Crystal Structure Theory and Applications, 2012, 1, 79-83
http://dx.doi.org/10.4236/csta.2012.13015 Published Online December 2012 (http://www.SciRP.org/journal/csta)
Mechanical and Dielectric Properties of InTe Crystals
Teena Mathew1, Ayyappacharuparambil Gopalanachary Kunjomana1*, Keelapattu Munirathnam1,
Kunnath Appukuttan Chandrasekharan1,
Muthukrishnan Meena2, Chelliah Kamalakshiammal Mahadevan2
1Research Centre, Department of Physics, Christ University, Bangalore, India
2Physics Research Centre, S. T. Hindu College, Nagercoil, India
Received October 15, 2012; revised November 17, 2012; accepted November 26, 2012
ABSTRACT
The mechanical properties of indium telluride (InTe) crystals grown by the Bridgman technique were investigated at
room temperature using a Vickers hardness tester. The microhardness is observed to vary nonlinearly with the applied
load, 10 - 100 g. The cleaved ingots are found to have high value of microhardness (222.44 kg/mm2 at a load of 25 g),
which reflects an appreciable degree of strength due to their covalent bonding and homogeneity. The studies revealed
that the dislocations in the grown crystals offered a resistance to fresh dislocations due to interaction. At higher loads,
plastic deformation induces by slip, exhibiting a decrease in hardness from the peak value. The dielectric constant and
dielectric loss of indium telluride crystals were evaluated in the frequency range, 1 kHz - 1 MHz for different tempera-
tures (35˚C - 140˚C). The frequency dependence of AC conductivity was analyzed as a function of temperature. The
effect of temperature and frequency on the dielectric response of InTe crystals has been assessed on their cleavage faces
and the obtained results are discussed.
Keywords: Indium Telluride; Bridgman Technique; Microhardness; Dielectric Constant; Dielectric Loss; AC
Conductivity
1. Introduction
Indium telluride (InTe), a prominent semiconducting III-
VI compound, finds potential application in the fabrica-
tion of switching devices and has been used in semicon-
ductor hetero-structures [1,2]. Among all the mechanical
properties, hardness is a key factor governing the quality
of such structures. Hence, considerable literature [3-6]
exists on the microhardness studies of compound semi-
conducting crystals. The anisotropy of mechanical pro-
perties is associated with structural defects, chemical
bonding, plastic deformation and their tendency towards
crack formation and cleavage. Kunjomana and Chand-
rasekharan [3] have carried out the microindentation
analysis on the prism faces of GaTe whiskers. The effect
of annealing on the microhardness of zone-melted
InxBi2−xTe3 (x = 0.1 to 0.5 at% In) was studied by Pandya
et al. [4]. The mechanical properties of pure and doped
InP have also been investigated [5]. It is reported that
impurity hardening is much more pronounced at high
temperatures than at room temperature. Arivuoli et al. [6]
have described the growth and microhardness studies of
arsenic, antimony and bismuth chalcogenides. However,
the microindentation analysis of indium monotelluride
crystals has not been reported so far.
Under controlled conditions, InTe crystallizes in a
layer structure with the space group I4/mcm as described
by Chattopadhyay et al. [7]. There exists strong covalent
bonding within the layer planes with weak van der Waals
bonding perpendicular to them, resulting in easy clea-
vage. The studies on the dielectric behaviour of chalco-
genide materials are advantageous for understanding
their conduction mechanism and the origin of dielectric
losses [8]. The AC conductivity and dielectric properties
of Sb2Te3 thin films have been investigated in the fre-
quency range, 0.4 - 100 kHz as a function of temperature
[9]. Hegab et al. [10] have evaluated the dielectric pro-
perties and frequency dependence of AC conductivity of
amorphous Ge15Se60X25 (X = As or Sn) thin films depo-
sited by thermal evaporation. Bose and Purkayastha [11]
have determined the dielectric constants of In2Te3 crys-
tals grown by the Bridgman method. But, InTe, being a
member of III-VI family, is less investigated, as far as its
dielectric properties are concerned. In view of the above
considerations, the present report aims to investigate the
mechanical and dielectric properties of indium monotel-
luride crystals.
*Corresponding author.
C
opyright © 2012 SciRes. CSTA

T. MATHEW ET AL.
80
2. Experimental
2.1. Growth and Structural Analysis
Stoichiometric InTe crystals were grown from melt by
the Bridgman method, using a vertical single zone fur-
nace. The high pure (99.999%) indium and tellurium
were filled in a precleaned quartz ampoule of length 80
mm and inner diameter 10 mm, sealed under a vacuum of
~10–6 mbar and synthesized using a muffle furnace. The
temperature profile of the furnace was studied for per-
forming the growth experiments. The compound was
melted by raising the temperature above the melting
point (696˚C) in a tapered ampoule for a period of 48 h
and translated at a rate of 5 mm/h. The X-ray Powder
Diffraction (XRD) data of the grown crystals were re-
corded with a Philips X’pert diffractometer, subjecting
Cukα (λ = 1.5418 Å) radiation. Energy Dispersive
Analysis by X-rays (EDAX) was carried out to assess the
chemical homogeneity of the grown samples.
2.2. Mechanical Measurements
The mechanical strength of a grown crystal plays an im-
portant role in investigating the quality of a crystalline
surface for any desired application. It is essential to know
about the dislocation motion and stress relationships in-
volved in the crystal for studying the mechanical proper-
ties. Therefore, a Vickers projection microscope (MVH-I)
was employed to perform the indentations on the clea-
vage planes of the grown InTe crystals. The diamond in-
denter is in the form of a square pyramid, opposite faces
of which make an angle of 136˚ with one another. Sub-
sequent impressions were made after a time lapse of 30
min to allow for any elastic recovery. In order to avoid
mutual influence of the indentations, the process was
carried out at different sites such that the distance be-
tween consecutive indentation marks is greater than the
diagonal length (d). The microhardness was computed
for various loads using the “Quantimet software” coupled
with the tester.
2.3. Dielectric Measurements
The dielectric characteristics of InTe crystals were inves-
tigated by monitoring the capacitance (Ccrys) and dielec-
tric loss factor (tanδ) using a LCR meter (AGILENT
4284A) for different frequencies, viz. 100 Hz, 1 kHz, 100
kHz and 1 MHz. A good conductive surface layer was
prepared by coating the samples with silver paste. The
temperature was increased up to 140˚C and the electrical
parameters were recorded while cooling. The geometrical
dimensions of the crystals were measured using travel-
ling microscope and screw gauge (least count = 0.01
mm).
3. Results and Discussion
X-ray powder diffraction analysis of the sample con-
firmed the formation of InTe with tetragonal crystal
structure. The estimated cell parameters, a = b = 8.437 Å
and c = 7.139 Å are found to be quite consistent with the
JCPDS card 30 - 0636. The density of the grown crystals
(6.336 g/cm3) calculated from the powder diffraction data
supports the material property reported in the literature
[12,13]. The EDAX profile (Figure 1) revealed the ratio
of atomic percentages of In and Te as 49.98: 50.02 at%,
which shows reasonable agreement with the standard
value.
In order to study the mechanical properties of a mate-
rial, it is desirable to examine optically flat surfaces, free
from any microstructures or irregularities. The crystals
have been carefully cleaved at liquid nitrogen tempera-
ture and the polished slices were subjected to indentation.
The Vickers hardness number is computed using the for-
mula [14],
2
1.8544 kgmmHvP d2 (1)
where P is the applied load in kilograms and d is the
mean diagonal length in millimeters. Figure 2 represents
the results of microhardness measurements on the (001)
Figure 1. EDAX spectrum of InTe sample.
0.00 0.02 0.04 0.06 0.08 0.10
80
100
120
140
160
180
200
220
240
Microhardness Hv (kg/mm2)
Load P (kg)
Figure 2. Plot of microhardness with load for InTe crystals.

T. MATHEW ET AL. 81
plane of InTe crystals. The applied load was varied from
10 - 100 g, maintaining the dwell time at 15 s for all the
samples.
The nonlinear behavior of hardness depends on in-
ternal and applied stress, work hardening and intrinsic
plastic resistance of the material. The value of micro-
hardness increases with increase in load and is found to
be maximum (222. 44 kg/mm2) at 25 g. This is attributed
to the fact that one of the indium atoms has tetrahedral
coordination with four tellurium atoms and exhibits sp3
hybridization [13]. Moreover, the presence of covalent
bonding and the interaction between dislocations have a
pronounced effect on the hardening mechanism. It attains
a minimum value equal to 101.6 kg/mm2 at a load of 100
g. The decrease in hardness of InTe crystals is because of
the gliding between the layers on the cleavage plane of
InTe. Beyond 100 g, the hardness remains constant, due
to decrease in the resistance to the movement of disloca-
tions. However, it is found to be greater than that of other
class of semiconducting monotelluride compounds such
as ZnTe (82 kg/mm2), CdTe (56 kg/mm2), CuTe (19.2
kg/mm2) etc. [14]. Thus, a proper control on the growth
conditions ensures quite an appreciable strength and qua-
lity of InTe crystals, which makes them suitable for the
preparation of hetero-structures.
The study of dielectric behavior of chalcogenide
semiconducting crystals reveals structural information,
which helps to understand the conduction mechanism.
Hence in the present work, the dielectric constant of the
crystal was estimated in the frequency range 1 kHz to 1
MHz by applying the relation [15],




aircrys airair
air cryscrys1 rAACCA AC

 



 (2)
where Acrys is the area of the crystal touching the elec-
trode and Aair is the area of the electrode. Since the crys-
tal area was smaller than the plate area of the cell, air
capacitance (Cair) was also measured [15]. Figure 3
shows the frequency dependence of dielectric constant of
indium telluride crystals at different temperatures. The
dielectric constant (εr) decreases with increase in fre-
quency and shows a steeper dependence at high fre-
quency region. Similar results were reported on the di-
electric properties of Sb2Te3 thin films [9]. At low fre-
quencies, εr depends on deformational (electronic and
ionic) and relaxation (orientational and interfacial) po-
larization. When the frequency is increased, the dipoles
will no longer be able to rotate rapidly and the oscilla-
tions begin to lag behind the field. As the frequency is
further increased, the dipoles will be randomly aligned
and the orientation is stopped. Hence, the dielectric con-
stant decreases at higher frequency, approaching a con-
stant value, corresponding only to the interfacial polari-
zation.
The dependence of dielectric constant on temperature
at various frequencies, 1 kHz, 10 kHz, 100 kHz and 1
MHz, is plotted in Figure 4. The dielectric constant in-
creases with increase in temperature and this behavior
becomes predominant at higher temperature and lower
frequency. The increase in dielectric constant with tem-
perature is due to the fact that, the orientational polariza-
tion is governed by the thermal motion of molecules. The
dipoles do not orient at low temperature, but as the tem-
perature increases, the orientation of dipoles is facilitated
and thus increases the value of orientational polarization,
which in turn increases εr [16].
Figures 5 and 6 indicate the variation of dielectric loss
with frequency and temperature respectively. It is found
that, the dielectric loss decreases with frequency and in-
creases with temperature. The origin of the dielectric
losses is associated with the relaxation phenomena,
which is divided into three parts: conduction losses, di-
pole losses and vibrational losses. As the temperature
increases, conductivity as well as electrical conduction
losses increase and hence the value of the dielectric loss
(tanδ) increases [9].
At high frequency, AC conductivity (σac) increases
with frequency, according to the equation [16],
91215
0
20
40
Dielectric constant
Ln()
35oC
50oC
70oC
90oC
100oC
120oC
140oC
Figure 3. Frequency dependence of dielectric constant at
different temperatures.
4080 120
0
10
20
30
Temperature (oC)
Dielectric constant
1 kHz
10 kHz
100 kHz
1 MHz
Figure 4. Temperature dependence of dielectric constant at
different frequencies.

T. MATHEW ET AL.
82
91215
0.07
0.14
0.21
300C
400C
500C
700C
1000C
1200C
Dissipation factor
Ln
Figure 5. Frequency dependence of dissipation factor at
different temperatures.
255075100 125
0.0
0.1
0.2
0.3
Dissipation facto
r
Temperature (oC)
1kHz
10kHz
100kHz
1MHz
Figure 6. Temperature dependence of dissipation factor at
different frequencies.

s
ac
A

  (3)
where A is the constant, dependent on temperature and s
is the frequency exponent.
It is clear from Figure 7 that σac increases with fre-
quency, obeying Equation (3). The values of s calculated
from the slopes of the plot are shown in Table 1. The
frequency exponent decreases from 0.8059 to 0.7228
with increase in temperature from 35˚C to 100˚C. It was
found to be less than unity and slightly decreased with
temperature. This result proposes the conduction mecha-
nism of the grown crystals as due to Correlated Barrier
Hopping (CBH). According to this model, the hopping of
carriers between two sites over a barrier separating them
is responsible for the observed conductivity [10].
4. Conclusion
Good quality crystals of indium telluride (InTe) were
grown by the Bridgman technique. The stoichiometry of
the compound was confirmed by X-ray powder diffrac-
tion and chemical analysis. At a load of 25 g, the micro-
hardness is found to be 222.44 kg/mm2, whereas at
91215
-18
-15
-12
-9
Ln ac
Ln()
350C
500C
700C
900C
1000C
1200C
1400C
Figure 7. Logarithmic plots of AC conductivity against fre-
quency at different te mper atures.
Table 1. Values of frequency exponent at different tempe-
ratures.
Temperature (˚C) Frequency exponent (s)
35 0.8059
50 0.7952
70 0.7535
90 0.7304
100 0.7228
higher loads, a decrease in hardness was observed due to
slip mechanism. Further, the hardness remains constant
and exhibits comparatively larger value than that of other
telluride samples. The dielectric properties of the grown
InTe crystals were studied for different frequencies as a
function of temperature. The increase in dielectric con-
stant as well as dielectric loss with temperature is due to
the enhanced polarization of the system. The AC con-
ductivity was observed to vary as ωs in the chosen fre-
quency range. The decrease in the value of s with tem-
perature suggests that, the CBH model is the predomi-
nant mechanism responsible for conduction.
5. Acknowledgements
The authors would like to thank the University Grants
Commission, New Delhi for providing the facilities to
perform microindentation analysis of the samples. Thanks
are due to Prof. Guru Row, Department of Solid State
and Structural Chemistry Unit, IISc, Bangalore for struc-
tural characterization.
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