dielectric properties of mno2 doped lif-b2o3-bi2o3...

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

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

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


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


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


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) .


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.


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)


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.


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


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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dielectric properties of mno2 doped lif-b2o3-bi2o3...

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