Growth, structural, optical, thermal and mechanical studies of novel semi-organic NLO active single crystal: Heptaaqua-p-nitrophenolato strontium (I) nitrophenol

ARTICLE IN PRESS Journal of Crystal Growth 312 (2010) 793–799

Contents lists available at ScienceDirect

Journal of Crystal Growth journal homepage: www.elsevier.com/locate/jcrysgro

Growth, structural, optical, thermal and mechanical studies of novel semi-organic NLO active single crystal: Heptaaqua-p-nitrophenolato strontium (I) nitrophenol M. Jose a, B. Sridhar b, G. Bhagavannarayana c, K. Sugandhi a, R. Uthrakumar a, C. Justin Raj a, D. Tamilvendhan d, S. Jerome Das a,n a

Department of Physics, Loyola College, Chennai 600034, India Indian Institute of Chemical Technology, Tamaka, Hyderabad 500607, India Materials Characterization Division, National Physical Laboratory, Dr. K. S. Krishnan Marg, New Delhi 110012, India d Department of Chemistry, National Institute of Technology, Trichy 620015, India b c

a r t i c l e in fo

abstract

Article history: Received 24 September 2009 Received in revised form 1 December 2009 Accepted 4 December 2009 Communicated by M. Fleck Available online 22 December 2009

Novel single crystals of Heptaaqua-4-nitrophenolato strontium(I) nitrophenol (HNSN) were successfully grown using slow evaporation solution growth technique at constant temperature (303 K) with dimensions 40  12  6 mm3. The formation of the new crystal has been confirmed by single-crystal Xray diffraction, NMR, FT-IR and UV–vis–NIR studies. The crystalline perfection was analyzed by highresolution X-ray diffraction (HRXRD) rocking curve measurements. Thermal analysis has also been carried out, and the thermal behavior of HNSN crystal has been studied. The dielectric loss and dielectric constant measurements as a function of frequency and temperature were measured for the grown crystal. The mechanical strength of the crystal is estimated by Vicker’s hardness test. The powder second harmonic generation (SHG) has been confirmed by Nd: YAG laser. & 2009 Elsevier B.V. All rights reserved.

Keywords: A1. X-ray diffraction A1. Growth from solution A1. Characterization B2. Thermal properties B2. Nonlinear optical crystal

1. Introduction Second-order nonlinear optical (NLO) materials are proved to be interesting candidates for number of applications like second harmonic frequency conversion, electro-optic modulation and optical parametric oscillation/amplification, etc., [1,2]. Even though organic nonlinear optical materials with aromatic ring have been attracting much attention because of their high nonlinearity, fast response and high optical damage threshold [3–5], their practical applications are limited due to poor mechanical, thermal stabilities and the inability to produce and process large crystals. Inorganic NLO crystals typically have high melting point, excellent mechanical, thermal properties and high degree of chemical inertness but unfortunately they have relatively modest nonlinearities compared with their organic counterparts. In order to overcome these difficulties, semi-organic materials have been proposed in which the high optical nonlinearity of a purely organic compound is combined with

n

Corresponding author. Tel.: + 91 44 2817 5662; fax: + 91 44 2817 5566. E-mail addresses: [email protected], [email protected] (S. Jerome Das). 0022-0248/$ - see front matter & 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.jcrysgro.2009.12.016

the favorable mechanical and thermal properties of inorganics. In these crystals, polarizable organic molecules are stoichiometrically bonded with inorganic host. Most recently, our research group has synthesized yet another new promising semi-organic non-linear optical material, Heptaaqua-4-nitrophenolato strontium(I) nitrophenol (HNSN) single crystal. Second Harmonic Generation (SHG) requires materials with non-centrosymmetric structure in which the more or less parallel alignment of molecules with a high hyperpolarazibility results in large values of the second-order nonlinear susceptibilities. In a centrosymmetric structure, however, the even-order nonlinear susceptibilities are zero in the electric dipole approximation [6]. Quite a few numbers of reports are available in the literatures which show that centrosymmetric media [7–14] or film [15,16] also exhibit NLO properties. Further the non-zero SHG found in powders of centrosymmetric crystals has been attributed to possible impurities and crystal defects [17,18]. However the experimental evidence provided in this paper by the well established HRXRD studies confirms that the HNSN single crystal possesses excellent quality free from impurities and defects. Hence the observation of SHG in this case is certainly not due to crystal imperfections. But a dipole allowed contribution to the nonlinear radiation may, however, still appear at surfaces or

ARTICLE IN PRESS 794

M. Jose et al. / Journal of Crystal Growth 312 (2010) 793–799

interfaces where the inversion symmetry is no longer present. Hence, second harmonic light could be reflected from the interface of the two centrosymmetric media [19,20]. In the present work, high quality single crystals of HNSN have been grown by slow evaporation solution growth technique and it was found to exhibit SHG, which was confirmed by Kurtz powder Perry technique [21], using Nd: YAG laser. In this paper, we report for the first time the material synthesis, crystal growth, structure, optical, thermal, mechanical, dielectric and second harmonic generation (SHG) properties of Heptaaqua-4-nitrophenolato strontium(I) nitrophenol (HNSN) single crystals.

2. Experimental 2.1. Material synthesis The title compound was synthesized from paranitrophenol (99% purity) and strontium hydroxide (octahydrate 99% purity) in the stoichiometric ratio 1:1. The synthesized material was further purified by repeated re-crystallization using triple distilled water as solvent. The purified compound stirred continuously resulted in a homogenous solution which was then kept undisturbed at a constant temperature of 313 K to obtain seed crystals by spontaneous nucleation. Seed perfection is very important for growing single crystals with high purity because defects in the seed crystal could cause spurious crystallization and flaws. To ensure growth of good quality single crystal, a seed obtained from spontaneous nucleation was suspended in the supersaturated solution of Heptaaqua-4-nitrophenolato strontium(I) nitrophenol (HNSN). Then the solution was allowed to evaporate at room temperature, which yielded yellowish crystal of dimensions 40  12  6 mm3 within a period of 25 days. The photograph of as-grown single crystals is shown in Fig. 1.

3. Results and discussion

direct methods using SHELXS97 and refinement was carried out by full-matrix least-squares technique using SHELXL97 [23]. Anisotropic displacement parameters were included for all nonhydrogen atoms. All the water H atoms were located in difference Fourier maps and their positions parameters and the isotropic displacement parameters Uiso(H) values were set equal to 1.5Ueq(O), were refined. All other H atoms were positioned geometrically and were treated as riding on their parent C atoms, ˚ and with Uiso(H) values of 1.2Ueq(C) with C–H distance of 0.93 A, for other H atoms. The crystal and refinement data are given in Table 1. Molecular graphics were computed using DIAMOND [24] program. The asymmetric unit of the compound, [Sr. C6H4NO3. (H2O)7]. C6H4NO3, the Sr atom is eight coordinated by oxygen atom (O2) of nitro group of the 4-nitrophenolate and seven water oxygen (O1W–O7W) atoms, while the uncoordinated 4nitrophenolate ion is hydrogen bonded to the two coordinated water molecules which is shown in Fig. 2. The eight coordinate SrII complex assumes a distorted square antiprism coordination geometry. The bond lengths and angles of the 4-nitrophenolate ions are comparable to those found in related structures reported in the Cambridge Structural Database ˚ The [25,26]. The average Sr–O (water) distance is 2.621(2) A. crystal packing involves segregation of hydrophilic and hydrophobic regions alternating along the crystallographic a axis (Fig. 3). The hydrophilic regions contain the Sr metal ions and oxygen atoms of the water molecules and 4-nitrophenolate ions. The hydrophobic regions contain the inversion-related 4nitrophenolate ions and bridges the hydrophilic regions and lead to the formation of an extended three-dimensional frame work, with alternating ‘organic’ and ‘inorganic’ sheets (Fig. 3). 3.2. High-resolution X-ray diffractometry studies The crystalline perfection of the grown single crystal was characterized by HRXRD by employing a multicrystal X-ray diffractometer developed at NPL [27]. The well-collimated and monochromated MoKa1 beam obtained from the three mono-

3.1. Crystal structure analysis X-ray data of the HNSN single crystal was collected at room temperature (294(2) K) using a Bruker Smart Apex CCD diffractometer with graphite monochromated MoKa radiation ˚ with o-scan method. Preliminary lattice para(l = 0.71073 A) meters and orientation matrices were obtained from four sets of frames. Integration and scaling of intensity data were accomplished using SAINT program [22]. The structure was solved by

Table 1 Crystal data and structure refinement for HNSN single crystal. Empirical formula Formula weight Temperature Wavelength

C6 H18 N O10 Sr, C6 H4 N O3’ 489.94 294(2) K 0.71073 A˚

Crystal system Space group Unit cell dimensions

Orthorhombic Pbca

Volume

Fig. 1. Photograph of as-grown single crystal of HNSN.

a =24.5620(3) A˚

a = 901

b = 21.720(1) A˚ c = 7.115(1) A˚

b = 901

g =901

3795.8(6) A˚ 3 Z 8 Density (calculated) 1.715 Mg/m3 Absorption coefficient 2.911 mm  1 F (0 0 0) 2000 Crystal size 0.13  0.07  0.05 mm3 1.66–25.001 y range for data collection Index ranges  29 o =h o = 29,  25o = k o = 25,  8o = l o =8 Reflections collected 34104 Independent reflections 3352 [R(int)= 0.0337] 100% Completeness to y = 25.001 Refinement method Full-matrix least-squares on F2 Data/restraints/parameters 3352/0/310 1.020 Goodness-of-fit on F2 Final R indices [I42sigma(I)] R1 =0.0218, wR2= 0.0535 R indices (all data) R1 =0.0300, wR2= 0.0579 Extinction coefficient 0.0053(2) Largest diff. peak and hole 0.303 and  0.296 e.A˚  3

ARTICLE IN PRESS M. Jose et al. / Journal of Crystal Growth 312 (2010) 793–799

795

Fig. 2. A view showing the atom numbering scheme. Displacements ellipsoids are drawn at the 30% probability level and H atoms are shown as small spheres of arbitrary radii. The dashed lines indicate the hydrogen bonds.

Fig. 3. The crystal packing viewed down a axis. The Sr eight coordination is shown as polyhedra. H atoms not involved in hydrogen bonding are omitted for clarity and the hydrogen bonds are shown as dashed lines.

chromator Si crystals set in dispersive ( + ,  , ) configuration has been used as the exploring X-ray beam. The specimen crystal is aligned in the ( +,  ,  ,+ ) configuration. Due to dispersive configuration, though the lattice constant of the monochromator crystal(s) and the specimen are different, the unwanted dispersion broadening in the diffraction curve (DC) of the specimen crystal is insignificant. The specimen can be rotated about the vertical axis, which is perpendicular to the plane of diffraction, with minimum angular interval of 0.4 arc s. The DC was recorded by the so-called o scan wherein the detector was kept at the same angular position 2yB with wide opening for its slit. Fig. 4 shows the high-resolution diffraction curve (DC) recorded for the grown single crystal using (1 2 1) diffracting planes in symmetrical Bragg geometry by employing the multicrystal X-ray diffractometer with MoKa1 radiation. As seen in the figure, the DC contains a single sharp peak and indicates that the specimen is free from structural grain boundaries. The FWHM (full width at half maximum) of the curve is 11 arc s which is very close to that expected from the plane wave theory of dynamical X-ray diffraction [28] for an ideally perfect crystal. It is interesting to see the asymmetry of the DC. For a particular angular deviation (Dy) of glancing angle with respect to the peak position, the scattered intensity is much more in the negative direction in comparison to that of the positive direction. This feature clearly indicates that the crystal contains predominantly vacancy type of defects than that of interstitial defects. This can be well understood by the fact that due to vacancy defects which may be due to fast growth, as shown schematically in the inset, the lattice around these defects undergo tensile stress and the lattice parameter d (interplanar spacing) increases and leads to give more scattered (also known as diffuse X-ray scattering) intensity at slightly lower Bragg angles (yB) as d and sin yB are inversely

Fig. 4. Diffraction curve recorded for HNSN single crystal for (1 2 1) diffracting planes by employing the multicrystal X-ray diffractometer with MoKa1 radiation.

proportional to each other in the Bragg equation (2d sin yB = nl; n and l being the order of reflection and wavelength respectively which are fixed). However, these point defects with much lesser density as in the present case hardly affect the performance of the devices based on such crystals. If the concentration is high, the FWHM would be much higher and often lead to structural grain boundaries [29]. Point defects up to some extent are unavoidable due to thermodynamical considerations. It may be mentioned here that though the unit cell volume (and hence the lattice

ARTICLE IN PRESS 796

M. Jose et al. / Journal of Crystal Growth 312 (2010) 793–799

Fig. 6. 1H NMR Spectrum of HNSN.

Fig. 5. FT-IR spectrum of the grown crystal.

parameter), which contains the vacancy reduces considerably, as the number of unit cells which undergo tensile stress around the defect core and cause X-ray scattering along the negative side of the peak are much more than that of the unit cells which contain the vacancy defects, the d-value around the defect core increases and hence one expects more scattered intensity on the negative side of the peak when the crystal contains predominantly the vacancies 3.3. FT-IR spectral analysis In order to analyze the synthesized compound qualitatively for the presence of functional groups in the molecule, the FT-IR spectrum is recorded between 450 and 4000 cm  1 using KBr pellet technique by Brukker IFS 66v FT-IR spectrometer. The spectrum obtained is shown in Fig. 5. The absorption peak at 3434 cm  1 is due to asymmetric and symmetric OH stretching (Lattice water). The peak corresponding to 1648 and 1312 cm  1 brings forth HOH bending and NO2 stretching vibration, respectively. The sharp peaks at 1811 and 1930 cm  1 are assigned to overtones and combination bands for 1,4 disubstituted aromatic ring. The asymmetric and symmetric stretches of NO2 group are observed at 1587 and 1312 cm  1, respectively. The corresponding CN vibration is positioned at 819 cm  1. The peaks at 1496, 1464 and 1429 cm  1 are due to ring skeletal vibrations. The 1,4 disubstituition is also evident by a sharp peak at 852 cm  1 due to CH out-of-plane bend. The peak at 1117 cm  1 is due to the CO stretching mode. 3.4.

1

H NMR spectral analysis

The 1H NMR spectrum of HNSN was recorded by a Bruker Advance III 500 MHz FTNMR spectrophotometer using D2O as solvent. The 1NMR spectrum (d in ppm) of HNSN is depicted in Fig. 6. It exhibits three non-overlapping peaks (3.037s, 4.74d, 6.2d) indicating three different proton environments. The singlet peak at 11.10 ppm in free p-nitrophenol was not observed in HNSN supporting the presence of deprotonated form of p-nitrophenol in the form of anion is coordinated so as to balance the positive charge of strontium by one. The signal at d (6.269 and 6.250 ppm, J =9.5 Hz) is assigned to the deshielded hydrogen adjacent to NO2 group. The doublet at d (4.742 and 4.723 ppm, J= 9.5 Hz) is assigned to hydrogen adjacent to OH group. Charge transfer from nitrophenol group to strontium caused the upfield shift for H of H2O molecule (3.037s) ppm.

Fig. 7. UV–vis–NIR absorption spectrum for HNSN single crystal.

The identicalJ value (J= 9.5 Hz) indicates the coupling nature of two sets of protons on adjacent sp2hybridised carbon atoms that splits one another must be identical. 3.5. DRS-UV–visible analysis The DRS–UV–vis spectrum of the grown crystal recorded between 200 and 2000 nm using a Varian Cary 5E UV–vis–NIR spectrometer covering the entire UV, visible and near-infrared region is shown in Fig. 7. Between 500 and 2000 nm the material is observed to be nearly transparent and the absorption is less and insignificant. The reduced absorption in the entire visible and near-infrared region is an important requirement for NLO device applications. The steep increase in absorption below 500 nm is due to the colour of the material absorbing in and beyond the visible region [30]. 3.6. Thermal analysis The thermal stability was studied by thermo-gravimetric (TG) and differential thermal analyses (DTA). The thermal analyses were carried out using NETZSCH STA 409C/CD between 25 and 1200 1C at a heating rate of 10 1C/min in a nitrogen atmosphere. The TG and DTA curves are shown in Fig. 8. TG curve illustrates a weight loss of 25% between 25 and 150 1C due to loss of water of crystallization. The sharp weight loss starting close to 400 1C is

ARTICLE IN PRESS M. Jose et al. / Journal of Crystal Growth 312 (2010) 793–799

797

Table 2 Centrosymmetric crystals with their relative SHG efficiency. Crystal

SHG efficiency

Reference

Methyl-2-(2,4dinitrophenylamino)-3Phenylproponate (p-nitrophenol,hexamethylenetetramine, phosphoric acid and water) super molecular crystal R, S-serine

0.2 times of KDP 4.1 times of KDP

14

0.02 times of KDP 2.34 times of KDP 0.42 times of KDP

Glycine picrate Heptaaqua-4-nitrophenolato strontium (I) nitrophenol

7

8 11 Present work

Fig. 8. TG/DTA thermogram of HNSN single crystal.

130

110

Hv (kg/mm2)

assigned to the degradation of paranitrophenolate into fragments and their subsequent volatilization. The sharp endothermic peak at 108 1C is found to be matching with the first weight loss in TGA which is assigned to energy required for loss of water of crystallization. The melting point of paranitrophenol is 114 1C. But there is no separate endotherm in addition to that of water of crystallization. Hence the endoderm due to loss of water of crystallization might be immediately accompanied by melting. The exothermic peak appearing close to 400 1C is matching with the major weight loss in TGA. From this analysis, it is obvious that the material can be exploited for NLO applications upto 108 1C. The sharpness of the endothermic peak shows good degree of crystallinity and purity of the grown crystal [31].

90

70

50

3.8. Microhardness studies Hardness of the material is a measure of resistance it offers to local deformation or damage under an applied stress [32] and it plays a key role in device fabrication. The indentation hardness is measured as the ratio of the applied load to the projected area of indentation. Microhardness measurements are made on the smooth surface of the grown sample at room temperature using Shimadzu HMV-2000 fitted with Vickers pyramidal indentor. The

100

150

Load P (x10-3kg)

3.7. NLO studies

2.5 2 1.5

log p

Quantitative measurements of relative SHG efficiency of HNSN single crystals with respect to the well-known SHG material KDP were made by the Kurtz and Perry technique. Finely powdered crystals of HNSN were densely packed in a micro capillary tube of uniform bore. A laser beam from an Nd: YAG laser (Specraphysics DCR 11) of fundamental wavelength 1064 nm, 8 ns pulse width with 10 Hz pulse rate was made to fall normally on the sample cell. The transmitted fundamental wave was passed over a monochromator (Czerny Turner monochromator), which separates 532 nm(second harmonic signal) from 1064 nm, and absorbed by CuSO4 solution, which removes the 1064 nm light and passed through a filter to remove the residual 1064 nm light and an interference filter with bandwidth of 4 nm and central wavelength of 532 nm. The green light was detected by a photomultiplier tube (Hamamatsu, R2059). KDP crystal powdered to the identical size was used as reference material in the SHG measurements. It was found that the SHG output of KDP and HNSN were 94 and 40 mV, respectively at a given pulse energy of 9.35 mJ/pulse. Some of the earlier reported centrosymmetric crystals and their relative SHG efficiencies are given in Table 2.

50

0

1 0.5 0 1.3

1.4

1.5 log d

1.6

1.7

Fig. 9. (a) Plot of load vs. Hardness number. (b) Plot of log d vs. log p.

load P is varied between 25 and 100 g, keeping the time of indentation constant at 15 s for all trials. The hardness of the material Hv is determined by the relation Hv ¼

1:8544P kg=mm2 d2

where, P is the applied load in kg, and d is the diagonal length of indentation impression in mm. Fig. 9(a) shows the plot of hardness number with load indicating the reverse indentation size effect (ISE) where the hardness value increases with increasing load. Examination of the indented surfaces of the sample reveals the appearance of multiple cracks around indentations when P is greater than 100 g which may be due to the release of internal stresses generated locally by indentation. The plot of log d against log p shown in Fig. 9(b) is a straight line,

ARTICLE IN PRESS 798

M. Jose et al. / Journal of Crystal Growth 312 (2010) 793–799

namely, electronic, ionic, dipolar and space charge polarization. Space charge polarization is generally active at lower frequencies and high temperatures and betokens the perfection of the crystal [36]. Further, the space charge polarization will reckon on the purity and perfection of the material. Its influence is large at higher temperature and is noticeable in the low frequency region [37]. The characteristic of low dielectric loss with high frequency for a given sample as evident from Fig. 10(b) suggests that the sample possesses good optical quality with lesser defects [38,39] and this parameter is of vital importance for nonlinear optical applications.

550 500

Dielectric constant

450 400 40 deg C 350 60 deg C 300

80 deg C

250

100 deg C

4. Conclusions

200

Optical quality single crystals of HNSN were grown using solution growth technique. The unit cell parameters of the title compound were evaluated by single crystal X-ray diffraction analysis. The high-resolution XRD measurements substantiate the excellent quality of the crystal free from major defects like structural grain boundaries and inclusions. The functional groups were confirmed by FT-IR and 1H NMR spectroscopic techniques. The optical transparency window in the visible and near IR (420–1400 nm) regions was found to be good for nonlinear optical applications. Differential thermal analysis carried out on the grown crystal indicates that the material does not sublime before it melts at 108 1C. The dielectric constant and dielectric loss studies establish the normal behavior. The micro hardness observations showed that hardness increases with increase of load, which confirms the reverse indentation size effects of the crystal. The second harmonic generation property was confirmed by the Kurtz–Perry powder technique. Further work is under progress to improve the SHG efficiency of the title compound by molecular engineering technique.

150 100 1

2

3

4 log f

5

6

7

1.4 1.2 40 deg C Dielectric loss

1

60 deg C 80 deg C

0.8

100 deg C 0.6 0.4

Acknowledgment

0.2 0 0

2

4

6

8

log f Fig.10. (a) Dielectric constant vs. log f. (b) Dielectric loss vs. log f.

which is in good agreement with Mayer’s law [33]. According to Onitsch [34] and Hanneman [35], the HNSN single crystal belongs to the softer material category as n, the work hardening coefficient was determined to be 2.22.

3.9. Dielectric studies Good quality single crystals of HNSN were cut and polished on a soft tissue paper with fine grade alumina powder. In order to ensure good electrical contact between the crystal and the electrodes, the crystal faces were coated with silver paste. The dielectric measurements were carried out in the frequency range 50–5 MHz and temperature range 313–373 K with the help of an impedance analyzer, HIOKI 3532-50 LCR HiTESTER. Fig. 10(a) shows the plot of dielectric constant (er) as a function of frequency. It is observed that the dielectric constant decreases with increase in frequency for all temperatures. The large values of dielectric constant at low frequency enumerates the contribution from all four known sources of polarization

The authors thank Dr. P. K. Das, Indian Institute of Science, Bangalore, for support in SHG measurements, Dr. M. Palanisamy, Department of Chemistry, Anna University, Chennai and Dr. Jeya Rajendran, Department of Chemistry Loyola College, Chennai for fruitful discussions and useful suggestions. The corresponding author SJD would like to acknowledge the financial assistance extended by University Grants Commission, New Delhi. References [1] D.S. Chemla, J. Zyss, in: Nonlinear Optical Properties of Organic Molecules and Crystals, Academic Press, INC, 1987, p. 297. [2] D.M. Burland, Chem. Rev. 94 (1994) 1. [3] D. Josse, R. Heirle, I. Ledoux, J. Zyss, Appl. Phys. Lett. 53 (1988) 2251. [4] B.F. Levine, C.G. Bethea, C.D. Thermond, R.T. Lynch, J.L. Bernstein, J. Appl. Phys. 50 (1979) 2523. [5] R. Hierle, J. Badan, J. Zyss, J. Cryst. Growth 69 (1984) 545. [6] D.S. Chemla, J. Zyss, Nonlinear Optical Properties of Organic Molecules and Crystals, Vols 1 and 2, Academic, New York, 1986. [7] Guo Wensheng, Guo Fang, Wei Chunsheng, Liu Qitao, Zhou Guangyong, Wang Dong, Shao Zhongshu, Sci. China Ser. B: Chem. 45 (2002) 267. [8] K.E. Rieckhoff, W.L. Peticolas, Science 147 (1965) 610. [9] T. Ishihara, K. Koshino, H. Nakashima, Phys. Rev. Lett. 91 (2003) 253901. [10] E.W. Meijer, E.E. Havinga, G.L.J.A. Rikken, Phys. Rev. Lett. 65 (1990) 37. [11] Mohd. Shakir, S.K. Kushwaha, K.K. Maurya, Manju Arora, G. Bhagavannarayana, J. Cryst. Growth 311 (2009) 3871. [12] A. Chandramohan, R. Bharathikannan, J. Chandrasekharan, P. Madeswaran, R. Renganathan, V. Kandavelu, J. Cryst. Growth 310 (2008) 5409. [13] K. UdayaLakshmi, N.P. Rajesh, K. Ramamurthi, Babu Varghese, J. Cryst. Growth 311 (2009) 2484. [14] Joo-Hee Lee, Kimoon Kim, Jong-Hyun Kim, Jong-Jean Kim, Bull. Korean Chem. Soc. 13 (1992) 268.

ARTICLE IN PRESS M. Jose et al. / Journal of Crystal Growth 312 (2010) 793–799

[15] G.J. Ashwell, G. Jefferies, D.G. Hamilton, D.E. Lynch, M.P.S. Robertz, G.S. Bahra, C.R. Brown, Nature 375 (1995) 385. [16] Anna Samoc, Marek Samoc, Vesselin Z. Kolev, Barry Luther-Davies, Symposium on Photonics Technologies for 7th Framework Program, 250, , 2006. [17] K.E. Rieckhoff, W.L. Peticolas, Science 147 (1965) 610. [18] M. Delfino, Mol. Cryst. Liq. Cryst. 52 (1979) 271. [19] F. Brown, M. Matsuoka, Phys. Rev. 185 (1969) 985. [20] S.X. Dou, M.H. Jiang, Z.S. Shao, X.P. Tao, Appl. Phys. Lett. 54 (1989) 1101. [21] S.K. Kurtz, T.T. Perry, J. Appl. Phys. 39 (1968) 3798. [22] SMART & SAINT. Software Reference manuals. Versions 6.28a & 5.625, Bruker Analytical X-ray Systems Inc., Madison, Wisconsin, U.S.A., (2001). [23] G.M. Sheldrick, Acta Cryst. A 64 (2008) 112. [24] K. Brandenburg, H. Putz, DIAMOND. Release 3.0c. Crystal Impact GbR, Bonn, Germany (2005). [25] F.H. Allen, Acta Cryst. B 58 (2002) 380. [26] I.J. Bruno, J.C. Cole, P.R. Edgington, M. Kessler, C.F. Macrae, P. McCabe, J. Pearson, R. Taylor, Acta Cryst. B 58 (2002) 389. [27] Krishan Lal, G. Bhagavannarayana, J. Appl. Cryst. 22 (1989) 209.

799

[28] B.W. Batterman, H. Cole, Rev. Mod. Phys. 36 (1964) 681. [29] G. Bhagavannarayana, S. Parthiban, Subbiah Meenakshisundaram, Cryst. Growth Des. 8 (2008) 446. [30] G. Ryu, C.S. Yoon, J. Cryst. Growth 191 (1998) 190. [31] A.S.H. Hameed, G. Ravi, R. Dhanasekaran, P. Ramasamy, J. Cryst. Growth 212 (2000) 227. [32] W. Mott, in: Micro Indentation Hardness Testing, Butterworths, London, 1956, p. 206. [33] E. Meyer, Z. Ver, Dtsch. Ing 52 (1908) 645. [34] E.M. Onitsch, Mikroskopie 95 (1950) 12. [35] M. Hanneman, Metall. Manch. 23 (1941) 135. [36] N.V. Prasad, G. Prasad, T. Bhimasankaran, S.V. Suryanarayan, G.S. Kumar, Indian J. Pure Appl. Phys. 34 (1996) 639. [37] C.P. Smyth, in: Dielectric Behavior and Structure, Mc Graw Hill, New York, 1955. [38] C. Balarew, R. Duhlew, J. Solid Sate Chem. 55 (1984) 1. [39] P.M. Ushasree, R. Jayavel, P. Ramasamy, Mater. Chem. Phys 61 (1999) 270.