Indian Journal of Pure & Applied Physics
Vol. 51, November 2013, pp. 784-787
AC conductivity and dielectric behaviour of CuZnSnO4 compound
prepared by powder technology
Salma M Shaban1*, Bushra S Mahdi & Raad M S Al-Haddad
Department of Physics, College of Science, University of Baghdad, Baghdad
*E-mail: [email protected]
Received 3 September 2012; revised 20 June 2013; accepted 25 September 2013
A new type of oxides like CuZnSnO4 compound was synthesized by powder technology and pressed it as a pellet of
8.4 mm diameter and 1 mm thickness. X-ray diffraction patterns for the prepared samples have been studied. The behaviour
of the dielectric (i.e. dielectric constant ε1 and dielectric loss ε2) and ac conductivity have been investigated. The sharply
decrease of dielectric constant ε1 was noticed at low frequency range and was independent of frequency at high frequency
range. Otherwise, the variation of the dielectric loss ε2 with frequency is shown and the absorption peak located at 120 Hz
frequency at room temperature and moves to higher frequency with the increase of temperature. It was found that after
critical frequency, ac conductivity logσ increases nonlinearly with the increase of temperature but there is no variation at
low frequency up to the critical frequency. The frequency exponent (s) is determined, and the data suggest that s increases
with temperature. The variation of s with temperature suggests that ac conduction is due to the correlated barrier hopping.
These data confirmed that this compound has good stability at high frequencies for waveguide devices and is useful as
dielectric material at low frequencies.
Keywords: Materials, Dielectric constants, Conductivity, X-ray diffraction
1 Introduction
The oxides of compounds have been popular
subjects of fundamental studies for over a century.
These oxides are also important in modern technology
as catalysts and optoelectronic applications. Most of
them often show oxygen deficiency which it plays a
central role in determining their properties and
chemical activities1. Three types of oxides as CuO,
Sn2O3, ZnO were used to prepare a new type of oxide
(CuZnSnO4 compound) as pellets by powder
technology method. In the present paper, the
structure, dielectric behaviour and ac conductivity of
CuZnSnO4 compound have been investigated.
CuZnSnO4 compound is a new type of electronic
materials with high dielectric constant at room
temperature and low frequencies. Also it has good
stability at higher frequencies. Dielectric oxides
constitute a large proportion of materials which have
wide range of technological applications. There is an
increasing demand on dielectric materials to surpass
their present abilities to be of use in the fast changing
world of electronics2.
2 Experimental Details
Samples of CuZnSnO4 compound were prepared by
powder technology (solid-state reaction) of proper
composition powder mixtures of CuO, ZnO, and
Sn2O3 oxides. Each oxide pre-calcined at 500oC for 1
h to remove hydroxide and carbonate impurities. The
appropriate molar ratios of the oxides are mixed
together and grinding in a gate mortar. After that put
it in oven at 900oC for 6 h. Then it is pressed into
pellet of 8.3 mm diameter and 1mm thickness at 4
Mpa. After that the pellets sintered in air at 850oC for
16 h. To study ac conductivity and the behaviour of
the dielectric constant, we put the pellet of CuZnSnO4
between two Cu electrodes into electrical oven which
is connected to LCR system of a programmable
automatic LCR bridge (PM 60304 Philips) in order to
measure the capacitance C and the conductance G as a
function of temperatures and frequencies. X-ray
diffraction technique using CuKĮ source of
wavelength 1.54 Å was used to measure the structure
of CuZnSnO4 bulk.
3 Results and Discussion
3.1 Structure
The XRD pattern of the prepared CuZnSnO4 bulk is
shown in Fig. 1. The XRD spectra exhibit several
peaks corresponding to diffraction lines of
polycrystalline structure in CZTO. The structure of
CZTO is cubic structure and this depends on the
conditions of preparation of samples which includes
SHABAN et al.: AC CONDUCTIVITY AND DIELECTRIC BEHAVIOUR OF CuZnSnO4
785
Fig. 1 — XRD pattern of CuZnSnO4 bulk
Table 1 — Diffraction angle of CZTO as a function of diffraction
angle for CuO, Sn2O3, SnO, SnO2, ZnO compounds
No, of
peak
2θ
CZTO
2θ
CuO
2θ
Sn2O3
2θ
SnO
2θ
SnO2
2θ
ZnO
1
2
3
4
5
6
7
8
9
10
11
12
29.46
34.84
35.8
36.24
38.85
42
45.97
48.7
52
54
55.2
58.46
35.2
38.1
48.2
53.1
57.8
26.3
32.89
40.37
-
31.6
43.7
-
27
33.99
47.2
51.5
53.96
-
34.2
36.5
47.6
57.2
50.5
-
Table 2 — XRF of CuZnSnO4 compound
Elements of CuZnSnO4
Composition
Copper (Cu)
Zinc (Zn)
Tin (Sn)
35.36
32.96
30.25
the sintering temperature. In future, the effect of
sintering temperature on CZTO structure will be
studied. The structure of CZTO was compared with
the structure of each one of CuO, ZnO, SnO, Sn2O3,
SnO2. This indicates that the peaks become stronger
and sharper and the diffraction angle shifts towards
higher angle diffraction with the product of CZTO
which indicates diffraction angle of CZTO as a
function of diffraction angle of ASTM cards for CuO,
Sn2O3, SnO, SnO2, ZnO compounds as shown in
Table 1. Also XRF confirms the composition of the
compound and the images of atomic force microscopy
confirm the polycrystalline structure of the
compound.
3.2 X-ray fluorescence
Elemental analysis was performed by means of
XRF using the ARL Advant’X (Thermo)
spectrometer (Joint Use Center SFU) with an Rh
Fig. 2 — AFM images of CuZnSnO4 pellet for two different cross
section (a and b)
anode X-ray tube. The composition of CuZnSnO4
bulk was determined by X-ray fluorescence analysis
(XRF). Table 2 indicates the composition ratio of
each element in the compound.
3.3 Atomic Force Microscopy AFM
Figure 2 shows the AFM ( SPM Scanning Probe
Microscope) of CuZnSnO4 compound for the
information:Code: PELLET Grain No.: 45 average
diameter: 269.09 nm. Different sizes of nano-grains
are noticed in Fig. 2 and this confirms the
polycrystalline structure of the compound and found
to be in a good agreement with the results of XRD
analysis.
3.4 Dielectric behaviour
The frequency dependence of dielectric constant ε1,
was calculated by the equation:
ε1 = Cd / Aε0
…(1)
786
INDIAN J PURE & APPL PHYS, VOL 51, NOVEMBER 2013
where C is the measured capacitance, d the thickness,
A the area and ε0 is the dielectric permittivity of a
vacuum. The frequency dependence of dielectric
constant for CZTO samples shows in Fig. 3. It is
obvious that the dielectric constant decreases sharply
with frequency at radio frequency (low frequency)
and independent of frequency at microwave
frequency (high frequency). Generally, low frequency
dispersion (LFD) is believed to be associated with
mobile charge carriers, electrons or ions. The
presence of dielectric dispersion phenomenon at low
frequency is believed to be due to the presence of
trapping levels3.
Figure 4 shows the variation of dielectric constant
as a function of temperature at selected frequencies
(10 kHz, 100 kHz, 1 MHz and 2 MHz). The increase
of dielectric constant with increase of temperature
is,generally, due to the increase of trapped charge
carriers at the grain boundaries4.
The dielectric constant varied from 0.2 to o.31
values in the temperature range 300-523 K in the
frequency range 10-100 kHz but at 1 MHz and
2 MHz, the variation is from 0.18 to 0.33 at the same
temperature range and frequency range. The dielectric
constant at frequency 10 kHz has two maxima, the
first maxima appeared when the temperature reached
323 K; the second one appeared when the temperature
reached 423 K. This can be attributed to the strong
relaxation contribution leading to high dielectric
constants at low frequencies and/or high temperatures
and then to the electronic and ionic polarizability5.
However, the intensity of peaks decreases with
frequency increasing. As we see from Fig. 4, the
dielectric constant has approximately the same value
for all frequencies at temperature 523 K.
Figure 5 shows the dependence of dielectric loss
with frequency which exhibits a dielectric loss peaks
in the frequency range 120-400 Hz. The frequency
Fmax corresponding to the peak has dependence on the
temperature and moves to higher frequency with the
increase of temperature and this is due to the decrease
of relaxation time with temperature as indicated
below.
The type of relaxation present in the samples can be
determined from Fig. 5 according to Eq. (2)
τ =1/ωm = 1/ 2ʌFm
… (2)
where ωm is the angular frequency at the maximum
energy loss and Fm is the frequency corresponding to
maximum energy loss. The observed values of
relaxation times are τ1 = 1.3×10−3s at room
temperature, τ2=7.9×10−4 s for each of temperature
(323, 373, 423, and 473) K, τ3= 3.9×10−4 s for 523 K.
It is clear that the relaxation time decreases with
increase of temperature and this may be explained to
the increase in grain size than at the grain boundary6.
3.5 AC conductivity
Fig. 3 — Dependence of dielectric constant of CuZnSnO4 sample
Fig. 4 — Dielectric constant as a function of temperature for
CuZnSnO4
The behaviour of ac conductivity of the CuZnSnO4
samples has been studied within the temperature
range from room temperature to 523 K. Figure 6
shows the variation of log ac conductivity (logı) with
frequency. From 100 Hz to 40 kHz region, since the
Fig. 5 — Dielectric loss as a function of frequency for CuZnSnO4
pellet
SHABAN et al.: AC CONDUCTIVITY AND DIELECTRIC BEHAVIOUR OF CuZnSnO4
787
where A0 is constant, Ȧ the angular frequency and s is
the frequency exponent. The temperature dependence
of the frequency exponent, s, in Eq. (3) shown in
Fig. 7. We found that the value of s decreases with the
increase of temperatures. The results show that s
increased at low temperature and decreased at high
temperature. The peaks appeared when temperature
reached 373 K. This means that the obtained
experimental results agree with the correlated barrier
hoping model8 CBH.
Fig. 6 — Logarithmic scale of a.c conductivity as a function of
frequency
Fig. 7 — Frequency Exponent s as a function of temperature for
CuZnSnO4
frequency is low and the electric field cannot perturb
the hopping conduction mechanism of charged
particles, the conductance is approximately equal to
the dc value and the conduction mechanism is the
same as that for dc conduction, (i.e., hopping of
charged particles from one localized site to another).
The conductivity begins to increase nonlinearly after
the frequency exceeds the critical frequency 100 kHz.
In the region of critical frequency up to 1 MHz, we
notice systematic minima values and this can be
attributed to the increase of dielectric constant7.
Generally, it can be noticed that the conductivity
increases with the increase of temperature.
From Fig. 7, frequency exponent s can be evaluated
according to the equation of ac conductivity (σac) as:
σac = A0Ȧs
… (3)
4 Conclusions
A new type of oxides, like CuZnSnO4 compound
was synthesized by powder technology and pressed it
as pellet of diameter 8.4 mm and 1 mm thickness in
order to study its structure, the behaviour of complex
dielectric constant and ac conductivity. XRD analysis
ensures the formation of mixture of hexagonal and
cubic structure due to preparation conditions.
CuZnSnO4 compound has a dielectric constant which
decreases sharply with the increase of frequency. The
peak of dielectric loss in the ∈2-logȦ spectrum moves
to higher frequency with the increase of temperature.
Moreover, the frequency exponent was calculated
from ac conductivity data and was found to have
maximum peak at 373 K. The mechanism of ac
conductivity results is matched with the correlated
barrier hoping model CBH.
References
1 Peiwei V, Weifeng Z, Peng Z, & Luang N, Physica B, 406
(2011) 1253–1257.
2 Xueyun S, Xianghua Z, Junbin Z, Yuzhe J & Xiangdong M,
Materials Sciences and Applications, 3 (2012) 838-842.
3 Lanje A, Sharma S & Pode R, Advances in Appl Sci Res, 1(2)
(2010) 36.
4 Amrut S, Lanje I, Satish J, Ramchandara B, Raghumani S &
Ningthoujam O, Advances in Appl Sci Res, 1(2) (2010) 36.
5 Cohn J L, Peterca M & Neumeier J J, J Appl Phys, 97 (2005)
034102.
6 Jong W, SeIn O, Kyoungtae E, SungHoon C, Hyun-Woo K,
Tae-Woong K & Han-Ki K, Japanese Journal of Applied
Physics, 51 (2012) 115801.
7 Salama A & Hammad F, J Mater Sci Technol, 25(3) (2009)
280.
8 Vikas P, Shailesh P, Manik C, Prasad G, Ratnakar S,
Shashwati S & Pradeep J, J of Surface Engineered Materials
and Advanced Technology, (1) (2011) 35-41.