What is the Difference Between Face-Centered Cubic and Body-Centered Cubic

The main difference between face-centered cubic and body-centered cubic is their structure. In a face-centered cubic crystal structure, atoms are arranged in a cube, and there is an atom at each of the cube’s eight corners (vertices) and an additional atom at the center of each of the six faces, whereas in body-centered cubic crystal structure, there is an atom at each of the cube’s eight corners, similar to face-centered cubic structure, but there is also one atom located at the center of the cube.

Crystal structures are ordered arrangements of atoms or molecules within a crystalline material. These structures are fundamental to understanding the properties and behavior of various materials, from metals and minerals to polymers and biological molecules. Body-Centered Cubic (BCC) and Face-Centered Cubic (FCC) are two common crystal structures.

Key Areas Covered

1. What is a Face-Centered Cubic  
     – Definition, Structure, Features
2. What is a Body-Centered Cubic
     – Definition, Structure, Features
3. Similarities Between Face-Centered Cubic and Body-Centered Cubic
     – Outline of Common Features
4. Difference Between Face-Centered Cubic and Body-Centered Cubic
    – Comparison of Key Differences

Key Terms

Face-Centered Cubic, FCC, Body-Centered Cubic, BCC

What is a Face-Centered Cubic

A face-centered cubic (FCC) is a type of cubic crystal lattice, which means that the unit cell of the crystal is shaped like a cube. This cube has atoms positioned at each of its eight corners, forming the vertices. Additionally, there is an atom at the center of each of the cube’s six faces. As a result, a face-centered cubic unit cell contains a total of four atoms. This arrangement is often represented schematically as ABCABC layers in three dimensions, highlighting the layering of atoms.

One of the key features of the FCC structure is its high coordination number, which is the number of nearest neighbor atoms that each atom in the structure is in direct contact with. In the case of face-centered cubic, each atom is in contact with 12 nearest neighbor atoms. This high coordination number results from the structure’s densely packed nature.

Figure 1: Face-Centered Cubic

Face-centered cubic also has a high packing density, which measures how efficiently space is occupied by atoms in the crystal lattice. The packing density of FCC is approximately 74%. Copper, aluminum, gold, lead, and iridium are a few examples of materials with face-centered cubic structures.

The arrangement of atoms in the FCC structure directly influences the mechanical, thermal, electrical, and optical properties of materials. Many materials undergo phase transformations at different temperatures and pressures. 

Moreover, FCC materials find applications in a wide range of industries, including electronics, aerospace, construction, and automotive. For example, the electrical conductivity of FCC copper is crucial in electrical wiring, while the lightness and corrosion resistance of FCC aluminum make it suitable for aircraft construction.

What is a Body-Centered Cubic

Body-centered cubic (BCC) is a crystal structure in which atoms are arranged in a repeating cubic lattice, with atoms at the corners of the cube and one atom at the center of the cube. This cube contains atoms at each of its eight corners, forming the vertices. This arrangement is often represented as ABA layers in three dimensions, emphasizing the central atom’s position within the cube. Compared to some other crystal structures, the BCC structure has a relatively lower packing density. The packing density of BCC is approximately 68%. Materials with body-centered cubic structures include iron, chromium, and tungsten.

Figure 2: Body-Centered Cubic

There are many significances of body-centered cubic structures. They are the arrangement of atoms in the BCC structure that directly influences the mechanical properties of materials. BCC metals also tend to be strong and have good impact resistance, making them suitable for structural applications.

Understanding the BCC structure is essential for predicting and engineering phase transformations in materials. This knowledge is crucial in heat treatment processes and alloy development. Furthermore, BCC materials often serve as a base for designing alloys with specific characteristics. 

Similarities Between Face-Centered Cubic and Body-Centered Cubic

• Face-centered and body-centered cubics are based on a cubic lattice system.
• Moreover, both are closely packed structures.
• They are commonly found in metallic structures.
• In addition, both have high metallic strength.

Difference Between Face-Centered Cubic and Body-Centered Cubic

Definition

Structure

In a face-centered cubic crystal structure, atoms arrange themselves in a cube with an atom at each of the cube’s eight corners (vertices) and an additional atom at the center of each of the six faces. On the other hand, in a body-centered cubic crystal structure, atoms occupy each of the cube’s eight corners, much like in the face-centered cubic structure, but with an additional atom at the center of the cube.

Packing Density

Face-centered cubic has a higher packing density compared to the body-centered cubic.

Position of Atoms

Each atom in a face-centered cubic structure is in contact with 12 neighboring atoms, whereas each atom in a body-centered cubic structure is in contact with 8 neighboring atoms.

Space Efficiency

Face-centered cubic is higher in space efficiency than body-centered cubic.

Examples

Copper, aluminum, gold, lead, and iridium are materials with face-centered cubic structures, while iron, chromium, and tungsten are some materials with body-centered cubic structures.

Conclusion

In general, the main difference between face-centered cubic and body-centered cubic is their structure. In a face-centered cubic crystal structure, atoms arrange themselves in a cube with an atom at each of the cube’s eight corners (vertices) and an additional atom at the center of each of the six faces. On the other hand, in a body-centered cubic crystal structure, atoms occupy each of the cube’s eight corners, much like in the face-centered cubic structure, but with an additional atom at the center of the cube.

Reference:

1. “Face-centred cubic structure.” Encyclopedia Britannica
2. “Body-centred cubic structure.” Encyclopedia Britannica.

Image Courtesy:

1. “FCC primative-cubic cells” By Owen Graham – Own work (Public Domain) via Commons Wikimedia
2. “Cubic-body-centered” By Original: Daniel Mayer, DrBob Vector: Stannered – Crystal structure (CC BY-SA 3.0) via Commons Wikimedia