Crystals are solids in which atoms, ions, or molecules are arranged in a regular and repetitive pattern. In crystallography, these arrangements are divided into seven major systems: Cubic, Tetragonal, Orthorhombic, Hexagonal, Rhombohedral, Monoclinic, and Triclinic.
Of these, the cubic crystal system is the simplest, most symmetrical, and most common. The hallmark of this system is that all three axes are of equal length and all angles are 90°. This means that the unit cell is shaped like a perfect cube.
What is Cubic Crystal Structure?
Cubic Crystal Structure is a crystal system in which all three axes have the same length and all angles are perpendicular to each other (right angle).
Lattice Parameters:
- a = b = c
- α = β = γ = 90°
This structure is the system with the most symmetry, so it is also called an isometric system.
Bravais Lattices (Cubic System):
There are three types of Bravais lattices in the cubic system:
- Simple Cubic (SC) – Atoms only at the corners.
- Body-Centered Cubic (BCC) – An atom at the corners as well as the center.
- Face-Centered Cubic (FCC) – Atoms at the corners as well as the center of each face.
Properties
- Symmetry: Highest degree of symmetry (three equal axes, all perpendicular).
- Angles: All angles 90°.
- Lattice: Three types – SC, BCC, FCC.
- Packing Efficiency: Simple Cubic → 52%, Body-Centered Cubic → 68%, Face-Centered Cubic → 74%
- Coordination Number: SC = 6, BCC = 8, FCC = 12
- Mechanical Properties: The FCC structure is more ductile, while the BCC is stronger but brittle.
- Optical Property: Isotropic—that is, having the same properties in all directions.
Examples of Cubic Crystals
- Simple Cubic (SC): Polonium (Po)
- Body-Centered Cubic (BCC): Iron (Fe), Chromium (Cr), Tungsten (W), Sodium (Na), Potassium (K)
- Face-Centered Cubic (FCC): Copper (Cu), Aluminum (Al), Silver (Ag), Gold (Au), Nickel (Ni)
Uses of Cubic Crystal Structure
- Metallurgy
- Electronics and Electrical Equipment
- Jewelry
- Aviation and Engineering
- Scientific research
Visualizing the Cubic unit cell
A cubic unit cell is shaped like a cube with all edges of equal length and all angles at 90°.
- Simple Cubic: Atoms are only at the corners.
- Body-Centered Cubic: Atoms are at the corners and in the middle.
- Face-Centered Cubic: Atoms are at the corners and in the center of each face.
Looking at it, it appears as if the atoms in a dice are arranged at equal distances.
Conclusion
The cubic crystal structure is the most basic and most balanced system in crystallography. In crystallography, all three axes are of equal length and all angles are 90°. This system is most commonly found in metals, minerals, and industrial materials.
Elements such as copper, iron, gold, silver, and aluminum are classic examples of the cubic structure. Its high symmetry, stability, and simplicity make it of paramount importance in materials science, engineering, and metallurgy.