Question

How many nearest and next nearest neighbour respectively eaxh potassium has in bcc lattice?

Answer 1

In a bcc lattice the 1st nearest neighbour is at the distance of
$\frac{ \sqrt{3}a }{2}$
Here 'a' is the lattice parameter or the edge length.

The 2nd nearest neighbour is at the distance of
$a$

Therefore for the center atom( It will apply for all the other's as well),

1st nearest neighbour = 8 (atoms at corner) ,

2nd nearest neighbour = 6 (atoms at the center of other 6 cubes).

Please refer to the pic once.