Effect of metallic dopants on potassium acid phthalate (KAP) single crystals

Article abstract of DOI:10.1016/j.physb.2010.03.004

Optically transparent single crystals of Cu²⁺ and Zn²⁺ doped potassium acid phthalate (KAP) were grown in aqueous solution by slow evaporation technique at room temperature. Single crystal X-ray diffraction analysis confirmed the changes in the lattice parameters of the doped crystals. The presence of functional groups in the crystal lattice has been determined qualitatively by Fourier transform infrared (FTIR) analysis. Optical absorption studies revealed that the doped crystals possess very low absorption in the entire visible region. The dielectric constant has been studied as a function of frequency for the doped crystals at temperatures viz., 328, 348, 368 K. Further the influence of metal dopants on the dielectric behaviour has been studied which clearly exhibited the ferroelectric properties of the crystal.

Full text of DOI:10.1016/j.physb.2010.03.004

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Physica B 405 (2010) 2605–2609
Contents lists available at ScienceDirect
Physica B
journal homepage: www.elsevier.com/locate/physb
Effect of metallic dopants on potassium acid phthalate (KAP) single crystals
n
V. Chithambaram a, S. Jerome Das b, R. Arivudai Nambi c, K. Srinivasan d, S. Krishnan d,
a Department of Physics, AMET University, Kanathur-603 112, Chennai
b Department of Physics, Loyola College, Chennai-600 034, India
c Department of Chemistry, AMET University, Kanathur, Chennai-603 112, India
d Department of Physics, R. M. K. Engineering College, Kavaraipettai-601 206, India
a r t i c l e i n f o
a b s t r a c t
Optically transparent single crystals of Cu2+ and Zn2+ doped potassium acid phthalate (KAP) were grown
in aqueous solution by slow evaporation technique at room temperature. Single crystal X-ray diffraction
analysis confirmed the changes in the lattice parameters of the doped crystals. The presence of functional
groups in the crystal lattice has been determined qualitatively by Fourier transform infrared (FTIR)
analysis. Optical absorption studies revealed that the doped crystals possess very low absorption in the
entire visible region. The dielectric constant has been studied as a function of frequency for the doped
crystals at temperatures viz., 328, 348, 368 K. Further the influence of metal dopants on the dielectric
behaviour has been studied which clearly exhibited the ferroelectric properties of the crystal.
& 2010 Elsevier B.V. All rights reserved.
Article history:
Received 15 December 2009
Received in revised form
28 February 2010
Accepted 1 March 2010
Keywords:
Metallic dopants crystal growth
Optical properties
Dielectric constant
Ferroelectric properties
1. Introduction
was purified by repeated recrystallization for further growth runs.
Nitrates of copper and zinc were taken as dopants with 2%
concentration by weight in the mother solution. The solution was
saturated at room temperature and then filtered with 0.2
Semi-organic crystals have attracted considerable interest due to
their large nonlinear optical coefficients, high resistance to laser
induced damage, low angular sensitivity and excellent mechanical
hardness [1,2]. Potassium acid phthalate (KAP), a semi organic crystal
with formula KðC6H4COOH:COOÞ, is well known for its application
in the production of crystal analyzer for long-wave X-ray spectro-
meter [3,4]. KAP possesses piezo-electric, pyro-electric, elastic and
non-linear optical properties [5–9] with excellent physical properties
having good record for the long term stability in devices [10–12].
KAP crystals are the promising candidates for the qualitative
and quantitative X-ray spectral analysis of light elements such as
Fe, Al, Mg, F and Si in a long wave spectral area and act as good
monochromators [13,14]. Further, the parent crystal exhibits ionic
and molecular properties with wide range of application by virtue of
its polar nature [15]. Motivated by this, single crystals of pure, Zn2+
and Cu2+ doped KAP crystals were grown in the aqueous solution by
slow evaporation technique. Thus the grown crystals were subjected
to various characterizations and were discussed in detail.
mm
porosity filter. The growth parameters were kept constant for all the
growth runs with different dopants. Optically transparent crystals
of metal ion doped KAP were obtained with larger dimensions
13 ꢀ 10 ꢀ 2 and 12ꢀ 11 ꢀ 2 mm3, respectively after an optimum
growth period of 45 days and are shown in Fig. 1 and Fig. 2.
3. Results and discussion
3.1. Single crystal X-ray diffraction
The single crystal X-ray diffraction analysis on Cu2+ and Zn2+
doped potassium acid phthalate single crystals (KAP) was recorded
using ENRAF NONIUS CAD4 automatic X-ray diffractometer.
This analysis has revealed that the single crystals of doped KAP
crystallize in orthorhombic system with space group Pca21. The
calculated lattice parameters for the Cu2+ and Zn2+ doped KAP
crystals are compared with that of pure KAP [16] and are given in
Table 1. The XRD results have confirmed that the incorporation of
metal ions in the KAP crystal lattice does not change the crystal
structure though there is a small change in the lattice parameters.
2. Crystal growth
Pure KAP was synthesized by the incorporation of analar grade
(AR) potassium hydroxide and phthalic acid in the aqueous solution
in the ratio 1:1 by slow evaporation technique. The synthesized salt
3.2. FTIR analysis
n Corresponding author. Tel.: +91 44 27973295; fax: +91 44 27925193.
The FTIR analysis of pure and metal ion doped potassium acid
phthalate (KAP) single crystals were carried out between 400
E-mail address: skrishnanjp@gmail.com (S. Krishnan).
0921-4526/$ - see front matter & 2010 Elsevier B.V. All rights reserved.
doi:10.1016/j.physb.2010.03.004

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V. Chithambaram et al. / Physica B 405 (2010) 2605–2609
and 4000 cmꢁ1 using IFS BRUKKER 66v spectrometer and the
resultant spectra for the pure and doped crystals are shown in
Figs. 3 and 4. In the FTIR spectrum of pure KAP crystals, carbonyl
group (CQO) was observed around 1700 cmꢁ1. C–H stretching
band in the region, which is less than 900 cmꢁ1, appears due to
C–H bending vibrations. For Cu2+ doped KAP, carbonyl group
(CQO) was observed around 1674 cmꢁ1 whereas for Zn2+ doped
KAP, it was at 1680 cmꢁ1. C–H stretching vibrations appear at
2890 and 2910 cmꢁ1 for Cu2+ and Zn2+ doped KAP, respectively.
Carboxylic O–H stretching vibration is seen to produce multiple
bands near 3050 cm–1 for Cu2+ doped KAP while for Zn2+ doped
KAP, it appears at 3100 cmꢁ1. The variation in the FTIR spectrum
for the doped crystals is due to the incorporation of metal ions.
The vibrational assignments for the pure and doped KAP crystals
are given in Table 2.
vibrations appear at 2900 cmꢁ1 and CQC exists at 3000 cmꢁ1
.
.
Aromatic ring groups appear in the frequency range 1550 cmꢁ1
The C–OH in-plane and out of plane bands were observed as weak
bands at 1470 and 940 cmꢁ1. Carboxylic O–H stretching vibration
was seen to produce multiple bands near 3000 cmꢁ1. Absorption
3.3. Optical transmission studies
The optical transmission spectrum of the pure and metal ion
doped potassium acid phthalate (KAP) single crystals was
recorded in the range 200–2000 nm using VARIAN CARY 5E
spectrophotometer (Fig. 5 and Fig. 6). A large absorption was
found at 300 nm due to the
Zꢁp transition of the carbonyl group
of the carboxyl function. The resultant spectrum for pure and
doped KAP crystals shows that the crystal has very low
absorbance in the entire visible and IR region. The UV cut-off
wavelength for Cu2+ doped KAP is at 270 nm, whereas for Zn2+
doped KAP, it is at 240 nm. This results in a high percentage of
transmission, which is one of the most desired properties for the
crystals used for the device fabrication.
Fig. 1. Photograph of Cu2+ doped KAP crystal.
3.4. Dielectric studies
Good quality single crystals of Cu2+ and Zn2+ doped KAP were
selected for dielectric measurements using HIOKI 3532-50
LCR HITESTER. The selected samples were cut using a diamond
saw and polished using paraffin oil. Silver paint was applied
on the both faces to make a capacitor with the crystal as a
dielectric material. The dielectric constant is calculated using the
Fig. 2. Photograph of Zn2+ doped KAP crystal.
Fig. 3. FTIR spectrum of pure KAP crystal.
Table 1
Lattice parameter values for pure and doped KAP crystals.
KAP
Cu2+ doped KAP
Zn2+ doped KAP
˚
a (A)
9.60
6.46
9.65
6.50
9.58
6.47
˚
b (A)
˚
c (A)
13.85
13.36
13.28
System
Orthorhombic
Pca21
Orthorhombic
Pca21
Orthorhombic
Pca21
Space group
3
˚
Volume (A )
858.921
838.006
823.128

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Fig. 4. FTIR spectrum of Zn2+ and Cu2+ doped KAP crystals.
Table 2
Frequency assignment for pure and doped KAP crystals.
Pure KAP crystal
Cu2+ doped
KAP crystal
Zn2+ doped
KAP crystal
Assignment
1690
2900
1470
940
1674
2890
1486
950
1680
2910
1475
920
CQO stretching
C–H stretching
C–O–H in plane
C–O–H out of plane
O–H stretching
C–H bending
3000
900
3050
920
3100
910
Fig. 6. Transmission spectrum of Cu2+ and Zn2+ doped KAP crystals.
three different temperatures viz., 328, 348, 368 K and the results
are shown in Figs. 7 and 8, respectively. From the graphs, it was
clear that dielectric constant decreases as the frequency increases
at all temperatures. The dielectric constant has high values in the
low frequency regions for both the metal ion doped KAP crystals.
The very high values of dielectric constant at low frequencies may
be due to the presence of all the four polarizations namely, space
charge, orientational, electronic and ionic polarization and its low
values at high frequencies may be due to the loss of significance of
these polarizations. But from 4 to 5 MHz, there is a sudden
increase in the value of dielectric constant for both metal ion
doped KAP crystal and this type of behaviour is due to the stray in
the capacitance [17–21].
Fig. 5. Transmission spectrum of pure KAP crystal.
relation
Cd
e’ ¼
ð1Þ
e0A
3.4.2. Variation of dielectric loss with frequency for Cu2+ and Zn2+
doped KAP crystals
where C is the capacitance, d is the thickness, A is the area and e0
is the absolute permittivity of the free space.
The variation of dielectric loss was also studied as a function of
frequency for Cu2+ and Zn2+ doped KAP crystals at three different
temperatures such as 328, 348, 368 K and the results are shown in
Figs. 9 and 10, respectively. It is evident that the dielectric loss
decreases with increase in the frequency for all the temperatures.
This suggests that the dielectric loss is strongly dependent on the
3.4.1. Variation of dielectric constant (
and Zn2+ doped KAP crystals
e
’) with frequency for Cu2+
The variation of dielectric constant (
e’) was studied as a
function of frequency for Cu2+ and Zn2+ doped KAP crystals at

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V. Chithambaram et al. / Physica B 405 (2010) 2605–2609
3.4.3. Variation of dielectric constant (
and Zn2+ doped KAP crystals
The variation of dielectric constant (
e
’) with temperature for Cu2+
250
200
150
100
50
e’) with temperature at
328 K
348 K
368 K
different frequencies of the applied ac field for Cu2+ and Zn2+
doped KAP crystals is shown in Figs. 11 and 12, respectively.
3.5
3
2.5
2
328 K
348 K
368 K
1.5
1
0
0
2
4
6
8
log f
0.5
0
Fig. 7. Plot of dielectric constant vs. log f for Cu2+ doped KAP crystal.
0
2
4
6
8
-0.5
log f
1400
Fig. 10. Plot of dielectric loss vs. log f for Zn2+ doped KAP crystal.
328 K
348 K
368 K
1200
1000
800
600
400
200
0
50 Hz
100 Hz
200 kHz
700 kHz
5 mHz
250
200
150
100
50
0
2
4
6
8
log f
0
Fig. 8. Plot of dielectric constant vs. log f for Zn2+ doped KAP crystal.
320
330
340
350
360
370
Temperature (K)
Fig. 11. Temperature dependence of dielectric constant (e
’) for Cu2+ doped KAP
12
crystal.
10
8
1 kHz
3 kHz
100 Hz
200 Hz
700 Hz
328 K
348 K
368 K
1000
900
800
700
600
500
400
300
200
100
0
6
4
2
0
0
2
4
6
8
-2
log f
Fig. 9. Plot of dielectric loss vs. log f for Cu2+ doped KAP crystal.
320
330
340
350
360
370
Temperature (K)
frequency of the applied field and very low dielectric loss
indicates the very high purity of both the metal ion doped
crystals.
Fig. 12. Temperature dependence of dielectric constant (e
’) for Zn2+ doped KAP
crystal.

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2609
The temperature dependent dielectric constant (
doped KAP crystals shows that the dielectric constant (
e
’) for metal ion
’) initially
Acknowledgements
e
increases up to 348 K then decreases gradually. This indicates that
Cu2+ and Zn2+ doped KAP crystals begin to undergo phase
transition from paraelectric to ferroelectric at 348 K, which is
called as the Curie temperature (Tc). Thus the peak at 348 K
indicates the ferroelectric phase transition for both Cu2+ and Zn2+
doped KAP crystals.
The scientific supports extended by Sophisticated Analytical
Instruments Facility, Indian Institute of Technology, Chennai are
gratefully acknowledged. The encouragement and support rendered
by Department of Physics, AMET University is acknowledged.
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potassium acid phthalate (KAP) have been grown from aqueous
solution by slow evaporation technique under room temperature.
The Cu2+ and Zn2+ doped KAP crystals were characterized by
single crystal X-ray diffraction and confirmed that the crystals
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FTIR analysis. The optical transmission studies revealed that
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