Research Journal of Chemical Sciences ______ ______________________________ ______ ____ ISSN 2231 - 606X Vol. 2 ( 5 ), 78 - 80 , May (201 2 ) Res.J.Chem.Sci. International Science Congress Association 78 Short Communication Investigations on Growth, Theoretical and Dielectric Properties of L - Glutamic Acid Hydrobromide (GHB) NLO Single Crystal Suresh S. 1 * and Mani P. 2 1 *Department of Physics, Loyola College, Chennai - 600 034, INDIA 2 Department of Physics, Hindustan Institute of Technology, Padur, INDIA Available online at: www.isca.in (Received 23 rd January 201 2 , revised 1 st March 201 2 , accepted 13 th March 201 2 ) Abstract Single crystals of L - glutamic acid hydrobromide (GHB) were grown from aqueous solution by slow evaporation technique. Single crystal X - ray diffraction analysis shows that the crystal belongs to monoclinic system with the space group P2 1 2 1 2 1 . Several solid - state physical parameters have been determined for the grown single crystals. The dielectric constant and the dielectric loss of the grown crystal were studied as a function of frequency at room temperature. Keywords : Single crystal, g rowth from solution, X - ray diffraction, d ielectric constant and d ie lectric loss . Introduction The nonlinear optical properties of the organic molecular crystals have received a great deal of interest for the past two decades due to their extensive application in the fields like laser technology, telecommunication, optical information processing and storage 1,2 . The nonlinear response of the crystal is due to the application of strong sources of electric field which gives rise to the second and higher order nonlinear properties like second harmonic generation, d - c rec tification, three frequency generation such as mixing, sum generation, self focusing, Kerr effect 3 , two photon absorption and Raman scattering. One can explore all these nonlinear effects from the asymmetric systems by attributing them into high intense op tical beam. The linear properties of all the centrosymmetric systems could be given by scon nk tnso χ (1) . In general, the effect of s econd h armonic g eneration (SHG) described by the third rank polar tnso χ (2) is forbidden in linear systems but it is predominant in non - centrosymmetric systems. The performance of the organic NLO materials in the optical region placed a great demand on these materials owing to which, several attempts have been made by the scientists to identify the good quality nonli near organic crystals. In this work an attempt has been made to locate a new class of organic NLO materials involving charge transfer from donor to acceptor followed by proton transfer from the acceptor. This paves the way for the formation of intermolecul ar hydrogen bonding, which is the root cause for the NLO property in such materials 4 . In the present study, growth has been carried out by using slow evaporation technique 5 and some solid – state physical parameters such as valance electron plasma energy, Pe nn gap, Fermi energy and electronic polarisability have been determined for L - glutamic acid hydrobromide single crystal. The dielectric constant and the dielectric loss have been determined as a function of frequency at room temperature for the L - glutamic acid hydrobromide single crystal. Material and Methods Crystal growth: Single crystal of GHB were grown from L - Glutamic acid and hydrobromic acid taken in the equimolar ratio in aqueous solution by slow evaporation method. The solution was stirred continuously using magnetic stirrer for 3 days. The prepared solution was filtered and kept undisturbed at room temperature. Tiny seed crystals with good transparency were obta ined due to the spontaneous nucleation. Among them, defect free seed crystal was suspended in the mother solution, which was allowed to evaporate at room temperature. Large size single crystals were obtained due to collection of monomers at the seed crysta l sites from the mother solution. Fig ure 1 shows as grown single crystal of GHB. Figure 1 Photograph of a GHB crystal Research Journal of Chemical Sciences ______ _ _ _______________________________ ______________ _ ____ ISSN 2231 - 606X Vol. 2 ( 5 ), 78 - 80 , May (201 2 ) Res.J.Chem.Sci International Science Congress Association 79 Results and Discussion Single - crystal X - ray diffraction and fundamental parameters: From the single crystal X - ray diffraction data, it was confirmed that the grown crystal belongs to orthorhombic system with the non - centrosymmetric space group of P2 1 2 1 2 1 . The cell parameters are: a = 5.37 , b = 11.75 , c = 13.39 . These values agre ed well with the reported values [5]. The molecular weight of the grown crystal is M = 221 g, and total number of valence electron Z = 54 . The density of the grown crystal was found to be ρ = 1.42 g cm - 3 and dielectric constant at 1 MHz is = 187.6 . The valence electron plasma energy, is given by (1) where Z is th totl numb of vlnc lctons, ρ is th nsity and M is the molecular weight of the GHB single crystal. The Plasma energy is terms of Penn gap and Fermi energy [6] in eV is given as (2) and (3) Polizbility, α is obtin using th ltion [7] (4) where S 0 is a constant for a particular material and is given by (5) Th vlu of α so obtin gs ll ith tht of Clausius - Mossotti equation, which is given by, (6) where the symbols have their usual significance. N a is Avagadro number and the calculated fundamental data on the grown crystal of GHB are listed in table1. Table - 1 Some theoretical data for GHB single crystal Parameters Values Plasma energy (eV) 22.46 Penn gab ( eV) 2.11 Fermi gap (eV) 18.24 Polarizability (cm 3 ) Penn analysis 7.203 x 10 - 23 Polarizability (cm 3 ) Clausius - Mossotti Equation 7.121 x 10 - 23 Dielectric studies: Single crystal of GHB was subjected to dielectric studies using a HIOKI HITESTER MODEL 3532 - 50 LCR meter and conventional two terminal sample holder. Dielectric permittivity measurements were carried out with the sample of dimension 2 2 1 mm 3 have been placed inside a dielectric cell whose capacitance were measured at room temperature for different frequencies. The techniques used for the measurement of dielectric constant are either reflection coefficient s or resonant frequencies. In the later case, material is characterized to load a resonant cavity and the sample permittivity is evaluated from the shift of the resonant frequency value compared to that of the empty (unload) cavity. The dielectric constant and dielectric loss have been calculated using the equations (7) and (8). (7) (8) Where d is the thickness of the sample, A is the area of the sample. The observations are made in the frequency range 50 Hz to 5 MHz at room temperature. Fig ure 2 and 3 represent the plots of dielectric constant and dielectric loss against frequency. From the graph it is observed that dielectric constant is maximum at 100 Hz since all types of polarization such as electronic, ionic, orientation and space charge polarizations occur at lower frequency. Fig ure 3, it is observed that the dielectric loss decreases with increase in frequencies at room temperatu re. Because of the inertia of the molecules and ions at high frequencies, the orientation and ionic contributions of polarization are small 8 . So, the magnitude of polarization increases with the decrease of frequencies. Figure - 3 Dielectric constant vs lo g f Research Journal of Chemical Sciences ______ _ _ _______________________________ ______________ _ ____ ISSN 2231 - 606X Vol. 2 ( 5 ), 78 - 80 , May (201 2 ) Res.J.Chem.Sci International Science Congress Association 80 Figure - 4 Dielectric loss vs log f Conclusion Single crystals of GHB were grown by using the slow evaporation technique. The lattice parameters were calculated by single crystal X - ray diffraction and it was confirmed that the crysta ls belong to the monoclinic system with the space group P2 1 2 1 2 1 . The physical parameters such as valence electron plasma energy, Penn gap, Fermi energy and electronic polarisability have been determined for the GHB crystal. The variation of dielectric constant and dielectric loss were studied as a function of frequency at room temperature. References 1. 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