Growth and characterization of single crystals of KDP doped with k2cro4 from aqueous solution of different pH values

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.