Solids

Q. 1.  (a)       If the radius of the Br ion is 0.182 nm, how large a cation can fit in each of the tetrahedral hole.

            (b)       AgI crystallizes in a cubic closed packed ZnS structure. What fraction of tetrahedral site is occupied by Ag ion ?

            (c)       At what temp. range, most of the metals becomes super conductors ?

Ans.    (a)       For a tetrahedron the limiting ratio is 0.225 – 0.414

                        For largest cation highest value 0.414 would be considered.

                        r+ / r– = 0.414

                        r+ = 0.414 × 0.182 = 0.075 nm.

            (b)       In FCC there are 8 tetrahedral voids. Out of this ½ is occupied by Ag cation.

            (c)        2 k – 5 k.