Substitutional impurities are usually chemically similar to the substance that constitutes the bulk of the sample, and they generally have atomic radii that are within about 15% of the radius of the host. is a different atom of about the same size that simply replaces one of the atoms that compose the host lattice ( Figure 12.15 "Common Defects in Crystals"). In contrast, a substitutional impurity A point defect that results when an impurity atom occupies a normal lattice site. *In addition to enough iron to bring the total percentage up to 100%, most steels contain small amounts of carbon (0.5%–1.5%) and manganese (<2%). Magnets in electric motors and transformers Knives, cutting tools, drill bits, and springsġ5%–20% Cr, 1%–5% Mn, 5%–10% Ni, 1%–3% Si, 1% C, 0.05% PĬutlery, instruments, and marine fittings Table 12.3 Compositions, Properties, and Uses of Some Types of Steel Name of Steel We begin with solids that consist of neutral atoms, specifically metals, and then turn to ionic compounds. In this section, we discuss how defects determine some of the properties of solids. Applying an external stress to a crystal, such as a hammer blow, can cause microscopic regions of the lattice to move with respect to the rest, thus resulting in imperfect alignment.Cooling at more realistic rates usually results in one or more components being trapped in the “wrong” place in a lattice or in areas where two lattices that grew separately intersect. Even if a substance were 100% pure, forming a perfect crystal would require cooling the liquid phase infinitely slowly to allow all atoms, ions, or molecules to find their proper positions.It is impossible to obtain any substance in 100% pure form.These defects occur for three main reasons:
(typically more than 10 4 per milligram), ranging from variable amounts of impurities to missing or misplaced atoms or ions. In contrast, real crystals contain large numbers of defects Errors in an idealized crystal lattice. The crystal lattices we have described represent an idealized, simplified system that can be used to understand many of the important principles governing the behavior of solids. To understand the origin and nature of defects in crystals.