When we think of the internal structure of a solid, the first thing that comes to mind is crystals. Crystals are solids in which atoms or ions are arranged in a regular, repeating pattern. Crystal structures are as beautiful as they are important in science. According to crystallography, the crystals found in the world are divided into seven main systems: Cubic, Tetragonal, Orthorhombic, Hexagonal, Rhombohedral, Monoclinic, and Triclinic.
Of these, the Tetragonal Crystal System is a form that resembles a cubic, but its length is different in one direction. This system is considered unique and is found in many metals, gemstones, and compounds.
What is Tetragonal Crystal Structure?
A tetragonal crystal structure is a system in which two sides of the unit cell are equal, while the third side is of a different length. All angles are 90°, so it resembles a compressed cube.
Lattice Parameters:
- a = b ≠ c
- α = β = γ = 90°
There are two main types of lattices in the tetragonal system:
- Simple (Primitive) Tetragonal: Where atoms are located only at the corners.
- Body-Centered Tetragonal: Where an atom is present at the corners as well as in the center.
Properties
- It has fourfold rotational symmetry.
- Two axes (a and b) are of equal length, while the third (c) is different.
- All angles are at 90°.
- It resembles a cubic system, but appears slightly different in height or depth.
- Crystals of this system are anisotropic, meaning their physical and optical properties change with direction.
- It has two Bravais lattices: Primitive and Body-Centered.
- Many tetragonal materials exhibit phase transitions with temperature.
Examples of Tetragonal Crystals
- Zircon (ZrSiO₄): Gemstones and measuring the age of the Earth (Geochronology).
- Rutile (TiO₂): In paints, cosmetics, sunscreens and light reflective substances.
- White Tin (β-Sn): In soldering and alloy manufacturing.
- Indium (In): In electronic devices, touchscreens and solar cells.
- Apophyllite: As decoration and gemstone.
Uses of Tetragonal Crystal Structure
- Gems and Jewelry Industry
- Paint and Color Industry
- Electronics and Energy Sector
- Geology and Scientific Research
- Industrial Materials
Visualizing the Tetragonal unit cell
Imagine the tetragonal unit cell as a cube, but its height is different from the other two edges. Two of the three edges are equal (a = b), and the third (c) can be either long or short. All angles are 90°, making it look like a rectangular box.
Conclusion
The tetragonal crystal structure is a system of moderate symmetry that closely resembles the cubic structure. It is characterized by having two edges of equal length and a different third. This system is found in many metals, minerals, and gemstones.
Zircon, rutile, tin, and indium are prime examples. Their stability, luster, and direction-dependent properties make them extremely important in industry, geology, and electronic technologies.