Growth and characterization of single crystals of KDP doped with KCI from aqueous solution

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.