Journal of Minerals & Materials Characterization & Engineering, Vol. 10, No.9, pp.805-815, 2011 Printed in the USA. All rights reserved
Growth, Thermal, Mechanical and Dielectric Studies of Glycine Doped
Potassium Acid Phthalate Single Crystals
T. Baraniraj
and P. Philominathan
Department of Physics, Roever college of Engineering & Technology, Perambalur 621 212,
Department of Physics, A.V.V.M Sri Pushpam College (Autonomous), Poondi, Thanjavur-
613 503, India
*Corresponding Author:
Single crystals of glycine doped potassium acid phthalate (KAP) have been grown from low
temperature solution growth method by employing slow evaporation of the solvent at room
temperature. The grown crystal was subjected to various studies such as X-ray diffraction
(XRD), Fourier Transform Infrared (FTIR), UV-visible and Second Harmonic Generation (SHG)
studies. The thermal stability, mechanical strength and dielectric constant were also measured.
The various studies revealed the influence of the glycine on KAP and the investigations indicated
that glycine played an important role in the changes of the spectral, optical and mechanical
properties of KAP crystals.
Keywords: nonlinear optics; growth from solution; X-ray diffraction; dielectric constant
Second order nonlinear optical (SONLO) materials have recently attracted much attention
because of their potential applications in emerging optoelectronic technologies [1,2]. It has been
reported that organic crystals have very large nonlinear susceptibility compared with inorganic
crystals, but their use is impeded by low optical transparency, poor mechanical strength, low
laser damage threshold and inability to produce and process large crystals [3,4]. The inorganic
NLO materials have excellent mechanical and thermal properties with optical nonlinearities
because of the lack of extended π-electron delocalization. The semiorganic NLO materials
806 T. Baraniraj and P. Philominathan Vol.10, No.9
combine good qualities of both organic and inorganic materials. Hence, in recent years much
attention has been paid to semiorganic NLO materials. Crystals of phthalic acid derivatives are
potential candidates for NLO and electro-optic processes [5]. KAP, a semiorganic material, is
one of the well- studied important NLO crystals in the alkali metal acid phthalate (MAP) family
[6-8]. MAP crystals are well known for their applications in the long-wave X-ray spectrometers
[9]. Recently MAP crystals were used as substrates for a deposition of thin films of organic
nonlinear materials [10]. KAP crystallizes in the orthorhombic system with a=6.46Å, b=9.60Å
and c=13.85Å and space group Pca2
[11]. The influence of metal ion impurities like sodium,
lithium and rubidium on the physical, chemical and mechanical properties of KAP single crystals
have been reported [12]. The amino acids play an important role in the field of nonlinear optical
crystals [13, 14]. Amino acid may be used as dopant in order to enhance the material property
such as nonlinear optical [15]. On the basis of the above considerations, in the present
investigation we report the growth and characterization of glycine doped KAP single crystals.
Commercially available KAP salt (AR grade) was dissolved gradually in deionized water until a
saturated solution was obtained. The calculated amount of 3mol% glycine was added to the
solution with stirring. Then the solution was filtered and crystallization was allowed to take place
by slow evaporation under room temperature. Optically transparent crystal of size 7x5x2mm
was obtained in a period of 45 days. The as-grown crystal is shown in Fig. 1.
Fig. 1. Grown crystal of glycine doped KAP
Vol.10, No.9 Growth, Thermal, Mechanical and Dielectric Studies 807
Single crystal X-ray diffraction analysis was carried out using ENRAF NONIUS CAD-4 X-ray
diffractometer with MoK
(λ=0.1770 Å) to identify the structure and to determine the lattice
parameter values. X-ray powder pattern of the crystal was recorded on a SIEFERT X-ray
diffractometer using CuK
(1.5406Å) radiation. The sample was scanned over the range 10 to 50˚
at a scan rate 1
. To measure the SHG efficiency, Kurtz powder technique was performed
on the grown crystals. The FTIR spectrum was recorded in the range 400-4000cm
employing a
Perkin-Elmer spectrometer by KBr pellet method to analyse the incorporation of glycine into
KAP. To study the linear optical properties, the optical absorption spectra was measured in the
range 200 to 1100nm using the instrument Lambda-35 UV-Vis-NIR spectrophotometer. The
microhardness measurements for the grown crystals were made using Leitz-Wetzlar
microhardness tester fitted with a Vicker’s diamond pyramidal indentor attached to an incident
light microscope. The dielectric measurements on the grown crystals were carried out using the
instrument HIOCKI 3532-50 LCR HITESTER.
4.1. Single Crystal X-ray Diffraction Analysis
Single crystals of glycine doped KAP crystallized in the orthorhombic system with space group
. The lattice parameters were found to be: a=6.50Å, b=9.65Å, c=13.36Å and α=β=γ=90
This analysis revealed that the incorporation of glycine in the KAP crystal does not change the
crystal structure though there is a small change in the lattice parameters.
4.2. Powder X-ray Diffraction Analysis
The powder XRD pattern was recorded and the peaks were indexed using single crystal XRD
data. The recorded diffractogram pattern is shown in Fig. 2. From this analysis, it is observed
that the indexed peaks were slightly shifted when compared to that of pure KAP [16] indicating
the incorporation of glycine into KAP.
808 T. Baraniraj and P. Philominathan Vol.10, No.9
10 20 3040 50
2 0 0
4 0 0
6 0 0
8 0 0
1 0 0 0
1 2 0 0
1 4 0 0
(1 3 1)
Intensity (a.u.)
(d e g re e )
(1 1 0)
(0 2 0)
(1 1 1)
(2 0 0)
(1 2 1)(1 3 0)
(2 0 1)(0 3 1)
(1 3 1)
(0 4 0)
(3 1 0)
(0 4 1)
(3 2 0)
(3 1 1)
(2 4 0)
(0 3 2)
(2 2 2)
(4 1 0)
(3 0 2)
(3 2 1)
(3 3 2)
(1 2 3)
(0 3 3)
(2 2 3)
(4 2 2)
Fig. 2. Powder XRD pattern of glycine doped KAP
4.3. FTIR Spectral Analysis
The FTIR spectrum of glycine doped KAP is shown in Fig. 3. The vibrational frequencies
obtained for glycine doped KAP and pure KAP are presented in Table 1. The presence of glycine
in the lattice of KAP has been found from the O-H stretching vibration of KAP, as the O-H
stretching vibration is more sensitive to hydrogen bonding interaction with the doped amino
acids [17]. The characteristic O-H stretching peaks at 3415 and 2478cm
are shifted to 3466 and
, indicating the substitution of glycine on the hydrogen site rather than on the potassium
site. The asymmetric stretching vibration of the carboxylate ion is shifted to higher energy
) compared to pure KAP (1562cm
Vol.10, No.9 Growth, Thermal, Mechanical and Dielectric Studies 809
Fig. 3. FTIR spectrum of glycine doped KAP
Table 1. Vibrational frequency assignments for pure and glycine doped KAP
Pure KAP[12] glycine doped KAP Assignments
[present work]
3415 3466 O-H stretching hydrogen bond
1544 1569 -C=O carboxylate ion=O asymmetric
1382 1379 -C=O carboxylate ion=O symmetric
1288 1278 C-O stretching
1087 1091 C-C-O stretching
852 849 C-H out of plane bending
767 764 C-C stretching
684 685 C-O wagging
550 552 C=C-C out of plane ring deformation
450 441 C= plane bending
810 T. Baraniraj and P. Philominathan Vol.10, No.9
4.4. Thermal Analyses
The TGA/DTA analyses of glycine doped KAP single crystal were carried out between 50 and
1200˚C at a heating rate of 20k/min in nitrogen atmosphere and are shown in Fig. 4. The TGA
curve shows a sharp weight loss at 290˚C without any intermediate stages, which is assigned as
melting point of the crystal. There is no weight loss below 290˚C, illustrating the absence of
absorbed water in the crystal. It is reported that the melting point of the pure KAP is 290˚C [18].
Hence, we can conclude that there is no change in the melting point of the KAP due to the
addition of glycine. From the DTA trace, the endothermic peak observed at 317˚C may be
attributed to decomposition of glycine doped KAP. These analyses indicate that the compound
could be used for the fabrication of any optical devices below its melting point.
200 400 600 80010001200
Temperature /°C
DTA /(mW/mg)
TG /%
[1] BASEL610.dsv
Mass Change: -40.61 %
Mass Change: -17.38 %
Mass Change: -7.81 %
Peak: 866.1 °C, 15.24 mW/mgPeak: 920.8 °C, 15.06 mW/mg
Peak: 1021.9 °C, 7.985 mW/mg
Peak: 603.1 °C, 8.542 mW/mg
Peak: 317.0 °C, -0.7845 mW/mg
Fig. 4. TGA/DTA trace of glycine doped KAP
4.5. Linear Optical Assessment
UV-visible spectral study is a useful tool to determine the transparency, which is an important
requirement for a material to be optically active [19]. Glycine doped KAP crystal of thickness
2mm was employed for this study. The recorded spectrum (Fig. 5) shows that the crystals have
very low absorbance in the entire visible and IR region. The UV cut-off wavelength for glycine
Vol.10, No.9 Growth, Thermal, Mechanical and Dielectric Studies 811
doped KAP is at 300nm. This results in high percentage of transmission, which is one of the
most desired properties for the crystals used for the device fabrication.
Fig. 5. UV-vis. absorption spectrum of glycine doped KAP
4.6. Second Harmonic Generation Efficiency Measurement
The Kurtz and Perry powder technique remains an extremely valuable tool for initial screening
of materials for second harmonic generation. The fundamental beam of wavelength 1064nm
from Q-switched Nd: YAG laser (Pro lab 170 Quanta ray) was used to test SHG property of the
pure and glycine doped KAP. Pulse energy of 4 mJ/pulse, pulse width of 10 ns and repetition
rate of 10 Hz was used in both measurements. The fundamental beam was filtered using an IR
filter and photomultiplier tube (Philips photonics) was used as the detector. KDP was used as the
reference material and the output power intensity of pure and glycine doped KAP were observed.
A second harmonic signal of 35mV and 40mV were obtained from pure and glycine doped KAP
respectively, with reference to 62mV of KDP. Thus, the SHG efficiency of pure and glycine
doped KAP is roughly 0.6 times that of KDP.
4.7. Dielectric Study
Dielectric measurement is one of the useful methods for characterization of electrical response in
crystalline and ceramic materials. A study of the dielectric properties provides information about
electric fields within the solid materials. Frequency dependence of these properties gives great
812 T. Baraniraj and P. Philominathan Vol.10, No.9
insight into the materials applications. Single crystals of glycine doped KAP cut in the
rectangular specimen of thickness 1.2mm and area of cross section 6mm
is subjected to
dielectric studies. Silver paste is coated on both the surfaces of the sample to make contact
between the crystal and the copper electrodes. The capacitance (C) and dissipation factor (D) of
the parallel plate capacitors formed by the copper plate and electrode having the sample as
dielectric medium have been measured. The dielectric constant (ε) and dielectric loss (tanδ) were
calculated using the relations, ε = Cd/Aε
and tanδ = Dε, Where d is the thickness of the sample,
A is the area of the sample and ε
is the permittivity of free space. The variation of dielectric
constant and dielectric loss with frequency at room temperature are shown in Fig. 6 and 7
respectively. The dielectric constants have high values in the lower frequency region and then it
decreases with the applied frequency. The high value of ε at lower frequencies may be due to the
presence of all the four polarizations namely, space charge, orientational, electronic and ionic
polarization and its low value at higher frequencies may be due to the loss of significance of
these polarizations gradually. The low value of dielectric loss at high frequency suggests that the
glycine doped KAP crystals possesses enhanced optical quality with lesser defects and this
parameter is of vital importance for nonlinear optical materials in their applications.
Dielectric constant (
Log freque ncy
Fig. 6. Variation of dielectric constant with frequency
Vol.10, No.9 Growth, Thermal, Mechanical and Dielectric Studies 813
1 2 3 45 6 7
0 .0
0 .2
0 .4
0 .6
0 .8
1 .0
Dielctric loss (tan
Log frequency
Fig. 7. Variation of dielectric loss with frequency
4.8. Microhardness Studies
The Vicker’s microhardness measurement was carried out on the grown crystals to assess the
mechanical property. The static indentations were made at room temperature with a constant
indentation time of 10s for all indentations. The indentation marks were made on the surfaces by
varying the load from 10 to 100g. The Vicker’s microhardness number Hv of the pure and
glycine doped KAP were calculated using the relation Hv=1.8544P/d
. Where P is the
applied load in Kg and d is the average diagonal length of the indentation in mm. A graph plotted
between hardness number (Hv) and applied load (P) is shown in Fig. 8. At lower load, there is
an increase in hardness with load, for both the crystals, which can be attributed to the work
hardening of the surface layer. Beyond 100g, significant cracking occurs, which may be due to
release of internal stress generated with indentation. The work hardening coefficient of pure and
glycine doped KAP is found to be 1.76 and 1.66 respectively. According to Onitsch, 1.0 n
1.6 for hard material and n > 1.65 for soft materials. Hence, it is concluded that pure and glycine
doped KAP belongs to soft materials.
814 T. Baraniraj and P. Philominathan Vol.10, No.9
02 04 06 08 01 0 0
1 0
2 0
3 0
4 0
5 0
6 0
7 0
Hardness number Hv (Kg/mm
L oa d P (g )
P ure K A P
Glycine d oped K A P
Fig. 8. Vicker’s microhardness plot
Good optical quality single crystals of glycine doped potassium acid phthalate (KAP) have been
grown from aqueous solution by slow evaporation technique under room temperature. The
grown crystals were characterized by single crystal X-ray diffraction and confirmed that the
crystals belong to orthorhombic system. The presence of glycine was confirmed qualitatively
using FTIR analysis. The optical absorption study revealed that glycine doped KAP crystals have
low absorption in the entire visible region and the UV cut-off wavelength was found at 300nm.
The variation of dielectric constant and dielectric loss were studied as a function of frequency.
The hardness value of glycine doped KAP is measured to be higher than pure KAP. With
promising structural, optical and mechanical properties, glycine doped KAP is a potential
material for frequency conversion applications.
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