Question

For a given primitive cell volume V, which monoatomic crystal will have its nearest neighbours furthest away, between simple cubic, BCC, and FCC?

Answer 1

In the bcc structure each atom has 8 nearest neighbours (coordination number) at a distance of

d = 2r = sqrt(3a/2)a approximately 0.866a and 6 next-nearest neighbours at a distance of

d= a 2.3r approximately 1.15 d . It is remarkable that there is a smaller number of nearest

neighbours compared to the close-packed structures but for the bcc structure the next-nearest

neighbours are only slightly further away which makes it possible for those to participate in bonds.