Classification of Solids and Crystal Structure

Abstract

Classification of solids can be based upon atomic arrangement, binding energy, physical and chemical properties or the geometrical aspects of the crystalline structure. In one class, the atoms in a crystalline solid are set in an irregular manner, without any short- or long-range order in their atomic arrangement. This class of solids is commonly known as noncrystalline or amorphous materials. In another class, the atoms or group of atoms of the solid are arranged in a regular order. These solids are usually referred to as crystalline solids. The crystalline solids can be further divided into two categories: the single crystalline and the polycrystalline solids. In a single crystalline solid, the regular order extends over the entire crystal. In a polycrystalline solid, however, the regular order only exists over a small region of the crystal, ranging from a few hundred angstroms to a few centimeters. A polycrystalline solid contains many of these small single crystalline regions surrounded by the grain boundaries. Distinction between these two classes of solids—amorphous and crystalline—can be made through the use of X-ray or electron diffraction techniques.