Which of the following statement is correct for fcc lattice?
Which of the following statement is correct for fcc lattice?
There are equal number of octahedral and tetrahedral voids in a unit cell.
The tetrahedral voids are present at the edge centers
Octahedral voids are present at the body center and edge centers.
Its packing efficiency (PE) is higher than hcp lattice PE.
Solution
(a) There are equal number of octahedral and tetrahedral voids in a unit cell for fcc lattice is incorrect statement. The number of octahedral and tetrahedral void in unit cell for fcc lattice is 4 and 8 respectively.
(b) The tetrahedral voids are present at the edge centers is incorrect as they are present on each body diagonal, i.e. diagonal of cubic unit cell.
(c) Octahedral voids are present at the body center and edge centers. Statement $(c)$ is correct.
(d) Its packing efficiency (PE) is higher than hcp lattice PE is incorrect.
The packing efficiency of hcp is $74 \%$ and that of fcc is also $74 \%$. It is higher in comparison to packing efficiency of simple cube and bcc which have values 52.4 and $68 \%$ respectively.