Abstract:
Single crystals of pure potassium dihydrogen orthophosphate
KHff'04(KDP) and KDP doped with KCI crystals in the ratios (viz 95: 05,
90:10, 85:15 and 80:20) have been grown from acqueous solutions by
slow evaporation process at room temperature using the seeding
technique. The growth rates were measured for all of the five crystals
along both the x and z direction. The growth rates along x axis for pure
KDP and KDP doped with KCI are found to be 1.28 x1(f5mm/sec, 1.67
xl (f5mm/sec, 1.51 xl (f5mm/sec. 1.32 x 1(f5mm/sec, 1.68 x 1(f5mm/sec
and along the z axis the respective values are found to be 3.06 x 1(f
5mm/sec, 4.09 x 1(f5mm/sec, 5.32 x 1(f5 mm/sec, 5.00 x 1(f5mm/sec, 4.98
x 1(f5mm/sec. The growth rate constants of pure KDP and KDP doped
with KCl in different ratios are found to be 31.1 x l(f~mm%ec, 69.4 x
l(f~mm%ec, 108.5 x l(f1£mm%ec, 70.4 x 1(f~mm4/sec, 118.7 x 1(f'
2.6~mm4/sec respectively.
The grown crystals exhibit the normal habit, a tetragonal prism in
combination with a bipyramld. The grown crystals are found to be
elongated along the z-axis.
Infrared spectroscopic study and X-ray diffraction analysis are
carried out on the grown crystals at room temperature to find the crystal
parameters. It has been noted that the P04 spectrum seems displaced to
higher frequencies. This might indicate weakening of the hydrogen bond
and a possible transition to a hydroxyl bond. The tetragonal unit cell of
"
\ ~.-.
I~""C--
lattice for pure KDP measures 7.42A along the base edge 'a' and 7.30A
in height and cia ratio is found to be 0.98. D.C. electrical conductivity
measurements have been carried outfor all of the grown crystals at room
temperature and with temperature variation upto 20(J'C and with voltage
variation upto 150 V by twoprobe method The results reveal that the d.c.
electrical conductivity increases with the increase of doping
concentration. Conductivity is found in the order of 1(f7 mho/m. The
increase of conductivity values of KDP crystal doped with chloride
impurity may be attributed by the replacement of (H'pO.,)J ions by cr
ion. The electrical conduction in KDP crystals is found to be protonic.
A.C. breakdown voltage isfound to be around 4.68 kV/cm for pure KDP
and for KDP doped with KCI in the ratios (viz 95:05, 90:10, 85:15 and
80:20) are 4.42 kV/cm, 4.03 kV/cm, 4.66 kV/cm, 3.90 kV/cm respectively.
The activation energy for conduction in KDP isfound to be 0.78 ,10
0.04 ev' For pure KDP the activation energy is 0.374 eV in the
temperature range 21'C to 17SOCand for the doped crystals energy
values are found to be 0.351 eV, 0.236 eV, 0.277 eVand 0.314 eV
respectively.
