Structure of Materials An Introduction to Crystallography, Diffraction and Symmetry

The previous chapters dealt with crystalline and quasicrystalline structures, in which one has both translational and rotational or just rotational symmetry, respectively. In the present chapter we describe what happens when there is no more evidence of any long-range crystallographic order. We introduce the concept of an amorphous material and discuss its implications for diffraction patterns. Since the absence of long-range order does not imply absence of local order, we describe some basic ideas about short-range ordering and apply these ideas to a number of different systems in which amorphous compounds can be formed. We conclude the chapter with a description of a few experimental techniques suitable for the study of local ordering.

Introductory comments

The word amorphous means without shape or structure. In amorphous solids, atomic positions lack crystalline (periodic) or quasicrystalline order but do have short-range order. Amorphous metals are usually structurally and chemically homogeneous, which gives them isotropic properties attractive for many applications. Chemical and structural homogeneity can lead to corrosion resistance while isotropic magnetic properties are important in materials for power transformation and inductive components. The absence of crystallinity alters the traditional micromechanisms for deformation of the solid, giving many amorphous metals attractive mechanical properties.