dielectric properties of mno2 doped lif-b2o3-bi2o3...
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International Journal of Pure and Applied Physics.
ISSN 0973-1776 Volume 13, Number 3 (2017), pp. 403-415
© Research India Publications
http://www.ripublication.com
Study of Dielectric Properties of CuO Doped
LiF-B2O3 Glasses
Dr. D.B.R.K. Murthy1,*, R.V.S.N. Uma Devi2, G.Anand3 ,
A. Satyanarayana Murthy4
1Associate professor in Physics, Department of Physics, M.R.College(A),
Vizianagaram, India. 2Lecturer in chemistry, Department of Chemistry, M.R.College(A), Vizianagaram,
India. 3Lecturer in Physics, Department of Physics, M.R.College(A), Vizianagaram, India. 4Lectrer in Physics, Department of Physics, Maharani college, Peddapuram, India.
*(Corresponding author )
Abstract
Alkali fluoro borate glasses like LiF-B2O3 are considered as best materials for
using phosphors, lasers, solar energy converters and in a number of other
electronic devices. These are more moisture resistant when compared with
alkali oxy borate glasses. Further when these glasses are mixed with different
network modifying ions we may expect the structural modifications and the
local field variations around the dopant transition metal ion. These changes
may have strong bearing on spectroscopic properties of the transition metal
ion. During the last few years large varieties of new inorganic glasses have
been developed and characterized.
Keywords: Phosphors, Dopant, Dielectric constant, Dielectric loss,
INTRODUCTION
Copper ions have strong bearing on electrical, optical and magnetic properties of
glasses. A large number of interesting studies are available on the environment of
copper ion in various inorganic glass systems [6-10]. These ions subsist in different
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404 Dr. D.B.R.K. Murthy, et al
surroundings (ionic, covalent) in glass matrices. The content of copper in different
environments exist in the glass depends on the quantitative properties of modifiers
and glass formers, size of the ions in the glass structure, their field strength, mobility
of the modifier cation etc.
Hence, the connection between the position of the copper ion and the physical
properties of the glass is highly interesting Cu2+ ions are well-known paramagnetic
ions and it is also quite likely for copper ions to have link with phosphate groups;
strengthen the glass structure and may raise the chemical resistance of the glass.
Though considerable number of studies is available on some CuO containing glasses
most of them are restricted to spectroscopic studies [11-14].
Very few studies are available on electrical properties of these glasses and most of
them are restricted to the d.c. conductivity measurements. Virtually no devoted
studies on dielectric properties such as dielectric constant ', loss tan , a.c
conductivity ac of LiF-B2O3:CuO system are available. Study on these properties of
glasses helps in assessing their insulating character and can also be used as a tool to
throw some light on the structural aspects of the glasses as mentioned earlier.
PRESENT STUDY
The clear objective of this paper is to have a comprehensive understanding over the
influence of of copper ions on the insulating character of LiF-B2O3 glass system, by
a systematic study of dielectric properties (dielectric constant ', loss tan
conductivity ac over a moderately wide range of frequency and temperature .
Glasses of the following composition are chosen for the present study:
C0: 40 LiF-60 B2O3 : 0.0 CuO
C1: 39.9 LiF-60 B2O3: 0.1 CuO
C2: 39.8 LiF-60 B2O3: 0.2 CuO
C3: 39.7 LiF-60 B2O3: 0.3 CuO
C4: 39.6 LiF-60 B2O3: 0.4 CuO
1. Physical Parameters
From the measured values of density d and calculated average molecular weight M , various physical parameters such as copper ion concentration Ni, mean copper ion
separation Ri, which are useful for understanding the physical properties of these
glasses are evaluated and presented in Table 1
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Study of Dielectric properties of CuO doped LiF-B2O3 glasses 405
Table 1: Summary of data on various physical parameters of LiF-B2O3: CuO Glasses
Property Glass C0 Glass C1 Glass C2 Glass C3 GlassC4
CuO mol % pure (0.1 %) (0.2 %) (0.3 %) (0.4 %)
Density d (g/cm3) 2.138 2.141 2.145 2.149 2.152
Avg. Mol. wt. 52.32 52.38 52.43 52.48 52.54
Cu2+ ion concentration - 2.46 4.92 7.39 9.86
NI (1021ions/cm3)
Inter ionic distance of - 0.74 0.58 0.51 0.46
Cu+2 ion RI (nm)
2. Dielectric Properties
The dielectric constant ' at room temperature (30 OC) and at 1 kHz of pure LiF-
B2O3 glasses is measured to be 13.9 and this value is found to increase with the
decrease in frequency. With the addition of CuO, the value 1 is observed to increase
up to 0.2 mol % beyond that it is found to decrease with considerable frequency
dependence, exhibiting larger values at lower frequencies. The dielectric loss, tan at
room temperature with the concentration of CuO has exhibited a similar behavior.
Fig. 1 and Fig. 2 represent the variation of dielectric constant and loss (for different
concentrations of CuO) with frequency measured at room temperature.
Figure 1
Variation of dielectric constant with frequency at room temperature of LiF-B2O3
glasses doped with different concentrations of CuO
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406 Dr. D.B.R.K. Murthy, et al
Figure 2
Variation of dielectric loss at room temperature of LiF-B2O3 glasses doped with
different concentrations of CuO.
The temperature dependence of 'at different frequencies for glass C2 is shown in Fig.
3; 'is found to increase with temperatures slowly up to about 100oC and beyond this
temperature it increases rapidly especially at lower frequencies.
Fig. 4 shows a comparison plot of the temperature dependence of ' for LiF-B2O3
glasses doped with different concentrations of CuO measured at 1 kHz. The rate of
increase of '
0.2 mol % of CuO.
Figure 3
Variation of dielectric constant with temperature at different frequencies for
LiF- B2O3 glasses containg 0.2 mol% of Cuo
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Study of Dielectric properties of CuO doped LiF-B2O3 glasses 407
Figure 4
A comparison plot of variation of dielectric constant ( at 1KHz) with temperature for
LiF – B2O3: CuO glasses.
A summary of data on the dielectric constant and loss of LiF-B2O3: CuO glasses are
presented in Table 2 and Table 3.
Table 2: Summary of Data on dielectric constant of LiF-B2O3: CuO Glasses
1 kHz 10 kHz
t oC → 30oC 100 oC 200 oC 30 oC 100 oC 200 oC
Glass
C0 15.3 16.2 17.7 14.9 15.5 17.1
C1 17.7 18.0 19.8 16.9 17.4 18.9
C2 18.9 19.5 21.6 17.8 18.9 21.1
C3 14.7 15.5 17.0 14.0 14.9 16.4
C4 14.1 14.9 16.3 13.4 13.8 15.6
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408 Dr. D.B.R.K. Murthy, et al
Table 3
Summary of data on dielectric loss of LiF-B2O3: CuO Glasses
Glass (Tan δmax)avg Temp. region Activation energy δ
of relaxation oC for dipoles(e V)
C0 0.10 79-98 2.62 0.53
C1 0.14 76-95 2.58 0.57
C2 0.21 70-92 2.46 0.68
C3 0.16 75-94 2.50 0.62
C4 0.13 78-90 2.55 0.55
The temperature dependence of tan at different frequencies for LiF-B2O3: CuO
glasses containing 0.4 mol % of CuO is shown in Fig. 5; Fig. 6 shows the
temperatur for the glasses doped with different concentrations
of CuO measured at 10 kHz.
Figure 5
Variation of dielectric loss with temperature at different frequencies for
LiF–B2O3 glasses containg 0.4 mol % of Cuo (glassC4) .
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Study of Dielectric properties of CuO doped LiF-B2O3 glasses 409
Figure 6
A comparison plot of variation of dielectric loss at (10KHz) with the temperature for
LiF – B2O3: CuO glasses.
Fig. 7 shows the variation of dielectric constant with the concentration of CuO (at
200 oC) measured at 1 kHz where as the Fig. 8 shows the variation of dielectric loss
with the concentration of CuO (at 1500C) measured at 10 kHz;
Figure 7
Variation of dielectric constant with the concentration Cuo for LiF – B2O3 glasses at
200ºC measured at 1 KHz.
Figure 8
Variation of dielectric loss with the concentration CuO for LiF – B2O3
glasses at 150ºC measured at 10 KHz.
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410 Dr. D.B.R.K. Murthy, et al
The value of dielectric constant and loss continued to increase with the concentration
of CuO up to 0.2 mol % and there after these values are found to decrease.
Using the relation:
f = fO exp( –Wd/KT) (1)
The effective activation energy, Wd, for the dipoles is calculated and furnished in
Table 4; the value of activation energy is found to be the lowest for glass C2 and
highest for glass C0.
The a.c. conductivity ac is calculated at different temperatures using the equation:
ac = ωε1ε0 tanδ
(where ε0 is the vacuum dielectric constant, ω is the angular frequency )
for different frequencies and the plots of log ac against 1/T are shown in Fig. 9 for
glass C4 at different frequencies; Fig. 10 shows the variation of ac with 1/T for
glasses doped with different concentrations of CuO measured at 10 kHz. The
conductivity is found to increase with the concentration of CuO up to 0.2 mol % and
there after it is found to decrease.
Figure 9
Variation of ac with 1/T for glass C4 at different frequencies of Cuo at (10KHz)
Figure 10
Variation of ac with 1/T for glass C4 doped with different concentrations of Cuo at
(10 KHz)
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Study of Dielectric properties of CuO doped LiF-B2O3 glasses 411
Table 4
Summary of data on a.c. conductivity of K2O-ZnO-P2O5:CuO Glasses
N(Ef) in 1021 eV-1/cm3) A.E for
Glas Austin Butcher Pollak conduction (eV)
Glass C0 -- --- ---- 0.37
Glass C1 1.54 0.64 1.551 0.35
Glass C2 2.78 1.15 2.694 0.26
Glass C3 1.71 0.74 1.698 0.34
Glass C4 1.62 0.71 1.632 0.31
From these plots, the activation energy for conduction in the high temperature region
over which a near linear dependence of log ac with 1/T could be observed is
evaluated and presented in Table .4; the activation energy is found to vary linearly
with the conductivity.
RESULTS – DISCUSSION:
The important results of present study on dielectric properties LiF-B2O3: CuO glasses
are summarized below:
The dielectric constant ε1 at room temperature (30 OC) and at 100 kHz of
The pure glass is measured to be 12.8 and the value is found to increase with
the decrease in frequency. The dielectric loss at room temperature for pure
glasses exhibited similar behaviour.
With the introduction of CuO (0.2 mol %) in to LiF-B2O3: CuO glass matrix,
the values of dielectric constant and loss are found to increase and continued
to increase up to 0.2 mol % and beyond this concentration dielectric constant
and loss are found to decrease with increase in the concentration of CuO.
The variation of dielectric constant of LiF-B2O3: CuO glasses with
temperature shows a considerable increase especially at lower frequencies.
The variation of dielectric loss of pure and CuO doped LiF-B2O3 glasses with
temperature exhibited dipolar relaxation effects.
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412 Dr. D.B.R.K. Murthy, et al
The ac conductivity ac for CuO doped glasses has been observed to decrease
up to 0.2 mol % and there after the conductivity is found to increase.
The activation energy for ac conduction is estimated to be the lowest for glass
C2 and the highest for glass C0.
The dielectric constant of a material is due to electronic, dipolar and space charged
polarizations. All these are active at low frequencies. In fact the nature of variations of
' with frequency indicate which type of contributions are present.
The space charge contribution depends on the purity and perfection of the glasses. Its
influence in general is negligible at very low temperature and noticeable in the low
frequency region. The dipolar orientation effects can sometimes be seen in the glasses
even up to 106 Hz. Recollecting the data, the slight increase in the dielectric constant
and loss at room temperature, particularly at low frequencies for pure and CuO doped
LiF-B2O3 glasses may be ascribed to defects produced in the glass network which
contribute to the space charge polarization.
The temperature has a complicated influence on the dielectric constant. Generally,
increase in the temperature of glasses decreases the electronic polarization. The
increase of ionic distance due to the increase in temperature, influence the ionic and
electronic polarizations. The decrease in the electronic dielectric constant for many
solids is found to be less than 3 % for temperature changes of about 400oC. Similarly,
it appears that the changes in the ionic polarization are not large. Even the presence of
dipoles and their contribution to dielectric constant, we know from Debye`s theory
'is inversely proportional to temperature. As such it is expected that dielectric
constant of CuO doped LiF-B2O3 glasses should not change considerably with
temperature. However, we find a large increase of ' and tan (beyond relaxartion
region); such a behaviour can only be attributed to the space charge polarization due
to bonding defects of the type mentioned earlier in the glasses [44-48].
The change in 'and tan with temperature are smaller at higher frequencies as this
type of polarization decreases appreciably with frequency.
Variation of 'and tan with temperature is observed to be the highest for the glasses
containing 0.2 mol % concentration of CuO. This indicates an increase in the
distortion in LiF-B2O3: CuO glass network, thus resulting the enhancement of the
space charge polarization, which ultimately causes larger increase of '
values, as observed. Obviously this is due to increasing modifying action of CuO
similar to PbO. As modifiers, these oxides enter the glass network by breaking up B-
O-B bonds and introduce dangling bonds.
The bonding defects thus produced create easy pathways for the migration of charges
that would build up space charge polarization leading to the increase in the dielectric
parameters of the glasses dielectric parameters [49].
When the concentration of CuO is greater than 0.2 mol % in these glasses, we have
observed the dielectric constant and loss to decrease. At such concentrations it seems
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Study of Dielectric properties of CuO doped LiF-B2O3 glasses 413
that there is a possibility for the reduction of Cu2+ ions into Cu+ ions. These Cu+ ions
may be blocked in tetrahedral coordination in the glass network and make network
more stable leading to a decrease in the dielectric parameters.
CONCLUSION
Finally the analysis of the results on dielectric properties of LiF-B2O3:CuO indicate
that there is an increasing rigidity of glass network than the concentration of CuO is
more foe 0.2 mol %, beyond it decreases.
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