Studies on the growth of thiourea a(H2Ncs NH2) single crystals from temperature solution and its characrization

Abstract

The growth of thiourea single crystals by the solution method has been investigated. The crystals were grown from aqueous solution by slow cooling technique. The influence of pH on the metastable region of thiourea solution has been studied. The results indicated that the growth rate of the thiourea crystal along the c-direction [001] was faster if the pH is increased. The stability of the saturated solutions with different pH values of the solutions has been assessed by measuring the metastable zone width by a nucleation method. To improve the quality of the thiourea crystal, urea (an organic compound) with different mole concentrations (viz. 5 M%, 10 M%, 20 M% etc.) was added as impurity to see the influence on the growth kinetics and habit modification. The grown crystals were characterized by FT-IR spectroscopy, UV spectroscopy and powder X-ray diffraction. FT-IR and UV spectra provided information about the presence of functional groups and compound. In the FT-IR spectrum, the corresponding =CH, =CH, C=S, N-C-N, COH stretching modes of vibrations and NH2 group deformation at different wave numbers are observed. Optical absorption spectra were recorded in the wavelength region from 200 to 11OOnmusing Shimadzu-160 spectrometer (UVVIS- NIR). In determining the range of optical window and percentage of transmission C-cut crystal plates with 3mm thickness was used. The UV absorption peaks were observed at 244nm and 349nm and absorption rates of 0.252 and 0.029 are observed. The graph suggests that the minimum wavelength is approximately 360nm for the grown thiourea crystals. Powder X-ray diffraction spectra were recorded using CuKa radiation. The reflections were indexed using the conventional procedures and lattice parameters were calculated. The values are found to be in good agreement with ASTM standard data. The micro-hardness studies have been performed on thiourea single _ crystals. The Vickers micro-hardness values are found to decrease with the increase of applied load. The work-hardening index 'n' is calculated from the plot drawn between log d and log p and the value is found less than 2 (slope of the line) for all the thiourea samples which reveals that the Vickers hardness decreases and indicating the softening nature according to Mayer's relation. The growth features on the surface of thiourea crystals are observed by etching study. It is known that the surface morphologies are associated with cleavage, deformation and surface preparation process, clear surface edge with growth striation. A hexagonal growth spiral is observed on the [001] faces of thiourea crystals. Dielectric properties of the grown crystals were investigated by two-probe method at room temperature using an impedance analyzer. The dielectric constant, dielectric loss and ac electrical conductivity were measured at room temperature in the frequency range of 50 kHz to 10 MHz. It is observed that the dielectric constant gradually decreases as the frequency increases. A.C conductivity gradually increases with increasing frequency. This may be attributed to space charge polarization I-V characteristics on the grown thiourea crystals with different thickness were studied at room temperature, to explore the behavior of the contacts. The results reveal that current increases non-linearly with the voltage. D.C electrical conductivity was measured on the grown crystal at room temperature by using the conventional two-probe method. The non-linear variation of D.C conductivity is expected due to the enhanced diffusion of charge carriers along dislocations and grain boundaries.