International
Tables for
Crystallography
Volume C
Mathematical, physical and chemical tables
Edited by E. Prince

International Tables for Crystallography (2006). Vol. C. ch. 3.4, p. 168

Section 3.4.2.3. Equatorial setting using a rotation camera

P. F. Lindleya

a ESRF, Avenue des Martyrs, BP 220, F-38043 Grenoble CEDEX, France

3.4.2.3. Equatorial setting using a rotation camera

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Methods for equatorial setting are well described by Jeffery (1971[link]). The aim is to identify reciprocal-lattice layer lines from X-ray oscillation photographs and, by measuring the degree and directions of curvature of the zero-layer line, to adjust the crystal setting until the layer-line patterns are made perpendicular to the rotation axis, i.e. the crystal lattice vector perpendicular to these reciprocal-lattice layers lies parallel to the rotation axis. For crystals of well defined morphology, initial alignment of a crystal lattice vector with the rotation axis can be achieved optically, often to within a degree. For setting errors of less than 5°, reciprocal-lattice layer lines should be readily identifiable on X-ray oscillation diffraction patterns. The use of unfiltered X-radiation often assists in this regard (as well as reducing exposure times), and a device described by Kulpe (Kulpe, 1963[link]; Kulpe & Dornberger-Schiff, 1965[link]) may prove useful in the identification of the zero-layer equatorial pattern on photographic films.

For accurate final setting, a general `double-oscillation' method such as that of Weisz & Cole as modified by Davies (Jeffery, 1971[link]) is preferred, although Suh, Suh, Ko, Aoki & Yamazaki (1988[link]) have provided a rationale for adjustment of both goniometer arcs simultaneously from a `single-oscillation' photograph. With the `double-oscillation' technique, two single oscillations, separated by a φ reading of 180°, are recorded on the same image, but with significantly different exposure times, so that the patterns are related by a mirror plane and are readily distinguishable. The goniometer arcs are placed at 45° to the X-ray beam. Measurements of the relative displacements of the two patterns at the 2θ = 90° position on the image readily yield corrections to both goniometer-head arcs. No translational movement of the film cassette is required, but the crystal must diffract to at least a θ angle of 45°. Hanson (1981[link]) has devised a technique suitable for a Weissenberg camera that is a combination of double oscillation with displacements and measurements at low-2θ angles. This method is particularly suitable for crystals with large unit cells.

In the case where layer lines are not readily locatable, but the crystal unit-cell dimensions are known, Jeffery (1971[link]) also describes an equatorial setting technique that relies on the indexing of at least three low-angle Laue streaks.

Okazaki & Soejima (1986[link]) have described two simple goniometer attachments that may prove useful for crystals that have been mounted so that the angular movements required to achieve setting exceed the range commonly available on goniometer heads.

References

First citation Hanson, I. R. (1981). A rapid and accurate method of aligning a crystal on a Weissenberg goniometer. J. Appl. Cryst. 14, 353. Google Scholar
First citation Jeffery, J. W. (1971). Methods in X-ray crystallography, pp. 149–169, 441–444. London/New York: Academic Press. Google Scholar
First citation Kulpe, S. (1963). Instrument for setting single crystals from X-ray oscillation photographs. Acta Cryst. 16, 837–838. Google Scholar
First citation Kulpe, S. & Dornberger-Schiff, K. (1965). A special application of the crystal setter. Acta Cryst. 18, 812–813. Google Scholar
First citation Okazaki, A. & Soejima, Y. (1986). Goniometer-head attachments for crystal characterization in Weissenberg or precession geometry. J. Appl. Cryst. 19, 412–413.Google Scholar
First citation Suh, I.-H., Suh, J.-M., Ko, T.-S., Aoki, K. & Yamazaki, H. (1988). Rationale of a quick adjustment method for crystal orientation in oscillation photography. J. Appl. Cryst. 21, 521–523.Google Scholar








































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