Corundum (Al2O3) type Structure:

This type structure is exhibited by oxides of trivalent metals for examples Fe₂O₃, Al₂O₃, Cr₂O₃, Mn₂O₃ etc.

General formula is M₂O₃:

In Corundum  Structure:

O^-2 = ions forms HCP unit cell:

M⁺³ = Occupied  2/3 (66.66%) of octahedral voids (OV): and 33.33% OV are empty and TVs are 100% empty.

In Hexagonal close packing (HCP): Formula determination:

O^-2 = HCP = O₆

M⁺³=2/3 x 6 = M₄

=M₄O₆  or  M₂O₃

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