CoachA crystal is a solid whose particles (atoms, ions or molecules) are arranged in a pattern that repeats periodically in three dimensions. A solid without such long-range order is an amorphous solid (glass, most plastics). The perfect crystal model describes a crystal as infinite and without defects: no missing or extra atoms, no impurities, no boundaries.
Examples
Example 5.21 (Steel)
Carbon, of covalent radius (half the distance in diamond), is too large for the sites of iron without distortion, but much less so in -iron, whose octahedral sites are the largest. Steel is made by dissolving carbon in hot -iron; quenched, the carbon is trapped as the iron returns to a body-centred structure, which it distorts, and the distorted crystal is hard.