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Asian Journal of Scien ce and Technology
Vol. 1, Issue 11, pp.067-069, November, 2011
ISSN: 0976-3376
1,* Sakthivel, N. and 2Anbarasan, P.M.
1Department of Physics, Maha Barathi Engineering College, Villupuram - 606 201 2Department of Physics, Periyar University, Salem - 636 011 Received 8th March, 2011; Received in revised from; 7h April, 2011; Accepted 5th June, 2011; Published online 12th November, 2011
1-Hydroxyurea Hydrate an intriguing new organic material for frequency conversion has been grown by slow evaporation solution growth technique at room temperature. Their structural and physicochemical properties were characterized by X-ray powder diffraction, Dielectric studies, UV-Vis spectra and Hardness studies. The crystal belongs monoclinic symmetry with the space group P21/c, a well-known noncentrosymmetric space group thus satisfying the requirements for second-order NLO activity. The material has a wide transparency in the entire visible region. It is found that the cutoff wavelength lies in the UV region. The mechanical response of the crystal has been studied using Vickers microhardness technique. Key words: Crystal Growth, Dielectric studies, UV-Vis studies, Hardness studies.
large value of hyperpolarizability. In this work 1-hydroxyurea hydrate crystal was grown by slow evaporation technique. The In recent years the need of nonlinear optical materials [1-3] is grown crystals were subjected to Dielectric, Optical and much more than other materials because of their applications in optoelectronics and photonics. Second order nonlinear optical materials have recently attracted much attention Solubility Studies
because of their potential applications in emerging optoelectronic technologies. Materials with large second order The commercially available 1-hydroxyurea hydrate (CH6N2O3) optical nonlinearities, short transparency cutoff wavelength was further purified by repeated recrystallization process. In and stable physico thermal performance are needed in order to order to obtain organic single crystals of high quality, realize many of these applications. Especially the organic NLO purification of starting material was found to be an important crystals are attracted attention because of the low cost and step. The recrystallized salt was the charge material for the flexibility of molecular design, which we need for applications growth of 1-hydroxyurea hydrate. To grow bulk crystals from with using suitable donor and acceptor. Organic crystals are solution by slow evaporation technique, it is desirable to select having some special properties of large optical nonlinearity[4- a solvent in which it is moderately soluble. The size of a 5] and low cut-off wavelengths in UV region, therefore the crystal depends on the amount of material available in the organic NLO crystals are required for use in optical devices. solution, which in turn is decided by the solubility of the Organic materials are often formed by weak vander Waals and material in that solvent. Hence, we have determined the hydrogen bonds and hence possess a high degree of solubility as deionized water. Solubility in deionized water delocalization. However, these organic crystals have certain was found good and the crystals grown were found to have limitations such as poor mechanical and thermal stability. The better shape and transparency. Good transparent single crystals contribution from the delocalized π – electrons belonging to were obtained after ten days. Fig. 1 shows the Solubility curve the organic ligand results in wide optical transmittance and of 1-hydroxyurea hydrate. Fig. 2 shows the grown crystal of 1- high nonlinear electro – optic coefficients. Many device hydroxyurea hydrate with an optimized solution pH value of applications of NLO require single crystals in the bulk form. 1- hydroxyurea hydrate is an organic NLO material possessing
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Asian Journal of Science and Technology, Vol. 1, Issue 11, pp.067-069, November, 2011
Mechanical Behaviour

Hardness of the material is a measure of resistance, It offers to
deformation. The transparent crystals free from cracks were
indentation were made on the grown surface with the load ranging from 25gms-200gms using Vickers microhardness tester. Leitz-Wetzlar fitted with a Vickers diamond pyramidal indenter and attached to an incident light microscope. The indentation time was kept as 5s for all the loads. The Vickers hardness number Hv was calculated from the following equation Where P is the applied load in kg and d is the diagonal length of the indentation impression in micrometer and 1.8554 is Fig. 1. Solubility curve of 1-hydroxyurea hydrate
constant of a geometrical factor for the diamond pyramid. Fig. 4 shows the variation of mechanical behaviour of 1- hydroxyurea hydrate with applied load. In ideal circumstance the hardness value should be independent of applied load. But in practice the load dependence is observed. As the load is increased there is steep fall in hardness. The decrease of microhardness with increasing load is in agreement with normal indentation size effect (ISE) as observed by others.The decrease of microhardness in 1-hydroxyurea hydrate crystal is attributed to certain type of impurities incorporated into the lattice. Fig. 2. Grown crystal of 1-hydroxyurea hydrate
Powder X-ray diffraction analysis

The XRD data of the crystal still possesses monoclinic
symmetry with the space group P21/C, a well-known noncentrosymmetric space requirements for second-order NLO activity. The lattice parameter values of the crystal have been calculated using least-squares fit method and they are found to be a = 8.329 Ǻ , b = 4.662 Ǻ , c = 8.829 Ǻ, α=γ=90º, β=122.40º respectively. Fig. 4. Plot of Hv versus Load of 1-hydroxyurea hydrate
The crystallographic data obtained in the present study were found to be in good agreement with the data reported in Dielectric Studies
literature.The chemical structure of 1-hydroxyurea hydrate capacitance, C, and tan d, were obtained using a computer controlled LCR HiTester (HIOKI,3532-50) for different frequencies in the range100Hz–1MHz. The dielectric constant[9-10] of a material is generally composed of four types of contributions, viz. ionic, electronic, orientational and space charge polarizations. All of these may be active at low frequencies. The nature of variations of dielectric constant with frequency and temperature indicates the type of contributions that are present in them. The dipolar orientational effect can be seen in some materials at high frequencies and ionic and electronic polarizations below 103 Hz. The large value of εr at low frequency and at low temperature is due to the presence of space charge polarization, which depends on the purity and perfection of the Fig. 3. Chemical Structure of 1-hydroxyurea hydrate
sample. Fig. 5 shows the variation of dielectric constant with frequency measured at room temperature for the 1- 069
Asian Journal of Science and Technology, Vol. 1, Issue 11, pp.067-069, November, 2011
hydroxyurea hydrate crystal. The dielectric constant is a takes place at a wavelength of 198 nm. This absorbance maximum at low frequency and decreases with increasing of maximum at 198 nm was assigned to -* transition and may frequency for the crystals. The increase in the dielectric be attributed to the excitation in the C=O group. The absence constant at low frequency is attributed to space-charge of the absorption in the visible region is the necessity for this compound as it is to be exploited for NLO applications in the room temperature. Conclusion

Good quality single crystals of 1-hydroxyurea hydrate were grown by slow evaporation solution growth technique. The X- ray diffraction revealed the crystallization of material in transparency also adds to the possible application of the material is the field of nonlinear optics. The results of optical transparency are encouraging. Moreover, its lower cutoff wavelength with wide optical transparency window in the visible region makes this material suitable for extensive investigations. These crystals have very good characteristics for fabrication and the results of optical transparency in suggesting the material with potential applications in nonlinear optics. Fig. 5. Variation of dielectric constant with frequency for 1-
hydroxyurea hydrate crystal

The authors are thankful to Shri.Ch.Seshendra Reddy and
Shri.C.R. Kesavulu, Department of Physics, Sri Venkateswara University, Tirupati 517 502, India for measurements. REFERENCES
1. Chemla,D.S. and Zyss,J., (Eds.),1987. Nonlinear Optical Properties of Organic Molecules and Crystals, Academic 2. Chen, C.T., Bai, L., Wang, Z.Z. and Li, R.K., 2006, Development of new NLO crystals for UV and IR applications. J. Crystal Growth, 292(2): 169-178. 3. Zhengdong,L., Baichang,W., Genbo,S. and Gongfan,H., 1997, Crystal growth and optical properties of 4- Fig. 6. UV–Vis spectrum of 1-hydroxyurea hydrate
aminobenzophenon (ABP), J. Crystal Growth.,171:506- 4. Ezhil Vizhi, R. and Kalainathan, S., 2008, Growth and Nonlinear Optical studies
characterization of a new organic NLO material: 1,3 Diglycinyl thiourea, Materials Letters, 62(4-5): 791-794. A quantitative measurement of the conversion efficiency of 1- 5. Prasad, P.N. and Williams,D.J.,1991, Introduction to hydroxyurea hydrate was determined by the modified version Nonlinear Optical Effects in Organic Molecules and of powder technique developed by Kurtz and Perry [11-12]. The non-zero measured powder SHG signal is reliable with 6. Mott, B.W.,1956, Micro Indentation Hardness Testing, noncentrosymmetric crystal structure. The relative efficiency 7. Meyer,1951, Some aspects of the hardness of metals, of 1-hydroxyurea hydrate with that of KDP has been measured. It is found that the efficiency of the title crystal (60 8. Onitsch, E. M.,1947, Uber die Mikrohirte der Metalle, mV), which is 6 times greater than that of KDP (9 mV). The result of SHG is also supporting for further studies. 9. Macdonald,J.R., (Ed.), 1987,Impedance Spectroscopy, Optical Studies
10. Jonscher,A.K.,1983, Dielectric Relaxation in Solids, The UV/visible spectrum of 1-hydroxyurea hydrate was 11. Kurtz,S.K.,1968, New nonlinear optical materials, IEEE, recorded using The UV–vis transmittance has been performed using Perkin Elmer Lambda 35 UV visible spectrophotometer 12. Kurtz.S.K. and Perry.T.T.,1968, The Powder Technique in the region 200–1100 nm. The scanned spectrum is displayed for the evaluation of Nonlinear Optical Materials. The in Fig. 6. From Fig. 6 it is clear that the crystal is transparent in Journal of Applied Physics, 39(8): 3798-3813. the entire visible region and the transmittance takes place in the range between 315 to 1100nm. The maximum absorbance



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