GENERAL PHYSICS 2 REFRACTION OF LIGHT SENIOR HIGH SCHOOL GENPHYS2.pptx
Spinels
1. - Mixed metal oxides.
- Cubic close packed system, cubic sites occupied by oxide
ligand, which are weak field ligands.
- Contain tetrahedral and octahedral holes Based on type of
metal atom occupying them, they are classified into two
types
- i. Normal Spinels
- Ii. Inverse Spinels or antispinels
2. » A+n represents a metal atom of charge +n
occupying a tetrahedral site.
» B+m represents a metal atom of charge +m
occupying an octahedral site.
3. » Bivalent ions occupy tetrahedral sites, trivalent
ions occupy octahedral sites.
» General Formula :
» A+2B2
+3 O4 OR (AII)tet(BIII)2
octO4
» E.g Mn3O4 (i.e Mn+2Mn2
+3O4 )
» MgAl2O4 (known as spinel), ZnFe2O4,
FeCr2O4 (chromite) etc.
4. » All bivalent cations and half the trivalent cations
in octahedral holes. The other half of trivalent
cations are in tetrahedral holes.
» General Formula B+2B+3A+3O4 or
(BII)oct(BIII )oct(AIII)tetO4
5. » Since Oxide ions are weak field ligands, the
cations are found in high spin configurations.
» Finding out whether a given spinel is normal or
inverse, can be done by calculating CFSE for
both cases.
» Greater the CFSE, more stable the structure and
hence the spinel takes that structure.
6. » Value of 10Dq for a trivalent cation is 1.5 times
more than that of a bivalent ion of the same
element.
» Value of 10Dq is reduced by a factor of 4/9 on
going from an octahedral (B) site to a
tetrahedral site.