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in order to attain the desired local charge balance. However, under surplus concen-
tration of Ti
4
1
in the starting composition, the function of other cations is usually
met by Ti
4
1
itself. In the natural systems, titanates usually have Na
1
,K
1
,Ca
2
1
,
Sr
2
1
,Ba
2
1
, and other metals in their composition and the charge balance can be
well established in such compounds. In the earth's crust, silicon is more abundant
with a higher charge (
4) and lower coordination number (4). Hence, it forms a
more common partnership with Ti
4
1
in the earth's crust to form titanosilicates. The
other cations which play a major role in the charge compensation in titanium
minerals are: Zr
4
1
,Fe
3
1
,Fe
2
1
,Mn
2
1
,Mg
2
1
, and also the proton (H
1
).
Table 8.3
gives the common association of [TiO
6
]
8
2
in the structure of oxide compounds.
The said formula unit of column 1 of
Table 8.3
can be easily obtained directly
from the association symbol. For example, the radical formula corresponding to the
1
Table 8.3 Common Association of [TiO
6
]
8
2
in the Structure of Oxide Compounds
Symbol and Radical
Formula
Association Character
Structure Type
6(1) (TiO
6
)
8
2
Discrete octahedra
K
2
TiSi
3
O
9
, NaTi
2
(PO
4
)
3
,
K
2
TiSi
6
O
15
5(1)
1 (2)
(Ti
2
O
11
)
14
2
Octahedra sharing common
vertices
NaTi
2
Al
5
O
12
,Ba
4
Ti
2
PtO
10
,
TiTe
3
O
8
4(1)
2(2)
(TiO
5
)
6
2
Para octahedra sharing common
edges, infinite chain of
octahedra sharing transvertices
Leucosphenite, neptunite
tinakite
a. Linear
b. Zigzag
Pseudobrookite sphene
3(1)-3(2) (Ti
2
O
9
)
10
2
Para octahedra sharing common
faces
Hexagonal modification of
BaTiO
3
2(1)-4(2) (TiO
4
)
4
2
Infinite pillars of edge-shared
octahedral
Rutile
a. Linear
b. Zigzag layered network of
vertices shared octahedral
Brookite
1(1)-5 (2) (Ti
2
O
7
)
6
2
Double layered vertices shared
shared octahedra
Bi
2
(NbTi)O
9
,Bi
3
(TaTi)O
9
Sr
3
Ti
2
O
7
6(2) (TiO
4
)
4
2
Framework vertices shared
octahedra edge-shared
octahedra, vertices and faces
linked octahedra
Ilmenite, perovskite, pyrochlore
Ca
3
Ti
2
O
6
a
ThTi
2
O
6
CaTi
2
O
4
BaTiO
3
hexagonal
modification
3(2)-3(3) (Ti
2
O
5
)
2
2
6(3) (TiO
2
)
0
Ba
(Ti
7
Mg)O
16
Close packed layered octahedra
framework with vertices edges
shared octahedra
TiCl
2
, Til
2
, TiS
2
Rutile,
Brookite, anatase
6(4) (Ti
2
O
3
)
0
Framework with vertices, edges
and faces shared octahedra
Ti
2
O
3
corundum
