Crystal growth and dielectric, mechanical, electrical and ferroelectric characterization of n-bromo succinimide doped triglycine sulphate crystals

Article abstract of DOI:10.1016/j.physb.2011.05.048

Single crystals of triglycine sulphate (TGS) doped with n-bromo succinimide (NBS) were grown at ambient temperature by the slow evaporation technique. An aqueous solution containing 120 mol% of n-bromo succinimide as dopant was used for the growth of NBSTGS crystals. The incorporation of NBS in TGS crystals has been qualitatively confirmed by FTIR spectral data. The effect of the dopant on morphology and crystal properties was investigated. The cell parameters of the doped crystal were determined by the powder X-ray diffraction technique. The dielectric constant of NBS doped TGS crystal was calculated along the ferroelectric direction over the temperature range of 3060 °C. The dielectric constant of NBSTGS crystals decrease with the increase in NBS concentration and considerable shift in the phase transition temperature (T _C) towards the higher temperature observed. Pyroelectric studies on doped TGS were carried out to determine the pyroelectric coefficient. The emergence of internal bias field due to doping was studied by collecting PE hysteresis data. Temperature dependence of DC conductivity of the doped crystals was studied and gradual increase in the conductivity with the increase of dopant concentration was observed. The activation energy (ΔE) calculated was found to be lower in both the ferroelectric and the paraelectric phases for doped crystals compared to that of pure TGS. The micro-hardness studies were carried out at room temperature on thin plates cut perpendicular to the b-axis. Less doped TGS crystals show higher hardness values compared to pure TGS. Piezoelectric measurements were also carried out on 010 plates of doped TGS crystals at room temperature.

Full text of DOI:10.1016/j.physb.2011.05.048

Physica B 406 (2011) 3308–3312
Contents lists available at ScienceDirect
Physica B
journal homepage: www.elsevier.com/locate/physb
Crystal growth and dielectric, mechanical, electrical and ferroelectric
characterization of n-bromo succinimide doped triglycine sulphate crystals
n
Chitharanjan Rai a,b, K. Byrappa c, S.M. Dharmaprakash a,
a Department of Physics, Mangalore University, Mangalagangotri 574199, Karnataka, India
b Department of Electronics, Kalpataru First Grade Science College, Tiptur 572202, Karnataka, India
c Department of Geology, Mysore University, Manasagangotri 570006, Karnataka, India
a r t i c l e i n f o
a b s t r a c t
Article history:
Single crystals of triglycine sulphate (TGS) doped with n-bromo succinimide (NBS) were grown at
ambient temperature by the slow evaporation technique. An aqueous solution containing 1–20 mol% of
n-bromo succinimide as dopant was used for the growth of NBSTGS crystals. The incorporation of NBS
in TGS crystals has been qualitatively confirmed by FTIR spectral data. The effect of the dopant on
morphology and crystal properties was investigated. The cell parameters of the doped crystal were
determined by the powder X-ray diffraction technique. The dielectric constant of NBS doped TGS crystal
was calculated along the ferroelectric direction over the temperature range of 30–60 1C. The dielectric
constant of NBSTGS crystals decrease with the increase in NBS concentration and considerable shift in
the phase transition temperature (TC) towards the higher temperature observed. Pyroelectric studies on
doped TGS were carried out to determine the pyroelectric coefficient. The emergence of internal bias
field due to doping was studied by collecting P–E hysteresis data. Temperature dependence of DC
conductivity of the doped crystals was studied and gradual increase in the conductivity with the
Received 27 November 2010
Received in revised form
14 May 2011
Accepted 22 May 2011
Available online 27 May 2011
Keywords:
Doping
X-ray diffraction
Seed crystals
Ferroelectric
Hardness
Hysteresis
increase of dopant concentration was observed. The activation energy (DE) calculated was found to be
lower in both the ferroelectric and the paraelectric phases for doped crystals compared to that of pure
TGS. The micro-hardness studies were carried out at room temperature on thin plates cut perpendicular
to the b-axis. Less doped TGS crystals show higher hardness values compared to pure TGS. Piezoelectric
measurements were also carried out on 010 plates of doped TGS crystals at room temperature.
& 2011 Elsevier B.V. All rights reserved.
1. Introduction
added to the solution can enhance, suppress or stop the growth of
the crystal completely. The dopant effect depends on its concen-
Triglycine sulphate (TGS) crystals are the most suitable mate-
rial for developing detectors for infrared radiation, environmental
analysis monitors, earth observation cameras, astronomical tele-
scopes, military systems and target faces vidicons based on the
pyroelectric effects [1]. It is an extensively studied ferroelectric
material with a typical ferroelectric phase transition at 49 1C [2].
The crystal is monoclinic with space group P21 and P21/m below
and above the Curie temperature, respectively. The spontaneous
polarization takes place along the b-axis. All the three glycine
groups I–III participate in the polarization reversal in TGS crystal.
Considerable amount of work is done by several researchers to
improve the quality and properties of the TGS crystal by doping
the crystal with organic, inorganic and metal ions. The dopant
tration, temperature and pH of the solution. The effects of dopants
on the growth rate, quality of the crystals, habit of crystal
growing, physical parameters, etc. have been the subject of many
experimental studies [3–5]. Some of the dopants improved the
pyroelectric coefficient, reduced the dielectric constant and hence
helped in achieving good pyroelectric figure of merit. However,
the tendency of the crystals to depolarize with time is a serious
problem. Numerous studies have been reported on the minimiza-
tion of the depolarization effects [6–9]. Significant amount of
phosphoric acid in TGS crystal improved the pyroelectric coeffi-
cient and coercive field [10–13]. A few reports about the DC
conductivity of l-alanine, nitro aniline and phosphoric acid doped
TGS crystals are available [14,15]. Growth of triglycine sulphate
crystals with new and large molecular dopants to tailor the
properties so as to use the crystal for electrical applications is
the study of current interest. The literature on the studies of TGS
doped with n-bromo succinimide is not available. The present
paper deals with the growth and characterization of n-bromo
succinimide (NBS) doped TGS crystals.
n Corresponding author. Tel.: þ918242287363.
E-mail addresses: raichitharanjan@gmail.com (C. Rai),
smdharma@yahoo.com (S.M. Dharmaprakash).
0921-4526/$ - see front matter & 2011 Elsevier B.V. All rights reserved.
doi:10.1016/j.physb.2011.05.048

C. Rai et al. / Physica B 406 (2011) 3308–3312
3309
2. Experimental methods and materials
during the cooling run using a Keithley 610C electrometer with
the application of a constant field of 0.12 kV/cm. The samples
prepared for the capacitance measurement were also used for the
DC conductivity studies.
2.1. Crystal growth
Triglycine sulphate was synthesized at pH 2.5 using Analar
grade glycine (Merck India) and sulphuric acid taken in the molar
ratio 3:1. The purity of the TGS salt was enhanced by re-crystal-
lizing the salt three times. The purified salt was used as a basic
material for growing n-bromo succinimide doped TGS (NBSTGS)
crystals. Now onwards the new doped crystal is referred to as
NBSTGS. The TGS solution was prepared by dissolving TGS in
double distilled water. Saturated solution of TGS doped with four
different concentrations of (in the range of 1–20 mol%) n-bromo
succinimide (Merck India) was prepared at 45 1C and filtered
using sintered glass micro-fiber filter paper with porosity less
2.5. P–E hysteresis measurements
The crystal surfaces cleaved perpendicular to the ferroelectric
b-axis was used to examine the P–E hysteresis loops. The cleaved
plates (0 1 0) were polished to get a smooth and parallel surface.
The prepared sample for the study is now in the form of thin plate
of surface area about 25 mm2 and thickness 1.5 mm. The parallel
(0 1 0) faces were electroded with conducting silver paste. The
hysteresis measurements of the samples were carried out at room
temperature using a computer controlled automatic P–E loop
tester. While doing measurements the crystal sample is placed
inside a silicone oil bath.
than 2 mm. The filtered solution was poured into experimental
vessels and was kept in a dust free chamber for slow evaporation
at ambient temperature. After definite period of evaporation the
solution became supersaturated and tiny crystals were nucleated.
Defect-free seed crystals were taken out from the experimental
vessels and tied with the help of fine human hair from the scalp.
These seed crystals were slowly lowered in the saturated mother
solution and allowed to grow in these experimental vessels to get
the bulk crystals. Large numbers of crystals of various sizes were
grown in a time period of 20–45 days.
2.6. Piezoelectric and hardness measurements
The piezoelectric measurements for pure TGS and NBSTGS
were carried out on 010 plates at room temperature using PM300
Piezotest, UK, at 100 Hz with the application of 0.5 N dynamic
force. The samples were cleaved perpendicular to the b-axis and
polished till the thickness was reduced to 1.5 mm. The surface
area of the samples used in this study was approximately
25 mm2. The opposite faces were electroded with conducting
silver paste.
2.2. Powder X-ray diffraction and FTIR measurements
Powder X-ray diffraction data of pure TGS and NBSTGS crystals
The micro hardness of the crystals of pure TGS and NBSTGS
was measured at room temperature on the 010 plates with
Clemax fully automatic digital micro-hardness tester fitted with
a Vickers diamond pyramid indenter. Flat, parallel and polished
surfaces cut perpendicular to ferroelectric b-axis (0 1 0) are used
in the measurement.
were collected at room temperature using a BRUKER AXS D8
˚
Advanced X-ray Diffractometer with Cu K
(l¼1.5418 A) radia-
a
tion in the 2y
range from 201 to 701 at a scanning rate of 21 minꢀ1
for the finely crushed powder. To confirm the presence of various
functional groups in TGS and NBSTGS, Fourier transform infrared
(FTIR) spectrum was recorded in the range 400–4000 cmꢀ1 using
a Shimadzu-8700 FTIR Spectrometer for the powder sample by
the KBr pellet technique.
3. Results and discussion
3.1. Crystal growth and morphology
2.3. Dielectric measurements
Fig. 1 depicts the photograph of pure TGS and NBSTGS crystals.
We have grown large numbers of crystal by suspending the seed
crystals in doped TGS solution. Less than 20 mol% of dopant
concentration is suitable for growing optical quality bulk crystals
by suspending the seed crystals in the growth solution. The
quality of the crystals was found to be poor at higher concentra-
tions. Visible defects were observed around the seed crystal, as
the crystal grew bigger. The concentration of the dopant in the
growth solution has larger impact on the shape, size and quality
of the crystals harvested. It is found that the ac-plane area is
sensitive to the dopant concentration. This yields larger, 010
faces, which makes the crystal very suitable for IR applications.
The crystals are transparent, colorless, non-hygroscopic and
stable under ambient conditions.
The capacitance of the crystal sample was measured using a
HP4194A impedance/gain phase analyzer by heating the sample
at a rate of 1 1C/min using Metler hot stage FP90 over the
temperature range 30–60 1C. The data collected was used to
calculate the dielectric constant and transition temperature.
Samples for capacitance measurements were prepared in the
form of thin plate cleaved perpendicular to ferroelectric b-axis
from the regions of the crystals away from the seed so that they
contain no flaws. The cleaved samples were polished to get flat
and smooth surface of thickness approximately 1.5 mm. The
opposite faces were electroded with conducting silver paste. The
sample preparation technique is discussed in detail [16]. Before
conducting the electrical measurements the samples were kept at
60 1C for 24 h to remove any moisture present.
2.4. Pyroelectric current and DC conductivity measurements
3.2. Powder X-ray diffraction studies
Pyroelectric current and DC conductivity measurements were
carried out in a two-terminal cell by mounting the samples in an
unclamped condition. Pyroelectric current was measured over the
temperature range of 30–60 1C using a Keithley 610C electro-
meter. The sample preparation and current measurement techni-
que are discussed in detail [17].
Before conducting the DC conductivity measurements, the
crystal samples were heated to 65 1C and maintained there for
about an hour. Thereafter the leakage current was measured
Powder X-ray diffraction pattern of pure TGS and 20 mol%
NBSTGS crystals are shown in Fig. 2. The peaks observed in the
X-ray diffraction profiles for the pure TGS crystal matched well
with the reported ASTM data (organic index to the powder
diffraction file, Joint Committee of Powder Diffraction Standards
(1967)). The unit cell parameters of the grown crystals of TGS and
the literature values are compared [17]. The X-ray diffraction
analysis shows that the monoclinic structure of the TGS crystal
doped with different amounts of doping entities undergoes no

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C. Rai et al. / Physica B 406 (2011) 3308–3312
3.3. FTIR studies
In order to analyze the presence of n-bromo succinimide
qualitatively in TGS, the Fourier transform infrared spectra have
been recorded for the powder sample by the KBr pellet technique.
The FTIR spectra of pure TGS and NBSTGS (20 mol% doped) are
shown in Fig. 3. The spectrum of TGS shows broad and strong
absorption band in the range 2700–3600 cmꢀ1 due to O–H stretch-
ing of hydrogen bonded carboxyl groups and the N–H stretching
of NH3þ group. The C¼O stretching vibration of carboxyl group
displays its characteristic peak at 1685.7 cmꢀ1. The C–H bending
vibrations appear at 1494.7 cmꢀ1. The peak present at 1413.7 cmꢀ1
is assigned to N–H bending vibrations. The asymmetric and sym-
metric S¼O stretching frequencies can be assigned to frequencies
1301.9and 1175 cmꢀ1, respectively. Stretching modes of carboxyl
and sulphate ions are assigned to a strong band at 1126.4 cmꢀ1. The
peaks appearing due to torsional oscillations of NH3þ group are seen
at 619.1, 572.8and 501.5 cmꢀ1. The NBSTGS crystals also show a
strong and broad absorption band due to O–H stretching of hydro-
gen bonded carboxyl groups and the N–H stretching of NH3þ in the
range 2700–3600 cmꢀ1 with a peak at 3114.8 cmꢀ1. This peak
shifts towards higher wave number region as the dopant concentra-
tion is decreased. A new band appears at the frequency 1710.7 cmꢀ1
in NBSTGS corresponding to C¼O stretching vibration of carboxyl
group of n-bromo succinimide. Some of the bands are narrowed in
the spectra of the doped crystal, which is a clear indication of the
presence of dopant in the TGS lattice.
3.4. Dielectric studies
Fig. 1. (a) Pure TGS crystal and (b) NBSTGS (20 mol% doped) crystals.
The variation in dielectric constant of TGS and NBSTGS crystals
is depicted as a function of temperature (30–60 1C) in Fig. 4. The
phase transition temperatures were calculated by plotting inverse
dielectric vs. temperature plot in the vicinity of the transition
temperature and are presented in Table 1. It was observed that
Fig. 2. Powder X-ray diffraction pattern of pure TGS and NBSTGS (20 mol% doped)
crystals.
change. Despite low incorporation of dopant into the crystal
lattice there is a significant change in the unit cell parameters
of NBSTGS crystals. Lattice parameters of NBSTGS (20 mol%)
a¼9.185, b¼12.683, c¼5.742 and
b¼105.461 are found to be
higher compared to those of pure TGS and the monoclinic angle
is found to decrease with the increase of dopant concentration.
b
Fig. 3. FTIR spectra of pure TGS and NBSTGS (20 mol% doped) crystals.

C. Rai et al. / Physica B 406 (2011) 3308–3312
3311
the peaks of the dielectric curves are found to be suppressed and
broadened with the increase of dopant concentration. This may be
a clear indication of the presence of internal bias field in the
crystals [18,19]. Similar behavior is also observed in dopants like
iminodiacetic acid, alanine and urea. [16,20,21].
The doped crystals show smaller values of dielectric constant and
higher ferroelectric transition temperatures compared to undoped
TGS. The less doped crystals showing sharp peak as in like undoped
TGS signifies that the crystal is homogeneous and strain free. The
lowering of e0max and shifting of TC to higher value may be due to the
large sized NBS molecule, which goes substantially into the TGS
lattice and replaces some of the glycine molecules.
NBSTGS crystals is clearly observed in the P–E hysteresis loops.
The measured values of maximum polarization (Psþ) are 2.7, 2.11,
2.29, 2.0, and 2.27 m
C/cm2 for the TGS and 1, 5, 10 and 20 mol%
NBSTGS crystals, respectively. The internal bias fields (Eb) are
found to be zero for TGS and 0.65, 12, 21 and 3 kV/m for 1, 5, 10
and 20 mol% NBSTGS crystals, respectively, at room temperature.
The maximum polarisation in case of the pure TGS is 2.7 m
C/cm2
and this value is very close to the value reported by Hoshino
et al. [2]. The presence of internal bias field indicates that the
dopant reduces the depolarizing effect in TGS crystals. The value
of the internal bias field measured is maximum for 10 mol%
n-bromo succinimide doped TGS crystals.
The e0 value was found to decrease with increasing dopant
concentration and also it decreased with increasing frequency. The
dispersion observed in the dielectric constant in the low-frequency
range may be attributed to an increase due to the presence of
charged crystal defects [13], which is consistent with the observed
increase in the DC conductivity of the doped crystals.
3.7. DC conductivity studies
DC conductivity of undoped TGS and NBSTGS crystals was
determined in the temperature range 65–30 1C by applying a
constant field of 0.12 kV/cm. The temperature dependence of the
DC conductivity can be expressed as sDC
¼
s
o exp(
D
E/kBT), where
3.5. Pyroelectric studies
kB is Boltzman0s constant, T is the absolute temperature,
DE is the
activation energy and so is a constant. The variation of DC
conductivity with the reciprocal of temperature (1000/T) of TGS
and NBSTGS crystals is shown in Fig. 7. The DC conductivity at
temperature 35 1C and activation energy in ferroelectric and
paraelectric phases for TGS and NBSTGS crystals are presented
in Table 1. For undoped TGS the value of DC conductivity is
5.5 ꢁ 10ꢀ13 Oꢀ1 cm–1 and the activation energies in the ferro-
electric phase of 1.42 eV and in paraelectric phase of 0.71 eV are
observed. The values of DC conductivity and activation energies
measured for undoped TGS are in good agreement with the earlier
observations [14,15]. It was found that the conductivity of the
doped crystals increased with the doping concentration both in
ferroelectric and paraelectric phases. In the ferroelectric phase the
The direct method of Byer and Roundy [22] is used for
the studies. Fig. 5 shows the temperature dependence of the
pyroelectric coefficient for pure TGS and NBSTGS crystals; 1 mol%
doped TGS shows slightly higher pyroelectric coefficient compared
to pure TGS and the remaining samples studied show lower values
of pyroelectric coefficient.
3.6. P–E hysteresis studies
The hysteresis loops observed for TGS and NBSTGS crystals are
as shown in Fig. 6. The presence of internal bias field in the
Fig. 4. Dielectric constant vs. temperature of NBSTGS crystals. Inset shows the
Fig. 5. Pyroelectric coefficient vs. temperature of pure TGS and NBSTGS crystals.
temperature dependence of dielectric constant of pure TGS.
Table 1
Transition temperature, DC conductivity, activation energy, Vickers hardness number and piezoelectric coefficient of TGS and NBSTGS crystals.
Crystal
TGS
NBSTGS (1 mol%)
NBSTGS (5 mol%)
NBSTGS (10 mol%)
NBSTGS (20 mol%)
Transition temperature TC (1C)
49.12
5.55
1.42
0.71
238
41
49.8
9.87
1.39
0.60
294
34
49.9
11.49
1.36
0.53
330
42
50.1
14.08
1.33
0.47
361
41
50.0
16.25
1.25
0.42
320
53
DC conductivity at 35 1C (Oꢀ1 cmꢀ1) ꢁ 10ꢀ13
Activation energy—ferroelectric phase (eV)
Activation energy—paraelectric phase (eV)
Vickers hardness HV (kg/mm2)
Piezoelectric coefficient d33 (pC/N)

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C. Rai et al. / Physica B 406 (2011) 3308–3312
3.9. Piezoelectric studies
The d33 coefficient measurement was performed at room
temperature on the poled samples using a piezometer at fre-
quency 100 Hz with the application of 0.5 N dynamic force. The
crystal samples were poled at an electric field of 1.5 kV/cm for an
hour before the measurement of the d33 coefficient. The measured
values of the d33 coefficient for pure TGS and NBSTGS crystals are
presented in Table 1.
4. Conclusions
The NBS dopant has enhanced the growth in the ac-plane
compared to pure TGS crystals; 1–10 mol% of dopant concentration
is suitable for growing optical quality bulk NBSTGS crystals. The
transition temperature is found to increase with the increase in
dopant concentration. The dielectric and the P–E studies indicate the
presence of internal bias field in the crystal, which is essential to
prevent depolarization; 1 mol% doped crystals show slightly higher
value of pyroelectric coefficient compared to pure TGS. DC conduc-
tivity studies reveal that the activation energy for the NBSTGS crystals
is lower than that of pure TGS both in the ferroelectric and para-
electric phases with an enhancement in the DC conductivity. The
dopant has enhanced the hardness of the crystals except for 20 mol%
doped crystal. Not much variation is found in the piezoelectric
coefficients. Based on the observed values of higher transition
temperature, existence of internal field, lower dielectric constant
and higher hardness number it is concluded that NBSTGS crystals
are potential materials for pyroelectric detector applications.
Fig. 6. Well-saturated hysteresis loops of pure TGS and NBSTGS crystals.
Acknowledgements
C.R. is grateful to the University Grants Commission, New Delhi,
for the award of teacher fellowship under FIP. The authors are
thankful to Mr. Pramod Kumar Rai, CLCRI, Bangalore, for his help.
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3.8. Micro-hardness studies
In the present investigation a Vickers indenter was used to
measure the hardness of the crystal. The Vickers hardness is a
measure of hardness of a material calculated from the size of an
impression produced under load by a pyramid shaped diamond
indenter. The micro-hardness is calculated from the relation
Hv¼1.8544P/D2 kg/mm2, where P is the applied load and D2 is
the area of the indentation impression. The Vickers hardness
for undoped TGS and NBSTGS crystals with doping concentration
1 –20 mol% with a load of 5 gm is presented in Table 1. The
hardness values were found to increase for doped crystals
compared to undoped TGS crystal. Increase in dopant concentra-
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