The word "void" refers to gaps between constituent particles. In a densely packed structure, voids refer to the empty space between constituent particles (voids in chemistry). Solids can be packaged in one of three ways: one-dimensional (1D), two-dimensional (2D), or three-dimensional (3D).
When atoms are arranged in square close packing or hexagonal close packing, we see empty spaces between them in 2-dimensional structures.
These empty spaces are known as voids, and in hexagonal packing, these voids have triangular shapes and are referred to as triangular voids.
Tetrahedral and Octahedral Voids
In hexagonal packing, these triangular voids are seen in two different orientations. The apex of the triangle in one row points upward, while the apex of the triangle in the other row points downward.
In the three-dimensional structure, about 26% of total space is empty and not occupied by spheres in both CCP and HCP near packing in solids. Interstitial voids, interstices, or gaps are the names given to these empty spaces. The above voids in solids are proportional to the number of spheres present.
In a three-dimensional structure, there are two types of interstitial voids:
Tetrahedral Voids: In a cubic close-packed structure, the second layer's spheres are above the first layer's triangular voids. Each sphere touches the first layer's three spheres. It forms a tetrahedron by joining the centers of these four spheres, and the empty space created by joining the centers of these spheres forms a tetrahedral void.
Octahedral Voids: Octahedral voids are located next to tetrahedral voids. We get a void created by enclosing six spheres when the triangular voids of the first layer correlate with the triangular voids of the layer above or below it. Octahedral Voids refer to the empty space created by combining the triangular voids of the first and second layers.
Number of Voids
The number of these two types of voids depends on the number of closed packed spheres.
If the number of closed packed spheres is N, then
Difference Between Tetrahedral and Octahedral Voids
Did You Know?
The unit cell, or building block of a crystal, is the smallest repeating unit of the crystal lattice.
The identical unit cells are described in such a way that they fill the available space without overlapping. A crystal lattice is a three-dimensional arrangement of atoms, molecules, or ions within a crystal. It comprises a large number of unit cells. Per lattice point is occupied by one of the three constituent particles.
Numerous unit cells together make a crystal lattice. Constituent particles like atoms, molecules are also present. Each lattice point is occupied by one of these particles.
Primitive Cubic Unit Cell
Body-Centered Cubic Unit Cell
Face Centered Cubic Unit Cell