Question

An element crystallizes in fcc lattice having edge length `400 pm` Calculate the maximum diameter of an atom which can be place in interstitial site without distorting the structure.

Answer 1

Correct Answer - Diameter of greater void =117.16 pm
In case of fcc, lattice the largest void present in ocathedral.
In case of radius of void R and the radius of lattice spehre is r, then
`r=(sqrt(2)xxa)/(4)=(sqrt(2)xx400)/(4)=141.42pm`
[`because`a=400pm]
for an octahedral void, we have 2(r+R)=a
`therefore 2R=a-2rrArrrR=400-2xx141.42=117.16`
`therefore` Diameter of gretest void =117.16pm