Radius Ratio Rules
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Summary of Radius Ratios

One of the features that determines the type of hole a cation will occupy is the radius ratio, which is determined from the ionic radii of the cation and anion. The radius ratio is equal to the ratio of the radius of the cation, r+ , to the radius of the anion, r- .

Radius ratio = r+ / r-

 
Cation
Anion
Cation Radius
Anion Radius

Ranges of Radius Ratios

For tetrahedral geometry
0.225 < r+ / r-< 0.414

For octahedral geometry
0.414 < r+ / r-< 0.732

For cubic geometry
0.732 < r+ / r-< ~1

 

 
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