GTBL042-03 GTBL042-Callister-v2 September 6, 2007 15:33
3.6 Ceramic Crystal Structures • 47
Table 3.3 Coordination Numbers and Geometries for Various Cation–Anion
Radius Ratios (rC/rA)
Coordination Cation–Anion Coordination
Number Radius Ratio Geometry
2 <0.155
3 0.155–0.225
4 0.225–0.414
6 0.414–0.732
8 0.732–1.0
Source:W. D. Kingery, H. K. Bowen, and D. R. Uhlmann,Introduction to Ceramics,2nd
edition. Copyright©c1976 by John Wiley & Sons, New York. Reprinted by permission of
John Wiley & Sons, Inc.
bound to the nucleus, which results in a decrease in ionic radius. Conversely, ionic
size increases when electrons are added to an atom or ion.
EXAMPLE PROBLEM 3.4
Computation of Minimum Cation-to-Anion Radius Ratio
for a Coordination Number of 3
Show that the minimum cation-to-anion radius ratio for the coordination num-
ber 3 is 0.155.