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Saturday, April 17, 2021
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
Related Questions:
What are the normal spinel structures?
Rutile (TiO2) type Structure:
This type of structure is represented by TiO2 and other example are includes MnO2 , SnO2 , MgF2, NiF2 etc
In Rutile structure:
O-2 = ions forms hexagonal cubic
packing (HCP).
M+4 =Tetravalent cations are occupied 50 % (1/2) of octahedral voids (OV) while all the tetrahedral voids (TO) are empty.
HCP= Lattice points (LP) = O-2=
6
M+4 ions
= OV (50%) =6 x 1/2 = 3
M3O6
= MO2
It means
each HCP unit cell certain three (M+4 ) and six (O-2 )ions
Related Questions:
What are the normal spinel structures?
Pervoskite (ABO3) type structure:
ABQ3 is a proto type solid where A is
a divalent
cation and B is a tetravalent cation.
A+2 = Divalent cations
B+4 =Tetravalent cations
In Pervoskite structure:
A+2 = placed at corner of cubic unit cell
O-2 = placed at all the face centre
That
means A+2 and O-2 ions combinelly form CCP/FCC
like structure and
B+4 = Tetravalent cations occupy the central octahedral voids (25% of
total OV) i.e centre of the centre of the unit cell so general formula is ABO3
Other
examples are BaTiO3, SrTiO3
Related Questions:
What are the normal spinel structures?
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