Neutron Scattering

18 . Texture in Materials and Earth Sciences
Wolfgang Schäfer
Mineralogisch-Petrologisches Institut, University ofBonn
Forschungszentrum Jülich, MIN/ZFR, 52425 Jülich
1.0 Introduction
The topic texture` has to be assigned to the contributions about elastic neutron scattering and
the determination of crystal and magnetic structures by means ofBragg scattering using either
polyciystalline or single crystalline samples (compare Fig .18 .la and 18 .1d, resp .) . When
performing powder diffraction for the puiposes of refmements or even determinations of
crystal (or magnetic) structures, one initially assumes statistical distributions of all crystallite
orientations inside the polycrystalline material, thus ensuring that for the measurement ofeach
Bragg reflection hkl an almost equal and, with respect to statistical relevance, a sufficient
number of crystallites (small single crystals) is in reflection position . This is the prerequisite
for an even intensity distribution on the Debye-Scheuer cones of a powder measurement (see
Fig . 18 .1a) . Non-statistical distributions of crystallites, e .g. in case of plate- or rod-like cystal
grains or for non-powderized bulk sample material, result in prefeued orientations of special
scattering planes hkl and cause uneven (orientation dependent) intensity distributions on the
Debye-Scherrer cones (sec Fig . 18 .lb and 18 .1c) appraoching the appearance of single crystal
spots (Fig . 18 .1d) . The evolution of experimental intensities in crystal structure analysis is
generally hampered by the presence of preferred orientation . For instance, special correction
terms have to be applied during structure refmement calculations .
(a) (b) (c) (d)
Fig. 18.1 : hkl diffraction maxima (here X-ray scattering) shown as sectionsfrom Debye-
Scherrer cones obtainedfrom polycrystalline material ofrandom crystallite orientations (a),
weak (b) and strong (c) prefeued orientations. (d) shows single crystal diffraction spots.
18-1