Chalcogenide Letters Vol. 11, No. 5, May 2014, p. 241 - 247 CRYSTALLIZATION AND CHARACTERIZATION OF NLO ACTIVE GLYCINE COPPER SULPHATE CRYSTAL S. NALINI JAYANTHI a*, A.R. PRABHAKARANa, D. SUBASHINIb, K.THAMIZHARASANc a* PG and Research Department of Physics, Pachaiyappa’s College, Chennai, India. b Department of Physics, Dr. Ambedkar Govt. Arts College, Chennai, India. c Department of Physics, Sir Theagaraya College, Chennai, India. Single crystals of Glycine Copper Sulphate (GCS) have been grown by slow evaporation solution growth technique. To identify the morphology and structure, the as grown crystals were subjected to single crystal and powder X-ray diffraction analysis. The different mode of vibrations present in the crystal was identified with FT-IR spectrum. The optical transmission spectrum and second harmonic generation (SHG) have been studied to find its linear and non-linear properties. It is observed that the crystal has transparency window from 230 to 1100nm and its energy gap (Eg) found to be is 5.39eV. Second harmonic generation studies reveal that the crystal is suitable for frequency conversion application. The mechanical behavior has been assessed by vicker’s microhardness tester and Photoconducting measurements were carried out. (Received March 27, 2014; Accepted May 30, 2014) Keywords: Crystal growth, X-ray diffraction, FT-IR, NLO. 1. Introduction Semi-organic Nonlinear Optical materials have attracted attention due to their incorporated advantages of both organic and inorganic crystals [1]. Glycine is the simplest amino acid among the proteinogenic amino acids in that it is not chiral. It is a very good material to prepare large number of semi-organic crystals due to its capability of forming compounds with anionic, cationic and neutral chemical compounds. In the present investigation glycine copper sulphate crystals were grown by slow evaporation solution growth technique. The as grown crystals are subjected to single crystal XRD, Powder XRD, FT-IR, UV-Vis-NIR, Kurtz powder analysis, Vicker’s microhardness analysis and photo conductivity analysis. The results obtained are reported herein and discussed. However for the author’s best knowledge, there is no existing report about structural parameters of GCS crystals. Therefore, for the first time in this paper, microcrystalline size (D), strain values (ε), stacking fault (αst) and dislocation density for corresponding full width half maximum values (FWHM) are fully reported. 2. Experimental In the present investigation Glycine Copper Sulphate (GCS) crystals are synthesized according to the following chemical reaction by dissolving glycine and copper sulphate pentahydrate in the double distilled water. CH2NH2COOH + CuSO4.5H2O→Cu[CH2NH2COOH]SO4 + 5H2O * Corresponding author: [email protected] 242 The prepared solution was thoroughly stirred and allowed for evaporation. To improve the transparency of the crystal recrystallization process was done. Good quality seed crystals were obtained and that crystals are used to prepare good sized optically high quality crystals. In the growth period of 20 days the crystal dimensions up to 14 x 8 x 3 mm3 were obtained and shown in Fig.1. Fig.1. Photograph of as grown GCS crystal 3. Results and Discussion Single Crystal X-ray Diffraction analysis: The grown crystals have been subjected to single crystal X-ray diffraction studies using BRUKER NONIUS CAD-4 diffractometer to estimate the cell parameters. The single crystal data indicates that the GCS crystal belongs to triclinic system. The lattice parameters were found to be a = 5.958Å , b = 6.121 Å , c = 10.743 Å , α = 77.62 ̊ , β = 82.1 ̊ , ν = 72.23 ̊ with cell volume 391.7855Å3. The values were compared with the crystallographic data of glycine [2] and copper sulphate pentahydrate [3] and earlier reported values [4]. The as grown GCS crystals are distinct from glycine and copper sulphate pentahydrate crystallographic data and in good agreement with the reported values. This change may be due to the incorporation copper sulphate pentahydrate in glycine lattice. Powder X-ray diffraction analysis: The grown GCS crystals are crushed into fine powder and subjected X-ray powder diffraction analysis using monochromated CuKα radiation source (λ=1.540598A ̊ ). The sample was scanned for a 2θ range 10-70 ̊ at a scan rate 1 ̊ / min and the recorded spectrum is shown in Fig.2. Miller indices of the planes have been calculated and Bragg’s peaks are indexed. The sharp and well defined peaks indicate the good crystallinity of the crystal. Structural parameters such as micro crystalline size (D), strain values(ε), stacking fault (αst) and dislocation density for corresponding full width half maximum values (FWHM) are calculated and listed in Table 1. Table 1 Structural parameters of GCS crystal FWHM (deg) D nm ε lin m-4 αst δ Kg/m3 0.04 0.08 0.12 0.16 3.81198 1.97115 1.2597 0.971632 0.009504 0.0184109 0.0287933 0.0372612 0.02005 0.0321 0.077162 0.059883 6.88174x1016 2.57372x1017 6.30145x1017 10.5924x1017 -2 (-134) 200 (102) (111) 243 (231) (3-11) (333) (-301) (1-15) (-1-26) (105) (1-13) (223) 50 (020) (003) (013) 100 (-102) (010) (011) Intensity(CPS) 150 0 10 20 30 40 50 60 70 Position (2 Theta) Fig.2 Powder XRD pattern of GCS crystal FT-IR spectral analysis: FT-IR spectrum was recorded using Perkin Elmer Spectrum One in the range 400-4000cm-1 for the GCS crystal and it is shown in Fig.2. The peak observed at 531cm-1 is due to the torsional vibration of amino group [5]. The peal at 637 cm-1 indicates the presence of carboxylate group [6]. The bending of COO gives peak at 723 cm-1 [7]. The stretching vibration of SO4- occurs at 862cm-1 [8]. C-C-N asymmetric stretching is evident from the medium intensity peak at 1022 cm-1[9]. In pure glycine, NH3+ group appeared at 1133cm-1 but in our present investigation it shifted to 1126cm-1 . This confirms the existence of glycine in zwitterionic form[10]. Main IR bands of glycine are symmetric stretching of (COO-) and asymmetric stretching of (COO-) located at 1596 and 1412cm-1 respectively [11]. Here these two bands are shifted to 1621 and 1440cm-1. The peak at 2825cm-1 assigned to C- stretching mode vibration. O-H stretching at 3426cm-1 is due to water of crystallization. Optical absorption studies: UV-Vis-NIR spectrum of GCS crystals were recorded in the wavelength range 200 to 1100nm using the instrument Varien Carry 5E UV-Vis-NIR spectrophotometer is shown in Fig.4. From the spectrum it is observed that the absorbance is less than 1 unit in the entire visible region. The as grown crystal is very transparent in the wavelength range 230 to1100nm. This is the desirable property of a NLO material [12]. The UV cutoff wavelength lies near 366nm. The direct band gap energy of the GCS crystal is found to be 5.39eV using the equation E=hν. NLO studies: The Kurtz and Perry technique [13] was used to find the nonlinear property of the crystal. Microcrystalline KDP material was used as a reference material with GCS for SHG measurements. A high intensity Nd:YAG laser beam with input pulse of 6.2mJ as a optical source was allowed onto the powder samples. The second harmonic signal (532nm) 56mV and 156.3mV were obtained through KDP and GCS samples. Thus the SHG efficiency of the GCS crystal is 2.8 times higher than KDP crystal. This result confirms the non centrosymmetric structure and NLO behavior of the as grown GCS crystal. 244 Fig.3 FT-IR spectrum of GCS crystal 2.5 Absorbance 2.0 1.5 1.0 0.5 0.0 200 400 600 800 1000 Wavelength Fig.4. UV-Vis-NIR spectrum Micro Hardness TestVicker’s micro hardness study for GCS crystal is performed on polished smooth surface with different loads like 5g, 10g, 25g, 35g and 50g. The maximum load is restricted to 50g as micro cracks were developed at higher loads. Fig.5 shows the variation of Vicker’s hardness number against applied load. The plot indicates that the hardness of the crystal increases with increase in load and it is in agreement with Indentation Size Effect [14-17].The relation between load(P) and diagonal length of indentation(d) is given by Mayer’s law [18] which is P = a dn 245 Where a and n are constant for a particular material. Fig.6 shows the variation of log P with log d which is known as Mayer’s index number (or) work hardening coefficient (n). The value of “n” for a GCS crystal is calculated from the graph and it is 1.108. According to Onitsch, if n < 1.6 those materials are hard materials [19]. Hence, it is concluded that GCS crystal is a hard material. 60 50 2 Vickers Hardness (Kg/mm ) 55 45 40 35 30 25 20 0 10 20 30 40 50 -3 Load (x10 Kg) Fig.5 Variation of Vickers hardness number with load 1.8 Original data Linear fit 1.6 Log P 1.4 1.2 n=1.10825 1.0 0.8 0.6 1.30 1.35 1.40 1.45 1.50 1.55 1.60 1.65 Log d Fig.6 Plot of log P versus Log d Photoconductivity studies Photoconductivity study of GCS crystal was carried out using a KEITHLEY Picoammeter at room temperature. Initially the sample is covered with black paper to avoid external light radiation and the dark current (Id) was measured for different applied field. The sample is then exposed to 100W halogen lamp containing Iodine vapour and Tungston filament. The corresponding photocurrent (Ip) is measured for same values of applied field. The field dependent photo conductivity of GCS crystal is shown in Fig.7. Dark current of GCS crystal is found to be 246 less than that of Photo current and shows positive photo conductivity. This may be due to large number of mobile charge carriers generated by absorption of photons [20]. 450 Photo Current (IP) 400 Dark Current (Id) 350 CURRENT (nA) 300 250 200 150 100 50 0 0 500 1000 1500 2000 2500 3000 Field(V/Cm) Fig.7. Variation of Dark and Photo current with applied field 4. Conclusion A nonlinear optical single crystal, GCS was successfully grown by slow evaporation solution growth method. Single crystal XRD method reveals the crystalline nature of the as grown crystal and the structure is observed to be Triclinic. FT-IR analysis confirms the presence of various functional groups in the crystal. Optical transparency of the crystal is analyzed from UVVis-NIR spectrum. It is observed that the crystal is transparent in the entire visible region. 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