The ZnS zinc blende structure is cubic. The unit cell may be described as a face-centered sulfide ion sublattice with zinc ions in the centers of alternating minicubes made by partitioning the main cube into 8 equal parts (as shown in fig) (a) How many nearest neighbors does each Zn^(2+) have ? (b) How many nearest neighbors does each S^(2-) have? (c) what angle is made by the line connecting any Zn^(2+) to any two of its nearest neighbors ? (d) What minimum r_(+)//r_(-) ratio is needed to avoid anion -anion contact, if closest cation-anion pairs are assumed to touch ?

The ZnS zinc blende structure is cubic. The unit cell may be described

1.	The ZnS zinc blende structure is cubic. The unit cell may be described as a face-centered sulfide ion sublattice with zinc ions in the centers of alternating minicubes made by partitioning the main cube into 8 equal parts (as shown in fig) (a) How many nearest neighbors does each Zn^(2+) have ? (b) How many nearest neighbors does each S^(2-) have? (c) what angle is made by the line connecting any Zn^(2+) to any two of its nearest neighbors ? (d) What minimum r_(+)//r_(-) ratio is needed to avoid anion -anion contact, if closest cation-anion pairs are assumed to touch ?
Answer» C.N. of `Zn^(2+) " & " S^(2-) = 4 " & " 4` C.N. of `Zn^(2+) " & " S^(2-)` = 6 & 6 `109^(@)28` `(r_(Zn^(2+)))/(r_(S^(2-))) = 0.225` Solution :(a) As each `Zn^(2+)` ion is PRESENT in tetrahedral void, So it is coordination number is = 4 (b) Similarly `S^(2-)` ion have coordination number = 4 (c) As `Zn^(2+)` ion is present in tetrahedral void that's why line's connecting any two NEAREST NEIGHBOUR and `Zn^(2+)` have angle `= 109^(@)28` (d) For tetrahedral VOIDS radius ratio is `(r_(Zn^(2+)))/(r_(S^(2-))) = 0.225`