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Growth and characterization of glycine picrate single crystal
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Spectrochimica Acta Part A 71 (2008) 340–343
Growth and characterization of glycine picrate single crystal T. Uma Devi a,∗ , N. Lawrence b , R. Ramesh Babu c , K. Ramamurthi c a
Department of Physics, Cauvery College for Women, Tiruchirappalli 620018, India Department of Physics, St. Joseph’s College (Autonomous), Tiruchirappalli 620002, India c Crystal Growth and Thin Film Laboratory, School of Physics, Bharathidasan University, Tiruchirappalli 620024, India b
Received 23 June 2007; received in revised form 26 December 2007; accepted 27 December 2007
Abstract Glycine picrate (GP), an organic material, was synthesized and successfully grown by solution growth method. Cell parameters of the grown crystals were obtained from the single crystal X-ray diffraction analysis and the presence of functional groups was identified by FTIR study. Its optical properties were examined by UV–vis–NIR analysis, which shows that the crystal is transparent between the wavelengths 400 nm and 1000 nm. Thermal analysis carried out for the glycine picrate reveals that the crystal exhibits a single sharp weight loss at 214 ◦ C. The fluorescence spectrum of glycine picrate was recorded. The Vicker’s microhardness values were measured for the grown crystal. © 2008 Published by Elsevier B.V. Keywords: Solubility; Growth from solutions; Single crystal growth
1. Introduction Organic materials have been known for their applications in semiconductors [1], superconductors [2] and nonlinear optical devices [3,4]. Organic molecules have attracted great attention due to their ability to combine low cost and ease of processing in the assembly of optical devices. Picric acid forms stable picrates with various organic molecules through bonding or ionic bonding [5]. Investigations of amino acid picrates have attracted the attention of researchers in the recent past [6–10]. The crystal structure of glycine picrate (GP) was reported by Kai et al. [11]. However, to the best of our knowledge, no thorough report is available on solubility, metastable zonewidth and growth of GP. Hence in this work we report the growth of GP crystal employing temperature reduction method and its characterization. 2. Experimental procedure 2.1. Synthesis GP was synthesized by the reaction between picric acid (Loba Chime) and the amino acid, glycine (Merck) taken in equimolar ∗
Corresponding author. Tel.: +91 431 2751232; fax: +91 431 2407045. E-mail address: kavin [email protected] (T.U. Devi).
1386-1425/$ – see front matter © 2008 Published by Elsevier B.V. doi:10.1016/j.saa.2007.12.048
ratio. The reactants were thoroughly dissolved in double distilled water and stirred well using a temperature controlled magnetic stirrer to yield a homogeneous mixture of solution. Then the solution was allowed to evaporate at room temperature, which yielded yellow crystalline salt of GP. The chemical structure of GP is shown in Fig. 1. 2.2. Solubility and metastable zonewidth The solubility of GP in double distilled water was determined as a function of temperature, in the temperature range of 30–55 ◦ C. The beaker containing the solution was maintained at a constant temperature and continuously stirred using a magnetic stirrer. The amount of GP required to saturate the solution at this temperature was estimated and this process was repeated for different temperatures. The solubility data obtained in this work was utilized to estimate the metastable zonewidth. A constant volume of 100 ml of the solution was used in all the experiments. The solution was preheated to 5 ◦ C above the saturation temperature. Metastable zonewidth was measured by the conventional polythermal method [12–14], in which the equilibrium-saturated solution is cooled from the superheated temperature to a temperature at which the first speck is observed. This corresponds to metastable zonewidth at that particular temperature. The same procedure was carried out for various temperatures and the solubility curve along with metastable zonewidth is presented in Fig. 2.
T.U. Devi et al. / Spectrochimica Acta Part A 71 (2008) 340–343
341
Fig. 1. Chemical structure of GP.
2.3. Crystal growth Saturated aqua solution of GP was prepared at 30 ◦ C from recrystallized salt and this solution was filtered with microfilters. About 200 ml of this solution was taken in a beaker and placed in a constant temperature bath having an accuracy of ±0.01 ◦ C. One of the better quality crystals of 3 mm × 1 mm × 1 mm size obtained from slow evaporation of the solution at room temperature was used as seed crystal. Single crystal of GP was grown by reducing the temperature from 30 ◦ C at the rate of 0.1 ◦ C per day. Well-developed crystal of size 10 mm × 9 mm × 5 mm, harvested in a growth period of 7 days is shown in Fig. 3. 3. Characterization
Fig. 3. As grown GP single crystal. Table 1 Unit cell parameters of GP Parameters
Present work
Kai et al. [11]
˚ a (A) ˚ b (A) ˚ c (A) ˚ 3) V (A β System Space group
14.9628 (8) 6.7216 (1) 15.1746 (8) 1523 (1) 93.62◦ (1) Monoclinic –
14.968 (3) 6.722 (2) 15.165 (3) 1523.63 (6) 93.65◦ (2) Monoclinic P21 /a
3.1. X–ray diffraction studies 3.2. FTIR spectral analysis Crystal structure of the grown crystal of GP was confirmed by single crystal X-ray diffraction analysis. One of the transparent single crystals suitable for single crystal X-ray diffraction study was selected. X-ray diffraction data were collected using Enraf Nonius—CAD4 single crystal X-ray diffractometer. The unit cell parameters obtained are compared with the reported values in Table 1. The morphology of GP establishes that there are eight developed faces, out of which (0 0 1) plane is more prominent. Further for each plane there exists a parallel plane as shown in Fig. 4.
Fig. 2. Metastable zonewidth of GP.
The FTIR spectrum of the grown GP crystal was recorded in the KBr phase in the frequency region 400–4000 cm−1 using PerkinElmer spectrometer and is shown in Fig. 5. The phenolic O vibration produces peak at 1156 cm−1 [15]. Also, it reveals that picric acid necessarily protanates the carboxyl group. The observed vibrational frequencies and the tentative frequency assignments of GP are given in Table 2.
Fig. 4. The morphology of GP.
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T.U. Devi et al. / Spectrochimica Acta Part A 71 (2008) 340–343
Fig. 5. FTIR spectrum of GP. Table 2 Tentative vibrational frequencies assignment of GP
Fig. 7. Optical transmittance spectrum of GP.
GP (cm−1 )
Assignments [15]
3079 1628 1563 1492 1334 1269 1156 901 791 740 703 521
Aromatic ( (C–H) δ (N–H) νas (COO) ν (NH3 + ) ν (NO2 ) δ (O–H) Phenolic O δ C–N in plane ϕ NO2 ϕ NO2 δ ring ρ NO2
(ν) Symmetric stretching; (νas ) asymmetric stretching; (δ) bending; (ρ) rocking; (ϕ) scissoring.
3.3. Thermal analysis Differential thermal analysis (DTA) and thermogravimetric analysis (TGA) of GP carried out simultaneously employing NETZCH STA 409 Thermal Analyzer are shown in Fig. 6. GP weighing 10 mg was taken and heated at a rate of 10 ◦ C/min in inert nitrogen atmosphere. From the DTA curve it is observed that the material is stable up to 214 ◦ C, the melting point of the substance and then it undergoes irreversible endothermic transi-
Fig. 6. TG/DT analyses of GP.
tions at 246 ◦ C and 865 ◦ C. The melting point of the substance measured using a melting point apparatus was about 212 ◦ C. 3.4. Optical studies In order to determine the optical transmission characteristics of the grown crystal, UV–vis–NIR spectrum was recorded using Lambda (model35) spectrophotometer. Optically clear single crystal of thickness about 2 mm was used for this study. Fig. 7 shows the transmittance spectrum recorded in the wavelength range of 200–1000 nm. There is no appreciable absorption in the entire visible range, as in the case of all the amino acids [16]. GP is transparent in the range 400–1000 nm. 3.5. Microhardness study Microhardness testing is one of the best methods for understanding the mechanical properties of materials [17]. The mechanical strength of the GP crystal was measured using a Leitz hardness tester fitted with a diamond indenter attached
Fig. 8. Plot of HV vs. load.
T.U. Devi et al. / Spectrochimica Acta Part A 71 (2008) 340–343
343
Fig. 9. (a) Excitation spectrum and (b) emission spectrum.
to Leitz incident light microscope. Indentations were made for various loads from 2 g to 12 g. Several trials of indentation were carried out on the prominent (0 0 1) face and the average diagonal length was calculated for an indentation time of 8 s. The Vickers hardness number (HV ) of the crystal was calculated using the relation HV = 1.8544 P/d2 , where P is the applied load in kg and d is the average diagonal length of impression in mm. Fig. 8 shows the variation of HV with load for GP. Cracks were observed for loads more than 12 g. Since glycine picrate is a fairly soluble compound, it is expected to be a soft material and is evident from the microhardness test. 3.6. Fluorescence studies Fluorescence may be expected generally in molecules that are aromatic or contain multiple conjugated double bonds with a high degree of resonance stability [18]. Fluorescence finds wide application in the branches of biochemical, medical and chemical research fields for analyzing organic compounds. The excitation and emission spectra for GP were recorded using FP6500 Spectrofluorometer. The excitation spectrum was recorded in the range 220–350 nm (Fig. 9a). The sample was excited at 325 nm. The emission spectrum (Fig. 9b) was measured in the range 340–600 nm. A peak at about 510 nm was observed in the emission spectrum. The results indicate that GP crystals have a green fluorescence emission. 4. Conclusions Transparent well-developed GP single crystal was grown by temperature reduction technique. The crystal structure was confirmed by single crystal XRD study. The functional groups were identified by FTIR analysis. From the thermal analysis it was found that the material is stable up to its melting point of 214 ◦ C. The optical behavior was studied using UV–vis–NIR analysis and found that there is no absorption between 400 nm and 1000 nm. Fluorescence spectrum showed that GP has blue fluorescence emission. Vickers hardness values measured on (0 0 1) plane shows that GP is a soft material.
Acknowledgements One of the authors (TU) is grateful to the Reddy Educational Trust, Tiruchirappalli 18, for extending the lab facility and Prof. K. Paul Angelo, Department of Chemistry, St. Joseph’s College (Autonomous), Tiruchirappalli, for fruitful discussions. The authors thank Sophisticated Analytical Instrumentation Facility, Indian Institute of Technology, Chennai for the help. References [1] J.P. Farges, Organic Conductors, Marcel Dekker, New York, 1994. [2] T. Ishiguro, K. Yamaji, Organic Superconductors, Springer, Berlin, 1990. [3] Ch. Bosshard, K. Shutter, Ph. Pretre, J. Hulliger, M. Florsheimer, P. Kaatz, P. Gunter, Organic NLOM, Gordan and Breach, London, 1995. [4] S.X. Dou, D. Josse, J. Zyss, J. Opt. Soc. Am. B 10 (1993) 1708–1715. [5] S. Yamaguchi, M. Goto, H. Takayanagi, H. Ogura, Bull. Chem. Soc. Jpn. 61 (1988) 1026–1028. [6] H. Takayanagi, M. Goto, K. Takeda, Y. Osa, J. Pharm. Soc. Jpn. 124 (2004) 751–767. [7] M.B. Mary, V. Sasirekha, V. Ramakrishnan, Spectrochim. Acta 65A (2006) 414–420. [8] T.S. Martins, J.R. Matos, G. Vicentini, P.C. Isolani, J. Therm. Anal. Calorim. 86 (2006) 351–357. [9] T. Uma Devi, N. Lawrence, R. Ramesh Babu, K. Ramamurthi, J. Cryst. Growth 10 (2008) 116–123. [10] P. Srinivasan, T. Kanagasekaran, R. Gopalakrishnan, G. Bhagavannarayana, P. Ramasamy, Cryst. Growth Des. 6 (2006) 1663–1670. [11] T. Kai, M. Goto, K. Furuhata, H. Takayanagi, Anal. Sci. 10 (1994) 359–360. [12] S.A. deVries, P. Goedtkindt, W.J. Huisman, M.J. Zwanenburg, R. Feidenhans’l, S.L. Bennett, D.M. Smilgies, A. Stierle, J.J. De Yoreo, W.J.P. van Enckevort, P. Bennema, E. Vlieg, J. Cryst. Growth 205 (1999) 202–214. [13] J. Nyvlt, R. Rychly, J. Gottfried, P. Wurzelova, J. Cryst. Growth 6 (1970) 151–162. [14] N.P. Zeitseva, L.N. Rashkovich, S.V. Bagatyareva, J. Cryst. Growth 148 (1995) 276–282. [15] G. Socrates, Infrared Characteristic Group frequencies, Wiley-Interscience, Chichester, UK, 1980. [16] V. Krishnakumar, R. Nagalakshmi, Spectrochim. Acta 64A (2006) 736–743. [17] B. Lal, K.K. Bamzai, P.N. Kotru, Mater. Chem. Phys. 78 (2003) 202–207. [18] H.H. Willard, L.L. Merritt Jr., J.A. Dean, F.A. Settle Jr., Instrumental Methods of Analysis, Sixth ed., Wadsworth Publishing Company, USA, 1986, pp. 609.
Spectrochimica Acta Part A 71 (2008) 340–343
Growth and characterization of glycine picrate single crystal T. Uma Devi a,∗ , N. Lawrence b , R. Ramesh Babu c , K. Ramamurthi c a
Department of Physics, Cauvery College for Women, Tiruchirappalli 620018, India Department of Physics, St. Joseph’s College (Autonomous), Tiruchirappalli 620002, India c Crystal Growth and Thin Film Laboratory, School of Physics, Bharathidasan University, Tiruchirappalli 620024, India b
Received 23 June 2007; received in revised form 26 December 2007; accepted 27 December 2007
Abstract Glycine picrate (GP), an organic material, was synthesized and successfully grown by solution growth method. Cell parameters of the grown crystals were obtained from the single crystal X-ray diffraction analysis and the presence of functional groups was identified by FTIR study. Its optical properties were examined by UV–vis–NIR analysis, which shows that the crystal is transparent between the wavelengths 400 nm and 1000 nm. Thermal analysis carried out for the glycine picrate reveals that the crystal exhibits a single sharp weight loss at 214 ◦ C. The fluorescence spectrum of glycine picrate was recorded. The Vicker’s microhardness values were measured for the grown crystal. © 2008 Published by Elsevier B.V. Keywords: Solubility; Growth from solutions; Single crystal growth
1. Introduction Organic materials have been known for their applications in semiconductors [1], superconductors [2] and nonlinear optical devices [3,4]. Organic molecules have attracted great attention due to their ability to combine low cost and ease of processing in the assembly of optical devices. Picric acid forms stable picrates with various organic molecules through bonding or ionic bonding [5]. Investigations of amino acid picrates have attracted the attention of researchers in the recent past [6–10]. The crystal structure of glycine picrate (GP) was reported by Kai et al. [11]. However, to the best of our knowledge, no thorough report is available on solubility, metastable zonewidth and growth of GP. Hence in this work we report the growth of GP crystal employing temperature reduction method and its characterization. 2. Experimental procedure 2.1. Synthesis GP was synthesized by the reaction between picric acid (Loba Chime) and the amino acid, glycine (Merck) taken in equimolar ∗
Corresponding author. Tel.: +91 431 2751232; fax: +91 431 2407045. E-mail address: kavin [email protected] (T.U. Devi).
1386-1425/$ – see front matter © 2008 Published by Elsevier B.V. doi:10.1016/j.saa.2007.12.048
ratio. The reactants were thoroughly dissolved in double distilled water and stirred well using a temperature controlled magnetic stirrer to yield a homogeneous mixture of solution. Then the solution was allowed to evaporate at room temperature, which yielded yellow crystalline salt of GP. The chemical structure of GP is shown in Fig. 1. 2.2. Solubility and metastable zonewidth The solubility of GP in double distilled water was determined as a function of temperature, in the temperature range of 30–55 ◦ C. The beaker containing the solution was maintained at a constant temperature and continuously stirred using a magnetic stirrer. The amount of GP required to saturate the solution at this temperature was estimated and this process was repeated for different temperatures. The solubility data obtained in this work was utilized to estimate the metastable zonewidth. A constant volume of 100 ml of the solution was used in all the experiments. The solution was preheated to 5 ◦ C above the saturation temperature. Metastable zonewidth was measured by the conventional polythermal method [12–14], in which the equilibrium-saturated solution is cooled from the superheated temperature to a temperature at which the first speck is observed. This corresponds to metastable zonewidth at that particular temperature. The same procedure was carried out for various temperatures and the solubility curve along with metastable zonewidth is presented in Fig. 2.
T.U. Devi et al. / Spectrochimica Acta Part A 71 (2008) 340–343
341
Fig. 1. Chemical structure of GP.
2.3. Crystal growth Saturated aqua solution of GP was prepared at 30 ◦ C from recrystallized salt and this solution was filtered with microfilters. About 200 ml of this solution was taken in a beaker and placed in a constant temperature bath having an accuracy of ±0.01 ◦ C. One of the better quality crystals of 3 mm × 1 mm × 1 mm size obtained from slow evaporation of the solution at room temperature was used as seed crystal. Single crystal of GP was grown by reducing the temperature from 30 ◦ C at the rate of 0.1 ◦ C per day. Well-developed crystal of size 10 mm × 9 mm × 5 mm, harvested in a growth period of 7 days is shown in Fig. 3. 3. Characterization
Fig. 3. As grown GP single crystal. Table 1 Unit cell parameters of GP Parameters
Present work
Kai et al. [11]
˚ a (A) ˚ b (A) ˚ c (A) ˚ 3) V (A β System Space group
14.9628 (8) 6.7216 (1) 15.1746 (8) 1523 (1) 93.62◦ (1) Monoclinic –
14.968 (3) 6.722 (2) 15.165 (3) 1523.63 (6) 93.65◦ (2) Monoclinic P21 /a
3.1. X–ray diffraction studies 3.2. FTIR spectral analysis Crystal structure of the grown crystal of GP was confirmed by single crystal X-ray diffraction analysis. One of the transparent single crystals suitable for single crystal X-ray diffraction study was selected. X-ray diffraction data were collected using Enraf Nonius—CAD4 single crystal X-ray diffractometer. The unit cell parameters obtained are compared with the reported values in Table 1. The morphology of GP establishes that there are eight developed faces, out of which (0 0 1) plane is more prominent. Further for each plane there exists a parallel plane as shown in Fig. 4.
Fig. 2. Metastable zonewidth of GP.
The FTIR spectrum of the grown GP crystal was recorded in the KBr phase in the frequency region 400–4000 cm−1 using PerkinElmer spectrometer and is shown in Fig. 5. The phenolic O vibration produces peak at 1156 cm−1 [15]. Also, it reveals that picric acid necessarily protanates the carboxyl group. The observed vibrational frequencies and the tentative frequency assignments of GP are given in Table 2.
Fig. 4. The morphology of GP.
342
T.U. Devi et al. / Spectrochimica Acta Part A 71 (2008) 340–343
Fig. 5. FTIR spectrum of GP. Table 2 Tentative vibrational frequencies assignment of GP
Fig. 7. Optical transmittance spectrum of GP.
GP (cm−1 )
Assignments [15]
3079 1628 1563 1492 1334 1269 1156 901 791 740 703 521
Aromatic ( (C–H) δ (N–H) νas (COO) ν (NH3 + ) ν (NO2 ) δ (O–H) Phenolic O δ C–N in plane ϕ NO2 ϕ NO2 δ ring ρ NO2
(ν) Symmetric stretching; (νas ) asymmetric stretching; (δ) bending; (ρ) rocking; (ϕ) scissoring.
3.3. Thermal analysis Differential thermal analysis (DTA) and thermogravimetric analysis (TGA) of GP carried out simultaneously employing NETZCH STA 409 Thermal Analyzer are shown in Fig. 6. GP weighing 10 mg was taken and heated at a rate of 10 ◦ C/min in inert nitrogen atmosphere. From the DTA curve it is observed that the material is stable up to 214 ◦ C, the melting point of the substance and then it undergoes irreversible endothermic transi-
Fig. 6. TG/DT analyses of GP.
tions at 246 ◦ C and 865 ◦ C. The melting point of the substance measured using a melting point apparatus was about 212 ◦ C. 3.4. Optical studies In order to determine the optical transmission characteristics of the grown crystal, UV–vis–NIR spectrum was recorded using Lambda (model35) spectrophotometer. Optically clear single crystal of thickness about 2 mm was used for this study. Fig. 7 shows the transmittance spectrum recorded in the wavelength range of 200–1000 nm. There is no appreciable absorption in the entire visible range, as in the case of all the amino acids [16]. GP is transparent in the range 400–1000 nm. 3.5. Microhardness study Microhardness testing is one of the best methods for understanding the mechanical properties of materials [17]. The mechanical strength of the GP crystal was measured using a Leitz hardness tester fitted with a diamond indenter attached
Fig. 8. Plot of HV vs. load.
T.U. Devi et al. / Spectrochimica Acta Part A 71 (2008) 340–343
343
Fig. 9. (a) Excitation spectrum and (b) emission spectrum.
to Leitz incident light microscope. Indentations were made for various loads from 2 g to 12 g. Several trials of indentation were carried out on the prominent (0 0 1) face and the average diagonal length was calculated for an indentation time of 8 s. The Vickers hardness number (HV ) of the crystal was calculated using the relation HV = 1.8544 P/d2 , where P is the applied load in kg and d is the average diagonal length of impression in mm. Fig. 8 shows the variation of HV with load for GP. Cracks were observed for loads more than 12 g. Since glycine picrate is a fairly soluble compound, it is expected to be a soft material and is evident from the microhardness test. 3.6. Fluorescence studies Fluorescence may be expected generally in molecules that are aromatic or contain multiple conjugated double bonds with a high degree of resonance stability [18]. Fluorescence finds wide application in the branches of biochemical, medical and chemical research fields for analyzing organic compounds. The excitation and emission spectra for GP were recorded using FP6500 Spectrofluorometer. The excitation spectrum was recorded in the range 220–350 nm (Fig. 9a). The sample was excited at 325 nm. The emission spectrum (Fig. 9b) was measured in the range 340–600 nm. A peak at about 510 nm was observed in the emission spectrum. The results indicate that GP crystals have a green fluorescence emission. 4. Conclusions Transparent well-developed GP single crystal was grown by temperature reduction technique. The crystal structure was confirmed by single crystal XRD study. The functional groups were identified by FTIR analysis. From the thermal analysis it was found that the material is stable up to its melting point of 214 ◦ C. The optical behavior was studied using UV–vis–NIR analysis and found that there is no absorption between 400 nm and 1000 nm. Fluorescence spectrum showed that GP has blue fluorescence emission. Vickers hardness values measured on (0 0 1) plane shows that GP is a soft material.
Acknowledgements One of the authors (TU) is grateful to the Reddy Educational Trust, Tiruchirappalli 18, for extending the lab facility and Prof. K. Paul Angelo, Department of Chemistry, St. Joseph’s College (Autonomous), Tiruchirappalli, for fruitful discussions. The authors thank Sophisticated Analytical Instrumentation Facility, Indian Institute of Technology, Chennai for the help. References [1] J.P. Farges, Organic Conductors, Marcel Dekker, New York, 1994. [2] T. Ishiguro, K. Yamaji, Organic Superconductors, Springer, Berlin, 1990. [3] Ch. Bosshard, K. Shutter, Ph. Pretre, J. Hulliger, M. Florsheimer, P. Kaatz, P. Gunter, Organic NLOM, Gordan and Breach, London, 1995. [4] S.X. Dou, D. Josse, J. Zyss, J. Opt. Soc. Am. B 10 (1993) 1708–1715. [5] S. Yamaguchi, M. Goto, H. Takayanagi, H. Ogura, Bull. Chem. Soc. Jpn. 61 (1988) 1026–1028. [6] H. Takayanagi, M. Goto, K. Takeda, Y. Osa, J. Pharm. Soc. Jpn. 124 (2004) 751–767. [7] M.B. Mary, V. Sasirekha, V. Ramakrishnan, Spectrochim. Acta 65A (2006) 414–420. [8] T.S. Martins, J.R. Matos, G. Vicentini, P.C. Isolani, J. Therm. Anal. Calorim. 86 (2006) 351–357. [9] T. Uma Devi, N. Lawrence, R. Ramesh Babu, K. Ramamurthi, J. Cryst. Growth 10 (2008) 116–123. [10] P. Srinivasan, T. Kanagasekaran, R. Gopalakrishnan, G. Bhagavannarayana, P. Ramasamy, Cryst. Growth Des. 6 (2006) 1663–1670. [11] T. Kai, M. Goto, K. Furuhata, H. Takayanagi, Anal. Sci. 10 (1994) 359–360. [12] S.A. deVries, P. Goedtkindt, W.J. Huisman, M.J. Zwanenburg, R. Feidenhans’l, S.L. Bennett, D.M. Smilgies, A. Stierle, J.J. De Yoreo, W.J.P. van Enckevort, P. Bennema, E. Vlieg, J. Cryst. Growth 205 (1999) 202–214. [13] J. Nyvlt, R. Rychly, J. Gottfried, P. Wurzelova, J. Cryst. Growth 6 (1970) 151–162. [14] N.P. Zeitseva, L.N. Rashkovich, S.V. Bagatyareva, J. Cryst. Growth 148 (1995) 276–282. [15] G. Socrates, Infrared Characteristic Group frequencies, Wiley-Interscience, Chichester, UK, 1980. [16] V. Krishnakumar, R. Nagalakshmi, Spectrochim. Acta 64A (2006) 736–743. [17] B. Lal, K.K. Bamzai, P.N. Kotru, Mater. Chem. Phys. 78 (2003) 202–207. [18] H.H. Willard, L.L. Merritt Jr., J.A. Dean, F.A. Settle Jr., Instrumental Methods of Analysis, Sixth ed., Wadsworth Publishing Company, USA, 1986, pp. 609.