Question

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 interstital void without distortion of the lattice.

Answer 1

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 greastest sphere will fit into octahedral void.
Radius of octahedral void ( R) = 0.414 R = ` 0.414 xx 141.4 " pm" = 58.54 "pm" `
Diameter of the greatest sphere fitting into the void = ` 2xx 58.54` pm = 117. 08 pm.