the periodic lattice distortion with = 0.295 b having no correlation among them perpendicular to the one-dimensional b-axis [55,56]. Corresponding to these x-ray streaks inelastic neutron scattering studies revealed the decrease in the phonon frequency for the wave vector = 0.295 b with decreasing temperature as shown in Fig. 19 [60]. This soft phonon is considered to be frozen out at the metal-insulator transition temperature 53 K causing the superstructure described above. This type... 

Figure Al-15 shows an example of this phenomenon, often called thermal asterism because of the radial direction of the diffuse streaks. This photograph was obtained from aluminum at 280°C in 5 minutes. Actually, thermal agitation is quite pronounced in aluminum even at room temperature, and thermal asterism is usually evident in overexposed room-temperature photographs. Even in Fig. 3-6(a), which was given a normal exposure of about 15 minutes, radial streaks are...

Electron diffraction patterns were taken from many crystal fragments of Ga-2434. Some typical patterns are shown in Fig. 1.3. From the reflection conditions (h - - k = 2n for hkO, I = 2n for Okl, hOl and 00/, h = 2n for 00 and k = 2n for 0 0) the space group is uniquely determined to be Pccn (56). The lattice parameters are a = 5.46, 6 = 5.54 and c = 51.3A, being in agreement with those obtained from X-ray diffraction. Weak diffuse streaks along [010] in Fig. 1.3(a) must be due to stacking faults, which have been observed locally as intergrowth defects. 

Analogous to the situation for YBCO-123, the diffuse streaks show a sinusoidal modulation with a period 11.5c 247- The distance d = 0.087c247 matches, well within the experimental error, the distance between the two BaO layers adjacent to a single CuO layer. We therefore suggest a symmetrical relaxation of the two BaO layers in a BaO—CuO—BaO triplet [7.51]. The occurrence of maxima of the modulations of the streaks at positions h = 0, implies that no offset in the plane exists between both BaO layers of the triplet. 

Blackwell and coworkers [19] have extensively studied the case of liquid crystalline main-chain copolymers produced by the random polymerization of two or three different monomers. The X-ray scattering patterns of these materials usually display a set of non-periodic diffuse streaks. These diffuse streaks were analyzed by extending the model of disorder of Hosemann to take into account chemical disorder. The description of the data by this model gave the correlation length of the ordering, information on the conformations of the repeat units and proved the random sequence of the copolymers. Subsequent molecular modelling studies revealed the detailed conformation of the repeat units. 

Fig. 8. a X-ray scattering pattern of a fiber of an organometallic main-chain LCP quenched from the nematic phase, b Schematic representation of a. (a) = wide angle diffuse ring (b) = diffuse spots due to the SmC fiuctuations (c) = equidistant diffuse streaks (d) = other weak diffuse spots e = faint lines due to a slight crystallization... 

Let us first consider the set of equidistant diffuse streaks (c) perpendicular to the director [la,b, 30]. These streaks are very similar to those observed on the X-ray scattering patterns of the nematic phases of main-chain LCPs discussed in Sect. 3.2 but they must be interpreted differently because the SmA phase shows (quasi) long-range positional order. These diffuse streaks also correspond to the intersection with the Ewald sphere of a set of equidistant diffuse planes. But here this set represents the Fourier transform of uncorrelated rows of side-chains displaced along the director from their equilibrium position inside the layers (Fig. 13). 

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