Institute of Physics, Academy of Sciences of the Czech Republic, Na Slovance 2,
CZ-182 21 Praha 8, Czech Republic
hybler@fzu.cz
Film methods served for several decades in X-ray laboratories for determination of lattice parameters, space groups, and for checking of quality of crystals. During the era of point detector diffractometers, the candidate crystals were very often studied by film methods prior data collection. More recently the X-ray film was sometimes replaced by image plates. Moreover the film images can now be digitized with aid of a scanner.
Now-a-days these methods, perhaps with few exceptions represent a chapter in a history of crystallography, rather than everyday reality in laboratories. Nevertheless, from time to time, let’s remember this piece of history.
The methods are as follows [1,2]:
Laue method [3,4]: Stationary crystal and film, unfiltered polychromatic radiation. Diffraction pattern registered on the flat film. Reciprocal lattice image collapsed and distorted. Possible front reflection or back reflection arrangement. In the later arrangement relatively large crystals can be studied. Still used for the orientation of bulk crystals.
Oscillation and rotation method: Rotating or oscillating crystal is mounted on the crystallographic head in the axis of cylindrical stationary film cassette, monochromatic (usually filtered) radiation. Reciprocal lattice image distorted and collapsed. Reflections are arranged on layers, corresponding to reciprocal lattice planes.
Weissenberg method [1,2]: Arrangement the same, one layer is selected by the cylindrical layer line screen. Moreover, the cassette is placed at the carriage moving there and back synchronously with the oscillation of crystal. The result is an un-collapsed but distorted image of one selected reciprocal lattice plane.
Precession method [5]: Both crystal and film are performing the precession motion in two synchronously moving gimbal rings. Circular layer line screen selects one reciprocal lattice plane. Because of the equality of crystal and film motions, an undistorted image of reciprocal lattice plane is recorded.
Cone-axis method [5]: Auxiliary to the precession method, provides circles corresponding to reciprocal lattice layers.
De Jong-Bouman method [1,2]: Crystal as well as the flat film is synchronously rotating. Alternative method to obtain undistorted and un-collapsed reciprocal lattice image.
Gandolfi method [6]: Provides powder patterns from single crystals due to an additional the rotation of the specimen.
The undistorted images of reciprocal lattice planes as well as powder diffraction data can be easily and more quickly obtained by processing of frames recorded by modern diffractometers with area detectors.
1. Helliwel, J.R., Single Crystal X-ray Techniques. In: International Tables for Crystallography. Dordrecht/Boston/London 1992, pp. 26-41. Kluwer Academic Publishers.
2. Buerger, M.J.: X-Ray Crystallography. London 1942, Wiley & Sons.
3. Amorós, J.L., Buerger, M.J., Amorós, M.C. de: The Laue Method. New York-San Francisco-London 1975, Academic Press.
4. Barett, Ch. S.: Structure of Metals. New York- Toronto -London 1952, McGraw Hill Book Company.
5. Buerger, M.,J.: The Precession Method in X-ray Crystallography. New York-London-Sydney 1964, John Wiley & Sons.
6. Gandolfi, G.: Mineral. Petrogr. Acta 13 (1967) 67-74.