Geoscience Reference
In-Depth Information
antimony antimonates at (a) lower and (b) higher oxygen potential
[116]
. Synthesis is
carried out in aqueous solutions in 70% NaOH, 60% KF, and 13% KHF
2
,at
temperature 550
C, with % fill 60
35
C.
70%, and at a temperature gradient of 20
In order to stabilize the pentavalent antimony, 10
15% H
2
O
2
is added. In Sb
2
O
5
,the
rich region (2.5:1) forms NaSbO
3
; with the change in the oxygen potential in the sys-
tem, other phases crystallizing in the system are Sb
3
1
Sb
5
1
O
4
and Na
3
Sb
3
3
1
Sb
2
5
1
O
11
.
In a highly concentrated aqueous solution of NaOH (
42%), Na
3
Sb
3
3
1
Sb
2
5
1
O
11
crystals are formed into prisms up to 5 mm size. In this system, the field of crystalliza-
tion of Sb
3
1
Sb
5
1
O
4
with 100% output does not exist. Antimonates can be crystallized
in the aqueous KF solutions with concentration 60% and 98% KHF
2
at temperatures
450
.
550
Cand60
70% fill
[116]
. In aqueous KHF
2
solutions, only two phases are
formed: Sb
2
O
3
and Sb
3
1
Sb
5
1
O
4
. The antimony antimonates exhibit antiferroelectric
properties. The solvothermal synthesis of complex antimonites is very popular in the
nanosize range owing to their unique physical properties.
9.5.3 Hydrothermal Synthesis of Garnets
Garnet, Y
3
Al
5
O
12
, has extensively been used as a host lattice for luminescent ions
and as substrates for the epitaxial deposition of magnetic garnets for magnetic bub-
bles. For these applications, large defect-free crystals are requested. Though garnets
are ordinarily grown from the flux, the hydrothermal technique is particularly
suitable for the preparation of these mixed oxide crystals of high quality and large
size. Such growth is easier to control on a seed and it takes place at a lower tem-
perature than the flux growth
[68,118,119]
.
Yttrium aluminum garnet, Y
3
Al
5
O
12
, crystallization has been studied in a variety
including (CO
3
)
,(OH)
, and halides. Among these, higher
of
solvents
H
2
O (6
M K
2
CO
3
)
(j)
(i)
(l)
(k)
YOOH
(a)
(b)
0.93
(d) (e)
(f)
YOOH
0.5
Al
2
O
3
(g)
(c)
Y
3
Al
5
O
12
YAlO
3
+ YOOH
Y
3
Al
5
O
12
+
Al
2
O
3
YAlO
3
+
Y
3
Al
5
O
12
YAlO
3
Y
3
Al
5
O
12
Y
2
O
3
Al
2
O
3
0.5
0.625
Figure 9.29 Phase diagram of Al
2
O
3
a
Y
2
O
3
a
H
2
O between 350
C and 450
C
[121]
.
