In face-centred cubic (fcc) crystal lattice, edge length is 400 pm. Find the diameter of the greatest sphere which can be fitted into the interstitial void without distortion of the lattice.

In face-centred cubic (fcc) crystal lattice, edge length is 400 pm. Fi

1.	In face-centred cubic (fcc) crystal lattice, edge length is 400 pm. Find the diameter of the greatest sphere which can be fitted into the interstitial void without distortion of the lattice.
Answer» SOLUTION :For FCC, radius of atom (R)=`a/(2sqrt2)=400/(2sqrt2)` pm =141.4 pm As octahedral void is bigger in size than the tetrahedral void, the greatest sphere will fit into octahedral voids Radius of octahedral void (r)=0.414 R=0.414 X 141.4 pm = 58.54 pm `therefore` Diameter of the greatest sphere FITTING into the void =2 x 58.54 pm =117.08 pm