SAME grain orientation determination

Diffracted intensities, proportional to pole densities, may be put on a times-random basis by comparing them with intensities diffracted by a random specimen [9.20]. The random specimen should be of the same material as the textured specimen and, for a transmission method, it should have the same value of fit if not, a correction has to be made that will depend on the transmission method involved. The random specimen itself is usually made by compressing and sintering a powder [9.11, 9.12]. The randomness of grain orientation in this specimen must be checked by determining its diffraction pattern with a diffractometer in the usual way the measured integrated intensities of all lines should agree with those calculated by Eq. (4-21). 

The presence of diffraction peaks indicates that crystalline grains are present. In order to determine if those peaks are from the same family of planes (parallel to each other), which indicate a highly-oriented material, or from various grain orientations (which is more typical in a powder or polycrystalline sample). 

The simplest technique is EDX, because no optical setup is needed. The drawback of this technique is that, due to preferential orientations and to the insufficient number of diffracting grains in the beam when working in a diamond anvil cell, the intensity of the diffracted peaks is not reliable, and cannot be used to determine the atomic positions in the unit cell. On the contrary, in ADX, even with preferential orientations and with poor grain statistics, by integrating a whole ring of diffraction corresponding to the same 0, the atomic positions may be deduced. 

Figure 1.28 Calculated SAME curves as a function of sample rotation about angle a and as a function of the orientation angle (pmet- The experimental curves for four different Zr grains are indicated together with the orientation angles

Figure 1.29 (a-d) SAME curves on an (0111) oriented Zr single grain after potentiodynamic formation to the indicated formation potentials (10-40 V). The symbols referto the experimental data, the lines represent the fit results (SAME determination of the orientation angles). Significant amplitude variations and phase shift of the A curves with respect to the curves are... 

On the other hand, the structure of Sa,2 was reported as tetragonal with the helices perpendicular to the c-axis of the unit cell (Table 20). The only reasonable possibility in structure determination was the one in which adjacent layers of hehces are oriented perpendicular to each other. The hehces of the layers have the same molecular structure and all the hehces in one layer have the same handedness. The closest packing of the helices is achieved if the molecules of parallel layers have opposite turns (see Fig. 19). This structure is unusual but not unlikely since Ae pitch of Ae sulfur helix is Ae same as Ae intermolecular Astance of neighboring helical axes, about 460 pm (see Table 20). The structure of Sa,2 is a cross-grained plywood structure . This peculiarity has caused Tuinstra to label this modification laminar sul-fiur (S ). 

To observe the equilibrium shape of a crystal experimentally, it is necessary to confirm that the crystal one wants to observe exhibits such a shape. Since the equilibrium shape of a crystal in a matrix is the same as the equilibrium shape of the matrix entrapped within the crystal, the equilibrium crystal shape can be determined by observing the shape of the entrapped matrix. If a number of randomly oriented grains exhibit an equilibrium shape, the shape can also be determined stereographically from the crystal plane orientations of the grains and the directions of the grain interfaces on a planar section that can be obtained by the electron backscattered diffraction technique. For metals for which the anisotropy in interfacial energy is low at their processing... 

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