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Growth and characterization of nonlinear optical crystal – Semicarbazide Picrate
Accepted Manuscript Growth and characterization of nonlinear optical crystal – Semicarbazide Picrate
R. Raja, S. Seshadri, V. Santhanam, D. Vedhavalli PII:
S0022-2860(17)30814-1
DOI:
10.1016/j.molstruc.2017.06.035
Reference:
MOLSTR 23921
To appear in:
Journal of Molecular Structure
Received Date:
03 January 2017
Revised Date:
07 June 2017
Accepted Date:
08 June 2017
Please cite this article as: R. Raja, S. Seshadri, V. Santhanam, D. Vedhavalli, Growth and characterization of nonlinear optical crystal – Semicarbazide Picrate, Journal of Molecular Structure (2017), doi: 10.1016/j.molstruc.2017.06.035
This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
ACCEPTED MANUSCRIPT
1
Growth and characterization of nonlinear optical crystal – Semicarbazide Picrate R. Raja a, S. Seshadri b,*, V. Santhanam c, D. Vedhavalli a a Department of Physics, SCSVMV UNIVERSITY, Kanchipuram Tamilnadu 631 561 India b Department of Physics, Dr. Ambedkar Govt. Arts college, Vyasarpadi, Chennai-39 India c Department of Chemistry, SCSVMV UNIVERSITY, Kanchipuram Tamilnadu 631 561India
Abstract Good-optical-quality single crystals of Semicarbazide Picrate (SP), a new organic charge transfer molecular complex salt, were successfully synthesized and grown by the slow evaporation solution growth technique.
The grown crystal is
analyzed by various instrumentation techniques. The structure of the grown crystal as determined by single crystal XRD diffraction analysis.
The
presence of functional groups in the SP crystals is confirmed by FT-IR vibrational analysis.
The
optical transparency has been studied using UV–vis spectrophotometer. The relative second harmonic generation (SHG) efficiency measurements reveal that the SP crystals is a efficient nonlinear optical (NLO) material having an activity 1.4 times as that of the reference material potassium dihydrogen phosphate.
The TG/DTA thermal analyses reveal
the purity of the sample and no decomposition is observed up to the melting point. The mechanical properties of the crystal are examined by Vicker’s microhardness test. The dielectric permittivity, dielectric loss and AC conductivity of the crystal are measured at various temperatures. Keywords:
SP,
SXRD,
NLO,
TG/DTA
Microhardness study *Corresponding author Tel.:.9445257477 E-mail address: [email protected] (S.Seshadri).
1. Introduction In recent years, communication has developed by leaps and bounds due to the development of photonics where materials with nonlinear optical (NLO) properties are used extensively for optical switching, optical modulators, data storage devices, optical information processing and high density optical disk data storage [1, 2]. Generally, Organic crystals having efficient bulk nonlinear optical properties [3-7] depend on its hyperpolarizabilities. The
organic
crystals
having
higher
hyperpolarizabilities, lower dielectric constant and thermal stabilities are expected to have high NLO properties. A conjugated structure is possible to those crystals having charge transfer between electron acceptors and donors [8-11].
Single
crystals of picrates are formed with picric acid and some organic molecules through the hydrogen bonding and π-π interactions.
The concept of
charge transition is made possible by the use of Picrates which contain activating Phenolic OH and Electron withdrawing nitro groups where by the salts with various organic bases are formed. The conjugated base, picrate formed has increased molecular hyperpolarizability because of the proton transfer. The NLO activity of the series of picrates has been reported by several authors [12-25].
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2
In the present work, we attempted to synthesis the molecular complex adduct of semicarbazide with picric acid involving charge transfer from donor to acceptor followed by proton transfer from the acceptor. Single crystal of semicarbazide picrate is grown
by
low-temperature
solution
growth
2.2 Crystal Growth Method
technique. The structural properties of the grown
The yellow colour precipitate was then filtered off,
crystal are characterized by single crystal XRD.
dried and repeatedly recrystallised using double
Fourier transform infrared spectroscopic analysis,
distilled water to enhance the degree of the purity of
UV-Vis analysis, and second harmonic generation
the salt.
measurements are also carried out. The dielectric
repeated recrystallization at room temperature with
permittivity, dielectric loss and ac conductivity of
continuous stirring for more than 6 hrs. Later, the
the grown crystal are measured at various
beaker with filtered solution is covered with a
temperatures. The thermal stability of the grown
perforated lid to avoid the fast evaporation. The
crystal is analysed by Thermo Gravimetric and
solution is thoroughly stirred for 5 hours using a
Differential
magnetic stirrer till it becomes homogenous
Thermal
Analysis.
Vickers
The saturated solution is prepared by
microhardness test is carried out for the grown
solution.
crystal to determine the mechanical stability of the
insoluble impurities.
crystal.
to evaporate at room temperature, in order to obtain
The solution is filtered to avoid any Then, the solvent is allowed
the maximum purification. The SP single crystals 2. Experimental procedure
are grown by slow evaporation method for a period
2.1 Material Synthesize
of 20 days. The grown crystals are shown in Fig.1.
Analar grade of semicarbazide and picric acid are dissolved in water separately and allowed to stir for 2 hours till the compound is completely dissolved and both the solutions are mixed and stirred well for 3 hours. Transfer of proton from the –OH group of picric acid to the semicarbazide enables an output of yellow coloured precipitate. The reaction involved in the synthesis of SP is illustrated in the following equation.
Fig.1. Grown crystal of SP
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3
3. Results and discussion
Table.1 Structure refinement data for SP Crystal.
3.1 Single crystal X-ray diffraction analysis
Empirical formula
The structure of the synthesized single crystal of SP
Formula weight
304.19
is analyzed by single crystal XRD. The refinement
Temperature
296(2) K
details of the SP crystal is analyzed by The Bruker
Wavelength
0.71073 Ǻ
APEX-II CCD single crystal X-ray diffractometer with MoKα (λ=0.71073A˚) radiation. Table 1
Crystal system, space Triclinic, P-1 group
summarizes the detail of crystal parameters, data
Unit cell dimensions
collection and refinement for the SP crystal.
C7 H8 N6 O8
a=5.0220(2) Ǻ α=78.9734(14) b=10.2077(3)Ǻ deg. c=1.5374(4) Ǻ β=81.0851(15) deg. γ=82.4710(14) deg.
From
the results of crystal data, it is inferred that SP crystal belongs to triclinic system with space group P-1. Volume
570.37(3) Ǻ3
Z, Calculated density
2, 1.771 Mg/ m3
Absorption coefficient
0.162 mm-1
F(000)
312
Crystal size
0.250 x 0.220 x 0.160 mm
Θ range for collection Limiting indices
data 1.815 to 24.999 deg. -5<=h<=5,
-12<=k<=10,
-
13<=l<=13 Reflections collected / 8031 / 1983 [R(int) = 0.0186] unique Completeness to theta
= 24.999
Refinement method
Full-matrix least-squares on F^2
Data/restraints/parameters
2929 / 0 / 252
Goodness-of-fit on F^2
1.867
Final
R
99.2 %
indices R1 = 0.0328,wR2 = 0.0705
[I>2sigma(I)] Fig.2. ORTEP diagram of SP Crystal
R indices (all data)
R1 = 0.0349, R2 = 0.0709
Extinction coefficient
0.107(7)
Largest diff. peak and 0.299 and -0.263 e. Ǻ-3 hole
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3.2 Optical characterization
powder with uniform particle size and then filled
3.2.1 UV-Visible analysis
into the micro capillary tube. Then high-intensity
The optical transmittance spectrum of SP crystal is
Nd:YAG laser (λ =1064 nm) with a pulse duration
recorded using Lamda 35 model Perkin Elmer UV-
of 10 ns is passed through the micro capillary tube.
Vis. Spectrophotometer in the range of 190 to 1100
The emission of bright green radiation (λ = 532 nm)
nm and the recorded spectrum is shown in Fig.3.
from the samples confirms the generation of second
The lower cut-off wavelength of the SP crystal is
harmonics. The second harmonic signal of SP
observed around 328 nm. The crystal shows the
crystal is obtained for an input energy 0.68mJ/pulse.
absence of absorption in the entire visible range and
The SHG value of reference KDP samples gives a
that is an essential parameter for an NLO crystal.
signal 17.3 mJ/pulse for the same input energy.
This crystal is used for suitable optical applications
Thus, it is observed that the SHG efficiency of SP
due to its wide transparency window in the part of
crystal is 1.4 times than that of the standard KDP crystal. The presence of strong intermolecular interactions can extend the level of charge transfer into the supra molecular realm thereby enhancing the SHG response [29]. 3.3 Fourier transform infrared spectroscopic analysis The FT-IR analysis of SP crystal is recorded using BRUKER IFS 66V FT-IR Spectrometer and the spectrum is shown in Fig. 4. The assignment of
visible region above 328 nm. From that the cut off wave length the optical band gap is found as 3.78eV using the relation (1). 𝐸𝑔 = ℎ𝑐/𝜆
--(1)
various bands are given in Table.2. The formation of the charge transfer complex of semicarbaide picrate is strongly evidenced by the presence of main characteristic infrared bands of the donor and acceptor in the spectrum of SP crystal with slight change in frequencies. These assignments are in
Fig.3.UV-Vis. Spectrum of SP crystal 3.2.2 Non linear optical studies Nonlinear optical property of the SP crystal is analyzed by Second Harmonic Generation (SHG) test. Kurtz and Perry method [26-28] is employed. The grown single crystal of SP is crushed to fine
good agreement with the reported picrate complex compounds [30]. The vibrations of the NO2 groups are observed at 1550, 1334 and 835 cm-1. The absorption at 1433 and 1274 cm-1 are due to C-C and C-N stretching vibrations.
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Table 2.FTIR assignment of SP S.no Wavenumber -cm-1 Assignment
5
3.5 Dielectric analysis Good quality single crystal of SP is selected to
1
3324
N-H stretching
measure dielectric permittivity, dielectric loss and
2
3255
N-H stretching
A.C conductivity. Readings are taken with HIOKI
3
3022
C-H asymmetric stretching C-H symmetric
4
2916
stretching
3532 -50 LCR meter in the frequency range of 50 Hz and 5MHz at various temperatures. The samples are cut and polished using wet cloth polishing sheet. The sample is electroded on either side with silver
5
1647
C=O stretching
6
1550
The resistance, capacitance and dissipation factor
7
1487
N-O2 asymmetric Stretching N-H bending
8
1433
C-C stretching
3.5.1 Dielectric permittivity and loss
9
1334
10
1274
N-O2 symmetric Stretching C-N stretching
11
1079
C-H in plane bending
12
936
C-N-H bending
13
835
NO2 scissoring
paste to enable it to act like parallel plate capacitor. values are measured using LCR meter. The dielectric constant of the SP crystal is calculated
through
the
capacitance
by
the
fundamental equation (2)
𝜀𝑟 =
𝐶𝑑
(2)
𝜀0𝐴
Where C is the capacitance, d is thickness of the sample,𝜀𝑜 = 8.854 ∗ 10 ‒ 12𝐹𝑚 ‒ 1is the permittivity of free space, A is the area of cross section. Fig 5 shows variation of dielectric values with various frequencies. From the figure it is observed that the dielectric permittivity decreases with increase in frequency for all temperatures and this is termed as anomalous dielectric dispersion. The dielectric loss (tan𝛿) is calculated by the equation (3) tan 𝛿 = 𝜀𝑟𝐷
(3)
Where, D is the dissipation factor. A material must have low dissipation factor for device fabrication. Fig. 4 FTIR Spectrum of SP crystal
ACCEPTED MANUSCRIPT Dielectric loss values are calculated from the
6
Fig.6. log f vs dielectric loss
experimental observations [31]. The very high values of tan𝛿 at low frequencies is due to presence of all forms of polarizations namely, space charge, orientation, ionic and electronic polarization. As
3.5.2 AC Conductivity studies The AC conductivity is calculated using the relation
𝜎𝑎𝑐 = 𝜔𝜀0𝜀𝑟𝑡𝑎𝑛𝛿
the frequency increases, the space charge cannot sustain and comply with external field and hence the
polarization
decreases.
Fig.6
shows
the
dielectric loss of the grown crystal at different frequencies. The low value of dielectric loss at high frequency reveals the high optical quality of the crystal with less electrically active defects. This is a most desirable property for NLO applications.
(4)
where, ω is angular frequency of applied electric field. The Fig.7 shows variation of ac conductivity for different frequencies. From the graph, it is observed the AC conductivity feebly increases up to the logarithmic of 6.30HZ. From the sharp increase observed in the logarithmic frequency at 6.47Hz indicates the dielectric breakdown frequency of the material.
Fig.5. log f vs dielectric permittivity Fig.7. log f vs AC conductivity 3.6 Vicker’s microhardness measurement The mechanical strength of the materials plays a key role in the device fabrication. Microhardness measurements are done for SP crystal using LeitzWetzlar hardness tester fitted with a Vickers diamond indenter at room temperature. The Vicker’s hardness is calculated using the standard formula
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7
Where k is the material constant and n is the
𝐻𝑉 =
1.8554𝑃 𝑑2
kg/mm2
(5)
Where P is the applied load in Kg, d in μm Elastic
stiffness
d is the indentation diagonal length. The above relation indicates that HV should increase with the increase in P if n > 2 and decrease with P when n <
and HV in Kg/mm2. 3.6.1
Mayer’s index (or work-hardening coefficient) and
and
yield
strength
2. The ‘n’ value is determined from the plot of log P vs. log d, as shown in Fig.9. The slope of the plot of
measurement The microhardness value correlates with other
log P versus log d gives the work hardening index
mechanical properties (i)yield strength (σy) (ii)
(n) and that is found to be 1.33. This mechanical
elastic stiffness constant (C11). Yield strength is a
strength is better for device fabrications [32, 33].
point at which material exceeds the elastic limit and will not return to its origin shape or length if the stress is removed. Yield strength is one of the important properties for device fabrication which can be calculated by the relation, (6)
𝜎𝑦 = 𝐻𝑣/3
The elastic stiffness constant gives an idea about tightness of bonding between neighbour atoms and
Fig.8. Load vs Hardness
is calculated using Wooster’s empirical relation as [31-33] 𝐶11 = 𝐻7/4 𝑣
(7)
The elastic stiffness constant and yield strength are tabulated in Table.3 Table 3 Elastic stiffness and Yield strength of SP Load (P) g 25 50 100
Hv (kg/mm2) 21.05 27.04 45.7
C11 (M Pa) 2.029 3.144 7.683
σy(M Pa) 68.81 88.39 149.4 Fig.9. LogP vs Log d
Meyer index (n) The Meyer’s index number is calculated from the Mayer’s law,
3.7 Thermal analysis Thermogravimetry (TG) and differential thermal
𝑛
𝑃 = 𝑘𝑑
(8)
analysis
(DTA)
studies
are
carried
out
simultaneously in inert (N) atmosphere at a slow
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8
heating rate of 20◦C/min from room temperature to
studies shows that SP belongs to the soft material
500◦C using Perkin Elmer thermal analyzer. TG &
category.
DTA curves are presented in Fig.10 From TG curve it is observed that the weight loss of 89.9% occurs at 161◦C .The compound is stable and there is no phase transition up to melting point and there is no decomposition [34]. This property enables its usage in lasers. The DTA curve shows a sharp endothermic peak at 160.9◦C which is the melting point of the crystal. This endothermic event is in good agreement with TGA trace.
References 1. Chemla.D.S, J.Zyss, Nonlinear Optical Properties of Organic Molecules, vol. 2, Academic Press, New York, (1987). 2.Sukhorukov.A.A, KivsharYu.S, J. Opt. Soc. Am. B, 19 (2002) 772. 3.Srinivasan.P, Kanagasekaran.T, Gopalakrishnan.R,Bhagavannarayana.G and P.Ramasamy, Cryst. Growth & Des. 6(7) (2006) pp 1663. 4.Gibbs.J.W, ‘Collected works', Longmans, Green and Co., New York, (1928). 5.MullinJ.W,
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Kumbakonam. 7.Noyes.A.A and WhitreyW.R, Z. Physik. Chem., Fig.10 TGA/DTA curve of SP 4. Conclusions Nonlinear optical single crystals of SP are grown by slow evaporation technique. The structure analysis is calculated by single crystal X-ray diffraction analysis. From the UV–Vis spectral analysis, it is found that the SP has a wide transparency range 354–1100 nm. The relative SHG efficiency of SP is found to be 1.4 times greater than that of KDP. The dielectric constant and dielectric loss are analyzed by dielectric measurements. Vickers’ microhardness
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ACCEPTED MANUSCRIPT HIGHLIGHTS
The Semicarbazide Picrate crystals were synthesized and grown from saturated solution by slow evaporation technique. Nonlinear Optical property of Semicarbazide Picrate were measured and the relative SHG efficiency is found to be 1.4 times greater than that of KDP. The mechanical stability of the crystals have been analysed which showed that SP belongs to the hard material category.
R. Raja, S. Seshadri, V. Santhanam, D. Vedhavalli PII:
S0022-2860(17)30814-1
DOI:
10.1016/j.molstruc.2017.06.035
Reference:
MOLSTR 23921
To appear in:
Journal of Molecular Structure
Received Date:
03 January 2017
Revised Date:
07 June 2017
Accepted Date:
08 June 2017
Please cite this article as: R. Raja, S. Seshadri, V. Santhanam, D. Vedhavalli, Growth and characterization of nonlinear optical crystal – Semicarbazide Picrate, Journal of Molecular Structure (2017), doi: 10.1016/j.molstruc.2017.06.035
This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
ACCEPTED MANUSCRIPT
1
Growth and characterization of nonlinear optical crystal – Semicarbazide Picrate R. Raja a, S. Seshadri b,*, V. Santhanam c, D. Vedhavalli a a Department of Physics, SCSVMV UNIVERSITY, Kanchipuram Tamilnadu 631 561 India b Department of Physics, Dr. Ambedkar Govt. Arts college, Vyasarpadi, Chennai-39 India c Department of Chemistry, SCSVMV UNIVERSITY, Kanchipuram Tamilnadu 631 561India
Abstract Good-optical-quality single crystals of Semicarbazide Picrate (SP), a new organic charge transfer molecular complex salt, were successfully synthesized and grown by the slow evaporation solution growth technique.
The grown crystal is
analyzed by various instrumentation techniques. The structure of the grown crystal as determined by single crystal XRD diffraction analysis.
The
presence of functional groups in the SP crystals is confirmed by FT-IR vibrational analysis.
The
optical transparency has been studied using UV–vis spectrophotometer. The relative second harmonic generation (SHG) efficiency measurements reveal that the SP crystals is a efficient nonlinear optical (NLO) material having an activity 1.4 times as that of the reference material potassium dihydrogen phosphate.
The TG/DTA thermal analyses reveal
the purity of the sample and no decomposition is observed up to the melting point. The mechanical properties of the crystal are examined by Vicker’s microhardness test. The dielectric permittivity, dielectric loss and AC conductivity of the crystal are measured at various temperatures. Keywords:
SP,
SXRD,
NLO,
TG/DTA
Microhardness study *Corresponding author Tel.:.9445257477 E-mail address: [email protected] (S.Seshadri).
1. Introduction In recent years, communication has developed by leaps and bounds due to the development of photonics where materials with nonlinear optical (NLO) properties are used extensively for optical switching, optical modulators, data storage devices, optical information processing and high density optical disk data storage [1, 2]. Generally, Organic crystals having efficient bulk nonlinear optical properties [3-7] depend on its hyperpolarizabilities. The
organic
crystals
having
higher
hyperpolarizabilities, lower dielectric constant and thermal stabilities are expected to have high NLO properties. A conjugated structure is possible to those crystals having charge transfer between electron acceptors and donors [8-11].
Single
crystals of picrates are formed with picric acid and some organic molecules through the hydrogen bonding and π-π interactions.
The concept of
charge transition is made possible by the use of Picrates which contain activating Phenolic OH and Electron withdrawing nitro groups where by the salts with various organic bases are formed. The conjugated base, picrate formed has increased molecular hyperpolarizability because of the proton transfer. The NLO activity of the series of picrates has been reported by several authors [12-25].
ACCEPTED MANUSCRIPT
2
In the present work, we attempted to synthesis the molecular complex adduct of semicarbazide with picric acid involving charge transfer from donor to acceptor followed by proton transfer from the acceptor. Single crystal of semicarbazide picrate is grown
by
low-temperature
solution
growth
2.2 Crystal Growth Method
technique. The structural properties of the grown
The yellow colour precipitate was then filtered off,
crystal are characterized by single crystal XRD.
dried and repeatedly recrystallised using double
Fourier transform infrared spectroscopic analysis,
distilled water to enhance the degree of the purity of
UV-Vis analysis, and second harmonic generation
the salt.
measurements are also carried out. The dielectric
repeated recrystallization at room temperature with
permittivity, dielectric loss and ac conductivity of
continuous stirring for more than 6 hrs. Later, the
the grown crystal are measured at various
beaker with filtered solution is covered with a
temperatures. The thermal stability of the grown
perforated lid to avoid the fast evaporation. The
crystal is analysed by Thermo Gravimetric and
solution is thoroughly stirred for 5 hours using a
Differential
magnetic stirrer till it becomes homogenous
Thermal
Analysis.
Vickers
The saturated solution is prepared by
microhardness test is carried out for the grown
solution.
crystal to determine the mechanical stability of the
insoluble impurities.
crystal.
to evaporate at room temperature, in order to obtain
The solution is filtered to avoid any Then, the solvent is allowed
the maximum purification. The SP single crystals 2. Experimental procedure
are grown by slow evaporation method for a period
2.1 Material Synthesize
of 20 days. The grown crystals are shown in Fig.1.
Analar grade of semicarbazide and picric acid are dissolved in water separately and allowed to stir for 2 hours till the compound is completely dissolved and both the solutions are mixed and stirred well for 3 hours. Transfer of proton from the –OH group of picric acid to the semicarbazide enables an output of yellow coloured precipitate. The reaction involved in the synthesis of SP is illustrated in the following equation.
Fig.1. Grown crystal of SP
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3
3. Results and discussion
Table.1 Structure refinement data for SP Crystal.
3.1 Single crystal X-ray diffraction analysis
Empirical formula
The structure of the synthesized single crystal of SP
Formula weight
304.19
is analyzed by single crystal XRD. The refinement
Temperature
296(2) K
details of the SP crystal is analyzed by The Bruker
Wavelength
0.71073 Ǻ
APEX-II CCD single crystal X-ray diffractometer with MoKα (λ=0.71073A˚) radiation. Table 1
Crystal system, space Triclinic, P-1 group
summarizes the detail of crystal parameters, data
Unit cell dimensions
collection and refinement for the SP crystal.
C7 H8 N6 O8
a=5.0220(2) Ǻ α=78.9734(14) b=10.2077(3)Ǻ deg. c=1.5374(4) Ǻ β=81.0851(15) deg. γ=82.4710(14) deg.
From
the results of crystal data, it is inferred that SP crystal belongs to triclinic system with space group P-1. Volume
570.37(3) Ǻ3
Z, Calculated density
2, 1.771 Mg/ m3
Absorption coefficient
0.162 mm-1
F(000)
312
Crystal size
0.250 x 0.220 x 0.160 mm
Θ range for collection Limiting indices
data 1.815 to 24.999 deg. -5<=h<=5,
-12<=k<=10,
-
13<=l<=13 Reflections collected / 8031 / 1983 [R(int) = 0.0186] unique Completeness to theta
= 24.999
Refinement method
Full-matrix least-squares on F^2
Data/restraints/parameters
2929 / 0 / 252
Goodness-of-fit on F^2
1.867
Final
R
99.2 %
indices R1 = 0.0328,wR2 = 0.0705
[I>2sigma(I)] Fig.2. ORTEP diagram of SP Crystal
R indices (all data)
R1 = 0.0349, R2 = 0.0709
Extinction coefficient
0.107(7)
Largest diff. peak and 0.299 and -0.263 e. Ǻ-3 hole
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3.2 Optical characterization
powder with uniform particle size and then filled
3.2.1 UV-Visible analysis
into the micro capillary tube. Then high-intensity
The optical transmittance spectrum of SP crystal is
Nd:YAG laser (λ =1064 nm) with a pulse duration
recorded using Lamda 35 model Perkin Elmer UV-
of 10 ns is passed through the micro capillary tube.
Vis. Spectrophotometer in the range of 190 to 1100
The emission of bright green radiation (λ = 532 nm)
nm and the recorded spectrum is shown in Fig.3.
from the samples confirms the generation of second
The lower cut-off wavelength of the SP crystal is
harmonics. The second harmonic signal of SP
observed around 328 nm. The crystal shows the
crystal is obtained for an input energy 0.68mJ/pulse.
absence of absorption in the entire visible range and
The SHG value of reference KDP samples gives a
that is an essential parameter for an NLO crystal.
signal 17.3 mJ/pulse for the same input energy.
This crystal is used for suitable optical applications
Thus, it is observed that the SHG efficiency of SP
due to its wide transparency window in the part of
crystal is 1.4 times than that of the standard KDP crystal. The presence of strong intermolecular interactions can extend the level of charge transfer into the supra molecular realm thereby enhancing the SHG response [29]. 3.3 Fourier transform infrared spectroscopic analysis The FT-IR analysis of SP crystal is recorded using BRUKER IFS 66V FT-IR Spectrometer and the spectrum is shown in Fig. 4. The assignment of
visible region above 328 nm. From that the cut off wave length the optical band gap is found as 3.78eV using the relation (1). 𝐸𝑔 = ℎ𝑐/𝜆
--(1)
various bands are given in Table.2. The formation of the charge transfer complex of semicarbaide picrate is strongly evidenced by the presence of main characteristic infrared bands of the donor and acceptor in the spectrum of SP crystal with slight change in frequencies. These assignments are in
Fig.3.UV-Vis. Spectrum of SP crystal 3.2.2 Non linear optical studies Nonlinear optical property of the SP crystal is analyzed by Second Harmonic Generation (SHG) test. Kurtz and Perry method [26-28] is employed. The grown single crystal of SP is crushed to fine
good agreement with the reported picrate complex compounds [30]. The vibrations of the NO2 groups are observed at 1550, 1334 and 835 cm-1. The absorption at 1433 and 1274 cm-1 are due to C-C and C-N stretching vibrations.
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Table 2.FTIR assignment of SP S.no Wavenumber -cm-1 Assignment
5
3.5 Dielectric analysis Good quality single crystal of SP is selected to
1
3324
N-H stretching
measure dielectric permittivity, dielectric loss and
2
3255
N-H stretching
A.C conductivity. Readings are taken with HIOKI
3
3022
C-H asymmetric stretching C-H symmetric
4
2916
stretching
3532 -50 LCR meter in the frequency range of 50 Hz and 5MHz at various temperatures. The samples are cut and polished using wet cloth polishing sheet. The sample is electroded on either side with silver
5
1647
C=O stretching
6
1550
The resistance, capacitance and dissipation factor
7
1487
N-O2 asymmetric Stretching N-H bending
8
1433
C-C stretching
3.5.1 Dielectric permittivity and loss
9
1334
10
1274
N-O2 symmetric Stretching C-N stretching
11
1079
C-H in plane bending
12
936
C-N-H bending
13
835
NO2 scissoring
paste to enable it to act like parallel plate capacitor. values are measured using LCR meter. The dielectric constant of the SP crystal is calculated
through
the
capacitance
by
the
fundamental equation (2)
𝜀𝑟 =
𝐶𝑑
(2)
𝜀0𝐴
Where C is the capacitance, d is thickness of the sample,𝜀𝑜 = 8.854 ∗ 10 ‒ 12𝐹𝑚 ‒ 1is the permittivity of free space, A is the area of cross section. Fig 5 shows variation of dielectric values with various frequencies. From the figure it is observed that the dielectric permittivity decreases with increase in frequency for all temperatures and this is termed as anomalous dielectric dispersion. The dielectric loss (tan𝛿) is calculated by the equation (3) tan 𝛿 = 𝜀𝑟𝐷
(3)
Where, D is the dissipation factor. A material must have low dissipation factor for device fabrication. Fig. 4 FTIR Spectrum of SP crystal
ACCEPTED MANUSCRIPT Dielectric loss values are calculated from the
6
Fig.6. log f vs dielectric loss
experimental observations [31]. The very high values of tan𝛿 at low frequencies is due to presence of all forms of polarizations namely, space charge, orientation, ionic and electronic polarization. As
3.5.2 AC Conductivity studies The AC conductivity is calculated using the relation
𝜎𝑎𝑐 = 𝜔𝜀0𝜀𝑟𝑡𝑎𝑛𝛿
the frequency increases, the space charge cannot sustain and comply with external field and hence the
polarization
decreases.
Fig.6
shows
the
dielectric loss of the grown crystal at different frequencies. The low value of dielectric loss at high frequency reveals the high optical quality of the crystal with less electrically active defects. This is a most desirable property for NLO applications.
(4)
where, ω is angular frequency of applied electric field. The Fig.7 shows variation of ac conductivity for different frequencies. From the graph, it is observed the AC conductivity feebly increases up to the logarithmic of 6.30HZ. From the sharp increase observed in the logarithmic frequency at 6.47Hz indicates the dielectric breakdown frequency of the material.
Fig.5. log f vs dielectric permittivity Fig.7. log f vs AC conductivity 3.6 Vicker’s microhardness measurement The mechanical strength of the materials plays a key role in the device fabrication. Microhardness measurements are done for SP crystal using LeitzWetzlar hardness tester fitted with a Vickers diamond indenter at room temperature. The Vicker’s hardness is calculated using the standard formula
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7
Where k is the material constant and n is the
𝐻𝑉 =
1.8554𝑃 𝑑2
kg/mm2
(5)
Where P is the applied load in Kg, d in μm Elastic
stiffness
d is the indentation diagonal length. The above relation indicates that HV should increase with the increase in P if n > 2 and decrease with P when n <
and HV in Kg/mm2. 3.6.1
Mayer’s index (or work-hardening coefficient) and
and
yield
strength
2. The ‘n’ value is determined from the plot of log P vs. log d, as shown in Fig.9. The slope of the plot of
measurement The microhardness value correlates with other
log P versus log d gives the work hardening index
mechanical properties (i)yield strength (σy) (ii)
(n) and that is found to be 1.33. This mechanical
elastic stiffness constant (C11). Yield strength is a
strength is better for device fabrications [32, 33].
point at which material exceeds the elastic limit and will not return to its origin shape or length if the stress is removed. Yield strength is one of the important properties for device fabrication which can be calculated by the relation, (6)
𝜎𝑦 = 𝐻𝑣/3
The elastic stiffness constant gives an idea about tightness of bonding between neighbour atoms and
Fig.8. Load vs Hardness
is calculated using Wooster’s empirical relation as [31-33] 𝐶11 = 𝐻7/4 𝑣
(7)
The elastic stiffness constant and yield strength are tabulated in Table.3 Table 3 Elastic stiffness and Yield strength of SP Load (P) g 25 50 100
Hv (kg/mm2) 21.05 27.04 45.7
C11 (M Pa) 2.029 3.144 7.683
σy(M Pa) 68.81 88.39 149.4 Fig.9. LogP vs Log d
Meyer index (n) The Meyer’s index number is calculated from the Mayer’s law,
3.7 Thermal analysis Thermogravimetry (TG) and differential thermal
𝑛
𝑃 = 𝑘𝑑
(8)
analysis
(DTA)
studies
are
carried
out
simultaneously in inert (N) atmosphere at a slow
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heating rate of 20◦C/min from room temperature to
studies shows that SP belongs to the soft material
500◦C using Perkin Elmer thermal analyzer. TG &
category.
DTA curves are presented in Fig.10 From TG curve it is observed that the weight loss of 89.9% occurs at 161◦C .The compound is stable and there is no phase transition up to melting point and there is no decomposition [34]. This property enables its usage in lasers. The DTA curve shows a sharp endothermic peak at 160.9◦C which is the melting point of the crystal. This endothermic event is in good agreement with TGA trace.
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ACCEPTED MANUSCRIPT HIGHLIGHTS
The Semicarbazide Picrate crystals were synthesized and grown from saturated solution by slow evaporation technique. Nonlinear Optical property of Semicarbazide Picrate were measured and the relative SHG efficiency is found to be 1.4 times greater than that of KDP. The mechanical stability of the crystals have been analysed which showed that SP belongs to the hard material category.