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Sanchit Gupta Grade: 12
        

In the zinc blende structure , zinc ions occupy alternate tetrahedral voids  and S2- ions exists as ccp. The radii of Zn 2+  and S2- ions are 0.83 A°  and 1.74 A° respectively. Then the edge length of the Zn unit cell is :-


(a) 2.57 A°   (b) 5.14 A°   (c) 2,96 A°      (d) 4.86 A°

7 years ago

Answers : (1)

SAGAR SINGH - IIT DELHI
879 Points
										

Dear student


 


The ionic radius of the zinc(II) ion is 0.74 Å and that of the sulfide ion is 1.70 Å. The ratio of radii for the cation and anion is thus r+/r- = 0.74/1.70 = 0.44.


With a radius ratio of 0.44, one might expect the zinc(II) ions to occupy octahedral holes; however, the value of 0.44 is only slightly larger than rhole/r = 0.414 for an octahedral hole. There is also some covalent character in the Zn2+-S2- interaction, which tends to shorten the interatomic distance. Experimentally, one finds that the zinc(II) ions occupy tetrahedral holes.


If the sulfide ions originally adopt a hexagonal closest-packed structure, the ZnS crystal is wurtzite. If the sulfide ions originally adopt a cubic closest-packed structure, the ZnS crystal is zinc blende.


The virtual reality displays depict the structure of zinc blende. The yellow spheres represent the sulfide ions and the blue spheres represent the zinc(II) ions.

6 years ago
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