Growth and characterization of thiosemicarbazide hydrochloride: A semiorganic NLO material

Article abstract of DOI:10.1016/j.saa.2011.07.007

Thiosemicarbazide hydrochloride (TSCHCL) was synthesized by mixing thiosemicarbazide and hydrochloride in 1:1 molar ratio in double distilled water. Single crystals of TSCHCL were grown by slow evaporation at room temperature and were characterized by single crystal X-ray diffraction study to determine the molecular structure and by FT-IR, ¹H and ¹³C NMR spectral analyses to confirm the synthesized compound. Thermogravimetric and differential thermal analyses reveal the thermal stability of the crystal. The transmission spectrum of TSCHCL showed that the crystal is transparent in the wavelength range 380-1100 nm. High resolution X-ray diffractometry (HRXRD) was employed to evaluate the perfection of the grown crystal. Mechanical properties of the grown crystal were studied using Vickers microhardness test. Second harmonic generation efficiency of the powdered TSCHCL was tested using Nd:YAG laser and is ～1.5 times that of potassium dihydrogen orthophosphate.

Full text of DOI:10.1016/j.saa.2011.07.007

Spectrochimica Acta Part A 82 (2011) 102–107
Contents lists available at ScienceDirect
Spectrochimica Acta Part A: Molecular and
Biomolecular Spectroscopy
journal homepage: www.elsevier.com/locate/saa
Growth and characterization of thiosemicarbazide hydrochloride:
A semiorganic NLO material
a
b,∗
b
c
R. Santhakumari , K. Ramamurthi , R. Ramesh Babu , Helen Stoeckli Evans ,
d
e
G. Bhagavannarayana , R. Hema
Department of Physics, Govt. Arts College for Women, Pudukkottai 622 001, Tamil Nadu, India
Crystal Growth and Thin Film Laboratory, School of Physics, Bharathidasan University, Tiruchirappalli 620 024, Tamil Nadu, India
Institute of Physics, University of Neuchatel, Rue Emile-Argand 11, CH-2009 Neuchatel, Switzerland
Materials Characterization Division, National Physical Laboratory, Dr. K.S. Krishnan Marg, New Delhi 110 012, India
Department of Physics, Seethalakshmi Ramsamy College of Arts and Science, Tiruchirappalli 620 002, Tamil Nadu, India
a
b
c
d
e
a r t i c l e i n f o
a b s t r a c t
Article history:
Thiosemicarbazide hydrochloride (TSCHCL) was synthesized by mixing thiosemicarbazide and
hydrochloride in 1:1 molar ratio in double distilled water. Single crystals of TSCHCL were grown by
slow evaporation at room temperature and were characterized by single crystal X-ray diffraction study
Received 20 March 2011
Received in revised form 21 June 2011
Accepted 3 July 2011
1
13
to determine the molecular structure and by FT-IR, H and C NMR spectral analyses to confirm the syn-
thesized compound. Thermogravimetric and differential thermal analyses reveal the thermal stability of
the crystal. The transmission spectrum of TSCHCL showed that the crystal is transparent in the wave-
length range 380–1100 nm. High resolution X-ray diffractometry (HRXRD) was employed to evaluate the
perfection of the grown crystal. Mechanical properties of the grown crystal were studied using Vickers
microhardness test. Second harmonic generation efficiency of the powdered TSCHCL was tested using
Nd:YAG laser and is ∼1.5 times that of potassium dihydrogen orthophosphate.
PACS:
8
6
6
4
1.10.Dn
1.66.Hq
5.60.+a
2.65.Ky
Keywords:
©
2011 Elsevier B.V. All rights reserved.
A1. Characterization
A2. Growth from solution
B1. Organic compound
B2. Nonlinear optical material
1
. Introduction
desired manner [8]. In addition, they have large structural diver-
sity. By adopting molecular engineering and chemical synthesis
one can easily refine the optical properties of organic molecules [9].
However, most of the organic NLO crystals are constituted by weak
van der Walls and hydrogen bonds with conjugated ␲ electrons. So
they are soft in nature and difficult to polish and these materials
also have intense absorption in UV region. In view of these prob-
lems, new types of hybrid NLO materials have been explored from
organic–inorganic complexes with stronger ionic bond. Recently
semiorganic crystals have been proposed as new candidates with
interesting nonlinear optical properties as they possess high ther-
mal and mechanical stability compared to organics. The various
semiorganic sub-networks induce noncentrosymmetry in the bulk
and enhance the thermal and mechanical stabilities through hydro-
gen bonding interactions [10–12]. It is almost a well proven fact
by both theory and experiment that for having a good second
harmonic generation (SHG) character, the material should have
a noncentrosymmetric crystalline structure that gives rise to a
large second order NLO susceptibility. For molecular materials,
it is widely assumed that the molecular structure as well as the
packing arrangement must also be noncentrosymmetric, unless a
In the recent past two decades, nonlinear optical (NLO) crys-
tals have attracted the scientists and technologists due to their
potential applications in the area of photonics including optical
information processing [1–4], high-energy lasers for inertial con-
finement fusion research [5], color display, electro-optic switches,
frequency conversion [6]. The organic compounds exhibit larger
NLO response than inorganic materials due to the presence of active
␲
-bonds. However, these materials have poor mechanical strength,
thermal stability, laser damage threshold. As organic materials
exhibit prominent NLO properties, it is very important to synthe-
size new organic NLO materials. Organic molecules containing ␲
electron conjugation systems asymmetrized by the electron donor
and acceptor groups are highly polarizable entities for NLO appli-
cations [7]. Molecular flexibility of organic materials is an added
advantage to enhance the nonlinear optical (NLO) properties in a
∗ Corresponding author. Tel.: +91 431 2407057.
E-mail address: krmurthin@yahoo.co.in (K. Ramamurthi).
1
386-1425/$ – see front matter © 2011 Elsevier B.V. All rights reserved.
doi:10.1016/j.saa.2011.07.007

R. Santhakumari et al. / Spectrochimica Acta Part A 82 (2011) 102–107
103
Fig. 1. The as-grown crystal TSCHCL.
magnetic dipole [13–15] or an electric quadrupole [16] contributes
to the bulk susceptibility. Consequently, most studies have focused
on dipolar molecular systems in which the optical nonlinearities
arise from intermolecular charge transfer [17–20]. However, a very
few reports are available in the literature which show that the
centrosymmetric crystals [21–24] or films [25] also exhibit NLO
properties. Coghi et al. [26] have reported on the three dimensional
crystal and molecular structure of thiosemicarbazide hydrochlo-
ride (TSCHCL). To our knowledge no systematic studies on the
growth and characterization of the thiosemicarbazide hydrochlo-
ride have been made. Hence, in this investigation we report for the
first time on the bulk growth and characterization of TSCHCL single
crystals.
Fig. 2. The powder XRD pattern of TSCHCL.
transparency in the entire visible region which makes the material
suitable for second harmonic generation.
3
.2. Fluorescence studies
Fluorescence may be expected generally in molecules that are
aromatic or contain multiple conjugated double bonds with a high
degree of resonance stability [28]. Fluorescence finds wide applica-
tion in the branches of biochemical, medical and chemical research
fields for analyzing semiorganic compounds. The excitation and
emission spectra for TSCHCL were recorded using Varian Carry
Eclipse, Fluorescence Spectrometer. The excitation spectrum was
recorded in the range 200-300 nm (Fig. 4) and the excitation peak
was observed about 242 nm. The emission spectrum (Fig. 5) was
measured in the range 250-600 nm and the emission peak was
observed about 400 nm. Thus the results indicate that TSCHCL crys-
tal has the blue fluorescence emission.
2
. Experimental procedure
2.1. Crystal growth
Analar grade thiosemicarbazide and hydrochloride were dis-
solved in pure distilled water separately in 1:1 molar ratio and the
two solutions were mixed together. The temperature of the satu-
◦
rated solution was maintained at 30 C with continuous stirring for
3
h. This solution was filtered in a beaker and sealed and housed
3
.3. FT-IR spectral analysis
◦
in Eurotherm-controlled constant temperature bath (CTB) at 30 C.
The solvent was allowed to evaporate slowly at room tempera-
ture at 30 C. Well defined crystals with good transparency were
appeared in the beaker in a growth period of 5 days. One of the best
crystals was selected as seed crystal. TSCHCL solution was saturated
at 32 C (100 ml beaker) in the constant temperature bath and the
The functional groups of TSCHCL are confirmed by record-
◦
ing Fourier transform infrared (FT-IR) spectrum in the range of
4
nique. The FT-IR spectrum of TSCHCL is shown in Fig. 6. The band
obtained at 1522 cm is due to the presence of imine group (C N).
−1
000–400 cm using Perkin Elmer Paragon-500 by KBr pellet tech-
◦
−1
◦
temperature was reduced to 30 C to supersaturate the solution
(
pH ∼ 4). The seed crystal was inserted into the beaker containing
70
60
50
40
30
the solution. Single crystal of size 18 mm × 5 mm × 6 mm was har-
vested by slow evaporation method in a growth period of 20 days
(
Fig. 1).
3
. Results and discussion
3
.1. Single crystal X-ray diffraction
The single crystal X-ray diffraction (XRD) study reveals
that TSCHCL (CH ClN S) belongs to orthorhombic crystal
6
3
system with space group Pbca. The lattice parameters are
◦
a = 7.4714(5) A˚ , b = 11.1788(10) A˚ , c = 11.8775(9) A˚ , ˛ = ˇ = ꢀ = 90
and V = 993.69(13) A˚ 3 and are in good agreement with the reported
values [26]. Finely crushed powder of TSCHCL crystal was scanned
20
◦
◦
in the 2ꢁ values ranging from 10 to 80 . The obtained peaks
were indexed and are shown in Fig. 2. The hydrogen bonded
supramolecular crystal with centrosymmetry can also exibit SHG
effect [26,27]. The recorded transmission spectrum (Fig. 3) of
TSCHCL shows the lower cutoff wavelength at 380 nm and a wide
200
400
600
800
1000
1200
Wavelength (nm)
Fig. 3. The transmission spectrum of TSCHCL.

1
04
R. Santhakumari et al. / Spectrochimica Acta Part A 82 (2011) 102–107
1
1
1
1
1
80
60
40
20
00
8
6
4
2
0
0
0
0
0
200
220
240
260
280
300
Wavelength (nm)
Fig. 4. Excitation spectrum of TSCHCL.
30
25
20
15
10
5
0
Fig. 7. The proton NMR spectrum of TSCHCL.
at 801 cm 1 is due to the C–Cl stretching vibration. The C S stretch
of the thiosemicarbaside moiety is observed at 1176 cm . Salts of
−
−
1
−
1
primary amines show strong, broad absorption between 3000 cm
−1
−1
and 2800 cm . The peak at 2638 cm is evident for the presence
of NH3+. The N–H deformation vibration is observed at 1616 cm
−1
[
29].
3
.4. 1H and 13C NMR spectral analyses
The proton NMR ( H) and carbon NMR (13C) spectral analyses
1
were carried out on the TSCHCL crystal in D O using Bruker AC200-
2
NMR Spectrometer and are shown in Figs. 7 and 8 respectively. In
the proton NMR spectrum of TSCHCL, NH2 and NH protons near
to the C S group merged together and appeared as broad peak at
200
300
400
500
600
Wavelength (nm)
ı = 7.45 ppm. Water in the D O solvent appeared at ı = 4.508 ppm.
2
Fig. 5. The emission spectrum of TSCHCL.
In the carbon NMR spectrum of TSCHCL, thiocarbon C S appeared
at ı = 182.70 ppm.
−
1
A weak absorption, observed at 2925 cm is due to C–H stretch-
3.5. High resolution X-ray diffraction analysis
−1
ing. The peak at 3505 cm is due to NH2 asymmetric stretching
−
1
and an absorption peak at about 3174 cm is due to NH symmet-
ric stretching (medium). The presence of C–H deformation out of
The high-resolution X-ray diffraction curve (DC) was recorded
for a typical TSCHCL single crystal specimen (Fig. 9) using (0 0 2)
diffracting planes in symmetrical Bragg geometry by employing the
−1
plane is evident from the vibration at 996 cm . The peak observed
1
00.0
9
8
7
6
5
4
3
2
0
0
0
0
0
0
0
0
3
821
801
441
3
505
1720
7
02
2364
996
3373
2638
1366
1522
1176
1
0
2925
58
0
1616
0
.0
4
000.0
3000
2000
1500
1000
400.0
-1
Wavenumber (cm )
Fig. 6. The FTIR spectrum of TSCHCL.

R. Santhakumari et al. / Spectrochimica Acta Part A 82 (2011) 102–107
105
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 (ꢁB) as
d and sin ꢁB are inversely proportional to each other in the Bragg
equation (2d sin ꢁB = nꢃ; n and ꢃ being the order of reflection and
wavelength respectively which are fixed). The inset in the curve
shows the schematic to illustrate how the lattice around the defect
core undergoes tensile stress. The converse explanation is true in
case of interstitial defects which cause compressive stress in the
lattice around the defect core leading to decrease of lattice spacing
and in turn results in more scattered intensity at the higher Bragg
angles. However, the single diffraction curve with reasonably low
FWHM indicates that the crystalline perfection is fairly good. The
density of such vacancy defects is however meagre and in almost
all real crystals including nature gifted crystals, such defects are
commonly observed and are many times unavoidable due to ther-
modynamical conditions and hardly affect the device performance.
More details may be obtained from the study of high-resolution
diffuse X-ray scattering measurements [31], which is however not
the main focus of the present investigation. It is worth to men-
tion here that the observed scattering due to point defects is of
short range order as the strain due to such minute defects is lim-
ited to the very defect core and the long range order could not
be expected and hence the change in the lattice parameter of the
overall crystal is not expected. It may be mentioned here that the
minute information like the asymmetry in the DC could be possible
as in the present sample only because of the high-resolution of the
multicrystal X-ray diffractometer used in the present investigation.
Fig. 8. The carbon NMR spectrum of TSCHCL.
multicrystal X-ray diffractometer with MoK␣ radiation. As seen in
1
the figure, the DC contains a single peak and indicates that the spec-
imen is free from structural grain boundaries. The full width at half
maximum (FWHM) of these curve is 32 arc s which is somewhat
more than that expected from the plane wave theory of dynamical
X-ray diffraction [30], for an ideally perfect crystal but close to that
expected for nearly perfect real life crystals. This much broadness
with good scattered intensity along the wings of the DC indicates
that the crystal contains point defects and their aggregates. It is
interesting to see the shape of the DC. As seen in Fig. 9, the DC is
not symmetric with respect to the Bragg peak position and indi-
cates that the density of vacancy and interstitial defects are not
same. For a particular angular deviation (ꢂꢁ) of glancing angle (ꢁ)
with respect to the Bragg peak position (taken as zero for the sake
of convenience), the scattered intensity is much more in the nega-
tive 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
arise due to fast growth), the lattice around these defects undergo
3.6. Thermal analysis
Thermogram provides information about decomposition pat-
terns of materials and weight loss [32]. The thermal stability of
TSCHCL was studied by thermogravimetric analysis (TGA) and dif-
ferential thermal analysis (DTA) using SDT Q600 V8.3 Build 101
◦
◦
instrument between the temperatures 50 C and 1100 C at a heat-
◦
ing rate of 10 C/min under Nitrogen atmosphere (Fig. 10). There are
four weight losses noted in the thermogram. A sharp peak at 152 C
◦
is due to the melting point of the crystal. The major weight losses
◦
◦
◦
are observed at 198 C, 253 C and 565 C. It is due to the decom-
position of TSCHCL. From the DTA curve it is observed that, the
◦
material is stable up to 152 C, the melting point of the substance.
Above this point, the material begins to attain an endothermic tran-
sition and begins to decompose. The sharpness of this endothermic
peak shows the good degree of crystallinity of the sample [33].
3.7. Second harmonic generation
Kurtz and Perry [34] second harmonic generation (SHG) test
was performed to estimate the NLO efficiency of powdered TSCHCL
crystal. Second-harmonic radiation generated by the randomly
oriented microcrystals was focused by a lens and detected by a
photomultiplier tube. The doubling of frequency was confirmed by
the green color of the output radiation whose characteristic wave-
length is 532 nm. The relative measured output from the specimen
with respect to KDP crystals shows that SHG efficiency of the grown
TSCHCL crystals is 1.5 times higher than that of KDP. Some of the
earlier reported centrosymmetric crystals with space group and
SHG efficiency are given in Table 1.
3.8. Microhardness analysis
Vickers microhardness test was carried out on TSCHCL crystal
using microhardness tester fitted with a diamond indenter. The
indentations were made using a Vickers pyramidal indenter for
loads 25, 50 and 100 g. The diagonals of the impressions were
Fig. 9. High resolution spectrum of TSCHCL.

1
06
R. Santhakumari et al. / Spectrochimica Acta Part A 82 (2011) 102–107
Fig. 10. TGA/DTA curve of TSCHCL.
5
5
5
5
4
4
4
4
4
3
3
6
4
2
0
8
6
4
2
0
8
6
the Vicker’s microhardness studies, it is observed that the hard-
ness value increases upto a load of 100 g. For load above 100 g
crack started developing around the indentation mark which may
be due to the release of internal stresses [35]. The presence of cracks
confirms the decrease in microhardness [36]. Work hardening coef-
ficient n, a measure of the strength of the crystal is computed from
the log P–log d plot and it is found to be 2.60. Onitsch [37] inferred
that the value of n lies between 1 and 1.6 for hard materials and
for soft materials it is above 1.6. Thus the TSCHCL crystal comes
under the soft materials category. Yield strength can also be calcu-
n−2
lated using the relation ꢄy = (Hv/3) (0.1)
, where ꢄy is the yield
strength, Hv is the hardness of the material and n is the logarithmic
exponent. According to the relation, the yield strength is found to
be 44.3 MPa and hence the grown TSCHCL crystal has relatively low
mechanical strength.
4. Conclusion
2
0
30
40
50
60
70
80
90 100 110
Load P (g)
Thiosemicarbazide hydrochloride was synthesized in
the aqueous solution. The single crystal of dimensions
Fig. 11. The microhardness behavior of the TSCHCL crystal.
1
8 mm × 5 mm × 6 mm was grown by the slow evaporation
◦
technique at 30 C in constant temperature bath. Determination of
unit cell parameters by the single crystal X-ray diffraction tech-
nique confirmed the identity of the synthesized material. From the
FTIR spectrum the presence of functional groups of the material
were confirmed. Thermal analyses indicated that the crystal has
measured using Shimadzu (Japan); Model HMV-2 hardness instru-
ment. The measurements were made on the well-developed (1 0 1)
plane. The indentation time was kept as 25 s for all the loads. Vick-
ers microhardness number (Hv) was evaluated from the relation
2
2
◦
Hv = 1.8544(P/d ) kg/mm , where P is the applied load in g and d
is the diagonal length of the impression in mm. The variation of
microhardness values with applied load is shown in Fig. 11. From
good thermal stability. A sharp peak observed at 152 C in the DTA
curve corresponds to the melting point of the material. Optical
transmittance window and the lower cut off wavelength identified
through UV–vis–NIR and fluorescence spectrum revealed that
TSCHCL is a potential candidate for optical devices. The micro-
hardness study revealed that the crystal develops cracks for load
above 100 g. High resolution X-ray diffraction study showed that
the perfection of the crystal is fair even though it contains a low
angle boundary.
Table 1
Centrosymmetric crystal with SHG property.
Crystal
Space
group
SHG efficiency
Reference
[21]
(
p-Nitrophenol,
P21/c
4.1 times of
KDP
hexamethylene tetramine,
phosphoric acid and water)
super molecular crystal
Acknowledgements
R, S-serine
P21/a
P21/a
Pbca
0.02 times of
KDP
2.34 times of
KDP
1.5 times that
of KDP
[22]
[24]
One of the authors (RS) thanks Dr. A. Elangovan, Reader, Depart-
ment of Chemistry, Bharathidasan University, Tiruchirappalli, Dr.
P. Thiruvasagam, Department of Chemistry, Sastra University,
Thanjavur, for their fruitful discussions and University Grants Com-
mission, Government of India for financial assistance [File No.
Glycine picrate
Thiosemicarbazide
hydrochloride (TSCHCL)
Present
work

R. Santhakumari et al. / Spectrochimica Acta Part A 82 (2011) 102–107
107
MRP 2976/2009 (RS)]. The authors acknowledge Prof. P.K. Das,
[15] Z. Shuai, J.L. Bredas, Adv. Mater. 6 (1994) 485–486.
[
[
16] P. Guyot-Sionnest, Y.R. Shen, Phys. Rev. B 38 (1988) 7985–7989.
17] J.F. Nicoud, R.J. Twieg, in: D.S. Chemia, J. Zyss (Eds.), Nonlinear Optical Properties
of Organic Molecules and Crystals, Academic Press, Orlando, 1987.
Department of Inorganic and Physical Chemistry, Indian Institute
of Science, Bangalore for extending the laser facilities for the SHG
measurement. HSE thanks the staff of the X-ray Application Lab
of the CSEM, Neuchâtel, for access to the X-ray diffraction equip-
ment. The authors thank CECRI, Karaikudi and Sastra University,
Thanjavur, for extending the lab facilities to record the fluorescence
spectrum and NMR spectrum respectively.
[18] P.N. Prasad, D.J. Williams, Introduction to Nonlinear Optical Effects in Molecules
and Polymers, John-Wiley & Sons Inc., New York, 1991, pp. 35–38.
[
19] S. Allen, in: G.J. Ashwell (Ed.), Molecular Electronics, vol. 207, Research Studies,
Taunton, 1992.
[20] G.J. Ashwell, D. Bloof (Eds.), Organic Materials for Nonlinear Optics III, Royal
Society of Chemistry Press, Cambridge, 1993.
[
21] G. Wensheng, G. Fang, W. Chunssheng, L. Qitao, Z. Guangyung, W. Dorig, S.
Zhongshu, Sci. China Ser. B: Chem. 45 (2002) 276–278.
References
[22] K.E. Rieckhoff, W.L. Peticolas, Science 147 (1965) 610–611.
23] T. Ishihara, K. Koshino, H. Nakashima, Phys. Rev. Lett. 91 (2003) 253901.
[
[
[
1] N.P. Prasad, Polymer 32 (1991) 1746–1751.
2] S.R. Marder, J.E. Sohn, G.D. Stucky (Eds.), Material for Nonlinear Optics, Ameri-
can Chemical Society, Washington, DC, 1991.
[24] M. Shakir, S.K. Kushwaha, K.K. Maurya, M. Arora, G. Bhagavannarayana, J. Cryst.
Growth 311 (2009) 3871–3875.
[25] A. Samoc, M. Samoc, V.Z. Koley, B. Luther-Davies, Symposium on Photonics
Technologies for 7th Frame Work Program Wroctaw, 2006, p. 250.
[
[
3] B.E.A. Saleh, M.C. Teich, In Fundamental of Photonics, Wiley, New York, 1991.
4] B.G. Penn, B.H. Cardelino, C.E. Moore, A.W. Sheilds, D.O. Frazier, Prog. Cryst.
Growth Charact. 22 (1991) 19–51.
[26] L. Coghi, A.M.M. Lanfredi, A. Tiripicchio, J. Chem. Soc. Perkin
1808–1810.
2 (1976)
[
[
5] N. Zaitseva, L. Carman, Prog. Cryst. Growth Charact. 43 (2001) 1–118.
6] J. Badan, R. Hierie, A. Perigaud, J. Zyss (Eds.), NLO Properties of Organic
Molecules and Polymeric Materials, American Chemical Society Symposium
Series, vol. 233, American Chemical Society, Washington, DC, 1993.
7] P. Tansuri, K. Tansuree, B. Gabriele, R. Lara, J. Cryst. Growth Des. 4 (2004)
[27] W.S. Guo, F. Guo, M. Deng, et al., Inclution properties of organic nonlinear optical
materials, Acta Chim. Sin. 59 (2001) 284–290.
[28] H.H. Willard, L.L. Merritt Jr., J.A. Dean, F.A. Settle Jr., Instrumental Meth-
ods and Analysis, sixth ed., Wadsworth Publishing Company, USA, 1986,
p. 609.
[29] R.M. Silverstein, F.X. Webster (Eds.), Spectrometric Identification of
Organic Compounds, sixth ed., John Wiley and Sons, Inc., Canada, 1998,
pp. 91–103.
[30] B.W. Batterman, H. Cole, Rev. Mod. Phys. 36 (1964) 681–742.
[31] K. Lal, G. Bhagavannarayana, J. Appl. Cryst. 22 (1989) 209–215.
[32] C.M. Earnet, Anal. Chem. 56 (1984) 1471–1475.
[33] Y. Le Fur, R. Masse, M.Z. Cherkaoui, J.F. Nicoud, Kristallogr. Z. 210 (1995)
856–860.
[
7
43–747.
[
[
8] A. Datta, S.K. Pati, J. Chem. Phys. 118 (2003) 8420–8427.
9] G. DeMatos, V. Venkataraman, E. Nogueria, M. Belsley, P.A. Criado, M.J. Dianez,
E. Perez Carrido, Synth. Met. 115 (2000) 225–228.
[
[
[
[
[
10] D.S. Chemla, J. Zyss (Eds.), Nonlinear Optical Properties of Organic Molecules
and Crystals, vols. 1 and 2, Academic Press, New York, 1987.
11] A. Criado, M.J. Dianez, S.P.L. Garrido, I.M. Fernandes, M.E. Belsley, M. De Gomes,
Acta Crystallogr. C 56 (2000) 888–889.
12] J. Zaccaro, J.P. Salvestrini, A. Ibanez, P. Ney, M.D.J. Fontana, Opt. Soc. Am. 178
[34] S.K. Kurtz, T.T. Perry, J. Appl. Phys. 39 (1968) 3798–3813.
[35] P.M. Ushasree, R. Jayavel, C. Subramanian, P. Ramasamy, Bull. Electrochem. 14
(1998) 407–410.
[36] H. Li, R.C. Bradt, Mater. Sci. Eng. A142 (1991) 51–61.
[37] E.M. Onitsch, Mikroskopie 95 (1950) 12–14.
(
2000) 427–432.
13] B. Koopmans, A.M. Janner, H.T. Jonkman, G.A. Sawatzky, E. Van der Woude,
Phys. Rev. Lett. 71 (1993) 3569–3572.
14] B. Koopmans, A. Anema, H.T. Jonkman, G.A. Sawatzky, F. Van der Woude, Phys.
Rev. B 48 (1993) 2759–2764.