Journal of Crystallization Process and Technology, 2013, 3, 130-135
http://dx.doi.org/10.4236/jcpt.2013.34021 Published Online October 2013 (http://www.scirp.org/journal/jcpt)
Bulk Growth and Characterization of D-(–)-Alanine Single
Crystals
Kalimuthu Moovendaran, Subramanian Natarajan*
School of Physics, Madurai Kamaraj University, Madurai, India.
Received July 2nd, 2013; revised August 2nd, 2013; accepted August 9th, 2013
Copyright © 2013 Kalimuthu Moovendaran, Subramanian Natarajan. This is an open access article distributed under the Creative
Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original
work is properly cited.
ABSTRACT
Single crystal of D-(–)-alanine (DALA), a non-linear optical material from the amino acid family was grown using a
home-made crystal growth setup. The crystals of DALA were also grown by slow evaporation solution technique (SEST).
The grown crystals were characterized by using single crystal X-ray diffraction, high resolution X-ray diffraction (HRXRD)
and UV-vis-NIR and CD spectroscopy. Measurements of Vicker’s microhardness, laser damage threshold (LDT) value
and second harmonic generation (SHG) efficiency are also reported. Thermal and dielectric studies were also carried out.
Keywords: D-(–)-Alanine; NLO Material; MKN Setup; HRXRD; CD; SHG
1. Introduction
The search for new materials with high optical nonlin-
earities is an important field of research due to their prac-
tical applications in harmonic generation, amplitude and
phase modulation, switching and other signal processing
devices. Alanine is the simplest amino acid with an
asymmetric carbon atom. L-Alanine and DL-Alanine are
the usually available forms of alanine. D-Amino acids do
not occur in nature and are usually synthesized by manu-
facturers. The crystals of L-alanine [1] and DL-alanine [2]
were grown by slow evaporation method, characterized
and their NLO property established. Recently, the spec-
tral characterization, second harmonic generation (SHG)
and hyper Raleigh scattering studies of D-(–)-alanine
were reported from our laboratory [3]. The bulk growth
of the single crystal of D-(–)-alanine has not been re-
ported till date. In the present investigation, a bulk single
crystal of D-(–)-alanine (DALA) was grown using a
home-made crystal growth setup. The crystals of DALA
were also grown by slow evaporation solution technique
(SEST). The crystals were characterized by using XRD,
HRXRD and spectroscopic techniques. Several useful
properties of the crystal, such as microhardness, LDT
and SHG were evaluated. Thermo gravimetric and dif-
ferential thermal analysis curves were recorded and in-
terpreted. Measurements of dielectric constant and loss
were also made.
2. Crystal Growth Experiments
2.1. Growth of DALA Crystals Using Slow
Evaporation Solution Technique (SEST)
D-Alanine (C3H7NO2) is a white crystalline powder with
a molecular weight of 89.09. Commercially available
D-alanine (M/s. Loba Chemie Pvt. Ltd., purity: 99%)
was further purified by recrystallising it once using water
as the solvent. A saturated solution of D-alanine was
prepared and allowed to evaporate at a room temperature
(30˚C). Transparent colourless crystals of size: 10 × 5 × 3
mm were obtained within a period of one week.
2.2. Growth of a Bulk Crystal Using a Home
Made Setup
A new setup was designed in our laboratory to conduct
several crystal growth experiments simultaneously [4].
The home made setup (called as MKN setup) is made up
of two large tanks and it consists of several ampoules,
dimmerstat, temperature controller, heating coil and a
thermometer. Constant temperature and uniform tem-
perature gradient were maintained, to increase the growth
rate and quality of the crystal grown. The details of this
setup has been given elsewhere [4,5]. A suitable seed
crystal was chosen from the crystals obtained by the *Corresponding author.

Bulk Growth and Characterization of D-(–)-Alanine Single Crystals
131
SEST experiment and mounted for the crystal growth
along the [020] direction. An aqueous saturated solution
was prepared and transferred to the growth ampoule. A
growth run for 20 days resulted in a crystal of sizes: 15
mm diameter and 45 mm length, the average growth rate
being about 2 mm per day. The photograph of the grown
crystal of DALA is shown in Figure 1.
3. Characterization
The grown crystal was subjected to single crystal X-ray
diffraction studies using an Enraf Nonius CAD-4/MACH
3 diffractometer, with MoKα radiation (0.71073 Å). The
accurate cell parameters of the grown crystals at room
temperature (25˚C) were obtained from the least-squares
refinement of the setting angles of 25 reflections. To
study the crystalline perfection of the grown crystals, a
multicrystal X-ray diffractometer developed at the Na-
tional Physical Laboratory, New Delhi [6] has been used
for recording the high-resolution diffraction curves (DCs)
for (0 2 0) diffracting plane in symmetrical Bragg ge-
ometry. The description of the above instrument has al-
ready been given elsewhere [7]. The transmittance of the
grown crystal (for a crystal of thickness: 2 mm) was
measured using a Perkin-Elmer Lambda-35 spectropho-
tometer in the wavelength range of 200 - 1100 nm with a
slit of width 2 nm and scan speed of 240 nm/min. CD
spectra were recorded in the wavelength range of 150 -
400 nm at room temperature, using a JASCO J-180 spec-
tropolarimeter. The aqueous solution (3 mM) of the sam-
ple was kept in a quartz cuvette of path length 0.1 cm.
Microhardness measurements were made on the cut and
polished plate of the crystal using a Shimadzu Micro-
hardness Tester (Model No. HMV2T) with a diamond
indenter. The well-polished crystal was mounted on the
platform of the microhardness tester and loads of differ-
ent magnitudes were applied over a fixed interval of time
(8 s). The laser damage threshold (LDT) measurement
has been carried out for the grown crystal using a
Q-swtiched Nd: YAG laser (λ = 1064 nm). The second
Figure 1. Photograph of the grown crystal.
harmonic generation behaviour of the powdered materi-
als was tested using the Kurtz and Perry method [8],
making use of the laser source described above. Simul-
taneous thermogravimetry (TG) and differential thermal
analyses (DTA) of powdered samples were performed in
the temperature range of 25˚C to 900˚C, using a Netzsch
STA 409 PC/PG thermal analyzer at a heating rate of
10˚C/min. An Al2O3 (alumina) crucible was used and it
served as a reference for the sample. Dielectric constant
and loss measurements were made using a HIOKI
352-50 LCR meter in the frequency range of 100 Hz - 1
MHz. Crystals of reasonable dimensions were cut from
the bulk crystal and polished using the solvent (water). A
silver coating was applied on the opposite sides of the
crystal and placed between two copper electrodes and
thus a parallel plate capacitor was formed.
4. Results and Discussion
4.1. Single Crystal X-Ray Diffraction
From the single crystal X-ray diffraction studies, the lat-
tice parameters were determined as: a = 6.043(3), b =
12.337(5) and c = 5.784(3) Å. These values are in agree-
ment with those reported by Sullivan et al. [9]. It is al-
ready known that this compound crystallizes in the or-
thorhombic system with the space group P212121. The
density of the single crystals of DALA was determined
as 1.37(2) gm/cm3 using the floatation method. The
melting point was found out as 290(2)˚C.
4.2. High-Resolution X-Ray Diffraction Analysis
The high-resolution diffraction curve (DC, Figure 2) was
recorded for the DALA single crystal using (0 2 0) dif-
fracting planes in symmetrical Bragg geometry by em-
ploying the multicrystal X-ray diffractometer described
above with MoKα1 radiation. On deconvolution of the
diffraction curve, it is clear that the curve contains an
additional peak which is 105 arc s away from the main
peak. The additional peak corresponds to an internal
structural low angle grain boundary. For better under-
standing, the schematic of a structural grain boundary is
given in the inset of Figure 2(a). As seen in the inset,
two regions of the crystal are misoriented by a finite an-
gle α also known as tilt angle. Tilt angle may be defined
as the misorientation angle between the two crystalline
regions on both sides of the structural grain boundary.
The two regions may be perfect. If the value of α is ≤1
arc min, it is considered as very low angle boundary. If α
> 1 arc min but less than a deg, it is considered as low
angle boundary. The tilt angle for the very low angle
boundary is 105 arc s with respect to the main crystal
block. The full width at half maximum (FWHM) of the
main peak and the boundary are respectively 23 and 30
arc s. The low FWHM values of main peak and the very

Bulk Growth and Characterization of D-(–)-Alanine Single Crystals
132
Figure 2. High resolution DC for the crystal.
low angle boundary indicate that the crystalline perfec-
tion of the specimen is reasonably good. It may be men-
tioned here that such minute defects could be detected
with well resolved peaks in the diffraction curve only
because of the high-resolution of the diffractometer,
characterized by very low values of wavelength spread
i.e. Δλ/λ and horizontal divergence for the exploring or
incident beam, which are respectively around 10−5 and
much less than 3 arc s of the multicrystal X-ray diffrac-
tometer used in the present studies.
4.3. UV-vis-NIR and CD Spectroscopic Studies
From the UV-vis-NIR transmission spectrum (Figure 3),
it is seen that the compound has no absorption in the re-
gion between 229 nm and 1100 nm. The optical trans-
mittance of the crystals grown using the MKN setup is
52%, which is 6% higher than that for the crystal grown
by SEST. The reason for the higher transparency of the
crystal grown using the MKN setup may be the absence
of inclusions, which reduces absorption of the UV-vis-
NIR radiation. The CD spectrum of DALA unambigu-
ously confirms its chiral purity and thus enables its char-
acterization as D-(–)-alanine (Figure 4). From the nega-
tive Cotton effect observed, it can be concluded that the
compound DALA is D-(–)-alanine.
4.4. Microhardness Studies
Microhardness is an important parameter which helps to
know about the mechanical properties of materials such
as fracture behavior, yield strength, brittleness index and
temperature of cracking. Figure 5 shows the plot be-
tween the hardness value (Hv) and load P. From the re-
sults, it is observed that the hardness value increases with
increase of load up to 50 g and with a further increase in
applied load, cracks have been observed on the crystal
surface due to the release of internal stress generated
locally by indentation. It is also observed that the me-
Figure 3. Transmission spectrum of DALA.
Figure 4. CD spectra of D-(–)-alanine.
Figure 5. Variation of Vickers hardness number with ap-
plied load.
chanical stability of the DALA crystal grown in the
MKN setup is higher compared to the crystals grown by

Bulk Growth and Characterization of D-(–)-Alanine Single Crystals
133
SEST. A plot obtained between log (P) and log (d) gives
a straight line (Figure 6). The relation connecting the
applied load (P) and diagonal length (d) of the indenter is
given by the Meyer’s law: P = adn, where, n is the Mey-
er’s index or work hardening coefficient and a, a constant
of proportionality. The work hardening coefficient value
(n) of the crystals grown using SEST and the MKN setup
were determined by the least-squares fit method and
found to have a values of 1.75 and 1.68, respectively.
Onitsch [10] has pointed out that n lies between 1.0 and
1.6 for moderately hard materials and it is more than 1.6
for soft materials. Hence, it is concluded that DALA sin-
gle crystal is a soft material.
4.5. Laser Damage Threshold (LDT)
Measurements
The laser damage threshold (LDT) measurement has
been carried out for the grown crystal using a Q-swtiched
Nd: YAG laser (λ = 1064 nm) with pulse width of 10 ns,
operated at the repetition rate of 10 Hz. The laser beam
(1 mm diameter) was focused on the sample using a lens
with focal length of 20 cm. The spot size of the focused
beam on the sample was 0.3 mm. The measured LDT
values of DALA single crystals grown using SEST and
the MKN setup are 6.8 GW/cm2 and 7.5 GW/cm2, re-
spectively. It is observed that the crystal grown in the
MKN setup has slightly higher LDT value than that of
the crystal grown by SEST.
4.6. Second Harmonic Generation (SHG)
Conversion Efficiency
Quantitative measurement of the SHG conversion effi-
ciency of the sample was made using the powder tech-
nique developed by Kurtz and Perry. The output from the
sample was monochromated to collect only the second
Figure 6. Plot of log d vs log P.
harmonic (λ = 532 nm), eliminating the fundamental and
the intensity was measured using a photomultiplier tube.
A SHG signal of 3 mV for the crystal was obtained for
an input energy of 3.9 mJ/pulse. The standard KDP crys-
tal gave a SHG signal of 13 mV for the same input en-
ergy. It is seen that the SHG efficiency of the sample
crystal is about 23% of that of the standard KDP crys-
tals.
4.7. Thermal Studies
In the TG-DTA (Figure 7), an endothermic peak ob-
served at 290˚C in DALA corresponds to the melting
point of the material. It is seen from the TG plot that the
melting and decomposition of the compound occur si-
multaneously. Hence, this compound may be useful for
its applications upto its melting point. The exothermic
peak observed at 466˚C is due to the phase transition
expected to happen in the carbon residue.
4.8. Dielectric Studies
The dielectric constant and dielectric loss of the DALA
crystal were studied as a function of frequency, at dif-
ferent temperatures (30˚C, 40˚C, 50˚C and 60˚C). How-
ever, the variation of dielectric constant and the dielectric
loss with frequency only at the room temperature (30˚C)
are shown in Figure 8. It is observed from the plots, that
both the dielectric constant (ε') and the dielectric loss (ε")
are decreasing rapidly and get saturated at high frequen-
cies. A comparison of the dielectric response of the crys-
tals suggests that the dielectric constant and dielectric
loss of the crystals grown using the MKN setup are less
compared to that for the crystal grown by SEST. The
low values of dielectric loss at high frequencies suggest
that the crystal grown using the MKN setup possesses
enhanced optical quality with low density of defects
[11].
Figure 7. TG-DTA plots of DALA.

Bulk Growth and Characterization of D-(–)-Alanine Single Crystals
134
(a)
(b)
Figure 8. (a) The variation of dielectric constant with fre-
quency; (b) The variation of dielec tri c loss wi th freque ncy.
5. Conclusion
Bulk NLO crystal of D-(–)-alanine was grown using a
home-made (MKN) crystal growth setup. The optical
transparency, the values of LDT, microhardness, dielec-
tric constant and dielectric loss are found to be better for
the crystal grown in the MKN setup compared to that
grown by SEST. The bulk crystal of DALA also pos-
sesses a high melting point and reasonably good crystal-
line perfection. The value of the SHG conversion effi-
ciency of the crystal was found to be about 23% of that
of the standard KDP crystal. Hence, the crystal of D-
(–)-alanine grown using the MKN setup may have some
applications as a NLO material.
6. Acknowledgements
The authors are thankful to Dr. G. Bhagavannarayana,
National Physical Laboratory, New Delhi, for the help in
recording the HRXRD curve. SN thanks the Council of
Scientific and Industrial Research, New Delhi for the
financial support under the Emeritus Scientist Scheme.
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