Question

In which structure the Copper and Aluminum crystallize?

• A. BCC
• B. FCC
• C. HCP
• D. Simple Cubic

Hint:

Face-Centered Cubic (FCC) metals are characteristically highly ductile and formable, even at low temperatures, because they possess 12 highly symmetric, close-packed slip systems. Common examples include \(\text{Cu}\), \(\text{Al}\), \(\text{Ni}\), \(\text{Ag}\), and \(\text{Au}\).

Answer 1

The Correct Option is B

Concept: Copper (\(\text{Cu}\)) and Aluminum (\(\text{Al}\)) are highly ductile, highly conductive metals. Under standard ambient temperature and pressure conditions, both metals minimize their total electronic free energy by organizing their atoms into a close-packed Face-Centered Cubic (FCC) crystal lattice.

Step 1: Crystallographic features of the FCC lattice.
In an FCC unit cell:
• Atoms are positioned at all 8 corners of the cube and at the centers of all 6 square faces.
• This arrangement forms a highly efficient, close-packed structure with an Atomic Packing Factor (APF) of \(0.74\), meaning \(74%\) of the unit cell volume is occupied by atomic spheres.
• Each individual atom has a coordination number of 12, meaning it directly touches 12 nearest-neighbor atoms.

Step 2: Connecting structure to metallic properties.
The FCC lattice contains 4 unique families of close-packed \(\{111\}\) planes, with 3 distinct close-packed \(\langle 110 \rangle\) slip directions running through each plane. This combination provides a total of 12 independent slip systems. Because these slip systems intersect symmetrically in space, dislocations can glide smoothly under stress along multiple directions without encountering structural locks that cause cleavage. This highly active slip network gives copper and aluminum their excellent ductility, exceptional formability, and high toughness.

Step 3: Verification.
Since both Copper and Aluminum share the FCC lattice configuration, option (B) is the correct choice.