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Journal of Minerals & Materials Characterization & Engineering, Vol. 10, No.10, pp.959-972, 2011
jmmce.org Printed in the USA. All rights reserved
Synthesis, Growth and Material Characterization of Bis L-Alanine Triethanol
Amine (BLATEA) Single Crystals Grown
by Slow Evaporation Technique
, P. Selvarajan
*, T. H. Freeda
Department of Physics, The M.D.T. Hindu College, Tirunelveli-627010, Tamilnadu, India.
Department of Physics, Aditanar College of Arts and Science, Tiruchendur-628216, Tamilnadu,
Department of Physics, S.T. Hindu College, Nagercoil-629002, Tamilnadu, India.
*Corresponding author: firstname.lastname@example.org
Bis L-alanine Triethanol amine (BLATEA) salt was synthesized by solution method and it was
subjected to solubility studies. Using the solubility data, the saturated solution of the synthesized
salt was prepared and single crystals of Bis L-alanine Triethanol amine (BLATEA) were grown
from aqueous solution by slow evaporation technique. X-ray diffraction (XRD) study was carried
out to confirm the crystal structure. FTIR study reveals the functional groups of the sample.
UV-Visible transmittance and absorption spectra were recorded for the sample to analyze the
transparency of the grown crystal. Vickers micro hardness values were measured for the sample
and from the microhardness study it is observed that BLATEA crystal is a soft material. SHG
generation study was carried out to confirm the NLO activity of grown sample and also BLATEA
crystal has been analyzed with dielectric measurements
Keywords: NLO crystal; Crystal growth; Single crystal; Characterization; XRD; FTIR;
microhardness; dielectric constant; activation energy
Many efforts are being made recently to combine amino acids with different organic and
inorganic acids and salts to synthesize outstanding Nonlinear Optical (NLO) materials and these
materials are of great interest because of their significant impact on LASER technology, optical
960 T. Vela, P. Selvarajan, T. H. Freeda Vol.10, No.10
communication and optical data storage and optical data processing etc . The overwhelming
success of molecular engineering in controlling NLO properties in the last decade has promoted
better initiatives in crystal engineering . Organic molecular crystals have received a great deal
of attention in recent years due to their extremely large optical non-linearities compared with
most of the inorganic crystals . The organic materials play in an important role in second
harmonic generation (SHG) . L-alanine  is an organic α-amino acid with the chemical
COOH. It is classified as non-polar amino acid and was first crystallized
by Bernal  and later by Simpson  and Destro et.al  and it is the simplest acentric crystal
with second harmonic generation efficiency of about 0.3 times that of the well known KDP [9-
11]. If L-alanine is mixed with different organic and inorganic acids and salts  to form novel
materials, it is expected to get improved NLO properties. Some complexes of L-alanine have
been recently crystallized and various studies have been investigated by many researches [13-
14]. Triethanol amine is an organic material with the molecular formula C
and it is a
liquid with an ammonia aroma. It is soluble in chloroform, water and alcohol and boiling at
C. It is used in dry cleaning soaps, cosmetics, textile processing and as corrosion inhibitor.
In this work, L-alanine and triethanol amine were used to form a new NLO crystal from aqueous
solution. Crystal growth from solution is an important process that is used in many applications
from laboratories to industrial scale . The aim of this work is to grow single crystals of
BLATEA by slow evaporation growth technique and to characterize the grown crystal by
various studies such as structural, optical, mechanical and dielectric studies.
2. EXPERIMENTAL TECHNIQUES
The title compound BLATEA was synthesized by taking the chemicals such as AR grade L-
alanine and triethanol amine in the molar ratio 2:1. The calculated amounts of the precursor
chemicals were dissolved in de-ionized water and stirred well using a magnetic stirrer for about 2
hours. The solution was heated until the synthesized salt of BLATEA was obtained. During the
synthesis, temperature of the solution was maintained at 50
C in order to avoid the
decomposition of the sample. The purity of the synthesized salt was improved by repeated re-
2.2 Solubility Study
The solubility of BLATEA in de-ionized water was determined as a function of temperature in
the range of 30 to 50
C. The beaker containing the solution was initially maintained at 30
and continuously stirred using a magnetic stirrer. The amount of BLATEA required to saturate
the solution at this temperature was estimated by gravimetrical method . The solubility
curve for BLATEA sample is shown in Figure 1. From the results, it is observed that solubility
Vol.10, No.10 Synthesis, Growth and Material Characterization 961
increases with temperature for the sample and the sample has positive temperature coefficient of
solubility. Solubility data is necessary to prepare the saturated solution of the sample at a
30 35 40 45 50
Fig. 1: Variation of solubility with temperature for BLATEA
2.3 Growth of BLATEA Crystals
Solution method with slow evaporation technique was adopted to grow the single crystals of the
synthesized salt of BLATEA. In accordance with the solubility data, the saturated solution was
prepared and it was constantly stirred for about 2 hours using a magnetic stirrer. Then it was
filtered using a 4 micro Whatmann filter paper and the filtered solution was kept in a borosil
beaker covered with a porous paper. The grown crystal was harvested after a period of 20 days
and it is displayed in the photograph (Fig.2).
962 T. Vela, P. Selvarajan, T. H. Freeda Vol.10, No.10
Fig. 2: The grown BLATEA single crystals
2.4 Characterization Methods
Single crystal XRD data for BLATEA crystal was obtained by employing Bruker-Nonious
MACH3/CAD4 single X-ray diffractometer with MoK
radiation (λ=0.71073 Å). To identify
the reflection planes, powder X-ray diffraction pattern of the powdered sample was obtained
using a powder X-ray diffractometer (PANalytical Model, Nickel filtered Cu K
λ= 1.54056 Å at 35 kV, 10 mA). The sample was scanned over the required range for 2Ө
). The FTIR spectrum of the sample was recorded using a Shimadzu 8400S
spectrometer by the KBr pellet technique in the range 400-4500 cm
. The optical spectra of
BLATEA crystal have been recorded in the region 190-1100 nm using a Perkin Elmer
(Model:Lambda 35) UV-vis-NIR spectrophotometer. Microhardness test was carried out using
a Leitz Weitzler hardness tester fitted with a diamond indenter. Smooth, flat face (001) of the
grown BLATEA crystal was polished and subjected to the hardness study. Indentations were
made for various loads from 25 g to 100 g. Several trials of indentation were carried out and the
average diagonal lengths were measured for an indentation time of 10 seconds. The Vickers
microhardness number was calculated using the relation Hv = 1.8544 P / d
where P is
the applied load and d is the diagonal length of the indentation [17,18]. The Second Harmonic
Generation (SHG) efficiency for the sample was measured by Kurtz-Perry powder technique
. The BLATEA crystal was powdered with uniform particle size using a ball mill and it was
packed densely between two transparent glass slides. An Nd:YAG laser was used as a light
source. This laser device can be operated in two different-modes. In the single-shot mode, the
laser emits an 8 ns pulse. While in the multi-shot mode, the laser produces a continuous train of 8
ns pulse at a repetition rate of 10 Hz. In the present study, a multi-shot mode of 8 ns laser pulse
with a spot radius of 1 mm was used. The experimental set-up for measuring SHG efficiency is
shown in Figure 3. The fundamental laser beam of 1064 nm wavelength was made to fall
normally on the sample cell(S). The power of the incident beam was measured using a power
meter. The filter F1 removes the 1064 nm light and the filter F2 is a BG-38 filter, which also
Vol.10, No.10 Synthesis, Growth and Material Characterization 963
removes the residual 1064 nm light. F3 is an interference filter with bandwidth of 4 nm and
central wavelength 532 nm. The green light was detected by a photomultiplier tube (PMT) and
displayed on a Cathode Ray Oscilloscope (CRO). KDP crystal was powdered into identical size
as BLATEA crystal and it was used as reference material in the SHG measurement.
Fig. 3: Experimental setup for measuring relative SHG efficiency
3. RESULTS AND DISCUSSION
3.1 Structural Characterization
Powder XRD method is useful for confirming the identity of a crystalline material and
determining the phase purity. Bis L-alanine triethanol amine (BLATEA) crystal was ground into
powder and it is subjected to powder X-ray diffraction studies. The powder XRD pattern of the
sample is shown in Figure 4. The well-defined peaks at specific 2Ө values show high
crystallinity of the grown crystals. All the reflections of powder XRD patterns of this work were
indexed using the INDEXING and TREOR software packages. The lattice parameters obtained
from the indexed XRD patterns using UNITCELL software package. Table 1 provides the lattice
parameters of BLATEA crystal from single crystal XRD study and it observed from the data that
the lattice parameters of BLATEA crystal obtained from powder XRD study are comparable
with those obtained from single crystal XRD study. From XRD studies, it is noticed that grown
BLATEA crystal crystallizes in orthorhombic structure.
964 T. Vela, P. Selvarajan, T. H. Freeda Vol.10, No.10
1 02 03 04 05 06 07 0
Two theeta (degree)
Fig. 4: Powder XRD pattern for powdered sample of BLATEA crystal
Table 1: Unit cell parameters for BLATEA crystal
3.2 Optical Characterization
The FTIR spectrum of the grown BLATEA crystal was recorded in the KBr phase in the
frequency region 450–4500 cm
using Perkin Elmer spectrometer and is shown in Figure 5. The
assignments for the absorption peaks / bands are provided in accordance with the data reported in
the literature . The CH
symmetric stretching, CH
symmetric bending and
O-H bending vibrations produce peak at 1454 cm
, 1412 cm
, 1360 cm
and 1302 cm
stretching and NH
scissoring vibrations produce peak at 3408 cm
. FTIR spectrum reveals that L-alanine is protonated by the carboxyl group. The observed
absorption peaks/bands and the wave number assignments of BLATEA sample are given in
Sample Cell parameters
Bis L-alanine Triethanol
Vol.10, No.10 Synthesis, Growth and Material Characterization 965
4000 35003000 2500 2000 15001000500
Fig. 5: FTIR spectrum for Bis L-alanine Triethanol amine sample
In order to determine the optical transmission characteristics of the grown crystal, UV–vis–NIR
spectrum was recorded using a spectrophotometer. Optically clear single crystal of thickness
about 2 mm was used for this study. UV-visible absorption and transmittance spectra of bis L-
alanine triethanol amine crystal in the wave length region 200-1100 nm are shown in Figures 6
and 7. This spectral study may be assisted in understanding electronic structure of the optical
band gap of the crystal.
In order to confirm Nonlinear Optical (NLO) property, microcrystalline form of the grown
crystal was packed between two transparent glass slides (sample cell). Second-harmonic
radiation generated by the randomly oriented micro crystals was focused by a lens and detected
by a photomultiplier tube after filtration of the incident or fundamental radiation of 1064 nm.
The doubling of frequency was confirmed by the green color of the output radiation whose
characteristic wavelength is 532 nm. The relative measured output from the specimen with
respect to KDP crystal shows that SHG efficiency of the grown BLATEA crystal is 0.61 times
that of KDP.
966 T. Vela, P. Selvarajan, T. H. Freeda Vol.10, No.10
Table 2: FTIR spectral assignments for BLATEA crystal
sym.str. and aromatic C-H
C-O band stretching
Vol.10, No.10 Synthesis, Growth and Material Characterization 967
200 300 400 500600 700 800 90010001100
1 9 4 ,1 .91 17
1 9 5 ,1 .91 5
Fig. 6: UV-Visible absorption spectrum for BLATEA crystal
200 300 400 500 600 70080090010001100
Fig. 7: UV-Visible transmittance spectrum for BLATEA crystal
968 T. Vela, P. Selvarajan, T. H. Freeda Vol.10, No.10
3.3 Mechanical Characterization
Mechanical strength of a crystal was studied by measuring microhardness and it plays an
important role in the fabrication of opto-electronic devices. The hardness of a material is a
measure of its resistance to plastic deformation. The permanent deformation can be achieved by
indentation, bending, scratching or cutting. In an ideal crystal, the hardness value should be
independent of applied load. But in a real crystal, the load dependence is observed. This is due to
normal indentation size effect (ISE) . The variation of Vickers hardness number (H
various loads for BLATEA crystal is shown in Figure 8. It was observed that microhardness
number increases with increase in load upto 100 g and further increase in load causes cracks
formation which leads the decrease in hardness value. This may be due to the release of internal
stress. Fig. 9 shows the variation of log P with log d for the crystal of this work. The work
hardening coefficient n was determined from the slope of log P versus log d plot using least
square fit method. The value of n was found to be 2.4. According to theory , if n > 1.6,
microhardness value increases with increasing load and decreases with increasing load if n <
1.6. The increase in H
for increasing in load observed in the present study is in good agreement
with the theoretical predication. Since the work hardening coefficient n is more than 1.6, the
grown BLATEA crystal belongs to the category of soft materials.
2 03 0405 0607 0809 01 0 01 10
Hardness number H
load p(gm )
Fig. 8: Variation of Vickers hardness number with load for BLATEA crystal
Vol.10, No.10 Synthesis, Growth and Material Characterization 969
1 .6 41 .6 61 .6 81 .7 01 .7 21 .7 4
Fig. 9: Variation of log P with log d for BLATEA crystal
3.4 Dielectric Characterization
The plots of frequency dependence of dielectric parameters such as dielectric constant (ε
dielectric loss (tan δ) of the grown sample of this work at different temperatures like 308 K,
328 K, 348 K and 368 K are displayed in the Figures 10 and 11. From the results, it is observed
that the dielectric parameters decrease with the increase in frequency and increase with increase
in temperature. The nature of decrease of ε
and tan δ with frequency suggests that BLATEA
crystal seems to contain dipoles of continuously varying relaxation times. The values of
dielectric constant and loss are low at higher frequencies because the dipoles and the charged
species of larger relaxation times may not be able to respond to these frequencies. Low value of
dielectric loss indicates that the grown crystal is of good quality i.e. the grown crystal is a
good quality dielectric material . Variation of the dielectric parameters with temperature is
generally attributed to the crystal expansion, the electronic, space charge and ionic polarizations
and also attributed to the thermally generated charge carriers and impurity dipoles. As far as
polarization is concerned, the increase in dielectric constant with temperature is essentially due
to the temperature variation of ionic and space charge polarizations and not due to the
temperature variation of orientational polarization [24,25]. AC conductivity (σ
) of the sample
has been determined using the relation σ
= 2πf ε
tan δ where f is the frequency of a.c.
is the dielectric constant, ε
is the permitivity of free space, tan δ is the dielectric loss
. AC conductivity values are fitted in the equation σ
exp(-E/kT) where σ
constant which depends upon the type of the sample, E is the activation energy, k is the
Boltzmann’s constant and T is the absolute temperature. A graph is drawn between ln σ
1/T which gives a straight line (Fig. 12). The slope of the straight line is equal to E/k from
970 T. Vela, P. Selvarajan, T. H. Freeda Vol.10, No.10
which the activation energy (E) is calculated to be 0.815 eV. The activation energy is the energy
required for the charge carriers to take part in the conduction process and the observed high
value of activation energy indicates that the sample is an insulating type material.
3.0 3.54.0 4.5 5.0 5.5 6.0
Fig. 10: Frequency dependence of dielectric constant (ε
) for BLATEA
crystal at different temperatures
3 .03 .54 .04 .55 .05 .56 .0
Fig. 11: Frequency dependence of dielectric loss (tan δ) for BLATEA
crystal at different temperatures
Vol.10, No.10 Synthesis, Growth and Material Characterization 971
2.72.8 2.9 3.0 3.1 3.2 3.3
1 00 0 /T (K
Fig. 12: Plot of ln σ
versus 1/T for BLATEA crystal at frequency of 1000 Hz.
BLATEA salt was synthesized by solution method by mixing L-alanine and triethanolamine in
2:1 molar ratio and the single crystals of BLATEA have been grown by slow evaporation
solution growth technique. The grown crystals were transparent and colourless. The solubility of
BLATEA sample was observed to be increasing with increase in temperature. The unit cell
parameters for BLATEA crystal have been found out by XRD method and the crystal structure is
confirmed to be orthorhombic. The spectroscopic techniques such as FTIR spectral analysis and
the optical absorption/transmission studies were carried out to characterize the grown crystals.
The NLO efficiency of BLATEA sample is found to be 0.61 times that of KDP. The
microhardness study indicates that the crystal belongs to the class of soft materials. The
dielectric parameters such as dielectric constant and loss factor of BLATEA were measured at
different frequencies and temperatures and the activation energy for the sample for the
conduction process was determined to be 0.815 eV.
The supports extended in the research by RRL (Trivandrum), CECRI (Karaikudi), Crecent
Engineering college (Chennai), St. Joseph’s College (Trichy) and M.K.University (Madurai) are
gratefully acknowledged. Also we thank authorities of Management of Aditanar College of Arts
972 T. Vela, P. Selvarajan, T. H. Freeda Vol.10, No.10
and Science, Tiruchendur, MDT Hindu College, Tirunelveli and S.T. Hindu College, Nagercoil
for the encouragement given to us to carry out the research work.
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