[disillusioned19]

Hi there,

First of all, I've been trying to work out the radius ratio for various structures however I'm not quite sure about what the unit cells actually look like! Does anyone out there know of a link which shows you the various ones?

My course focuses on cubic close packed structures (NaCl - rock salt) and the hexagonal close packed structure (ZnS - zinc blende) however I get really confused with coordination numbers! I would assume that a cubic close packed structure would have a cube as a unit cell, however it's also called 'octahedral' and likewise for the hexagonal close packed structure being called 'tetrahedral'. Is it that in cubic close packed arrangement, the cation is touching 8 other ions?

Could anyone clarify this, or suggest a way that they figure this out. I guess a large part of the problem is that I lack diagrams. The geometries confuse me such that I can't work them out!

[AWK]

http://cst-www.nrl.navy.mil/lattice/