Question

Distinguish tetrahedral and octahedral voids.

Answer 1

Sr. No.	Tetrahedral voids	Octahedral voids
1.	A single triangular void in a crystal is surrounded by four (4) spheres and is called a tetrahedral void.	A double triangular void like c is surrounded by six (6) spheres and is called an octahedral void.
2.	A sphere of second layer is above the void of the first layer, a tetrahedral void is formed.	The voids in the first layer are partially covered by the spheres of the layer.
3.	This constitutes four spheres, three in the lower and one in the upper layer. When the centres of these four spheres are joined a tetrahedron is formed.	This constitutes six spheres, three in the lower layer and three in the upper layer. When the centers of these six spheres are joined an octahedron is formed.
4.	The radius of the sphere which can be accommodated in an octahedral hole without disturbing the structure should not exceed 0.414 times that of the structure forming a sphere.	The sphere which can be placed in a tetrahedral hole without disturbing the close-packed structure should not have a radius larger than 0.225 times the radius of the sphere-forming the structure.
5.	Radius of a tetrahedral void `"r"/"R"` = 0.225	Radius of an octahedral void `"r"/"R"` = 0.414