** Next:** 4.1 Cubic structures
**Up:** The Study of Metals and Alloys
** Previous:** 3. Measurement of Debye-Scherrer Photographs

We must first have the values of for all lines on a powder photograph,
and, if the number is large, assigning indices *hkl* to them all may be
difficult. Fortunately, many metal and alloy structures are so simple that
their powder pattern can be recognized at a glance. Our first task is thus to
familiarize ourselves with these patterns.

The three most common structures are called face-centred cubic (f.c.c.), body-centred cubic (b.c.c.) and hexagonal close-packed (h.c.p.). They are illustrated in Fig. 4. The sequence of lines - in position and intensity - is characteristic of each structure and the scale of the pattern gives the dimensions of the unit cell; the smaller the scale of the pattern, the larger is the unit cell. Therefore there are more lines for a larger unit cell.

**Copyright © 1984, 1998 International Union of
Crystallography**