TYPES OF SOLIDS

Amorphous, polycrystalline, and single crystal are the three general types of solids. Each type is characterized by the size of an ordered region within the material. An ordered region is a spatial volume in which atoms or molecules have a regular geometric arrangement or periodicity. Amorphous materials have order only within a few atomic or molecular dimensions, while polycrystalline materials have a high degree

Figure 1.1 I Schematics of three general types of crystals: (a) amorphous, (b) polycrystalline, (c) single crystal.

of order over many atomic or molecular dimensions. These ordered regions. Or single crystal regions, vary in size and orientation with respect to one another. The single crystal regions are called grains and are separated from one another by grain boundaries. Single-crystal materials, ideally, have a high degree of order, or regular geometric periodicity, throughout the entire volume of the material. The advantage of a single-crystal material is that. in general, its electrical properties are superior to those of a non-single crystal material, since grain boundaries tend to degrade the electrical characteristics. Two-dimensional representations of amorphous, polycrystalline, and single-crystal materials are shown in Figure 1.1.