Question
Sun April 20, 2014 By: Pallavi Chaturvedi

what is the number of  next nearest or second nearest neighbour in NaCl and CsCl crystal

and what is the method to find it

Expert Reply
Sun April 20, 2014

In NaCl structure, each Na+ ion has 12 Na+ ions as the next neighbour.

The NaCl structure can be regarded as two interpenetrating FCC lattices. Each has 6 nearest neighbours of opposite charges, i.e, the co-ordination number is 6 (which is the number of nearest neighbours of an atom in a crystal).

Each Ca+ ion has 6 Cs+ ions as the next nearest neighbour at a distance of r = dCl-Cl-.

The CsCl is an ionic structure showing two interpenetrating simple cubic lattices, one for each kind of ion. It has a coordination number 8. 

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