Effect of divalent metal ion impurities (Ba²⁺, Ca²⁺ and Mg²⁺) on the growth, structural and physical properties of KAP crystals.

Single crystals of potassium hydrogen phthalate (KAP), a semi-organic compound, have been grown by slow evaporation method at room temperature from aqueous solution in the presence of divalent metal ionic impurities Ba(2+), Ca(2+) and Mg(2+). Elemental analysis by inductively coupled plasma optical emission spectroscopy (ICP-OES) proves the incorporation of these impurities into the grown crystals. Powder X-ray diffraction studies confirmed the phase formation and metal ions doping into KAP crystals. Thermogravimetric-differential thermal analysis (TG-DTA) shows the onset decomposition temperatures to be 255, 238, 251 and 250°C for pure, Ba(2+), Ca(2+) and Mg(2+) doped KAP crystals respectively. Microhardness studies revealed that all the three doped crystals have improved hardness values than that of undoped KAP crystal. Ca-KAP crystal exhibited the highest second harmonic generation (SHG) conversion efficiency of 16 mV with the output power of nearly half of the standard potassium dihydrogen phosphate (KDP) crystal. The grown crystals were also subjected to Fourier transform infrared (FTIR) spectroscopy, ultra violet-visible-near infrared (UV-NIR) spectroscopy studies and dielectric studies. Among the three investigated metal ion impurities, Ca(2+) ion seem to have positive influence on the growth, mechanical, thermal, dielectric and SHG characteristics of KAP which makes it suitable for applications.