Geoscience Reference
In-Depth Information
TiO
2
(anatase) at 500
C and lies at stoi-
chiometry: richer in KPO
3
than A-H
2
O. It moves to the left at lower temperatures.
Assuming the validity of the boundaries defined by the arrows 1, 2, and 3, the
appropriate phase boundaries have been drawn in
Figure 5.38
so as to terminate
in the complete phase diagram on the KPO
3
between the phase fields KTP and KTP
1
TiO
2
axis at K(TiO)PO. Thus, the
lines EC(1)G, F(3)H, and D(2)A terminate at KTP. The line EF schematically
represents the solubility of KTP at 500
C. It does not intersect A-D-H
2
O, so KTP
is incongruently saturating at 500
C, i.e., the mole ratio of KPO
3
/TiO
2
in the liq-
uid, where KTP is the only stable solid phase, not equal to the ratio in KTP.
Somewhere in the TiO
2
-rich part of the diagram, anatase would probably be the
sole stable phase and, in the KPO
3
-rich region, E would probably be the sole
stable phase. The authors did not try to find these boundaries because they are not
directly relevant to KTP growth.
Typical conditions used in growth runs are as follows:
Autoclave
Pt-lined, 1
v
ID
3
6
v
IL (2.5 cm
3
15 cm)
Mineralizer
2MK
2
HPO
4
1
0.5 M KPO
3
% Fill
75%
375
C
Crystallization temperature
425
C
Nutrient (dissolving) temperature
50
C
Temperature differential (
Δ
T)
Seed orientation (201), (011)
rates from 2.6 to 5.7 mil/day (
B
0.07
2
0.14 mm/day), (010) rate generally higher,
quality good
(Seed orientation based on a
5
12.80
˚
, b
5
6,400
˚
, c
5
10.580
˚
)
[148]
Spontaneous wall nucleation
moderate; crystals clear but not too well
formed
The growth rates are for the total increase in crystal thickness or time of the run.
Increasing
T to 75
C and increasing KPO
3
decreased the growth rate, but grow-
ing without KPO
3
, i.e., with the mineralizer (2 M K
2
HPO
4
) alone, did not markedly
affect the growth rate or quality. Growth in KH
2
PO
4
or KPO
3
alone was very slow.
In the growth of KTP, like quartz, the seed orientation is very important. The
growth rates are different in different seed orientations and the highest rate for
KTP has been obtained on the (011) seed crystal
[151]
.
The crystals grown at lower growth rates are superior in quality. Therefore,
proper care has to be taken to achieve the optimum growth rate under hydrother-
mal conditions by selecting appropriate growth parameters, because a combina-
tion of several growth parameters act upon the growth rate and crystal quality
of KTP.
5.5.2 Solubility of KTP
The solubility of KTP is an important aspect. The higher experimental
temperature
Δ
pressure adopted in the earlier works was due to the lack of accurate
data on the solubility of KTP and added to that the solubility of KTP is rather low
in most of the conventional solvents.
