Allotropes of metals, Polymorphism of metals

Some elements can change their crystalline structure, i. e. type of crystal lattice, depending on external conditions temperature and pressure. The ability of one element to exist in several crystalline modifications is called polymorphism or allotropy. About 30 metals exhibit temperature polymorphism, including iron, tin, cobalt, manganese, and titanium. Iron, for example, has a bodycentered cubic crystal structure at low temperatures. This structure is called αiron. However, at temperatures above 911 C, the atoms rearrange to form a facecentered cubic crystal structure. This modification is called γiron.