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Crystal growth, structural, thermal and mechanical behavior of l -arginine 4-nitrophenolate 4-nitrophenol dihydrate (LAPP) single crystals
Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 133 (2014) 396–402
Contents lists available at ScienceDirect
Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy journal homepage: www.elsevier.com/locate/saa
Crystal growth, structural, thermal and mechanical behavior of L-arginine 4-nitrophenolate 4-nitrophenol dihydrate (LAPP) single crystals M. Mahadevan a,b, K. Ramachandran b,⇑, P. Anandan c,d, M. Arivanandhan c, G. Bhagavannarayana e, Y. Hayakawa c a
Department of Physics, Adhiparasakthi Engineering College, Melmaruvathur 603319, India Department of Physics, SRM University, Vadapalani Campus, Chennai 600026, India c Research Institute of Electronics, Shizuoka University, Johoku, Naka-Ku, Hamamatsu 432-8011, Japan d Department of Physics, Thiruvalluvar College of Engineering and Technology, Vandavasi 604505, India e Materials Characterization Division, National Physical Laboratory, New Delhi 110012, India b
h i g h l i g h t s
g r a p h i c a l a b s t r a c t
Single crystals of LAPP were grown by
SEST method. Powder X-ray diffraction and Proton
NMR analyses were reported. Crystalline perfection was studied by
HRXRD curve. Thermal and mechanical behaviors
were studied.
a r t i c l e
i n f o
Article history: Received 20 March 2014 Received in revised form 12 May 2014 Accepted 25 May 2014 Available online 12 June 2014 Keywords: Crystal growth Proton NMR Thermal analysis Hardness Nonlinear optical material
a b s t r a c t Single crystals of L-arginine 4-nitrophenolate 4-nitrophenol dihydrate (LAPP) have been grown successfully from the solution of L-arginine and 4-nitrophenol. Slow evaporation of solvent technique was adopted to grow the bulk single crystals. Single crystal X-ray diffraction analysis confirms the grown crystal has monoclinic crystal system with space group of P21. Powder X-ray diffraction analysis shows the good crystalline nature. The crystalline perfection of the grown single crystals was analyzed by HRXRD by employing a multicrystal X-ray diffractometer. The functional groups were identified from proton NMR spectroscopic analysis. Linear and nonlinear optical properties were determined by UV–Vis spectrophotometer and Kurtz powder technique respectively. It is found that the grown crystal has no absorption in the green wavelength region and the SHG efficiency was found to be 2.66 times that of the standard KDP. The Thermal stability of the crystal was found by obtaining TG/DTA curve. The mechanical behavior of the grown crystal has been studied by Vicker’s microhardness method. Ó 2014 Elsevier B.V. All rights reserved.
Introduction ⇑ Corresponding author. Mobile: +91 9790834728. E-mail address: [email protected] (K. Ramachandran). http://dx.doi.org/10.1016/j.saa.2014.05.087 1386-1425/Ó 2014 Elsevier B.V. All rights reserved.
Amino acids are potential candidates for growth of nonlinear optical (NLO) single crystal. Since it has carboxyl group and amine
M. Mahadevan et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 133 (2014) 396–402
group, these can form zwitterions when it is dissolved in its respective solvents and capable of forming salt with other counter ions of either organic or inorganic. There are numerous amino acid based NLO crystals have been reported and their properties were studied [1–3]. L-arginine is one such important amino acid which gave large numbers of derivatives with its inorganic as well as organic compounds [4–6]. After the successful investigations carried out on the formation of NLO crystals of 4-nitrophenol derivative with its inorganic counterpart, 4-nitrophenols derivative with amino acids were investigated and found to have great importance of second harmonic generation application [7,8]. For the first time, L-argininium-4-nitro phenolate monohydrate (LARP) was synthesized and the crystal structure and nonlinear optical properties were reported by Srinivasan et al. [9]. Subsequently, L-arginine 4-nitrophenolate 4-nitrophenol dihydrate (LAPP) was grown as a single crystal and crystal structure and NLO properties were studied and compared with theoretical calculation [10]. However, properties like thermal, mechanical and other structural characterization like powder X-ray diffraction study, high resolution X-ray diffraction (HRXRD) studies were left unstudied. These properties and characterization should be precisely investigated in order to find the suitability of the crystal for its device fabrication. In the present investigation, single crystals have been grown from the super saturated solution by slow evaporation of solvent technique (SEST) using a suspended seed. The grown crystal has been confirmed by various characterizations and crystalline quality was studied by powder X-ray diffraction and HRXRD analyses. The structural, thermal, mechanical and optical properties have been studied by suitable methods and detailed report has been presented in this paper. Materials and methods
397
of the grown crystal. The crystalline perfection of the grown single crystals was characterized by HRXRD by employing a multicrystal X-ray diffractometer developed at NPL [12] as per the procedure described earlier [13]. Growth of single crystals Seed crystals were obtained from the super saturated solution at constant temperature (30 °C) by SEST method. Due to slow evaporation of the solvent, spontaneous nucleation occurs and these are grown into crystals of few mm3 size. Crystals with good habitual faces, transparency and less number of visible defects are selected as seed for growing bulk single crystals. A seed crystal was placed at the bottom of the beaker containing the super saturated solution and another seed crystal was suspended in the super saturated solution contained beaker. Both the beakers were kept in a constant temperature bath with accuracy of ±0.01 °C to maintain the growth solution at 30 °C. The beakers were covered separately by a perforated thin transparent sheet in order to enable the slow solvent evaporation. After a period of 30 days the seed crystals have grown to the critical dimension and the grown crystals were harvested carefully from the solution. The as grown crystals are shown Fig. 1. The crystal grown from the bottom of the beaker has the dimension of 20 20 3 mm3 (Fig. 1a) and the later has 10 8 8 mm3 (Fig. 1b). The crystals grown at the bottom of the beaker was observed to be flat which is due to the restricted exposure of the growing seed to its mother solution at the bottom side of the crystal. It was observed that the growth rate along ‘a’ and ‘b’ axes are higher than that of ‘c’ axis for the crystal grown at the bottom of beaker. On the other hand, the crystal grown by suspended seed method has approximately same growth rate along all the crystallographic direction.
Synthesis Results and discussion The as-purchased 4-nitro phenol (99% Pure) and L-arginine (Merck Product) were used as starting materials to prepare the solution for the synthesis of title compound. L-arginine and 4-nitro phenol were taken in equimolar ratio and dissolved one by one in excess of water by continuous stirring. After the solution became homogeneous, it was filtered and transferred to another beaker, then allowed to evaporate the excess water at bellow 40 °C. Yellow color crystalline salt was obtained at the bottom of the beaker. It was dried and purified by re-crystallization process. The seed crystals were obtained by SEST method from a super saturated solution prepared from the synthesized salt. These seed crystals were used to study the various characterization of the present investigation. Characterization techniques Single crystal X-ray diffraction analysis was performed by using ENRAF NONIUS diffractometer with Mo Ka (k = 0.7107 Å) radiation and the data was collected at 20 °C. Good quality seed crystals were ground as fine powder and the powder X-ray diffraction analysis was carried out to find the crystalline nature of the grown crystal using an X’PERT PRO diffractometer system. The molecular structure of the grown crystal was confirmed by Proton NMR spectral analysis by using JEOL GSX 400 instrument. Linear optical properties of the crystals were studied by UV–Vis spectrophotometer and nonlinear optical properties were tested by Kurtz Perry powder technique [11]. Thermo-gravimetric (TG) and differential thermal analysis (DTA) for the crystal samples were carried out in nitrogen atmosphere by EXSTAR TG/DTA 6200thermal analyzer to study the thermal properties of the as-grown crystal. Vicker’s microhardness test was carried out to find the mechanical strength
Single crystal X-ray diffraction study Single crystal X-ray diffraction analysis was carried out to identify the grown crystal on the single crystal with size of 0.35 0.25 0.25 mm3. The lattice parameters were determined and the crystal structure was solved by direct method and refined by full-matrix least-squares method. The determined lattice parameters are tabulated and compared with literature in Table 1, which confirm that the grown crystal is L-arginine 4-nitrophenolate 4-nitrophenol dihydrate (LAPP) as it coincides with the reported values [10]. It is observed that the grown crystal belonged to monoclinic crystal system with P21 space group. The molecular configuration and crystal packing diagram projected along ‘a’ axis are shown in Figs. 2 and 3, respectively. Powder X-ray diffraction study The grown crystals were made as fine powder and subjected to powder X-ray diffraction analyses. The diffraction data were collected at 298 K between 0° and 60° of diffraction angles with the source wave length of 1.5460 Å. The step size of 2h and the scan step time were fixed as 0.017° and 10.33 s respectively. The diffraction pattern contains various reflections corresponding to various crystallographic planes as shown in Fig. 4. The observed sharp peeks of the pattern ensure the good crystalline nature of the samples. Miller indices were calculated for different 2h and d spacing by the simulation from the lattice parameters obtained in single crystal X-ray diffraction study and the powder diffraction pattern was indexed.
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M. Mahadevan et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 133 (2014) 396–402
Fig. 1. Photographs of as-grown single crystals of LAPP (a) grown from the bottom of the beaker (b) grown from the suspended seed.
Table 1 Single crystal X-ray diffraction data in comparison with literature. Parameter
Present study
[10]
[9]
Name of the crystal Crystal system Space group Unit cell dimension a b c b Cell volume
LAPP Monoclinic P21
LAPP Monoclinic P21
LARP Orthorhombic P212121
7.8570(5) Å 10.3656 (6) Å 13.8120 (7) Å 98.177 (2) deg 1113.45 (11) Å3
7.8669 (5) Å 10.3764 (2) Å 13.8301 (2) Å 98.2128 (9) deg 1117.37 (3) Å3
5.1254(2) Å 9.3683 (3) Å 31.5145 (10) Å 90 deg 1513.21 (9) Å3
Proton NMR analysis Nuclear magnetic resonance (NMR) spectroscopy is an important tool to identify the synthesized compound. The purified LAPP sample was subjected to proton NMR spectral study by using deuterium oxide solvent and the recorded spectrum is shown in Fig. 5. The hydrogen atoms present in the various chemical environment give their signal at different chemical shift (d) position. Since the compound contains several functional groups hydrogen atoms in L-arginine and 4-nitrophenol, the spectrum pronounced several signals at different d position. The ortho and meta hydrogens present in the nitro phenol can see themselves as aligned (Parallel) or opposed (antiparallel) and come to resonance twice. Hence the ortho (2,6) and Meta (3,5) hydrogens appeared as doublet and gave their signals at 6.67 and 8.03 ppm respectively [14,15]. The CH and
CH2 groups present in the L-arginine molecules have given their signals at different d value according to their shielding nature. The CH proton gave its signal at 3.69 ppm. The protons associated with aliphatic CH2 (b, c and d as designated in the figure) in the arginine molecule have given their signals at 1.83, 1.68 and 3.15 ppm respectively [16]. The multiple splitting observed in these signals is due to the presence of amine groups in the arginine molecules. High resolution X-ray diffraction study (HRXRD) Fig. 6 shows the high resolution X-ray diffraction curve recorded using Mo Ka1 radiation for a typical LAPP single crystal specimen. On close observation one can realize that the curve is not a single peak. On deconvolution of the diffraction curve, it is clear that the curve contains three additional peaks. The solid line (convoluted curve) is well fitted with the experimental points represented by the filled circles, which are 132, 200 and 358 arc s away from the main peak (highest intensity peak). These three additional peaks correspond to three internal structural low angle (tilt angle >1 arc min but <1 deg.) boundaries [17] whose tilt angles (Tilt angle may be defined as the misorientation angle between the two crystalline regions on both sides of the structural grain boundary) are 132, 200 and 158 arc s from their adjoining regions. These internal structural low angle boundaries are mainly because of the agglomerated dislocations and the self generated strains by such defects [18]. The FWHM (full width at half maximum) of the main peak and the three low angle boundaries are respectively
Fig. 2. Molecular configuration and the atomic numbering scheme of LAPP crystal.
M. Mahadevan et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 133 (2014) 396–402
399
Fig. 3. Crystal packing diagram, projected along a axis.
168 and 54, 150 and 118 arc sate relatively low values of FWHM of the grains and low angular spread of the DC (1000 arc s = 17 arc min) depicts that the crystalline perfection is moderate. It may be mentioned here that such low angle boundaries could be detected in the diffraction curve only because of the highresolution of the diffractometer used in the present investigations. The influence of such defects may not influence much on the physical properties. However, a quantitative analysis of such unavoidable defects is of great importance, particularly in case of phase matching applications in nonlinear optical crystals as described in our recent article [19].
18000 (211) (201)
14000 12000 10000
(220) (13−2)
(142)
2000
(133)
(002)
4000
(200)
(110)
6000
(120) (121)
8000
(111) (020) (102)
Intensity (counts)
16000
Linear and nonlinear optical property studies
0 10
20
30
40
50
2θ (deg) Fig. 4. Powder X-ray diffraction pattern of LAPP.
60
It is imperative to have good optical transparency in an NLO crystal in the green visible region. Optical absorption spectrum for the grown crystal was recorded in the range between 180 to 1100 nm and is shown in Fig. 7. The grown crystal have UV cutoff
Fig. 5. Proton NMR spectrum of LAPP.
400
M. Mahadevan et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 133 (2014) 396–402
Diffracted X-ray intensity [c/s]
LAPP 300
200"
132"
158"
MoKα1 (+,−,−,+)
200
168" 100
0 -400
118"
54"
-200
150"
0
200
400
Glancing angle [arc s] Fig. 6. High resolution X-ray diffraction curve of LAPP crystal.
5
Absorbance (a.u.)
4
below 500 nm and above which the grown crystal is appreciably less absorbance in the visible to near IR range of the spectrum. So, the grown crystal is useful for optoelectronic applications and the second harmonic generation (frequency conversion) from the Nd: YAG Laser. The nonlinear optical property was studied by SHG efficiency of LAPP crystalline samples and it was found by Kurtz and Perry powder technique. The finely ground powder samples of the grown crystals was filled in quarts capillary tube and subjected to this test. The second harmonic output was generated by irradiating the powder samples by a pulsed laser beam of Nd: YAG laser with a pulse width of 8 ns with the energy of 2.1 mJ/pulse. The ability of the energy (frequency) conversion was confirmed by the emission of green light from the powder sample. KDP and Urea samples were used as reference materials and output power intensity of the samples. The output intensities for the samples of LAPP, KDP and Urea were converted as voltage by a photomultiplier tube and the measured output voltages were 68, 25.6 and 82 mV, respectively. Hence, the grown crystal has SHG efficiency of 2.66 times that of KDP and 0.83 time that of Urea. On the other hand, it was observed that the SHG efficiencies of L-arginine and 4-nitrophenol are much lesser than that of the crystalline powder of LAPP and are measured as 0.17 and 0.14 time that of KDP respectively. Thermal analysis
3
2
1
200
400
600
800
1000
Wavelength (nm) Fig. 7. UV–Vis–NIR spectrum for the grown crystal of LAPP.
1200
Thermal analyses were performed on the powder sample of grown crystal to study the thermal stability and melting point. The thermo gravimetric analysis (TGA) and differential thermal analysis curves of LAPP were obtained in the range between room temperature (28 °C) and 800 °C at a heating rate of 10 °C per min. The experiment was performed in nitrogen atmosphere and the TG & DTA plots are shown in Fig. 8. TGA curve shows a weight loss occurred in two stages and the same near100 °C is assigned to loss of water. This weight loss due to water is also associated with melting of the sample, which is clearly observed in the DTA curve as an endothermic transition occurred at 110 °C. At this temperature, 4-nitrophenol and water molecules were dissociated from the compound and the 4-nitrophenol started to melt as its melting point is nearly 110 °C. The second stage of TG curve shows nearly
Fig. 8. Thermogravimetric (TG) and differential thermal analysis (DTA) curve of LAPP crystal.
M. Mahadevan et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 133 (2014) 396–402
22 21
HV (Kg/mm2)
20 19 18 17 16 15 14 13 0
20
40
60
80
100
401
the crystal because of the inability of these lower loads to soften the bonding in the molecules. Beyond 100 g of load it was observed that the cracks were formed due to release of internal stress generated locally by indentation and the hardness values decreased further [20]. The Mayer’s index was calculated from the Mayer’s equation log P = log k + n log d, which is the relation between the applied load and indentation diagonal length, where k is the material constant and n is the Mayer’s index and it is also called as work hardening coefficient. The value of ‘n’ has been found by plotting a graph between log d and log P as shown in Fig. 10. The slope of the graph gives the value of n and it is found to be 1.69. According to Onitsch and Hanneman, ‘n’ should lie between 1 and 1.6 for moderately hard materials and above 1.6 for softer material category. Hence, the grown crystal is a soft material due to which the hardness values decreased when the load was increased [21].
Load (g) Fig. 9. Vicker’s hardness profile as a function of applied load of LAPP crystal along (0 0 1) plane.
Log P vs Log d Linear Fit of Log P
2.0
Log P
1.8
1.6
1.4
1.2
y = a + b*x Equation Adj. R-Square 0.99022 Log P Log P
1.0
Value Standard Error Intercept -1.45321 0.17187 Slope 1.6877 0.09668
Conclusions Good quality single crystals of LAPP have been grown by SEST method. The structural properties of the grown crystals were analyzed by X-ray diffraction and NMR methods. HRXRD curve was obtained and the grown crystal has a moderate crystalline perfection which may not affect the device performance. Linear and nonlinear optical property studies ensured that the grown crystal is useful for the device fabrication. It was found that the grown crystal has 478 nm cut off wavelength and SHG efficiency of 2.66 times that of KDP. Thermal stability of the grown crystals was studied by obtaining TG/DTA curves and found that the crystal is thermally stable up to 110 °C. By Vicker’s microhardness test, the crystal was found to be a soft material and the hardening coefficient was determined as 1.69. Hence from this investigation, the grown crystal was found to be well suitable for the nonlinear optical device. Acknowledgements
1.4
1.5
1.6
1.7
1.8
1.9
2.0
2.1
Log d Fig. 10. Plot of log d vs. log P for LAPP crystal along (0 0 1) plane.
70% of weight loss due to the decomposition of sample which is associated by an exothermic transition as observed at 253 °C in DTA curve. The remaining 18% of the sample was left in the crucible as a residual carbon. From this study, it is observed that the material has water molecules in its lattice and it has thermal stability till its melting point 110 °C. Hardness study Since the hardness of the crystals play vital role in the device fabrication, the material resistance with respect to localized plastic deformation should be studied. Vickers’ microhardness test was carried out on (0 0 1) plane of the grown crystal and the hardness number was calculated by the relation Hv = 1.8544 P/d2 kg/mm2, where Hv is the Vicker’s hardness number, P is the applied load in kilogram, and d is the average diagonal length of the impression corresponding to the load in mm. Before indentations were made, the crystal was lapped and cleaned to avoid the surface defects which may influence the hardness value. Fig. 9 shows the variation of hardness numbers with respect to load which evidenced that the microhardness value of LAPP has decreased when the load is increased due to normal indentation size effect (Indentation size is inversely proportional to the hardness of the material). It is observed that the hardness values are higher at lower loads for
The authors acknowledge Prof. P.K. Das, IISc Bangalore for SHG facility, NMR research center, Bangalore, IIT Madras for single crystal X-ray diffraction facility and Prof. R. Jayavel, Crystal growth center for his help in characterization and discussion. One of the authors (M.M) is thankful to Sakthi Dr. G.B. Senthil Kumar, Correspondent, Athiparasakthi Engineering College, Melmaruvathur, India for his constant motivation and support. References [1] A.M. Petrosyan, R.P. Sukiasyan, H.A. Karapetyan, S.S. Terzyan, R.S. Feigelson, J. Cryst. Growth 213 (2000) 103–111. [2] R.P. Sukiasyan, A.A. Karapetyan, A.M. Petrosyan, J. Mol. Struct. 888 (2008) 230– 237. [3] G. Ramesh Kumar, S. Gokul Raj, V. Mathivanan, M. Kovendhan, ThennetiRaghavalu, R. Mohan, Opt. Mater. 30 (2008) 1405–1409. [4] P. Anandan, T. Saravanan, G. Parthipan, R. Mohan Kumar, G. Bhagavannarayana, G. Ravi, R. Jayavel, Solid State Sci. 139 (2011) 915–922. [5] L. Wang, G.H. Zhang, X.T. Liu, L.N. Wang, X.Q. Wang, L.Y. Zhu, D. Xu, J. Mol. Struct. 1058 (2014) 155–162. [6] T. Baraniraj, P. Philominathan, Spectrochim. Acta A 75 (2010) 74–76. [7] M. Prakash, M. Lydia Caroline, D. Geetha, Spectrochim. Acta A 108 (2013) 32– 37. [8] B. Dhanalakshmi, S. Ponnusamy, C. Muthamizhchelvan, J. Cryst. Growth 313 (2010) 30–36. [9] P. Srinivasan, Y. Vidyalakshmi, R. Gopalakrishnan, Cryst. Growth Des. 8 (2008) 2329–2334. [10] L.N. Wang, X.Q. Wang, G.H. Zhang, X.T. Liu, Z.H. Sun, G.H. Sun, L. Wang, W.T. Yu, D. Xu, J. Cryst. Growth 327 (2011) 133–139. [11] S.K. Kurtz, T.T. Perry, J. Appl. Phys. 39 (1968) 3798. [12] Krishan Lal, G. Bhagavannarayana, J. Appl. Cryst. 22 (1989) 209–215. [13] P. Anandan, G. Parthipan, T. Saravanan, R. Mohan Kumar, G. Bhagavannarayana, R. Jayavel, Phys. B: Condensed Matter. 405 (2010) 4951– 4956.
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[14] P. Anandan, S. Vetrivel, R. Jayavel, C. Vedhi, G. Ravi, G. Bhagavannarayana, J. Phys. Chem. Solids 73 (2012) 1296–1301. [15] R.J. Abraham, M. Mobli, Magn. Reson. Chem. 45 (2007) 865–877. [16] R.M. Silverstein, G. Clayton Basseler, T.C. Morrill, Spectrometric Identification of Organic Compounds, V Ed., John Wiley & Sons Inc., New York, 1998. [17] G. Bhagavannarayana, R.V. Ananthamurthy, G.C. Budakoti, B. Kumar, K.S. Bartwal, J. Appl. Cryst. 38 (2005) 768–771.
[18] G. Bhagavannarayana, P. Rajesh, P. Ramasamy, J. Appl. Crystallogr. 43 (2010) 1372–1376. [19] G. Bhagavannarayana, B. Riscob, Mohd. Shakir, Mater. Chem. Phys. 126 (2011) 20–23. [20] P. Anandan, R. Jayavel, T. Saravanan, G. Parthpan, C. Vedhi, R. Mohan Kumar, Opt. Mater. 34 (2012) 1225–1230. [21] E.M. Onitsch, Mikroskopie 95 (1956) 12.
Contents lists available at ScienceDirect
Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy journal homepage: www.elsevier.com/locate/saa
Crystal growth, structural, thermal and mechanical behavior of L-arginine 4-nitrophenolate 4-nitrophenol dihydrate (LAPP) single crystals M. Mahadevan a,b, K. Ramachandran b,⇑, P. Anandan c,d, M. Arivanandhan c, G. Bhagavannarayana e, Y. Hayakawa c a
Department of Physics, Adhiparasakthi Engineering College, Melmaruvathur 603319, India Department of Physics, SRM University, Vadapalani Campus, Chennai 600026, India c Research Institute of Electronics, Shizuoka University, Johoku, Naka-Ku, Hamamatsu 432-8011, Japan d Department of Physics, Thiruvalluvar College of Engineering and Technology, Vandavasi 604505, India e Materials Characterization Division, National Physical Laboratory, New Delhi 110012, India b
h i g h l i g h t s
g r a p h i c a l a b s t r a c t
Single crystals of LAPP were grown by
SEST method. Powder X-ray diffraction and Proton
NMR analyses were reported. Crystalline perfection was studied by
HRXRD curve. Thermal and mechanical behaviors
were studied.
a r t i c l e
i n f o
Article history: Received 20 March 2014 Received in revised form 12 May 2014 Accepted 25 May 2014 Available online 12 June 2014 Keywords: Crystal growth Proton NMR Thermal analysis Hardness Nonlinear optical material
a b s t r a c t Single crystals of L-arginine 4-nitrophenolate 4-nitrophenol dihydrate (LAPP) have been grown successfully from the solution of L-arginine and 4-nitrophenol. Slow evaporation of solvent technique was adopted to grow the bulk single crystals. Single crystal X-ray diffraction analysis confirms the grown crystal has monoclinic crystal system with space group of P21. Powder X-ray diffraction analysis shows the good crystalline nature. The crystalline perfection of the grown single crystals was analyzed by HRXRD by employing a multicrystal X-ray diffractometer. The functional groups were identified from proton NMR spectroscopic analysis. Linear and nonlinear optical properties were determined by UV–Vis spectrophotometer and Kurtz powder technique respectively. It is found that the grown crystal has no absorption in the green wavelength region and the SHG efficiency was found to be 2.66 times that of the standard KDP. The Thermal stability of the crystal was found by obtaining TG/DTA curve. The mechanical behavior of the grown crystal has been studied by Vicker’s microhardness method. Ó 2014 Elsevier B.V. All rights reserved.
Introduction ⇑ Corresponding author. Mobile: +91 9790834728. E-mail address: [email protected] (K. Ramachandran). http://dx.doi.org/10.1016/j.saa.2014.05.087 1386-1425/Ó 2014 Elsevier B.V. All rights reserved.
Amino acids are potential candidates for growth of nonlinear optical (NLO) single crystal. Since it has carboxyl group and amine
M. Mahadevan et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 133 (2014) 396–402
group, these can form zwitterions when it is dissolved in its respective solvents and capable of forming salt with other counter ions of either organic or inorganic. There are numerous amino acid based NLO crystals have been reported and their properties were studied [1–3]. L-arginine is one such important amino acid which gave large numbers of derivatives with its inorganic as well as organic compounds [4–6]. After the successful investigations carried out on the formation of NLO crystals of 4-nitrophenol derivative with its inorganic counterpart, 4-nitrophenols derivative with amino acids were investigated and found to have great importance of second harmonic generation application [7,8]. For the first time, L-argininium-4-nitro phenolate monohydrate (LARP) was synthesized and the crystal structure and nonlinear optical properties were reported by Srinivasan et al. [9]. Subsequently, L-arginine 4-nitrophenolate 4-nitrophenol dihydrate (LAPP) was grown as a single crystal and crystal structure and NLO properties were studied and compared with theoretical calculation [10]. However, properties like thermal, mechanical and other structural characterization like powder X-ray diffraction study, high resolution X-ray diffraction (HRXRD) studies were left unstudied. These properties and characterization should be precisely investigated in order to find the suitability of the crystal for its device fabrication. In the present investigation, single crystals have been grown from the super saturated solution by slow evaporation of solvent technique (SEST) using a suspended seed. The grown crystal has been confirmed by various characterizations and crystalline quality was studied by powder X-ray diffraction and HRXRD analyses. The structural, thermal, mechanical and optical properties have been studied by suitable methods and detailed report has been presented in this paper. Materials and methods
397
of the grown crystal. The crystalline perfection of the grown single crystals was characterized by HRXRD by employing a multicrystal X-ray diffractometer developed at NPL [12] as per the procedure described earlier [13]. Growth of single crystals Seed crystals were obtained from the super saturated solution at constant temperature (30 °C) by SEST method. Due to slow evaporation of the solvent, spontaneous nucleation occurs and these are grown into crystals of few mm3 size. Crystals with good habitual faces, transparency and less number of visible defects are selected as seed for growing bulk single crystals. A seed crystal was placed at the bottom of the beaker containing the super saturated solution and another seed crystal was suspended in the super saturated solution contained beaker. Both the beakers were kept in a constant temperature bath with accuracy of ±0.01 °C to maintain the growth solution at 30 °C. The beakers were covered separately by a perforated thin transparent sheet in order to enable the slow solvent evaporation. After a period of 30 days the seed crystals have grown to the critical dimension and the grown crystals were harvested carefully from the solution. The as grown crystals are shown Fig. 1. The crystal grown from the bottom of the beaker has the dimension of 20 20 3 mm3 (Fig. 1a) and the later has 10 8 8 mm3 (Fig. 1b). The crystals grown at the bottom of the beaker was observed to be flat which is due to the restricted exposure of the growing seed to its mother solution at the bottom side of the crystal. It was observed that the growth rate along ‘a’ and ‘b’ axes are higher than that of ‘c’ axis for the crystal grown at the bottom of beaker. On the other hand, the crystal grown by suspended seed method has approximately same growth rate along all the crystallographic direction.
Synthesis Results and discussion The as-purchased 4-nitro phenol (99% Pure) and L-arginine (Merck Product) were used as starting materials to prepare the solution for the synthesis of title compound. L-arginine and 4-nitro phenol were taken in equimolar ratio and dissolved one by one in excess of water by continuous stirring. After the solution became homogeneous, it was filtered and transferred to another beaker, then allowed to evaporate the excess water at bellow 40 °C. Yellow color crystalline salt was obtained at the bottom of the beaker. It was dried and purified by re-crystallization process. The seed crystals were obtained by SEST method from a super saturated solution prepared from the synthesized salt. These seed crystals were used to study the various characterization of the present investigation. Characterization techniques Single crystal X-ray diffraction analysis was performed by using ENRAF NONIUS diffractometer with Mo Ka (k = 0.7107 Å) radiation and the data was collected at 20 °C. Good quality seed crystals were ground as fine powder and the powder X-ray diffraction analysis was carried out to find the crystalline nature of the grown crystal using an X’PERT PRO diffractometer system. The molecular structure of the grown crystal was confirmed by Proton NMR spectral analysis by using JEOL GSX 400 instrument. Linear optical properties of the crystals were studied by UV–Vis spectrophotometer and nonlinear optical properties were tested by Kurtz Perry powder technique [11]. Thermo-gravimetric (TG) and differential thermal analysis (DTA) for the crystal samples were carried out in nitrogen atmosphere by EXSTAR TG/DTA 6200thermal analyzer to study the thermal properties of the as-grown crystal. Vicker’s microhardness test was carried out to find the mechanical strength
Single crystal X-ray diffraction study Single crystal X-ray diffraction analysis was carried out to identify the grown crystal on the single crystal with size of 0.35 0.25 0.25 mm3. The lattice parameters were determined and the crystal structure was solved by direct method and refined by full-matrix least-squares method. The determined lattice parameters are tabulated and compared with literature in Table 1, which confirm that the grown crystal is L-arginine 4-nitrophenolate 4-nitrophenol dihydrate (LAPP) as it coincides with the reported values [10]. It is observed that the grown crystal belonged to monoclinic crystal system with P21 space group. The molecular configuration and crystal packing diagram projected along ‘a’ axis are shown in Figs. 2 and 3, respectively. Powder X-ray diffraction study The grown crystals were made as fine powder and subjected to powder X-ray diffraction analyses. The diffraction data were collected at 298 K between 0° and 60° of diffraction angles with the source wave length of 1.5460 Å. The step size of 2h and the scan step time were fixed as 0.017° and 10.33 s respectively. The diffraction pattern contains various reflections corresponding to various crystallographic planes as shown in Fig. 4. The observed sharp peeks of the pattern ensure the good crystalline nature of the samples. Miller indices were calculated for different 2h and d spacing by the simulation from the lattice parameters obtained in single crystal X-ray diffraction study and the powder diffraction pattern was indexed.
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Fig. 1. Photographs of as-grown single crystals of LAPP (a) grown from the bottom of the beaker (b) grown from the suspended seed.
Table 1 Single crystal X-ray diffraction data in comparison with literature. Parameter
Present study
[10]
[9]
Name of the crystal Crystal system Space group Unit cell dimension a b c b Cell volume
LAPP Monoclinic P21
LAPP Monoclinic P21
LARP Orthorhombic P212121
7.8570(5) Å 10.3656 (6) Å 13.8120 (7) Å 98.177 (2) deg 1113.45 (11) Å3
7.8669 (5) Å 10.3764 (2) Å 13.8301 (2) Å 98.2128 (9) deg 1117.37 (3) Å3
5.1254(2) Å 9.3683 (3) Å 31.5145 (10) Å 90 deg 1513.21 (9) Å3
Proton NMR analysis Nuclear magnetic resonance (NMR) spectroscopy is an important tool to identify the synthesized compound. The purified LAPP sample was subjected to proton NMR spectral study by using deuterium oxide solvent and the recorded spectrum is shown in Fig. 5. The hydrogen atoms present in the various chemical environment give their signal at different chemical shift (d) position. Since the compound contains several functional groups hydrogen atoms in L-arginine and 4-nitrophenol, the spectrum pronounced several signals at different d position. The ortho and meta hydrogens present in the nitro phenol can see themselves as aligned (Parallel) or opposed (antiparallel) and come to resonance twice. Hence the ortho (2,6) and Meta (3,5) hydrogens appeared as doublet and gave their signals at 6.67 and 8.03 ppm respectively [14,15]. The CH and
CH2 groups present in the L-arginine molecules have given their signals at different d value according to their shielding nature. The CH proton gave its signal at 3.69 ppm. The protons associated with aliphatic CH2 (b, c and d as designated in the figure) in the arginine molecule have given their signals at 1.83, 1.68 and 3.15 ppm respectively [16]. The multiple splitting observed in these signals is due to the presence of amine groups in the arginine molecules. High resolution X-ray diffraction study (HRXRD) Fig. 6 shows the high resolution X-ray diffraction curve recorded using Mo Ka1 radiation for a typical LAPP single crystal specimen. On close observation one can realize that the curve is not a single peak. On deconvolution of the diffraction curve, it is clear that the curve contains three additional peaks. The solid line (convoluted curve) is well fitted with the experimental points represented by the filled circles, which are 132, 200 and 358 arc s away from the main peak (highest intensity peak). These three additional peaks correspond to three internal structural low angle (tilt angle >1 arc min but <1 deg.) boundaries [17] whose tilt angles (Tilt angle may be defined as the misorientation angle between the two crystalline regions on both sides of the structural grain boundary) are 132, 200 and 158 arc s from their adjoining regions. These internal structural low angle boundaries are mainly because of the agglomerated dislocations and the self generated strains by such defects [18]. The FWHM (full width at half maximum) of the main peak and the three low angle boundaries are respectively
Fig. 2. Molecular configuration and the atomic numbering scheme of LAPP crystal.
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Fig. 3. Crystal packing diagram, projected along a axis.
168 and 54, 150 and 118 arc sate relatively low values of FWHM of the grains and low angular spread of the DC (1000 arc s = 17 arc min) depicts that the crystalline perfection is moderate. It may be mentioned here that such low angle boundaries could be detected in the diffraction curve only because of the highresolution of the diffractometer used in the present investigations. The influence of such defects may not influence much on the physical properties. However, a quantitative analysis of such unavoidable defects is of great importance, particularly in case of phase matching applications in nonlinear optical crystals as described in our recent article [19].
18000 (211) (201)
14000 12000 10000
(220) (13−2)
(142)
2000
(133)
(002)
4000
(200)
(110)
6000
(120) (121)
8000
(111) (020) (102)
Intensity (counts)
16000
Linear and nonlinear optical property studies
0 10
20
30
40
50
2θ (deg) Fig. 4. Powder X-ray diffraction pattern of LAPP.
60
It is imperative to have good optical transparency in an NLO crystal in the green visible region. Optical absorption spectrum for the grown crystal was recorded in the range between 180 to 1100 nm and is shown in Fig. 7. The grown crystal have UV cutoff
Fig. 5. Proton NMR spectrum of LAPP.
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Diffracted X-ray intensity [c/s]
LAPP 300
200"
132"
158"
MoKα1 (+,−,−,+)
200
168" 100
0 -400
118"
54"
-200
150"
0
200
400
Glancing angle [arc s] Fig. 6. High resolution X-ray diffraction curve of LAPP crystal.
5
Absorbance (a.u.)
4
below 500 nm and above which the grown crystal is appreciably less absorbance in the visible to near IR range of the spectrum. So, the grown crystal is useful for optoelectronic applications and the second harmonic generation (frequency conversion) from the Nd: YAG Laser. The nonlinear optical property was studied by SHG efficiency of LAPP crystalline samples and it was found by Kurtz and Perry powder technique. The finely ground powder samples of the grown crystals was filled in quarts capillary tube and subjected to this test. The second harmonic output was generated by irradiating the powder samples by a pulsed laser beam of Nd: YAG laser with a pulse width of 8 ns with the energy of 2.1 mJ/pulse. The ability of the energy (frequency) conversion was confirmed by the emission of green light from the powder sample. KDP and Urea samples were used as reference materials and output power intensity of the samples. The output intensities for the samples of LAPP, KDP and Urea were converted as voltage by a photomultiplier tube and the measured output voltages were 68, 25.6 and 82 mV, respectively. Hence, the grown crystal has SHG efficiency of 2.66 times that of KDP and 0.83 time that of Urea. On the other hand, it was observed that the SHG efficiencies of L-arginine and 4-nitrophenol are much lesser than that of the crystalline powder of LAPP and are measured as 0.17 and 0.14 time that of KDP respectively. Thermal analysis
3
2
1
200
400
600
800
1000
Wavelength (nm) Fig. 7. UV–Vis–NIR spectrum for the grown crystal of LAPP.
1200
Thermal analyses were performed on the powder sample of grown crystal to study the thermal stability and melting point. The thermo gravimetric analysis (TGA) and differential thermal analysis curves of LAPP were obtained in the range between room temperature (28 °C) and 800 °C at a heating rate of 10 °C per min. The experiment was performed in nitrogen atmosphere and the TG & DTA plots are shown in Fig. 8. TGA curve shows a weight loss occurred in two stages and the same near100 °C is assigned to loss of water. This weight loss due to water is also associated with melting of the sample, which is clearly observed in the DTA curve as an endothermic transition occurred at 110 °C. At this temperature, 4-nitrophenol and water molecules were dissociated from the compound and the 4-nitrophenol started to melt as its melting point is nearly 110 °C. The second stage of TG curve shows nearly
Fig. 8. Thermogravimetric (TG) and differential thermal analysis (DTA) curve of LAPP crystal.
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22 21
HV (Kg/mm2)
20 19 18 17 16 15 14 13 0
20
40
60
80
100
401
the crystal because of the inability of these lower loads to soften the bonding in the molecules. Beyond 100 g of load it was observed that the cracks were formed due to release of internal stress generated locally by indentation and the hardness values decreased further [20]. The Mayer’s index was calculated from the Mayer’s equation log P = log k + n log d, which is the relation between the applied load and indentation diagonal length, where k is the material constant and n is the Mayer’s index and it is also called as work hardening coefficient. The value of ‘n’ has been found by plotting a graph between log d and log P as shown in Fig. 10. The slope of the graph gives the value of n and it is found to be 1.69. According to Onitsch and Hanneman, ‘n’ should lie between 1 and 1.6 for moderately hard materials and above 1.6 for softer material category. Hence, the grown crystal is a soft material due to which the hardness values decreased when the load was increased [21].
Load (g) Fig. 9. Vicker’s hardness profile as a function of applied load of LAPP crystal along (0 0 1) plane.
Log P vs Log d Linear Fit of Log P
2.0
Log P
1.8
1.6
1.4
1.2
y = a + b*x Equation Adj. R-Square 0.99022 Log P Log P
1.0
Value Standard Error Intercept -1.45321 0.17187 Slope 1.6877 0.09668
Conclusions Good quality single crystals of LAPP have been grown by SEST method. The structural properties of the grown crystals were analyzed by X-ray diffraction and NMR methods. HRXRD curve was obtained and the grown crystal has a moderate crystalline perfection which may not affect the device performance. Linear and nonlinear optical property studies ensured that the grown crystal is useful for the device fabrication. It was found that the grown crystal has 478 nm cut off wavelength and SHG efficiency of 2.66 times that of KDP. Thermal stability of the grown crystals was studied by obtaining TG/DTA curves and found that the crystal is thermally stable up to 110 °C. By Vicker’s microhardness test, the crystal was found to be a soft material and the hardening coefficient was determined as 1.69. Hence from this investigation, the grown crystal was found to be well suitable for the nonlinear optical device. Acknowledgements
1.4
1.5
1.6
1.7
1.8
1.9
2.0
2.1
Log d Fig. 10. Plot of log d vs. log P for LAPP crystal along (0 0 1) plane.
70% of weight loss due to the decomposition of sample which is associated by an exothermic transition as observed at 253 °C in DTA curve. The remaining 18% of the sample was left in the crucible as a residual carbon. From this study, it is observed that the material has water molecules in its lattice and it has thermal stability till its melting point 110 °C. Hardness study Since the hardness of the crystals play vital role in the device fabrication, the material resistance with respect to localized plastic deformation should be studied. Vickers’ microhardness test was carried out on (0 0 1) plane of the grown crystal and the hardness number was calculated by the relation Hv = 1.8544 P/d2 kg/mm2, where Hv is the Vicker’s hardness number, P is the applied load in kilogram, and d is the average diagonal length of the impression corresponding to the load in mm. Before indentations were made, the crystal was lapped and cleaned to avoid the surface defects which may influence the hardness value. Fig. 9 shows the variation of hardness numbers with respect to load which evidenced that the microhardness value of LAPP has decreased when the load is increased due to normal indentation size effect (Indentation size is inversely proportional to the hardness of the material). It is observed that the hardness values are higher at lower loads for
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