How high polarity prefers wurtzite than zinc blende?
Answers
Answer:
The tetrahedrally oordinated bonding geometry plus the bond polarity determines the ZnO crystal structure which is hexagonal wurtzite type. Each Zn ion has four O neighbor ions and vice versa. This type of bonding is known in diamond type structure and is covalent. However if the partners (Zn and O here) have very different electronegativity then there can be a considerable amount of polarity. O is higly electronegative as high as 3.5 on the Pauling scale whereas Zn has quite a low value of electronegativity 0.91. So Zn and O can be considered as Zn^2+ and O^-2 ions and therefore the bonding is not covalent but somewhat ionic. The bond polarity menifests itself by the effective charg Z* which is about Z* = 1.15. This high bond polarity favors the wurtzite structure instead of zinc-blende structure for ZnO. The zinc-blende structure on the other hand is favored for tetrahedrally oriented bonds with lower polarity.