Question

A tetrahedral void in fcc is formed by atoms at:
A. 3 corners + 1 face-center
B. 3 face center + 1 corner
C. 2 face centres + 2 corners
D. 2 face centres + 1 corner +1 body center

Answer 1

The voids are defined as the gap present in the solid crystal between the constituent particles in the closed packed structure The effective number of tetrahedral holes is 8.

Complete step by step answer:
Face centered cubic cell is a type of unit cell where the atoms are present at the corners of the crystal lattice and at the centre of all the faces of the cube. The atoms present at the face centered are shared by two unit cells present adjacent to each other and half of each atom belongs to each cell. Only 12 atoms belong to a unit cell.
The voids are the gap present in the solid crystal between the constituent particles in the closed packed structure. The close packing is done in 1D close packing, 2D close packing and 3D close packing.
In the 2D close packing, the atoms are arranged in square close packing and hexagonal close packing where we can see empty gaps between the atom. These gaps are known as voids which are present in triangular shapes which are known as triangular voids.
Tetrahedral void is seen in a cubic close packed structure where the sphere of the second layer is present above the triangular void of the first layer. By joining the centre of four spheres it forms a tetrahedron and the empty space which is left out is known as tetrahedral void.
In a face-centered cubic cell, the tetrahedral void is formed from 1 corner and3 adjacent face centers.

Therefore, the correct option is B.

Note: The number of tetrahedral void in a cubic cell is double of the number of octahedral void. Apart from FCC the voids are only obtained in hexagonal primitive unit cells.