Geoscience Reference
In-Depth Information
Table 5.13 Difference Between Flux and Hydrothermally Grown KTP Crystals
Flux-Grown KTP
Hydrothermally Grown KTP
Temperature is constantly lowered and
crystals grow through continuous change
in solubility
Temperature is constant and crystal growth
occurs through continuous transport of
nutrient by convection currents
Growth temperature is high (
.
950
C)
Growth temperature is moderate (
,
500
C)
Pressure atmospheric
Pressure is
,
1.4 bar
Growth rate is
1 mm/day
Growth rate is
0.6 mm/day
$
,
Experimental duration: 7
10 days
Experimental duration: several weeks (
30
B
days)
Incorporation of (OH)
2
into the lattice, as
crystals are grown at lower temperature
Incorporation of fluxes into the lattice and
concentration of nonstoichiometric
defects occurs
Reduced stoichiometry, thermo-optic
effect, poorer quality, susceptible to
optical damage (less damage resistant)
Increased chemical stoichiometry, uniform
refractive index, high quality, higher
resistance to optical damage (most damage
resistant)
Cost of production—less expensive
Cost of production—very expensive
Limited or slow incorporation in laser
devices
More useful for laser applications
Poor in perfection, purity, and
homogeneity
Better, perfect, purity, and homogeneity
Suffers from blackening at the end part of
the negative pole when placed in DC field
Does not suffer from blackening at the end
part of the negative pole when placed in
DC field
Higher ionic conductivity
Lower ionic conductivity
Growth morphology is more or less the same
problem is the high melt viscosity. Its tendency to spuriously nucleate and also to
leave behind major structural defects in the crystals has motivated the researchers
to look for better fluxes. We have summarized the advantages and disadvantages of
both flux and hydrothermal methods and quality of KTP crystals in
Table 5.13
.
Similarly, the main problem with the use of the hydrothermal technique for the
growth of KTP crystals is the higher pressure
temperature conditions of growth.
In fact, when Zumsteg et al. (1976)
[134]
and Berlien and Gier (1976)
[142]
syn-
thesized KTP by the hydrothermal method, the pressure
temperature conditions
were quite high (P
5
1.5
3 kbar, T
5
650
700
C). The crystal size was not more
than a few millimeters since the experiments were carried out in small platinum or
gold capsules. Liu et al. (1982, 1984)
[143,144]
have reported the growth and prop-
erties of hydrothermally grown KTP. They prepared nutrient by the reaction of
KH
2
PO
4
and TiO
2
at 1250
C. The hydrothermal “flux” was 1.5 KH
2
PO
4
, 1.0 TiO
2
in Ag
2
or Au
2
lined autoclaves at a pressure of 24
28 kpsi (1.66
1.93 kbar) and
2
560
C in a gradient of 30
70
C. Growth rate on (011) was 0.2
520
1.8 mm/
2
2
2
week. The higher pressure
temperature conditions do not yield large size crystals
