Question

Which of the following statements is/are true for a FCC lattice?

• A. Tetrahedral void lies on edge centre
• B. Total of 8 tetrahedral voids lie along body diagonals
• C. It has about 32% vacant space
• D. If an interstitial species is placed in octahedral void its coordination number will be 6

Answer 1

Answer: (B), (D)

If an interstitial species is placed in octahedral void its coordination number will be 6

In an Fcc unit cell tetrahedral voids exist on body diagonal and octahedral voids exist on the edge centers and the body center.
The packing fraction of the fcc unit cell is 0.74 hence the vacant space is 26 %
When an interstitial species is placed in octahedral voids its immediate neighbours are at a distace of a/2 and total number of such species are six.