In metals, what is the term for the crystalline structure formed at high temperatures?

The correct answer, face-centered cubic (FCC), describes a crystalline structure that is commonly associated with metals, particularly at elevated temperatures. The FCC structure has atoms located at each corner and in the center of each face of the cubic cell. This arrangement allows for a higher packing density, which enhances the material's ability to absorb thermal energy and contributes to its ductility and strength.

At high temperatures, many metals tend to adopt the FCC structure due to its high symmetry and efficiency in packing, which minimizes the energy state of the system. This characteristic is particularly prevalent in metals like aluminum, copper, and gold, which exhibit excellent mechanical properties because of their FCC structure.

The other structures mentioned, such as hexagonal close-packed (HCP) and body-centered cubic (BCC), also occur in metals but typically under different conditions or in specific metals. The simple cubic structure generally does not occur in pure metals due to its lower packing efficiency. Thus, FCC is the most relevant and applicable term when discussing high-temperature crystalline structures in metals.