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Synthesis, growth and characterization of a novel semiorganic NLO crystal: Triglycine calcium dibromide
ARTICLE IN PRESS Journal of Crystal Growth 312 (2010) 1952–1956
Contents lists available at ScienceDirect
Journal of Crystal Growth journal homepage: www.elsevier.com/locate/jcrysgro
Synthesis, growth and characterization of a novel semiorganic NLO crystal: Triglycine calcium dibromide M. Esthaku Peter a, P. Ramasamy b,n a b
Department of Physics, Easwari Engineering College, Chennai-600089, India SSN College of Engineering, Kalavakkam-603110, India
a r t i c l e in f o
a b s t r a c t
Article history: Received 7 January 2010 Received in revised form 5 March 2010 Accepted 8 March 2010 Communicated by P. Rudolph Available online 19 March 2010
Triglycine calcium dibromide, a new semiorganic nonlinear optical material, has been grown by slow solvent evaporation technique for the first time. The size of the grown crystal is up to the dimension of 20 12 4 mm3. They were characterized by single crystal X-ray diffraction for confirming the coordination formed and FTIR spectral analysis for identifying the functional groups present in the compound. Optical behavior such as UV–vis–NIR transmission spectrum and second-harmonic generation were investigated to explore the NLO characteristics of the material. Thermal analysis was carried out to determine the melting point and the thermal stability of the grown crystal. Dielectric constant and dielectric loss measurements were carried out at different temperatures and frequencies. Mechanical studies were carried out on the as-grown crystal to find Vicker’s microhardness and yield strength. Laser damage threshold studies were also performed on the as-grown crystal. & 2010 Elsevier B.V. All rights reserved.
Keywords: A1. Characterization A1. Crystal structure A1. X-ray diffraction B2. Optical properties
1. Introduction Amino acids with inorganic compounds are promising materials for nonlinear optical applications, as the high optical nonlinearity of the purely organic amino acid tends to combine with the favorable mechanical and thermal properties of the inorganic salt. Nonlinear optical (NLO) materials are used in optical computing, optical communication, harmonic generators, medical diagnostics, frequency mixing and optical switching [1–3]. The potential development of optoelectronic devices based on the nonlinear polarization of molecular materials has aroused much recent interest [4,5]. The search for large second-order electric susceptibilities (that is, proportional to the square of an applied electric field) has concentrated on acentric organic or organometallic chromophores with an organic p-electron system coupling electron donor and acceptor groups [6]. Theoretical studies also show that hydrogen bonds can strongly enhance the nonlinear optical responses of bulk materials [7–10], which are widely existed in semiorganic crystals. Many semiorganic nonlinear optical materials have been grown by slow solvent evaporation technique, which are attracting a great deal of attention in the nonlinear optical field from application point of view. L-Hystidine Tetra-Fluoro-Borate (L-HFB) is a semiorganic nonlinear optical material whose single crystal exhibit more NLO properties than that of inorganic crystals like KDP, BBO,
n
Corresponding author. Tel.: + 91 9283105760; + 91 4427475166. E-mail addresses: [email protected], [email protected] (P. Ramasamy). 0022-0248/$ - see front matter & 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.jcrysgro.2010.03.015
LBO and many other semiorganic materials [11]. The crystal structures of many addition compounds of glycine with inorganic acids and metallic salts and also many metal complexes of glycine are known. Because of the biological and chemical importance of both glycine and calcium, a series of glycine complexes with calcium halides, viz CaC12, CaBr2 and CaI2, were crystallized and their structures are studied [12]. In this paper we are presenting growth and characterization of triglycine calcium dibromide for the first time.
2. Experimental procedure 2.1. Synthesis of the crystal Single crystals of triglycine calcium dibromide were grown from a saturated aqueous solution containing glycine (Merck) and calcium bromide (Lobo) in a molar ratio of 1:1. A necessary quantity of glycine is taken in a beaker and dissolved in Millipore water of resistivity 18.2 MO cm at room temperature until it attains saturated condition. After preparing saturated solution of glycine, the proportionate amount of calcium bromide was added little by little with continuous stirring of the solution for bringing a homogeneous mixture. Due to exothermic reaction, the temperature of the solution increases to 50 1C. The prepared solution of pH value 5.4 was filtered and allowed to evaporate slowly at ambient temperature. Colorless good optical single crystals of triglycine calcium dibromide of size 20 12 4 mm3
ARTICLE IN PRESS M. Esthaku Peter, P. Ramasamy / Journal of Crystal Growth 312 (2010) 1952–1956
1953
2.2. Single crystal X-ray diffraction X-ray diffraction studies were carried out to reveal the crystal structure of the grown crystal. The unit cell parameters obtained ˚ b¼14.752(3)A, ˚ c¼20.217(20)A, ˚ a ¼90.34(6)1, are a ¼9.095(6)A, b ¼90.46(7)1, c ¼90.07(4)1 and volume¼2713(3) A˚ 3. Triglycine calcium dibromide belongs to orthorhombic crystal structure with the space group Pbc21. When they are compared, the result is in good agreement with the reported values [12].
2.3. Fourier transform infrared spectrum Theoretical studies carried out by both Phillips–Van Vechten– Levine–Xue bond theory and chemical bonding theory of single crystal growth indicate that some important functional groups such as hydrogen bonds and ammonia group play a very important role in crystallization and nonlinear optical performances [13–15]. The Fourier transform infrared analysis of triglycine calcium dibromide single crystal was carried out between 4000 and 450 cm 1 using Perkin Elmer spectrum one FTIR spectrometer. Fig. 2 shows the resulting spectrum of that analysis, in which the functional groups present in the molecules can be identified by stretching vibration. In this spectrum the broad and strong band obtaining between 3049 and 2598 cm 1 is due to the NH3+ stretching vibration [16]. A weak asymmetrical NH3+ bending band occurs at 1627 cm 1 and a fairly strong symmetrical bending band occurs at 1522 cm 1. The carboxylate ion group COO absorbs strongly at 1591 cm 1 and more weakly at 1426 cm 1. These bands result from asymmetrical and symmetrical Cð_OÞ2 stretching respectively. This observation confirms that glycine molecules exist in zwitterionic form. The absorption at 515 cm 1 is due to the presence of oxygen–calcium bond [17]. Absorption peaks characterizing different functional groups are shown in the Table 1.
4000
3500
3000
528
515
504
670
1125 897
0
were harvested in forty days. The photograph of the as-grown single crystals of the same is shown in the Fig. 1. The title compound triglycine calcium dibromide is formed from the starting 1:1 molar ratio solution of glycine and calcium dibromide due to the more lattice energy benefit for 3:1 than 1:1 coordination of glycine and calcium dibromide. The expected chemical reaction is as follows: 3NH2CH2COOH+ 3CaBr2-[Ca(C2H5NO2)3]2 + 2Br¯ + 2CaBr2 (in solution).
1653
3049
20
1627 1591 1522 1426 14801415 1331
40
Fig.1. Photograph of as-grown triglycine calcium dibromide crystal.
595
1040
2017
2689 2598
60 3431
Transmittance %
80
1830
2386 2266
100
2500 2000 1500 Wavenumber (cm-1)
1000
500
Fig.2. FTIR spectrum of triglycine calcium dibromide crystal.
Table 1 Frequencies of the fundamental vibrations of TGCB crystal. Frequency in wavenumber (cm 1)
Assignment of vibrations [16–19]
3049 1627 1522 1591 1426 1653 1040 1331 897 670 515 504
NH3+ stretching NH3+ weak asymmetrical bending NH3+ strong symmetrical bending COO asymmetric stretch COO symmetric stretch N–H bending C–N stretching C–H bending O–H out of plane bending C–Br stretching Ca–O bond Torsional oscillations
2.4. Optical studies 2.4.1. UV–vis studies In order to reveal optical properties of the triglycine calcium dibromide single crystal, UV–vis–NIR transmission spectrum was recorded in the range of 200–1100 nm using Perkin Elmer Lamda 35 UV/vis spectrometer. The as-grown crystal of 2 mm thickness was used for recording the spectrum. Fig. 3 shows the transmittance curve, in which the lower cut off region is obtained at 240 nm. Further it is found that the maximum transmittance of the grown triglycine calcium dibromide single crystal is 52% and it has almost more than 45% transmittance from 400 to 1100 nm. 2.4.2. Laser damage threshold studies Laser damage threshold studies were made on the as-grown triglycine calcium dibromide crystal of 2 mm thickness using Nd:YAG laser of 532 nm wavelength and spot size about 140 mm in the method of multiple shots mode. A lens of focal length 8 cm was used to focus the light spot on the crystal. The pulse rate and frequency of the laser was adjusted to 7 ns and 10 pulse/s, respectively. When the laser beam of energies 10 and 20 mJ were made to be incident on the crystal for 30 s, respectively, there were no remarkable changes. But, when the beam energy was adjusted to 30 mJ for 32 s, the crystal got damaged.
ARTICLE IN PRESS 1954
M. Esthaku Peter, P. Ramasamy / Journal of Crystal Growth 312 (2010) 1952–1956
dibromide crystal. In the spectrum of thermogravimetric analysis, there is no weight loss up to 305 1C. Hence the crystal is devoid of any physically adsorbed water on it and also it is observed that there is a sudden weight loss occurring at the temperature 305 1C. The DTA response curve too shows a sharp endothermic peak at the same temperature. Further a small quantity of the fine powdered sample was taken in a microcapillary tube and heated up using Monatch melting point apparatus for confirming the thermal stability. From the thermal analysis, it is observed that triglycine calcium dibromide decomposes with melting at 305 1C temperature. Hence the grown triglycine calcium dibromide crystal is stable up to the temperature 305 1C and can be designed for device application up to the limitation of that temperature.
60
Transmittance (%)
50 40 30 20 10
2.6. Dielectric studies
0 400
200
600 800 Wavelength (nm)
1000
1200
Fig. 3. UV–vis–NIR spectrum of triglycine calcium dibromide crystal.
2
305.128
Weight %
80
0
60 -2
40
Microvolt Exo Down (μv)
TGA DTA
100
20 0
200
400
600
800
1000
-4 1200
Temperature (°C)
Dielectric studies of triglycine calcium dibromide single crystal were carried out as a function of temperature for various frequencies using Precision LCR meter AGILENT 4284A model. The as-grown transparent crystal of 2 mm thickness was selected as a sample for studying dielectric constant. Typical area of the sample for the experiment was 63 mm2. In order to make a contact with the electrodes, both the crystal surfaces were coated with fine graphite powder. The prepared sample was placed between the two electrodes and heated from room temperature to 160 1C using thermostat. Then it was annealed at thermostat itself. Capacitance and dielectric loss measurements were carried out with the sample as a function of temperature for the range of frequencies from 100 Hz to 1 MHz. Dielectric constant ‘er’ was calculated directly using the formula er ¼Ccrystal/Cair as the area of the crystal is equal to area of the electrode. Figs. 5 and 6 show the plots of dielectric constant and dielectric loss factor, respectively. The current investigations showed 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. Dielectric loss factor too corresponds to the dielectric constant plots at the given experimental frequencies ranging from 100 Hz to 1 MHz. Further it is found that dielectric constant is maximum at 160 1C temperature and tends to increase with the increase of the temperature since there is no phase change occurring below 305 1C. Moreover, due to the inertia of the
Fig. 4. TG/DTA curves of triglycine calcium dibromide crystal.
7.0 6.5
100 Hz 1 KHz 10 KHz 100 KHz 1 MHz
6.0 Dielectric Constant (εr)
2.4.3. NLO studies Since the process of second-harmonic generation (SHG) is relevant to new laser technology, and the electro-optic effect, SHG efficiency of the grown crystal was determined by Kurtz powder technique. The crystalline sample was ground into very fine powder and tightly packed in a microcapillary tube. Then it was mounted in the path of Nd:YAG laser beam of energy 1.95 mJ/pulse. When KDP crystal was used as a reference material, the transmitted beam voltage was 62 mV. But it was observed that the output voltage was 32.8 mV for the triglycine calcium dibromide crystal. Hence the SHG efficiency of triglycine calcium dibromide crystal is half of that of KDP crystal.
5.5 5.0 4.5 4.0 3.5
2.5. Thermal studies Simultaneous thermogravimetric analysis (TGA) and differential thermal analysis (DTA) were carried out between 30 and 1100 1C in nitrogen atmosphere at a heating rate of 10 1C/min using NETZSCH STA 409 C/CD TG/DTA instrument for the as-grown crystals to determine the melting point and the thermal stability of the crystal. Fig. 4 shows the resulting traces of TG/DTA for the triglycine calcium
3.0 2.5 40
60
80
100
120
140
160
Temperature (°C) Fig. 5. Dielectric constant of triglycine calcium dibromide crystal.
ARTICLE IN PRESS M. Esthaku Peter, P. Ramasamy / Journal of Crystal Growth 312 (2010) 1952–1956
1.66
0.7 100 Hz 1 KHz 10 KHz 100 KHz 1 MHz
0.6 0.5
1.64 1.62 Log d (mm)
Dielectric Loss
1955
0.4 0.3
1.60 1.58 1.56
0.2
1.54 0.1
1.52 0.0 60
40
80 100 120 Temperature (°C)
140
160
1.4
1.5
1.6 1.7 1.8 Log P (gram)
1.9
2.0
Fig. 8. Plot of log P and log d of triglycine calcium dibromide crystal.
Fig. 6. Dielectric loss of triglycine calcium dibromide crystal.
length of the indentation, work hardening coefficient or the Meyer index was calculated. Here, a is the constant for the given material. The work hardening coefficient ‘‘n’’ was calculated as 3.3 from the Fig. 8. According to Onitsch [21], if n lies between 1 and 1.6, then the grown crystal will be a harder material and it is more than 1.6 for soft materials [22,23]. Since the calculated work hardening coefficient ‘n’ is more than 1.6, the grown crystal is suggested that it comes under the category of soft material. Yield strength of the grown triglycine calcium dibromide single crystalline material was also calculated using the formula [24] sy ¼(Hv/3)(0.1)n 2, where sy is the yield strength, Hv is Vicker’s hardness and n is the logarithmic exponent. It was found to be 1.5 MPa from the relation and hence the grown triglycine calcium dibromide single crystal has low mechanical strength.
90 Vicker's Hardness (kg/mm2)
1.3
80
70
60
50
40
3. Conclusions 20
30
40
50
60 70 Load (gram)
80
90
100
110
Fig. 7. Hardness vs. load graph of triglycine calcium dibromide crystal.
molecules and ions at high frequencies, the orientation and ionic contribution of polarization are small [20]. So, the magnitude of polarization increases with the decrease of frequencies.
2.7. Mechanical studies Mechanical properties of the grown triglycine calcium dibromide crystals were studied using HMV2T Microhardness testor. The Vicker’s microhardness values were calculated from the standard formula Hv ¼1.8544 P/d2 kg/mm2, where P is the applied load and d is the mean diagonal length of the indentation. The corresponding trace is shown in the Fig. 7, from which it is observed that the hardness increases with the increase of load up to 100 g and crack occurs at that load. The maximum hardness obtained in this material is 90 kg/mm2. In order to find work hardening coefficient (n) of the grown crystal, another graph (Fig. 8) was drawn between logarithmic values of load and diagonal length of indentation. From Meyer’s law P¼adn connecting the relationship between applied load and diagonal
Semiorganic nonlinear optical crystal triglycine calcium dibromide has been grown by slow solvent evaporation technique from aqueous solution of glycine and calcium dibromide at room temperature. The grown crystal was confirmed by single crystal X-ray diffraction analysis and various functional groups present in the crystal were identified using FTIR spectrum. Optical studies reveal that the maximum transmittance under UV–vis–NIR radiation is 52% and the material has good transparency in the entire visible region. The crystal gets damaged at 30 mJ laser beam energy when it was subjected to laser damage threshold testing using multiple shots mode method. The grown crystal has NLO efficiency half of that of KDP crystal and has good thermal and mechanical stabilities. Its decomposition and melting temperature is at 305 1C suggesting that it has higher thermal stability. From the microhardness investigations made on the grown crystalline material, the crystal has maximum surface hardness about 90 kg/mm2 at 100 g load and is relatively soft material and having low yield strength.
Acknowledgement The authors are grateful to Prof. C.K. Mahadevan, Hindu College, Nagercoil for extending the facility to study dielectric properties of the sample.
ARTICLE IN PRESS 1956
M. Esthaku Peter, P. Ramasamy / Journal of Crystal Growth 312 (2010) 1952–1956
References [1] J. Lin, M.H. Lee, Z. Liu, C. Chen, C.J. Pickard, Phys. Rev. B 62 (1999) 13380. [2] P.N. Prasad, D.J. Williams, in: Introduction to Nonlinear Optical Effects in Molecules and Polymers, John-Wiley & Sons Inc., New York, 1991. [3] M. Iwai, T. Kobayashi, H. Furuya, Y. Mori, T. Sasaki, Jpn. J. Appl. Phys. 36 (1997) 76. [4] D. Eaton, Forensic Sci. 253 (1991) 281. [5] R. Dorn, D. Baums, P. Kersten, R. Regener, Adv. Mater. 4 (1992) 464. [6] W.M. Laidlaw, R.G. Denning, T. Verbiest, E. Chauchard, A. Persoons, Nature 363 (1993) 58. [7] Henryk Ratajczak Dongfeng Xue, J. Mol. Struct.: Theochem. 716 (2005) 207. [8] Henryk Ratajczak Dongfeng Xue, Chem. Phys. Lett. 371 (2003) 601. [9] Siyuan Zhang Dongfeng Xue, Chem. Phys. Lett. 301 (1999) 449. [10] Siyuan Zhang Dongfeng Xue, J. Solid State Chem. 135 (1998) 121. [11] N. Sinha, B.K. Sahas, K. Singh, N. Kumar, M.K. Singh, G.C. Gupta, B.Kumar Budakoti, Cryst. Res. Technol. 44 (2009) 167. [12] J.K. Mohana Rao, S. Natarajan, Acta Cryst. B 36 (1980) 1058.
[13] Zdzis"aw Latajka, Grzegorz Gajewski, Austin J. Barnes, Dongfeng Xue, Henryk Ratajczak, J. Mol. Struct. 928 (2009) 121. [14] Dongfeng Xue Dongli Xu, J. Cryst. Growth 310 (2008) 1385. [15] Xiue Ren, Dongli Xu, Dongfeng Xue, J. Cryst. Growth 310 (2008) 2005. [16] Robert M. Silverstein, Francis X. Webstar, in: Spectrometric Identification of Organic Compounds, John Wiley & Sons, Inc, New York, 1998. [17] Bharat B. Parekh, Mihir J. Joshi, Cryst. Res. Technol. 42 (2007) 127. [18] Y.R. Sharma, in: Elementary Organic Spectroscopy, S. Chand & Company Ltd, New Delhi, 2007. [19] John Coats, in: Interpretation of Infrared Spectra, A Practical Approach, John Wiley & Sons Ltd, Chichester, 2000. [20] Charles Kittel, in: Introduction to Solid State Physics, Wiley Eastern Limited, New Delhi, 1993. [21] E.M. Onitsch, Microscope 95 (1950) 12. [22] R. Ramesh Babu, S. Kumaresan, N. Vijayan, M. Gunasekaran, R. Gopalakrishnan, P. Kannan, P. Ramasamy, J. Cryst. Growth 256 (2003) 387. [23] N.P. Rajesh, V. Kannan, M. Ashok, K. Sivaji, P. Santhana Raghavan, P. Ramasamy, J. Cryst. Growth 262 (2004) 561. [24] J.P. Cahoon, W.H. Broughton, A.R. Kutzuk, Metall. Trans. 2 (1971) 1979.
Contents lists available at ScienceDirect
Journal of Crystal Growth journal homepage: www.elsevier.com/locate/jcrysgro
Synthesis, growth and characterization of a novel semiorganic NLO crystal: Triglycine calcium dibromide M. Esthaku Peter a, P. Ramasamy b,n a b
Department of Physics, Easwari Engineering College, Chennai-600089, India SSN College of Engineering, Kalavakkam-603110, India
a r t i c l e in f o
a b s t r a c t
Article history: Received 7 January 2010 Received in revised form 5 March 2010 Accepted 8 March 2010 Communicated by P. Rudolph Available online 19 March 2010
Triglycine calcium dibromide, a new semiorganic nonlinear optical material, has been grown by slow solvent evaporation technique for the first time. The size of the grown crystal is up to the dimension of 20 12 4 mm3. They were characterized by single crystal X-ray diffraction for confirming the coordination formed and FTIR spectral analysis for identifying the functional groups present in the compound. Optical behavior such as UV–vis–NIR transmission spectrum and second-harmonic generation were investigated to explore the NLO characteristics of the material. Thermal analysis was carried out to determine the melting point and the thermal stability of the grown crystal. Dielectric constant and dielectric loss measurements were carried out at different temperatures and frequencies. Mechanical studies were carried out on the as-grown crystal to find Vicker’s microhardness and yield strength. Laser damage threshold studies were also performed on the as-grown crystal. & 2010 Elsevier B.V. All rights reserved.
Keywords: A1. Characterization A1. Crystal structure A1. X-ray diffraction B2. Optical properties
1. Introduction Amino acids with inorganic compounds are promising materials for nonlinear optical applications, as the high optical nonlinearity of the purely organic amino acid tends to combine with the favorable mechanical and thermal properties of the inorganic salt. Nonlinear optical (NLO) materials are used in optical computing, optical communication, harmonic generators, medical diagnostics, frequency mixing and optical switching [1–3]. The potential development of optoelectronic devices based on the nonlinear polarization of molecular materials has aroused much recent interest [4,5]. The search for large second-order electric susceptibilities (that is, proportional to the square of an applied electric field) has concentrated on acentric organic or organometallic chromophores with an organic p-electron system coupling electron donor and acceptor groups [6]. Theoretical studies also show that hydrogen bonds can strongly enhance the nonlinear optical responses of bulk materials [7–10], which are widely existed in semiorganic crystals. Many semiorganic nonlinear optical materials have been grown by slow solvent evaporation technique, which are attracting a great deal of attention in the nonlinear optical field from application point of view. L-Hystidine Tetra-Fluoro-Borate (L-HFB) is a semiorganic nonlinear optical material whose single crystal exhibit more NLO properties than that of inorganic crystals like KDP, BBO,
n
Corresponding author. Tel.: + 91 9283105760; + 91 4427475166. E-mail addresses: [email protected], [email protected] (P. Ramasamy). 0022-0248/$ - see front matter & 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.jcrysgro.2010.03.015
LBO and many other semiorganic materials [11]. The crystal structures of many addition compounds of glycine with inorganic acids and metallic salts and also many metal complexes of glycine are known. Because of the biological and chemical importance of both glycine and calcium, a series of glycine complexes with calcium halides, viz CaC12, CaBr2 and CaI2, were crystallized and their structures are studied [12]. In this paper we are presenting growth and characterization of triglycine calcium dibromide for the first time.
2. Experimental procedure 2.1. Synthesis of the crystal Single crystals of triglycine calcium dibromide were grown from a saturated aqueous solution containing glycine (Merck) and calcium bromide (Lobo) in a molar ratio of 1:1. A necessary quantity of glycine is taken in a beaker and dissolved in Millipore water of resistivity 18.2 MO cm at room temperature until it attains saturated condition. After preparing saturated solution of glycine, the proportionate amount of calcium bromide was added little by little with continuous stirring of the solution for bringing a homogeneous mixture. Due to exothermic reaction, the temperature of the solution increases to 50 1C. The prepared solution of pH value 5.4 was filtered and allowed to evaporate slowly at ambient temperature. Colorless good optical single crystals of triglycine calcium dibromide of size 20 12 4 mm3
ARTICLE IN PRESS M. Esthaku Peter, P. Ramasamy / Journal of Crystal Growth 312 (2010) 1952–1956
1953
2.2. Single crystal X-ray diffraction X-ray diffraction studies were carried out to reveal the crystal structure of the grown crystal. The unit cell parameters obtained ˚ b¼14.752(3)A, ˚ c¼20.217(20)A, ˚ a ¼90.34(6)1, are a ¼9.095(6)A, b ¼90.46(7)1, c ¼90.07(4)1 and volume¼2713(3) A˚ 3. Triglycine calcium dibromide belongs to orthorhombic crystal structure with the space group Pbc21. When they are compared, the result is in good agreement with the reported values [12].
2.3. Fourier transform infrared spectrum Theoretical studies carried out by both Phillips–Van Vechten– Levine–Xue bond theory and chemical bonding theory of single crystal growth indicate that some important functional groups such as hydrogen bonds and ammonia group play a very important role in crystallization and nonlinear optical performances [13–15]. The Fourier transform infrared analysis of triglycine calcium dibromide single crystal was carried out between 4000 and 450 cm 1 using Perkin Elmer spectrum one FTIR spectrometer. Fig. 2 shows the resulting spectrum of that analysis, in which the functional groups present in the molecules can be identified by stretching vibration. In this spectrum the broad and strong band obtaining between 3049 and 2598 cm 1 is due to the NH3+ stretching vibration [16]. A weak asymmetrical NH3+ bending band occurs at 1627 cm 1 and a fairly strong symmetrical bending band occurs at 1522 cm 1. The carboxylate ion group COO absorbs strongly at 1591 cm 1 and more weakly at 1426 cm 1. These bands result from asymmetrical and symmetrical Cð_OÞ2 stretching respectively. This observation confirms that glycine molecules exist in zwitterionic form. The absorption at 515 cm 1 is due to the presence of oxygen–calcium bond [17]. Absorption peaks characterizing different functional groups are shown in the Table 1.
4000
3500
3000
528
515
504
670
1125 897
0
were harvested in forty days. The photograph of the as-grown single crystals of the same is shown in the Fig. 1. The title compound triglycine calcium dibromide is formed from the starting 1:1 molar ratio solution of glycine and calcium dibromide due to the more lattice energy benefit for 3:1 than 1:1 coordination of glycine and calcium dibromide. The expected chemical reaction is as follows: 3NH2CH2COOH+ 3CaBr2-[Ca(C2H5NO2)3]2 + 2Br¯ + 2CaBr2 (in solution).
1653
3049
20
1627 1591 1522 1426 14801415 1331
40
Fig.1. Photograph of as-grown triglycine calcium dibromide crystal.
595
1040
2017
2689 2598
60 3431
Transmittance %
80
1830
2386 2266
100
2500 2000 1500 Wavenumber (cm-1)
1000
500
Fig.2. FTIR spectrum of triglycine calcium dibromide crystal.
Table 1 Frequencies of the fundamental vibrations of TGCB crystal. Frequency in wavenumber (cm 1)
Assignment of vibrations [16–19]
3049 1627 1522 1591 1426 1653 1040 1331 897 670 515 504
NH3+ stretching NH3+ weak asymmetrical bending NH3+ strong symmetrical bending COO asymmetric stretch COO symmetric stretch N–H bending C–N stretching C–H bending O–H out of plane bending C–Br stretching Ca–O bond Torsional oscillations
2.4. Optical studies 2.4.1. UV–vis studies In order to reveal optical properties of the triglycine calcium dibromide single crystal, UV–vis–NIR transmission spectrum was recorded in the range of 200–1100 nm using Perkin Elmer Lamda 35 UV/vis spectrometer. The as-grown crystal of 2 mm thickness was used for recording the spectrum. Fig. 3 shows the transmittance curve, in which the lower cut off region is obtained at 240 nm. Further it is found that the maximum transmittance of the grown triglycine calcium dibromide single crystal is 52% and it has almost more than 45% transmittance from 400 to 1100 nm. 2.4.2. Laser damage threshold studies Laser damage threshold studies were made on the as-grown triglycine calcium dibromide crystal of 2 mm thickness using Nd:YAG laser of 532 nm wavelength and spot size about 140 mm in the method of multiple shots mode. A lens of focal length 8 cm was used to focus the light spot on the crystal. The pulse rate and frequency of the laser was adjusted to 7 ns and 10 pulse/s, respectively. When the laser beam of energies 10 and 20 mJ were made to be incident on the crystal for 30 s, respectively, there were no remarkable changes. But, when the beam energy was adjusted to 30 mJ for 32 s, the crystal got damaged.
ARTICLE IN PRESS 1954
M. Esthaku Peter, P. Ramasamy / Journal of Crystal Growth 312 (2010) 1952–1956
dibromide crystal. In the spectrum of thermogravimetric analysis, there is no weight loss up to 305 1C. Hence the crystal is devoid of any physically adsorbed water on it and also it is observed that there is a sudden weight loss occurring at the temperature 305 1C. The DTA response curve too shows a sharp endothermic peak at the same temperature. Further a small quantity of the fine powdered sample was taken in a microcapillary tube and heated up using Monatch melting point apparatus for confirming the thermal stability. From the thermal analysis, it is observed that triglycine calcium dibromide decomposes with melting at 305 1C temperature. Hence the grown triglycine calcium dibromide crystal is stable up to the temperature 305 1C and can be designed for device application up to the limitation of that temperature.
60
Transmittance (%)
50 40 30 20 10
2.6. Dielectric studies
0 400
200
600 800 Wavelength (nm)
1000
1200
Fig. 3. UV–vis–NIR spectrum of triglycine calcium dibromide crystal.
2
305.128
Weight %
80
0
60 -2
40
Microvolt Exo Down (μv)
TGA DTA
100
20 0
200
400
600
800
1000
-4 1200
Temperature (°C)
Dielectric studies of triglycine calcium dibromide single crystal were carried out as a function of temperature for various frequencies using Precision LCR meter AGILENT 4284A model. The as-grown transparent crystal of 2 mm thickness was selected as a sample for studying dielectric constant. Typical area of the sample for the experiment was 63 mm2. In order to make a contact with the electrodes, both the crystal surfaces were coated with fine graphite powder. The prepared sample was placed between the two electrodes and heated from room temperature to 160 1C using thermostat. Then it was annealed at thermostat itself. Capacitance and dielectric loss measurements were carried out with the sample as a function of temperature for the range of frequencies from 100 Hz to 1 MHz. Dielectric constant ‘er’ was calculated directly using the formula er ¼Ccrystal/Cair as the area of the crystal is equal to area of the electrode. Figs. 5 and 6 show the plots of dielectric constant and dielectric loss factor, respectively. The current investigations showed 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. Dielectric loss factor too corresponds to the dielectric constant plots at the given experimental frequencies ranging from 100 Hz to 1 MHz. Further it is found that dielectric constant is maximum at 160 1C temperature and tends to increase with the increase of the temperature since there is no phase change occurring below 305 1C. Moreover, due to the inertia of the
Fig. 4. TG/DTA curves of triglycine calcium dibromide crystal.
7.0 6.5
100 Hz 1 KHz 10 KHz 100 KHz 1 MHz
6.0 Dielectric Constant (εr)
2.4.3. NLO studies Since the process of second-harmonic generation (SHG) is relevant to new laser technology, and the electro-optic effect, SHG efficiency of the grown crystal was determined by Kurtz powder technique. The crystalline sample was ground into very fine powder and tightly packed in a microcapillary tube. Then it was mounted in the path of Nd:YAG laser beam of energy 1.95 mJ/pulse. When KDP crystal was used as a reference material, the transmitted beam voltage was 62 mV. But it was observed that the output voltage was 32.8 mV for the triglycine calcium dibromide crystal. Hence the SHG efficiency of triglycine calcium dibromide crystal is half of that of KDP crystal.
5.5 5.0 4.5 4.0 3.5
2.5. Thermal studies Simultaneous thermogravimetric analysis (TGA) and differential thermal analysis (DTA) were carried out between 30 and 1100 1C in nitrogen atmosphere at a heating rate of 10 1C/min using NETZSCH STA 409 C/CD TG/DTA instrument for the as-grown crystals to determine the melting point and the thermal stability of the crystal. Fig. 4 shows the resulting traces of TG/DTA for the triglycine calcium
3.0 2.5 40
60
80
100
120
140
160
Temperature (°C) Fig. 5. Dielectric constant of triglycine calcium dibromide crystal.
ARTICLE IN PRESS M. Esthaku Peter, P. Ramasamy / Journal of Crystal Growth 312 (2010) 1952–1956
1.66
0.7 100 Hz 1 KHz 10 KHz 100 KHz 1 MHz
0.6 0.5
1.64 1.62 Log d (mm)
Dielectric Loss
1955
0.4 0.3
1.60 1.58 1.56
0.2
1.54 0.1
1.52 0.0 60
40
80 100 120 Temperature (°C)
140
160
1.4
1.5
1.6 1.7 1.8 Log P (gram)
1.9
2.0
Fig. 8. Plot of log P and log d of triglycine calcium dibromide crystal.
Fig. 6. Dielectric loss of triglycine calcium dibromide crystal.
length of the indentation, work hardening coefficient or the Meyer index was calculated. Here, a is the constant for the given material. The work hardening coefficient ‘‘n’’ was calculated as 3.3 from the Fig. 8. According to Onitsch [21], if n lies between 1 and 1.6, then the grown crystal will be a harder material and it is more than 1.6 for soft materials [22,23]. Since the calculated work hardening coefficient ‘n’ is more than 1.6, the grown crystal is suggested that it comes under the category of soft material. Yield strength of the grown triglycine calcium dibromide single crystalline material was also calculated using the formula [24] sy ¼(Hv/3)(0.1)n 2, where sy is the yield strength, Hv is Vicker’s hardness and n is the logarithmic exponent. It was found to be 1.5 MPa from the relation and hence the grown triglycine calcium dibromide single crystal has low mechanical strength.
90 Vicker's Hardness (kg/mm2)
1.3
80
70
60
50
40
3. Conclusions 20
30
40
50
60 70 Load (gram)
80
90
100
110
Fig. 7. Hardness vs. load graph of triglycine calcium dibromide crystal.
molecules and ions at high frequencies, the orientation and ionic contribution of polarization are small [20]. So, the magnitude of polarization increases with the decrease of frequencies.
2.7. Mechanical studies Mechanical properties of the grown triglycine calcium dibromide crystals were studied using HMV2T Microhardness testor. The Vicker’s microhardness values were calculated from the standard formula Hv ¼1.8544 P/d2 kg/mm2, where P is the applied load and d is the mean diagonal length of the indentation. The corresponding trace is shown in the Fig. 7, from which it is observed that the hardness increases with the increase of load up to 100 g and crack occurs at that load. The maximum hardness obtained in this material is 90 kg/mm2. In order to find work hardening coefficient (n) of the grown crystal, another graph (Fig. 8) was drawn between logarithmic values of load and diagonal length of indentation. From Meyer’s law P¼adn connecting the relationship between applied load and diagonal
Semiorganic nonlinear optical crystal triglycine calcium dibromide has been grown by slow solvent evaporation technique from aqueous solution of glycine and calcium dibromide at room temperature. The grown crystal was confirmed by single crystal X-ray diffraction analysis and various functional groups present in the crystal were identified using FTIR spectrum. Optical studies reveal that the maximum transmittance under UV–vis–NIR radiation is 52% and the material has good transparency in the entire visible region. The crystal gets damaged at 30 mJ laser beam energy when it was subjected to laser damage threshold testing using multiple shots mode method. The grown crystal has NLO efficiency half of that of KDP crystal and has good thermal and mechanical stabilities. Its decomposition and melting temperature is at 305 1C suggesting that it has higher thermal stability. From the microhardness investigations made on the grown crystalline material, the crystal has maximum surface hardness about 90 kg/mm2 at 100 g load and is relatively soft material and having low yield strength.
Acknowledgement The authors are grateful to Prof. C.K. Mahadevan, Hindu College, Nagercoil for extending the facility to study dielectric properties of the sample.
ARTICLE IN PRESS 1956
M. Esthaku Peter, P. Ramasamy / Journal of Crystal Growth 312 (2010) 1952–1956
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