Studies on the nucleation kinetics of ammonium and potassium oxalate single crystals for non-linear optical applications

Abstract

Single crystals of pure Ammonium oxalate (AO) [(Nf4) 2 C204.H20], pure Potassium oxalate (KO) [K2C204.H20], Cobalt chloride [CoCh](O.OlM, 0.03M, 0.05M) doped AO, Potassium chloride (KCl) (O.lM, O.3M, 0.5M) doped KO and KO-AO (90:10, 80:20) mixed crystals have been grown from aqueous solutions by isothermal evaporation process and slow cooling process. The grown crystals have been characterized by studying the structural and electrical properties. The solubility of AO is 6.1 gm/100ml and the solubility of KO is 9.05 gm/IOOml at room temperature (26°C). The crystal system of AO is orthorhombic and the crystal system of KO is monoclinic. The growth rates were measured for all the grown crystals. The growth rates were found to decrease with the increase of dopant concentration of CoCh (O.OlM and 0.03M) with AO, KCl doped (O.1M and O.3M) with KO, 90:10 and 80:20 KO-AO mixed crystals than pure AO and pure KO crystal. The AO crystals are found to be elongated along c-axis and the KO crystals are elongated along a and b axes. Infrared spectroscopic study and X-ray powder diffraction analysis were carried out on the grown crystals at room temperature to identify the presence of functional group, bond nature and to determine lattice parameters respectively. The calculated lattice parameters of AO are: a = 8.796 A, b = 10.814 A, c = 3.714 A and the lattice parameters ofKO are:a = 8.2047A, b = 10.166 A, c = 3.555 A which are in good agreement with the ASTM standard values for pure form. The X-ray study also reveals that the structures are slightly distorted when the impurities are added in different mole concentrations. D.C. electrical conductivity measurements have been carried out for all of the grown pure AO, pure KO, CoCh (O.OlM, 0.03M) doped AO, KCl (O.1M, 0.3M) doped KO and KOAO (90: 10, 80:20) mixed crystals at temperatures ranging from room temperature to 70°C by using the conventional two-probe method. D.C. conductivity is found to increase with the increase of temperature and addition of dopant concentrations. Non-linear v :c -Ire, variation of D.C. conductivity is observed in the samples and this can be explained as due to the enhanced diffusion of charge carriers along dislocations and grain boundaries. The I-V characteristics at room temperature is found non-ohmic and the material is found highly insulating under the applied voltage 0 - 120 V and the current is found for the given samples in the ran~e ofO.007nA - 5.1 nA. Frequency dependence conductance is found increased with the increase in the frequency range (102 KHz - 104 KHz) and with the concentration of dopant [CoCh (O.OlM, 0.03M) doped with AO, KCI (O.1M, 0.3M) doped with KO and KO-AO (90:10, 80:20) mixed crystals]. The value of dielectric constant slightly decreases with the increase of frequency and the dielectric constant increases with the dopant concentration (O.OlM and 0.03M CoCh doped AO, O.lM and O.3M KCI doped KO, 90:10 and 80:20 KO-AO mixed crystals). At lower frequency «(102 KHz - 103 KHz) there is no dielectric loss but loss factor is becoming high and almost uniform in the frequency ranges from 103 KHz to 104 KHz.