Geoscience Reference
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temperatures of synthesis are required for growth. Laudise and Kolb
[120]
and
Kolb and Laudise
[121]
have studied the phase equilibria of Y
3
Al
5
O
12
and
Y
3
Fe
5
O
12
in the systems Y
2
O
3
a
H
2
O, respec-
tively. Brochier et al.
[122]
and Toudic and Passaret
[123]
have studied the hetero-
epitaxial growth of thin Y
3
Fe
5
2
x
Ga
x
O
12
and Gd
y
Y
3
2
x
Fe
5
2
x
Ga
x
O
12
films under
hydrothermal conditions using GdGaG as seed plates. Similarly, there are several
other reports on the hydrothermal epitaxial growth of garnet films
[124
Al
2
O
3
a
H
2
O and Y
2
O
3
a
Fe
2
O
3
a
127]
.
Figure 9.29
shows the part of the phase diagram Al
2
O
3
a
H
2
O between
350
C and 450
C at a pressure of 25,000 psi, where the K
2
CO
3
concentration is
constant at 6 M. Gd
3
Ga
5
O
12
appears to be incongruently saturating in contrast to
Y
3
Al
5
O
12
. Both growth rate and quality were poorer in (CO
3
)
Y
2
O
3
a
than in (OH)
2
at
comparable concentrations. Indeed, in 6.0 M K
2
CO
3
, under conditions where
growth in (OH)
2
was appreciable, seeds grew a negligible amount or dissolved
slightly. This is in contrast to Al
2
O
3
(corundum) where
Q
CO
3
because of the
higher coefficient of solubility, gives much larger rates than (OH)
2
.Thus,
ð
ð
Þ;
CO
3
is preferable to (OH)
2
. The optimum growth conditions for GdGa are
as follows
[121]
:
Þ
Excess Ga
2
O
3
: 2
3M
Solvent
:
420
C
80
C
Growth temperature
:
% Fill
:
70
72%
Seed orientation
:
(100) (111)
Growth rate
: As high as 0.6 mm/day flawed; improved quality
at rates near 0.25 mm/day
These authors have obtained a wide range of garnets using flux-grown nutrient:
Gd
2.34
Tb
0.66
Fe
5
O
12
Eu
1.9
Ga
l.l
Al
0.5
Fe
4.5
O
12
Er
2.0
Eu
1.0
Fe
4.3
Ga
0.7
O
12
Er
1.0
Eu
2.0
Fe
4.3
Ga
0.7
O
12
Ca
1.8
Bi
1.2
V
0.9
Fe
4.1
O
12
Ca
2.0
Bi
0.95
V
0.95
Fe
4.05
O
12
In most of the experiments on the hydrothermal growth of garnets, hydrothermal
tipping is used to avoid the seed attack during the warm-up stage.
For the epitaxial film growth of Er
1.0
Eu
2.0
Fe
4.3
Ga
0.7
O
12
on (110) seeds of
Gd
3
Ga
5
O
12
, the following conditions have been employed by Laudise and Kolb
[122]
:
330
445
C
Growth temperature
:
80
Δ
T
: 0
% Fill
:
60
65%
Solvent
:
10
20 M KOH
Ga
2
O
3
:
0.75 M
