Journal of Minerals & Materials Characterization & Engineering, Vol. 9, No.12, pp.1071-1080, 2010
jmmce.org Printed in the USA. All rights reserved
1071
Growth Kinetics and Optical and Mechanical Properties of Glycine Lithium
Sulphate (GLS) Crystals
S. Suresh1,*, A. Ramanand1, D. Jayaraman2 and S.M. Navis Priya3
1Department of Physics, Loyola College, Chennai-600 034, India.
2Department of Physics, Loyola Institute of Technology, Chennai-602 103, India
3Department of Physics, Jeppiaar Engineering College, Chennai-600 119, India.
*Corresponding Author: [e-mail]
ABSTRACT
Glycine Lithium Sulphate (GLS) is one of the potential materials for Non-linear optical property
applications. Single crystals of Glycine Lithium Sulphate (GLS) with very high degree of
transparency were grown from aqueous solution by slow evaporation technique. Single crystal
X-ray diffraction analysis reveals that the crystal belongs to orthorhombic system with the space
group Pna21. The density measurements were carried out by both theoretical and experimental
methods. The optical absorption study reveals the transparency of the crystal in the entire visible
region and the cut off wavelength has been found to be 350 nm. The dependence of extinction
coefficient (K) and refractive index (n) on the absorption has also been reported. The
mechanical properties were studied using Vickers microhardness tester. The dielectric studies
were also reported for grown crystals. The photoconductivity reveals the negative nature of the
photocurrent in these crystals.
Key Words: Slow evaporation technique, Single crystal, Optical absorption, Vickers
microhardness tester, Photoconductivity.
1. INTRODUCTION
Among the organic materials amino acids constitute a family in which glycine is the simplest of
all the amino acids. It has been reported that some complexes of amino acids with simple
inorganic salts may exhibit ferroelectric properties [1-3]. Hoshino et al [4] reported about the
dielectric properties of triglycine fluroberyllate. Some complexes of glycine with H2SO4 [5],
CaCl2 [6], CaNO3 [7], BaCl2 [8], SrCl2 [8], CoBr2 [9] and LiNO3 [10] form single crystals but

1072 S. Suresh, A. Ramanand, D. Jayaraman, S.M. Navis Priya Vol.9, No.12
none of these are reported to have nonlinear optical property. Single crystals of glycine sodium
nitrate [11] and benzoyl glycine [12] showed no centre of symmetry and their quadratic
nonlinear coefficients were examined [11,12]. The crystal structure of glycine lithium sulphate
(GLS) was solved by Michael Fleck and Ladislav Bohatý [13] and the growth and
characterization have been discussed by Balakrishnan et al [14]. In the present work, the growth
has been carried out in isothermal solvent evaporation technique. Vickers indentation test
enumerating the mechanical strength of the crystal has been determined and the stiffness
constant for the grown crystal have been calculated. The dielectric constant and dielectric loss
have been determined for the GLS crystal at various frequencies.
2. EXPERIMENTAL
A solution of glycine lithium sulphate was prepared by dissolving equimolar amount of glycine
and lithium sulphate. The solution was continuously stirrer using a magnetic stirrer of room
temperature. The chemical reaction may be represented as,
C2H5NO2 + Li2SO4 → [Li2( SO4 )(C2H5NO2)] (1)
The prepared solution was filtered and kept undisturbed in a constant temperature bath
maintained at a temperature of 40 °C. When evaporation taken place slowly, supersaturation is
activated. As a result, crystals with dimensions 12 × 11 × 5 mm3 were harvested in a period of 40
days. Fig.1 shows as-grown GLS crystal.
Fig.1 Grown single crystals of GLS
3. SINGLE CRYSTAL XRD
Single crystal X-ray diffraction (XRD) analysis for the grown crystals has been carried out to
identify the lattice parameters. The calculated lattice parameters are a = 5.0252 Å,b = 7.6366 Ǻ,

Vol.9, No.12 Growth Kinetics and Optical and Mechanical Properties 1073
and c=16.3975 Ǻ and the crystal belongs to orthorhombic structure with space group Pca21.
XRD results are in good agreement with the reported values [14].
4. DENSITY MEASUREMENTS
The density of GLS crystal was calculated by using the equation (2) [15]
/A
M
ZNabc
ρ
= (2)
where M is molecular weight of GLS, molecular unit cell Z = 4, NA is Avogadro’s number and a,
b and c are the cell parameters of GLS crystal. The theoretical density is found to be 9.3602
gm/cc. The density of GLS crystal was measured experimentally by the floatation method at
room temperature (32ºC), and the measured density can be obtained by the following equation
(
)
'
/
solvent
mmm ρρ =− (3)
where m is the mass of GLS crystal sample in the air, m΄ is the mass when the GLS crystal
sample was immersed in CCl4 and ρsolvent is the density of solvent (CCl4) used at measured
temperature. From this measurement, the density of the crystal is found to be 9.3693 gm/cc. The
experimentally measured density is in good agreement with the theoretically found value [16].
5. OPTICAL ABSORPTION
The optical absorption spectrum of Glycine Lithium Sulphate (GLS) single crystal was recorded
in the wavelength region ranging from 200 nm to 2000nm using a Varian Cary
5E spectrophotometer and is shown in Fig. 2. For optical fabrications, the crystal should be
highly transparent in a considerable region of wavelength [17, 18]. The UV cut off wavelength
for the grown crystal was found to be 350 nm, which makes it a potential material for optical
device fabrications.
11 log
dT
⎛⎞
α= ⎜⎟
⎝⎠
(4)
where T is the transmittance and d is the thickness of the crystal. As a direct band gap material,
the crystal under study has an absorption coefficient (α) obeying the following relation for high
photon energies (hν).
1/2
()
g
Ah E
h
υ−
α= υ (5)

1074 S. Suresh, A. Ramanand, D. Jayaraman, S.M. Navis Priya Vol.9, No.12
where Eg is the optical band gap of the crystal and A is a constant. The plot of variation of
(αhν)2 versus hν is shown in Fig. 3. Eg was evaluated by the extrapolation of the linear part [19].
The band gap is found to be 3 .50 eV and as a consequence of wide band gap, the grown crystal
has large transmittance in the visible region [20].
Fig. 2 Optical absorption spectrum of GLS Fig.3 Plot of α vs photon energy for
single crystal GLS single crystals
6. OPTICAL CONSTANTS
The optical constants (n, K) are determined from the transmission (T) and reflection (R)
spectrum based on the following relations [21]
2
2
(1) exp()
1Rexp( 2)
R
t
Tt
−−α
=−−α
(6)
where t is the thickness and α is related to extinction coefficient K by
4
K
π
αλ
= (7)
The reflectance (R) can be written in terms of refractive index (n) as [22]
()
()
2
2
1
1
n
Rn
−
=+ (8)

Vol.9, No.12 Growth Kinetics and Optical and Mechanical Properties 1075
The reflectance (R) in terms of absorption coefficient can be written as
11 exp(exp()
1 exp()
tt
Rt
±− −α+ α
=+−α (9)
From the above equation, the refractive index n can also be derived as
2
(1)3 103
2( 1)
RRR
nR
+±+ −
=− − (10)
Figs. 4 and 5 show the variation of reflectance (R) and extinction coefficient (K) as a function of
absorption coefficient respectively. From the graphs, it is clear that both the reflectance and
extinction coefficient depend on the absorption coefficient. Since the internal efficiency of the
device also depends on the absorption coefficient, by tailoring the absorption coefficient, one can
achieve the desired material to fabricate the optoelectronic devices.
Fig.4 Plot of α versus reflectance (R). Fig. 5 Plot of α versus extinction
coefficient (k).
7. DIELECTRIC PROPERTY
The dielectric studies on Glycine Lithium Sulphate single crystal has been carried out using
H1OKI 3532-50 LCR HITESTER. A rectangular sample of thickness 1.46 mm and area of cross-
section nearly equal to 39.7769 mm2 is placed between the two copper electrodes to form parallel
plate capacitors and silver paint is coated on the both surface of the sample for firm contact. The
dielectric study on GLS was carried out in the frequency range 50 Hz - 5MHz. Figs. 6 and 7
show the variation of dielectric constant and dielectric loss with applied frequency. The dielectric

1076 S. Suresh, A. Ramanand, D. Jayaraman, S.M. Navis Priya Vol.9, No.12
constant is found to be high in the lower frequency region and decreases continuously with
increase in frequency. In the lower frequency region the dielectric constant is high due to the
combination of all the polarizations such as electronic, ionic, dipolar and space charge. At high
frequency region, both the dielectric constant and dielectric loss is minimum, which confirms
that the grown crystal has minimum defects.
0
200
400
600
800
1000
1200
1400
0123 45678
log f
dielectric constant
0
0.5
1
1.5
2
2.5
3
3.5
4
4.5
5
02468
log f
Dielectric loss
Fig. 6 dielectric constant vs frequency Fig.7 dielectric Loss vs frequency
8. PHOTOCONDUCTIVITY
The photoconductivity studies of grown crystals were carried out by connecting the sample in
series with a dc power supply and a Pico ammeter (Keithley 480) at room temperature. The setup
is similar to that in the work of Ledorux [23]. The applied field was increased from 100 to 1800
V/cm, and the corresponding dark current and photocurrent were recorded. Fig.8 shows the
dependence of the dark current and photocurrent with respect to the applied field at room
temperature. The dark current and photocurrent increase linearly with respect to the applied field.
At every instant, the dark current is greater than the photocurrent, which is called negative
photoconductivity. This may be attributed due to decrease in either the number of free charge
carriers or their lifetime when subjected to radiation. According to the Stockmann model, the
forbidden gap in the material contains two energy levels in which one is situated between the
Fermi level and the conduction band while the other is located close to the valence band [24].
The second state has high capture cross-sections for electrons and holes. As it captures electrons
from the conduction band and holes from the valence band, the number of charge carriers in the
conduction bands gets reduced and the current decreases in the presence of radiation. Thus, the
crystal is said to exhibit negative photoconducting effect.

Vol.9, No.12 Growth Kinetics and Optical and Mechanical Properties 1077
Fig. 8 Dark current and photocurrent as a function of the applied field.
9. MECHANICAL PROPERTY
Microhardness studies of any system have a direct correlation with the crystal structure and are
very sensitive to the presence of any other phase or phase transition and lattice perfections are
prevalent in the system. The hardness of the material depends on the different parameters such as
lattice energy, Debye temperature, heat of formation and interatomic spacing [25]. The hardness
tests for GLS crystal was carried out by Leitz micro hardness tester with a diamond pyramidal
indenter. The diagonal length of the indentation for various applied loads in kg is measured for a
constant indentation period of 15 sec. The Vickers’ hardness number (Hv) is calculated using the
relation [26]
2
2/
8544.1 mmkg
d
P
HV= (10)
where P is the applied load in kg and d is the diagonal length in mm. The variation of Hv with the
applied load P is shown in Fig. 9 and a plot of log P versus log d for the grown crystal is shown
in Fig. 10 The plot between log P versus log d yields a straight line graph and its slope gives the
work hardening index n, and is found to be 3.09.
According to Meyer’s relation,
n dKP 1 = (11)

1078 S. Suresh, A. Ramanand, D. Jayaraman, S.M. Navis Priya Vol.9, No.12
where K1 is the standard hardness value which can be found out from the plot of P versus dn.
Since the material takes some time to revert to the elastic mode after every indentation, a
correction x is applied to the d value and the Kick’s law is related as
()
2
2xdKP += (12)
From Eqs. (11) and (12)
x
K
K
d
K
K
dn⎟
⎟
⎠
⎞
⎜
⎜
⎝
⎛
+
⎟
⎟
⎠
⎞
⎜
⎜
⎝
⎛
=
1
2
2/1
1
2
2/ (13)
The slope of dn/2 versus d yields (k2/k1)1/2 and the intercept is a measure of x. The striking factor
is that x is positive only when n<2 and negative for n>2 [27]. From the hardness value, the yield
strength (σv) can be calculated using the relation,
(){}
()
()
n
V
Vn
n
n
H−
⎥
⎦
⎤
⎢
⎣
⎡
−−
−
−−=
2
21
25.12
21
9.2
σ (14)
The load-dependent hardness parameters n, K1, and K2 and yield strength σv are calculated for
the grown crystal and are given in Table 1. The elastic stiffness constant (C11) following
Wooster’s empirical relation as C11 = Hv7/4 [28]. As indentation initiates plastic deformation in a
crystal, which is highly directional in nature, the hardness measurement may be a function of the
orientation of the indented crystal. Fig 10 shows the variation of Hv as a function of applied load
ranging from 10 g to 50 g on (0 1 2) face for GLS crystal. It is very clear from the figure that Hv
increases with increase of load. The calculated stiffness constant for different loads is shown in
Table 2.
0
0.5
1
1.5
2
2.5
1.61.62 1.64 1.661.681.71.72 1.74
log d
log p
Fig. 9 Variation of Hardness versus P Fig.10 Plot of log P versus log d

Vol.9, No.12 Growth Kinetics and Optical and Mechanical Properties 1079
Table 1. Hardness Parameters of the
GLS Crystals
Parameters Value
n
K1 (kg/mm)
K2 (kg/mm)
x (μm)
σv (MPa)
3.0929
6 x 1012
1.62 x 108
-5 x 10-8
926.197
10. CONCLUSIONS
Transparent single crystals of GLS have been grown successfully using slow solvent evaporation
technique. X-ray analysis reveals that GLS crystal belongs to orthorhombic structure with space
group Pna21. The density of GLS crystals is found to be 9.3693 g/cm3, which is in agreement
with theoretical value. UV - Visible absorption spectrum shows excellent transmission in the
entire visible region. The band gap energy for the grown crystal is found to be 3.50 eV. The
optical investigations show a high value of both extinction coefficient (K) and reflectivity (R)
indicating high transparency of the crystal, which confirms its suitability for optical device
fabrications. The dielectric constant and dielectric loss were studied as a function of frequency at
room temperature. Photoconductivity studies confirm that the crystal possesses a negative
photoconductivity.The mechanical properties were carried out to understand the hardness
parameters and stiffness constant of the grown crystals.
REFERENCES
[1] R. Pepinsky, Y. Okaya, D. P. Eastman, and T. Mitsui, Phys. Rev. 107 (1957) 1538.
[2] R. Pepinsky, K. Vedam, and Y. Okaya, Phys. Rev. 110 (1958) 1309.
[3] A. Deepthy and H. L. Bhat, J. Cryst. Growth 226 (2001) 287.
[4] S. Hoshino, Y. Okaya, and R. Pepinsky, Phys. Rev. 115 (1959) 1955.
[5] S. Hoshino, T. Mitsui, F. Jona, and R. Pepinsky Phys. Rev. 107 (1957) 125.
[6] S. Natarajan and J. K. Mohan Rao, Z. Kristallogr. 152 (1984) 179.
[7] S. Natarajan, K. Ravikumar, and S. S. Rajan, Z. Kristallogr. 168 (1984) 75.
[8] P. Narayanan and S. Venkataraman, Z. Kristallogr. 142 (1975) 52.
1188 T. Balakrishnan and K. Ramamurthi: Glycine lithium sulphate single crystal
© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim www.crt-journal.org
[9] K. Ravikumar and S. S. Rajan, Z.Kristallogr. 171 (1985) 201.
[10] J. Baran, M. Drozd, A. Pietraszko, M. Trzebiatowska, and H. Ratajczak J. Polish.
Chem. 77 (2003) 1561.
Table 2 Stiffness constant of GLS
Load P Hv(kg/mm3) C11 x 1014 Pa
20
50
100
88
130
153
2.52
5.00
6.65

1080 S. Suresh, A. Ramanand, D. Jayaraman, S.M. Navis Priya Vol.9, No.12
[11] M. Narayan Bhat and S. M. Dharmaprakash, J. Cryst. Growth 235(2002) 511.
[12] H. S. Nagaraja, V. Upadhyaya, P. Mohan Rao, S. Aithal, and A. P. Bhat, J. Cryst.
Growth 193 (1998) 674.
[13] Michel Fleck and Ladislav Bohaty, Acta Crystallogr.C 60, (2004) 291.
[14] T. Balakrishnan and K. Ramamurthi Cryst. Res. Technol. 41, No. 12, (2006) 1184 – 1188 .
[15] Wenwei Ge, Huaijin Zhang, Jiyang Wang , Donggang Ran, Shangquian Sun, Hairui Xia,
Junhai Liu, Xiangang Xu, Xiaobo Hu, and Minhua Jiyang, J.Cryst.Growth., 282 (2005 )
320-329.
[16] N. Vijayan, S. Rajasekaran, G. Bhagavannarayana, R. Rameshbabu, R. Gopalakrishnan, M.
Palanichammy, and P.Ramasamy, Cryst. Growth Des. 6, (2006) 2441
[17] Krishnakumar.V and Nagalakshmi .R, Spectrochim. Acta A, 61 (2005) 499-507.
[18] Krishnakumar.V and John Xavier.R, Spectrochim. Acta A ., 60, (2004) 709-714.
[19] Chawla .A.K, Kaur.D, and Chandra.R, Opt. Mater.29 (2007) 995-998 .
[20] Eya .D.D.O, Ekpunobi.A.J, and Okeke .C.E, Acad. Open Internet J. (2006)17 .
[21] Denton.R.E, Campbell.R.D and Tomlin .S.G, J. Phys., D5, (1972)852-863 .
[22] Ashour.A, El-Kadry .N, and Mahmoud.S.A, Thin Solid Films., 269 (1995) 117-120
[23] Xavier, F. P, Inigo, A. R., Goldsmith. G. J, Parphyrins, Journal of Porphyrins and
Phthalocyanines, , 3 (1999) 679-686 .
[24] Joshi, V. N. Photoconductivity; Marcel Dekker: New York, 1990.
[25] Jiaghong Gong, J. Mater Sci. Lett. 19 (2000) 515 .
[26] B. W. Mott, “Micro indentation hardness testing”, 1957.
[27] Rani Christhu Dhas, J. Benet Charles, and F. D. Gnanam, J. Cryst. Growth 137, (1994) 295
[28] Susmita Karan, et al., Mat. Scie. Engg. A 398 (2005) 198.