Neutron Scattering

In this contribution, however, we will exclusively focus on the positive aspects of prefened
orientations in polycrystalline material in view ofthe characterization and changes ofthe bulk
material properties. In material science, mechanical treatment and deformation is artificially
applied to generate prefened orientation and, thus, well defined material properties . In earth
sciences, preferred orientation exists in rocks by natural deformations over millions of years
and, thus, bears important information on longtime geological processes . The study of preferred
orientations in bulk polycrystalline material is an independent scientific discipline : the
texture analysis [1, 2] .
2 .0 Anisotropy by Structure and Texture
Texture is a property of condensed crystalline matter. In our daily life, we are offen in contact
wich solid state crystalline matter, e .g . minerals and rocks being the fundamental components
ofthe earth's crust, or metals and ceramics which are manufactured and used as technological
products . Ciystalline matter is characterized by its specific crystal structure which is defined
by a unit cell with its symmetrical atomic arangement and by its three-dimensional
periodicity . This crystal structure essentially determines the physical, chemical and technological
properties of a material, at least on a microscopic scale . The microscopic unit is
considered to bc a monocrystalline aggregate .
Generally, the properties of a single crystal are anisotropic, i.e . they are different in
different crystallographic directions . The thermal conductivity of graphite represents a typical
example of such a direction-dependent crystalline property . The sheet-like hexagonal crystal
structure built up by plane layers of carbon atoms with small interatomic distances inside the
layers and large distances between neighbouring layers (Fig . 18 .2) is responsible for a strong
anisotropy . The thermal conductivity within the layers is about four times larger compared to
the conductivity perpendicular to the layers along the hexagonal axis .
[1001
Fig. 18 .2 : Graphite structure built up
byplane sheets ofC atours (hatched)
arranged perdendicular to the hexagonal
c-axis
Fig . 18.3 : Property surface of the Young
modulus ofiron (left)for any directions [UI]
of the cubic crystal system (right)
18- 2