Abstract:
Single crystals of pure potassium dihydrogen orthophosphate KH2P04(KDP) and
K2Cr04 doped KDP crystals in the ratio (viz 95:05, 90:10, 85:15, 80:20 and
0.2KDP, OAKDP, 0.6KDP 0.8KDP) have been grown from aqueous solutions of
different pH values by slow evaporation process at room temperature using the
seeding technique. The pH value of the solution has been varied by the addition of
Phosphoric acid or potassium hydroxide. The growth rate constants of pure KDP
and KDP doped with K2Cr04 in different ratios are found to be 5.70xl0.3 mrn4/sec,
2.46xlO.3 mrn4/sec, 1.06xlO.3 mrn4/sec, 2.08xl0.3 mrn4/sec, 3.37xlO.3 mrn4/sec,
0.66x 10.3 mrn4/sec respectively.
The grown crystals exhibit the normal habit, a tetragonal prism in combination with
a bipyrarnid 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
crystal. It has been noted from IR study that the P04 band seems to be displaced to
the higher frequencies. This might indicate weakening of the hydrogen bond,
possible transition to a hydrogen bond. The tetragonal unit cell of lattice for pure
KDP measures 7.57A along the base edge 'a' and 7.219A in height and cia ratio is
found to be 0.95.
Microhardness of KDP and KDP doped with K2Cr04 crystals were determined
using Vickers microhardness tester. The results reveal that the microhardness of the
grown doped crystals varies with the applied load (varying from 5 to 100gm). The
variation shows that the decrease of microhardness continued till a load of 100 gm
and finally reduces to a constant value within the load I?f 100grns. After 100grns of
load the cracks begin to start.
