Face-centered cubic

Definition

Face-centered cubic (FCC) is a type of crystal structure where atoms are located at each corner of a cube and at the center of each face of the cube. This arrangement allows for efficient packing of atoms, leading to a high atomic coordination number, which is significant for understanding the physical properties of materials such as metals and ionic compounds.

5 Must Know Facts For Your Next Test

1. In an FCC structure, each unit cell contains four atoms, with contributions from both corner and face-centered positions.
2. The packing efficiency of the face-centered cubic structure is approximately 74%, which is among the highest for any crystal structure.
3. Common metals like copper, aluminum, and gold adopt the face-centered cubic structure due to its favorable properties for ductility and conductivity.
4. The atomic radius can be calculated in an FCC lattice using the relationship $$a = 2\sqrt{2}r$$, where 'a' is the lattice parameter and 'r' is the atomic radius.
5. FCC structures exhibit slip systems that allow for easy dislocation movement, contributing to their malleability and workability.

Review Questions

• How does the arrangement of atoms in a face-centered cubic structure contribute to its properties?
  • The arrangement of atoms in a face-centered cubic structure, with atoms at each corner and on each face, leads to a high coordination number of 12. This means that each atom is closely surrounded by others, promoting strong metallic bonding and high packing efficiency. As a result, materials with FCC structures often exhibit desirable properties such as high ductility and strength due to their ability to deform under stress without breaking.
• Discuss the significance of packing efficiency in relation to face-centered cubic structures compared to other crystal types.
  • Packing efficiency is crucial because it influences the material's density and stability. The face-centered cubic structure has a packing efficiency of about 74%, which is higher than body-centered cubic (BCC) structures but lower than hexagonal close-packed (HCP) structures. This high packing efficiency allows FCC metals to have more atoms within a given volume, resulting in better electrical conductivity and increased mechanical strength compared to less efficiently packed structures.
• Evaluate how the slip systems in face-centered cubic materials affect their mechanical behavior during deformation.
  • Face-centered cubic materials have multiple slip systems due to their atomic arrangement, allowing dislocations to move easily throughout the crystal lattice. This characteristic significantly enhances their mechanical behavior during deformation, making FCC materials more malleable compared to those with fewer slip systems, like body-centered cubic structures. As FCC metals can accommodate greater plastic deformation before failure, this property is vital in applications that require materials to withstand stress without fracturing.

Related terms

Coordination Number: The number of nearest neighbor atoms surrounding a central atom in a crystal structure.

Packing Efficiency: A measure of how closely atoms are packed together in a crystal structure, typically expressed as a percentage.

Lattice Parameter: The physical dimension of unit cells in a crystal lattice, which defines the size of the unit cell and can impact the overall properties of the material.