Modifier role of ZnO on the structural and transport properties of lithium boro tellurite glasses

Modifier role of ZnO on the structural and transport properties of lithium boro tellurite glasses

Journal of Non-Crystalline Solids 514 (2019) 35–45 Contents lists available at ScienceDirect Journal of Non-Crystalline Solids journal homepage: www...

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Journal of Non-Crystalline Solids 514 (2019) 35–45

Contents lists available at ScienceDirect

Journal of Non-Crystalline Solids journal homepage: www.elsevier.com/locate/jnoncrysol

Modifier role of ZnO on the structural and transport properties of lithium boro tellurite glasses

T



P. Naresha, , B. Kavithaa, Hajeebaba K. Inamdarb, D. Sreenivasua, N. Narsimlua, Ch. Srinivasa, Vasant Sathec, K. Siva Kumara a

Department of Physics, Osmania University, Hyderabad, Telangana -500007, India Department of Physics, J.B.Inst.of Eng&Tech,R.R Dist, Hyderabad, Telangana 500075, India c UGC-DAE Consortium for scientific research, Khandwa Road, Indore, M.P 452017, India b

A R T I C LE I N FO

A B S T R A C T

Keywords: Density Dissociation energy Structural studies AC conductivity Cole-Cole plots

To study the modifier role of ZnO on the structural and transport properties, the quaternary glass system xZnO(30-x) Li2O-10TeO2–60B2O3 (x = 0, 5, 10, 15 and 20 mol%) was prepared by the conventional melt quenching technique. Amorphous nature of the prepared glasses was confirmed by X-ray diffraction studies. Density (ρ) of the glass samples was measured by Archimedes' principle and it was found to vary non-linearly between 3.06 and 3.44 g/cm3 with the addition of heavy metal oxide (ZnO) mole concentration. Oxygen packing density (OPD) values also varied non-linearly between 66.78 and 74.69 g atm/1. Glass transition temperature (Tg) of the glass system was measured using temperature modulated differential scanning calorimeter and Tg was found to increase from 429 °C-449 °C with the increase of ZnO content. Based on the density and molecular weight of the glass composition, mechanical properties like Young's modulus (E), Shear modulus (S), Bulk modulus (K) etc., have been calculated with the help of Makishima-Mackenzie model in terms of the packing ratio (Vρ) and dissociation energy (Gt). FTIR and Raman spectroscopy studies reveal that the glass network consists of various types of BO3, BO4 units along with TeO3, TeO4 and ZnO4 structural units. To study transport properties, AC conductivity measurements were carried out on the glass system in the frequency range 5 Hz-35 MHz and it was observed that the ionic conductivity plays significant role. At low temperatures (30 °C and 50 °C) the results of conductivity did not give good results. AC conductivity of the studied glass system is increased with increase in frequency and temperature. The highest value of AC conductivity of the glass network is of the order 10−2 Ω−1 cm−1. Impedance plots (Cole-Cole) exhibited semicircle behaviour.

1. Introduction B2O3 is a well known inorganic glass forming oxide, with low melting point and good thermal stability. B2O3 glass network consists of basic structural units like BO4 and BO3. Various borate groups form due to the combination of the structural units in the glass network [1]. TeO2 is a conditional glass former, which cannot form a glass itself under normal conditions but forms a glass with the help of alkali or alkaline earth oxides and heavy metal oxides. Addition of small mole fractions of TeO2 into the borate glass network improves the stability and glass forming ability. Lithium oxide (Li2O) acts as a glass network modifier in the glass network. With the addition of Li2O to boro tellurite glass network, the physical, mechanical, structural and transport properties were changed. Li2O containing oxide glasses are widely used in solid state batteries, superionic conductors and solar cell applications.



Synthesis and structural studies on boro tellurite glasses containing ZnO are very interesting due to their high refractive index and optical transparency [2]. Boro tellurite zinc glasses are promising materials in fibre optics technology, solar cells, lasers and sensor applications and also widely used in optoelectronic memory switching devices, gas sensors, and optical waveguide applications [3–5]. Addition of heavy metal oxide (ZnO) into borate glass network increases the rate of glass polymerization or causes low rates of crystallization by creating chain like mechanisms in the base glass former. Mechanical properties play an important role in understanding and studying the chemical bonding between the atoms of crystals or amorphous materials. Mechanical properties also explain the rigidity of materials [6,7]. Elastic properties also explain the forces between the atoms or ions comprising the glass structure. Several researchers reported the results on binary and ternary glass systems. Ghada E. El-

Corresponding author. E-mail address: [email protected] (P. Naresh).

https://doi.org/10.1016/j.jnoncrysol.2019.03.042 Received 26 December 2018; Received in revised form 23 March 2019; Accepted 25 March 2019 0022-3093/ © 2019 Elsevier B.V. All rights reserved.

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“Mettler-Toledo: Model DSC1” instrument. The thermal moments were recorded in the form of endothermic peaks. The temperature of the samples is increased in a particular manner with the heating rate of 5 °C/min from room temperature to 600 °C with continuous liquid nitrogen with temperature accuracy: ± 0.2 °C. The FTIR spectra of the glasses were recorded using JASCO-4200 FTIR spectrometer in the range of 400-4000 cm−1at the rate of 32 scans. FTIR transmittance spectra were recorded on glass samples tests within the pellet shape. Before recording the spectra of glasses, the reference dry KBr pellet was also recorded. The Raman spectra of the present glass system was recorded at room temperature in the wave number range of 200 cm−1-2000 cm−1 with micro Raman system from a Jobin Yvon Horiba (LABRAM HR-800) spectrometer with spectral resolution 1 cm−1. The system is equipped with high stability confocal microscope to focus the laser beam using diode LASER of wavelength 473 nm was used for excitation. Raman spectra recorded as broad band which is composed of a number of overlapping peaks. The deconvolution of overlapped peaks has been made using Origin 8.5 software in order to find the exact position of peaks. The frequency dependent AC conductivity of the present glass samples of various compositions were studied in the frequency range 5 Hz to 35 MHz from room temperature to 400 °C for every 50 °C using LCR meter “Newton Model PSM-1735”. All the samples were prepared in the required dimensions of thickness 2 mm and 1 cm diameter painted with silver electrodes on both the surfaces and then placed under dynamic vacuum during measurement. Output of the computer connected LCR meter gives dielectric loss, parallel resistance, parallel capacitance and parallel inductance along with impedance.

Falaky et al. [8] studied the effect of ZnO on physical and mechanical properties of borate glasses in terms of the number of network bonds, average cross link density and various structural changes has been observed. Y.B. Saddeek et al. [9] studied thermal, mechanical and structural properties of B2O3–TeO2–Bi2O3 and Li2O -TeO2- B2O3 [10] glass systems. Raman and FTIR spectroscopic techniques are widely used to identify various vibrational modes and functional groups of glass compositions. Basically glasses are the amorphous materials which are composed of localized structures. A few reports are presented here to understand the structural studies on various glass systems. G. Lakshminarayana et al. [11] prepared TeO2-B2O3-BaO-ZnO-Na2OEr2O3-Pr6O11 glass system for gamma-rays shielding applications with the help of thermal, vibrational spectroscopic studies. N. Elkhoshkhany et al. [12] studied optical and structural behaviour of TeO2-Li2O-ZnONb2O5-Er2O3 glass system and the results show that the glass materials are suitable in the fibre drawing and non-linear optical applications. S. Rani et al. [13] reported the effect of Li2O on the physical, optical and structural properties of zinc boro tellurite glasses. AC conductivity measurements provide useful information concerning various dielectric relaxation phenomena related to the electrical or dielectric polarization process. The characteristic hopping lengths and hopping rates of carriers between localized states can be determined with high frequency measurements; on the other side low frequency data is more sensitive to slower relaxation process like the reorientation of dipoles etc. To the best of our knowledge few reports are available on the transport properties of zinc tellurite borate glasses containing lithium. In the present study B2O3 is the main glass former whereas TeO2 and Li2O act as network modifiers. The aim of the present work is to study the role of heavy metal oxide (ZnO) on the structural, electrical transport and impedance properties of the tellurite lithium borate glasses for solid state battery and optoelectronic device applications.

3. Results 3.1. X ray diffraction To confirm the amorphous nature or short range order of the prepared glass samples XRD measurements were carried out. The XRD patterns of present glass system are presented in the Fig. 1. The patterns are recorded with intensity or counts per second Vs Bragg's angle (2θ). The broad humps are observed at 280 for all the glasses.

2. Experimental 2.1. Preparation of glass Chemical composition of the present glass system was x ZnO-(30-x) Li2O-10TeO2–60B2O3 where x = 0,5,10,15 and 20 mol percentages for ZL1 to ZL5 respectively. For the preparation of glass samples, high purity analar grade chemicals (Sigma Aldrich-99.9%) like H3BO3, ZnO, TeO2, Li2CO3 are taken as the starting materials in the appropriate mole percentage. They were mixed thoroughly in the agate mortar to get homogeneity. The grounded mixture is taken in the porcelain crucible. The crucible was kept in the electrically heated cylindrical carbide rod furnace at 950 °C approximately ( ± 5 °C error) for 30 min. The molten mixture was stirred to get the homogeneity. It was poured on the pre heated metal plate of stainless steel at 150 °C then pressed with a metal disc. Transparent glasses were formed and then annealed at 300 °C in the furnace to avoid the thermal strains for 12 h. These glass samples have been kept inside the paraffin oil to avoid hygroscopic behaviour of the glasses.

3.2. Density and oxygen packing density (OPD) Density of the glass samples was measured by the following relation [2].

a x0.86 g/cm3 a−b

(1) ZL 1 ZL 2 ZL 3 ZL 4 ZL 5

Intensity (Arb units)

Density(ρ) =

2.2. Characterization techniques To determine the nature of the prepared glass samples, X-ray diffraction technique has been carried out using X-ray diffractometer with Cu kα radiation (1.54A0) at room temperature. The XRD patterns (Philips expert pro) were recorded in the range of 100–800 with counting rate 0.2/s. Density of the present glass system was measured using Archimede's principle. Xylene was used as the immersion liquid. Density measurements are carried out on VIBRA-HT density meter with an accuracy of 0.001. All the mechanical properties were evaluated using Makishima-Mackenzie model which depends on density. Glass transition temperature (Tg) of all the samples were recorded on

10

20

30

40

50

60

70

80

2 Fig. 1. XRD spectrograms of x ZnO-(30-x) Li2O-10TeO2–60B2O3 glass system. 36

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0

Code

B2O3

ZnO

TeO2

Li2O

Density (g/cm3)

Molecular weight(g)

OPD (g.atm/ 1)

Tg (°C)

ZL1 ZL 2 ZL 3 ZL 4 ZL 5

60 60 60 60 60

0 5 10 15 20

10 10 10 10 10

30 25 20 15 10

3.32 3.08 3.14 3.07 3.44

112.3 113.3 113.0 113.4 113.8

69.15 74.48 73.24 74.69 66.78

429 435 437 442 449

Heat Flow(mW)

Table 1 Glass composition details in mole% and physical parameters.

1000ρC g. atm/1 Mi

Endothermic

Gt =

3

Density (g/cm )

OPD (g.atm/1)

68

∑ xi Gi

(4) (5)

K = 2.4Gt Vρ2

(6)

3EK 9K − E

(7)

1 7.2V ρ

(8)

9

15

3

Dissociation energy (Gt)*(10 J/m ) Packing ratio (Vp) Young's modulus E (GPa) Bulk modulus K(GPa) Shear modulus S (GPa) Poisson's ratio(μ)

66

10

600

(3)

Property

3.05

5

550

Table 2 Mechanical properties of x ZnO-(30-x) Li2O-10 TeO2–60 B2O3 glass system.

3.15

0

500

Where packing factors of the various components was given as Vρ. Mechanical properties like dissociation energy per unit volume (Gt), Young's modulus (E), bulk modulus (K), shear modulus(S) and Poisson's ratio (μcal) can be calculated using above formulae. Theoretical values of mechanical properties are presented in the Table 2 and Fig. 4 represents the variation of dissociation energy and packing ratio of the prepared oxide glasses with the addition of network modifier ZnO. It is observed that the dissociation energy decreased with the addition of ZnO whereas packing ratio changes non-linearly. Young's modulus of the present glass system non-linearly decreases from 75.78 GPa to 70.15 GPa and bulk modulus is varied from 43.92GPa to 41.5GPa. Fig. 5 represents the variation of Young's modulus and bulk modulus of the present glass system. It is to found that Young's modulus is highest for the ZLI sample and lowest for ZL5. Shear modulus also changes non-linearly with respect to mole percentage of ZnO. Poisson's ratio values of the present glass system are found to vary non-linearly between 0.19 and 0.22 as the ZnO mole percentage increases.

74

3.10

450

∑ xi Vi

μcal = 0.5 −

76

70

400

E = 2Vρ Gt

S=

Density OPD

3.20

ρ M

Vρ =

Makishima-Mackenzie [14] proposed a successful theoretical model to evaluate the mechanical properties of the oxide glasses directly using a semi empherical formula in terms of the ionic packing ratio (Vp) and dissociation energy (Gt) of the chemical composition. Dissociation

3.25

350

energy measures the strength of a chemical bond. Theoretical mechanical properties of the present glass systems were calculated using the formulas.

3.4. Mechanical properties (theoretical)

72

300

Fig. 3. DSC thermographs of x ZnO-(30-x) Li2O-10TeO2–60 B2O3 glass system.

The rigidity of glass network and inter atomic bond strengths can be analysed from DSC measurements. The glass transition temperature (Tg) has been estimated from minima as occurred in the graph of temperature versus dH/dT. DSC thermographs of the present glass system are shown in Fig. 3 and Tg values are presented in Table 1. The glass transition temperature is increased from 429 °C to 449 °C linearly with the addition of ZnO content. ZL5 sample shows highest Tg in which ZnO mole percentage is high.

3.30

-10

Temperature( C)

3.3. Temperature modulated differential scanning calorimetry (TM-DSC)

3.35

-8

o

(2)

3.40

-4

-12 250

where ρ-Density, Mi -Molar mass and C - Number of oxygen ions present in the formula unit. The non-linear variation of density and OPD with ZnO content is shown in Fig. 2. Oxygen packing density (OPD) of the glass system is also changing non-linearly between 66.78 and 74.69 g atm/1 as the modifier oxide ZnO mole percentage is increased.

3.45

-2

-6

where a -weight of the glass sample in air.b- Weight of the glass sample immersed in xylene. The Density related physical parameters of the present glass system are presented in Table 1. It is found that non-linear change of density between 3.06 and 3.44 g/cm3 occurs with the addition of network modifier ZnO into glass network. Oxygen packing density (OPD) of the glass samples was calculated using the following relation

Oxygen packing density (OPD) =

ZL 1 ZL 2 ZL 3 ZL 4 ZL 5

Tg

20

ZnO mole percentage Fig. 2. Variation of density and OPD in x ZnO-(30-x) Li2O-10TeO2–60B2O3 glass system. 37

ZL 1

ZL2

ZL3

ZL4

ZL5

78.45 0.483 75.78 43.92 31.25 0.213

76.65 0.444 68.06 36.26 28.66 0.190

74.82 0.454 67.93 37.01 28.44 0.196

73.00 0.442 64.53 34.22 27.21 0.188

71.15 0.495 70.15 41.50 28.79 0.22

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0.50

3.5. FTIR spectra

0.49

Fourier Transform Infrared Spectra (FTIR) of the present glass system are shown in Fig. 6 in terms of wave number (400 cm−14000 cm−1) and transmittance. The spectrum is shown from 400 cm−1 to 1800 cm−1. The following band positions observed in the regions in the present system are 417-422 cm−1, 527545 cm−1,693–701 cm−1,759-770 cm−1, 973-1006 cm−1, 12441266 cm−1, 1364-1379 cm−1 and 3440–3455 cm−1. The detailed band assignments of the present glass system are given in Table .3.

Dissociation energy Packing ratio

78 77

0.48

76 0.47

75 74

0.46

Packing ratio(Vp)

3

Dissociation energy (J/m )

79

73 0.45 72

3.6. Raman studies 0.44

71 0

5

10

15

Raman spectra of the glass composition xZnO-(30-x) Li2O10TeO2–60B2O3 with x = 0,5,10,15 and 20 mol percentages are recorded at room temperature in the wave number range from 200 cm−1 to 2000 cm−1 as shown in Fig. 7. The typical deconvoluted Gaussian type fittings of Raman spectra are shown in Fig. 8 for better understanding. Raman peak centres (C) and peak width (W) are analysed as a function of wave number and presented in Table 4. In the present study various Raman peaks(bands) are observed in the following ranges as 273–377 cm−1, 463–497 cm−1,737-790 cm−1, 877–970 cm−1, 11241142 cm−1,1253-1265 cm−1and 1365–1376 cm−1. The detailed band assignments of Raman spectra are given in Table 5.

20

ZnO mole percentage

Fig. 4. Variation of dissociation energy and packing ratio with ZnO%.

Youngs modulus Bulk modulus

74

42

72 40 70 38 68

Bulk modulus (GPa)

44

,

Young s modulus (GPa)

76

3.7. AC conductivity and dielectric studies AC conductivity plays an important role to study the transport properties of the materials. As amorphous materials have only localized structures, we can understand how the transition of charge carriers transported within the localized structures. The frequency dependent AC conductivity can be calculated from the following relation

36

66

34

64 0

5

10

15

20

σac = ωε′ε0 tanδ

ZnO mole percentage

(9)



where ε - real part of dielectric permittivity, ε0- permittivity of vaccum and tan δ is the dielectric loss which can be calculated by the following relation

Fig. 5. Variation of Young's modulus and bulk modulus with ZnO mole%.

tan δ =

ε′ ′ ε′

(10)

1.0 Transmittance(%)

Transmittance (%)

0.8 0.7

0.8

0.6

ZL1 ZL2 ZL3 ZL4 ZL5

0.4

0.6 0.5

422

0.4

417

0.3

417

0.2

ZL1 ZL2 ZL3 ZL4 ZL5

1.0

0.9

0.2 1800

2100

2400

2700

3000

3300

3600

3900

4200

-1

Wave number(cm )

422

527 535 545

698

540

700 699

0.1 0.0 400

770

693

701

600

1244

764

1006

759

973 986 988

763

769

989

800

1000

1246 1251

1374 1364 1366 1374

1266

1200

1379

1400

-1 Wave number (cm ) Fig. 6. FTIR spectra of x ZnO-(30-x) Li2O-10 TeO2–60 B2O3 glass system. (Inset: FTIR spectra in the range 1800 cm−1-4000 cm−1) 38

1600

1800

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Table 3 FTIR band assignments of x ZnO-(30-x) Li2O-10 TeO2–60 B2O3 glass system. Characteristic bands (cm−1)

Assignment

417–422 527–545 693–701 759–770 973–1006 1244–1266 1364–1379 3440–3455

Vibrations of ZnO tetrahedral (ZnO4) units. Vibrations of LieO cations Te–O bending vibrations in the form of TeO3 and TeO6 units Bending vibrations of B-O-B in BO3 and BO4 structural units B–O–B bending vibrations in BO4 units Stretching vibrations of BeO bond from ortho borate groups. B–O stretching vibrations in BO3 units from various borate groups. H–O–H groups.

35000

Raman Intensity

from 100 °C to 400 °C. The highest conductivity is observed at 200 °C for this sample. In the present system the A.C conductivity values are varied non-linearly with the addition of ZnO. The AC conductivity is varied from 10−5–10−2 Ω−1 cm−1 for different mole percentages of ZnO at different temperatures. The DC conductivity values of the present glass system are more stable compared to AC conductivity results. This region is almost frequency independent and DC conductivity of the glasses is increasing with increase of temperature from 100 °C to 400 °C. For ZL1 and ZL2 samples DC conductivity values are increased up to three orders 10−9–10−6 Ω−1 cm−1and 10−10–10−7 Ω−1c m−1 respectively. For ZL3 and ZL5 it is increased up to two orders and only one order increased for ZL4 sample. Finally DC conductivity is varied from 10−10–10−6 Ω−1cm-1 for different mole percentages of ZnO at different temperatures.

ZL 1 ZL 2 ZL 3 ZL 4 ZL 5

40000

30000 25000 20000 15000 10000 5000

200

400

600

800

1000

1200

1400

1600

1800

Wave number (cm-1)

3.8. Cole-Cole plots

Fig. 7. Raman spectra of x ZnO-(30-x) Li2O-10 TeO2–60 B2O3 glass system.

The typical impedance plots (Cole-Cole plots) of the present glass system at different temperatures have been discussed here in terms of real part of complex impedance (Z/) and imaginary part of complex impedance (Z//). Real and imaginary part of complex impedance can be measured in terms of conductance and parallel capacitance using the following relations

where ε”- imaginary part of dielectric permittivity. In the present work, the frequency dependent AC conductivity of the studied glass system is analysed using Jonscher's universal power law [15,16] which is written as.

σtotal = σ(0) + Aωn

(11)

where σ(0) is the frequency-independent component, ‘A' is the temperature dependent constant, n- is the frequency exponent, and σac = Aωn represents the dissipative contribution to the total conductivity. The frequency dependent AC conductivity at different temperatures are shown in Fig. 9 for ZL 1 and ZL2 samples. AC conductivity values of the glass system are given in Table 6(a) and DC conductivity values are presented in Table 6(b). The variation of AC conductivity with frequency is mainly observed in three regions: (i) Low frequency region (ii) Almost Frequency independent region (D.C conductivity region) (iii) High frequency domain. AC conductivity is increased with increase of temperature for all the glass samples. Increase of temperature also causes conductivity relaxation. (See Table 6.) In the present system conductivity of all the glass samples at 30 °C and 50 °C have not shown good results because of impurities and hygroscopic nature of the samples. The conductivity of ZL1 sample is varied in the order from 10−4 to 10−3 Ω−1 cm−1 for various temperatures from 100 °C to 400 °C as shown in Fig. 9(ZL 1). The highest conductivity is observed at 400 °C for this sample. At higher frequencies the plots of AC conductivity merge into a single value. AC conductivity increased near to the glass transition (429 °C) with more stability and a little bit of fluctuations. Conductivity of ZL2 sample is varied in the same order with different multiples for various temperatures from 100 °C to 400 °C as shown in the Fig. 9 (ZL2). The highest conductivity is observed at 400 °C for this sample. ZL 3 sample exhibits highest conductivity in the order of (10−2) at 250 °C. In ZL5 sample Li2O content is lowest and ZnO percentage is highest. Conductivity of ZL5 sample is varied from 10−5 to10−2 Ω−1 cm−1 for various temperatures

Z′ =

G (G 2 + ω2C 2)

(12)

Z′ ′ =

ωC (G 2 + ω2C 2)

(13)

The impedance plots of the glass system are shown in Fig. 10 to Fig. 14 at the temperatures from 200 °C-350 °C at the high frequency domain for better understanding. In the present glass system at higher frequencies two depressed semicircles obtained for most of the glasses. Arrhenius plots of the present glass system are shown in Fig. 15 in terms of conductivity as a function of reciprocal temperature. Arrhenius plots (least square fit) show the same behaviour as the conductivity plots drawn with temperature. It is clear that conductivity is decreased with increase of reciprocal temperature. Figs. 11–13 4. Discussion 4.1. XRD In the XRD patterns of the glass system, no sharp peaks are observed. Absence of sharp peaks in the XRD spectra confirms the amorphous nature of the glasses. The broad humps are observed for all the glass samples which is the characteristic nature of amorphous materials. The appearance of broad humps may be attributed to the radial distribution. 4.2. Density and oxygen packing density Generally, density of zinc tellurite glasses increases with increasing 39

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ZL-1

12000

18000

ZL-2

16000 14000

8000

Raman intensity

Raman Intensity

10000

6000 4000 2000

12000 10000 8000 6000 4000 2000

0

0

-2000

200

400

600

800

1000

1200

1400

-2000 200

1600

400

600

800

1000

1200

1400

1600

Wave number(cm-1)

-1

Wave number (cm ) 18000

16000

ZL-3

ZL-4

16000

14000 14000

12000

Raman Intensity

Raman intensity

12000 10000 8000 6000 4000

10000 8000 6000 4000

2000

2000

0

0

-2000 200

400

600

800

1000

1200

1400

-2000 200

1600

400

600

800

1000

1200

1400

1600

-1

Wave number(cm )

-1

Wave number(cm )

18000

ZL-5

16000

Raman Intensity

14000 12000 10000 8000 6000 4000 2000 0 -2000

200

400

600

800

1000

Wave number(cm

1200 -1

1400

1600

)

Fig. 8. Deconvoluted Raman spectra of x ZnO-(30-x) Li2O-10TeO2–60B2O3 glass system.

in strong connectivity [18]. In the present study the net molecular weight of the glass system has been increased and it may be one of the reasons for the increase of density. Oxygen packing density (OPD) depends on the number of oxygen atoms and density. In the present system numbers of oxygens remain the same in the chemical compositions of glass system. Addition of ZnO causes the creation of non-bridging oxygens (NBOs) which leads to increase of OPD. The density of the glass system is non-linearly varied which may effect the decrease of OPD. The anomalous behaviour of density and OPD reveals that addition of ZnO causes continuous breakages of bonds between the atoms which are present in the glass

heavy metal oxide (ZnO) content [17]. The same behaviour is observed in borate glass when the modifier oxide content is increased. The change in density of such system is related to the density of modified basic structural units when introducing modifier oxide. In ZL1 sample, ZnO mole percent is zero and the density was found to be 3.32 g/cm3. For ZL2 sample density is suddenly decreased to 3.08 g/cm3. Decrease in density may be attributed to the structural changes in the presence of the three modifiers in the network. Further addition of ZnO causes increase in the density. This can be attributed to the heavier molecular weight of ZnO than lighter Li2O. The decrease in net molecular weight results in weak connectivity while increase in molecular weight results 40

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the cross-link density and dimensionality of the structure [23]. The range of Poisson's ratio is of the order of 0.1–0.2 for the materials having a high cross-link density and it is ranged between 0.3 and 0.5 for the materials will be with low cross-link density according to literature [24,25]. Poisson's ratio values of the present glass system are found to vary non-linearly between 0.19 and 0.22 which suggests that the glass system has a high cross-link density. Decrease of Poisson's ratio values indicate the change in the type of bonding due to creation of nonbridging oxygen [26,27].

Table 4 Raman band positions (C) in cm−1 and peak width (W) of glass system. ZL1

ZL2

ZL3

ZL4

ZL5

C

W

C

W

C

W

C

W

C

W

– 352 463 737 786 877 1138 1257 1365 1499

– 86 125 130 58 48 72 82 111 71

273 377 497 744 787 968 1131 1256 1375 1503

80 47 60 167 58 143 123 92 134 67

320 469 739 787 966 1141 – 1253 1376 1511

104 163 166 60 180 115 – 78 164 78

354 490 626 746 789 970 1142 1255 1374 1502

119 151 83 168 58 185 130 102 149 71

314 359 456 745 790 959 1124 1265 1371 1500

85 64 182 182 61 107 201 84 119 83

4.5. FTIR spectra

Basically, glass transition temperature (Tg) depends on cross link density of the atoms in the glass network. ZnO containing glasses exhibits high glass transition temperatures. Addition of ZnO causes the breaking of bonds in base glass former and creates non bridging oxygens (NBOs). Therefore the cross link density decreases and hence the structure became loosely packed. In the present system without ZnO content ZL1 sample show Tg as 429 °C and Tg is linearly increased with the increase of ZnO content. Molecular weight of ZnO is more than Li2O and when it is incorporated into glass matrix the covalent bonded linkages are formed between the ions. Due to the linkages the glass network has high cross link density which leads to the increase of Tg. This is in accordance with the increase of glass transition temperature with ZnO [2,19].

In borate glasses the FTIR bands of vibrational modes of BO3 and BO4 units can be seen in three regions. (1) The bands observed due to the asymmetric stretching modes of the BeO band of trigonal BO3 units in the range 1600–1200 cm−1 (2) 1200–800 cm−1 is assigned to the BeO band stretching of the tetragonal BO4 units and (3) 800–600 cm−1 is attributed to bending of B–O–B linkages [28–30]. In the FTIR spectra weak bands observed at 417-422 cm−1 are due to vibrations of ZnO tetrahedral (ZnO4) units [31–33]. A weak band appears at 415 cm−1due to the presence of LieO bonds in the lithium oxide containing glasses. In the present system a band appears in the range 527-545 cm−1due to vibrations of Li+ cations [34]. The band 693–701 cm−1 is assigned to TeeO bending vibrations in TeO3and TeO4 units. The band at 759–770 cm−1 is observed which is due to B-OB bending vibrations of BO3 and BO4 structural units [35–37]. The band at 1244–1266 cm−1 is assigned to the stretching vibrations of BeO bond from ortho borate groups. A band observed at 1375–1450 cm−1 is assigned to stretching vibrations of BeO in BO3 units from various types of borate groups [38,39].In addition to these bands there is a band observed due to water groups in the range 3440-3455 cm−1 [40]. Therefore it is may be concluded that the increase of ZnO causes the structural changes in the glass network.

4.4. Mechanical properties

4.6. Raman spectra

Dissociation energy per unit volume (Gt) of various oxides in the present study are GLi2O=77.9 × 109J/m3, GTeO2=54 × 109J/m3, GZnO = 41.4x109J/m3 and GB2O3= 82.8 × 109 J/m3 [20,21]. The standard values of packing factors (Vi) of various components in the glass system given as B2O3 = 20.8 × 10−6 m3/cal, −6 3 TeO2 = 14.7 × 10 m /cal, ZnO = 7.9 × 10−6 m3/cal and Li2O = 8 × 10−6 m3/cal [20,22]. For ZLI sample dissociation energy value is the highest due to strong bonds in the glass network. Addition of ZnO causes continuous breakage of glass network therefore less energy is required to break the remaining bonds in the glass network for the remaining samples. Therefore it is decreased with addition of ZnO. The non-linear variation of Young's modulus, bulk modulus and shear modulus may be due to the continuous changes in the structural units of the glass network. It may also due to the formation of non-bridging oxygens with the addition of ZnO. Poisson's ratio of amorphous glass materials is mainly depends on

In the present study, the band is observed at 273–377 cm−1 is due to the vibrations of ZneO bonds in tetrahedral (ZnO4) units [41,42]. The band position 463–497 cm−1 is obtained from the bending vibrations of –[Te–O–Te] or [O–Te–O] linkages [43]. The prominent and high intensified Raman peak observed in the range of 737-790 cm−1 is attributed to stretching vibration modes of TeO3 and TeO3+1 structural units [44,45]. Raman band at 877–970 cm−1 is assigned to stretching vibrations of BO4 units. A band is observed at 1124-1142 cm−1 for all the glass samples and it is assigned to stretching vibrations of BO4 units. Raman band in the range of 1365–1376 cm−1 assigned to asymmetric stretching vibrations of BO3 units from various borate groups [46]. The Raman bands above 1500 cm−1 have been assigned to the stretching of BeO bonds attached to a large number of borate groups [47,48]. For zero mole percentage of ZnO intensity of the Raman peaks is less and with addition of same network modifier the intensity is becoming highest. It may be due to the increase of non-bridging oxygens (NBOs). The conversion of the basic structural units from BO3 to BO4

network and structural changes. 4.3. Tm-DSC

Table 5 Raman band assignments of x ZnO-(30-x) Li2O-10TeO2–60B2O3 glass system. Characteristic bands (cm−1)

Assignment

273–377 463–497 737–790 877–970 1124–1142 1253–1265 1365–1376 1499–1511

Vibrations of ZneO bonds in tetrahedral (ZnO4) units Bending vibrations of –[Te–O–Te] or [O–Te–O] linkages Stretching vibrations of Te-O-B linkages Stretching vibrations of BeO in BO4 units Stretching vibrations of BeO in BO4 units. BeO asymmetric stretching vibrations of BO4 and orthoborate group or BeO stretching vibrations in BO3 units from boroxol rings. B–O stretching vibrations in BO3 units from different borate groups. stretching vibrations of BeO bonds attached to large number of borate groups

41

Journal of Non-Crystalline Solids 514 (2019) 35–45

P. Naresh, et al.

ZL 1

-3

10

ZL 2

-3

10

-4

10

-4

10

-5

-1 -1

cm )

-7

10

(

-6

10

o

100 C o 150 C o 200 C o 250 C o 300 C o 350 C o 400 C

-8

10

-9

10

-10

10

-11

10

-12

10

3.0

3.5

4.0

4.5

5.0 5.5 logf (Hz)

6.0

6.5

ac

ac

-5

10

(

-1

-6

10

-1

cm )

10

o

100 C o 150 C o 200 C o 250 C o 300 C o 350 C o 400 C

-7

10

-8

10

-9

10

-10

10

7.0

3.0

3.5

4.0

4.5

5.0

5.5

6.0

6.5

7.0

logf (Hz)

Fig. 9. Variation of σ

ac

with frequency of ZL1 and ZL2 samples.

Table 6 (a) AC conductivity values of x ZnO-(30-x) Li2O-10 TeO2–60 B2O3 glass system. Temperature (o C)

AC conductivity (σac) at various temperatures in (Ω−1 cm−1) ZL 1

100 °C 150 °C 200 °C 250 °C 300 °C 350 °C 400 °C

ZL 2 −4

5.6 × 10 4.7 × 10−4 2.0 × 10−3 5.5 × 10−3 2.0 × 10−3 4.0 × 10−3 6.0 × 10−3

ZL 3 −4

ZL 4 −4

1.0 × 10 1.0 × 10−3 2.0 × 10−3 1.2 × 10−3 1.5 × 10−3 1.8 × 10−3 2.5 × 10−3

ZL 5 −3

1.9 × 10 8.0 × 10−4 3.0 × 10−2 3.4 × 10−2 4.8 × 10−3 5.4 × 10−5 5 × 10−2

1.2 × 10 8.9 × 10−5 3.9 × 10−4 8.9 × 10−4 1.2 × 10−3 1.0 × 10−3 2.0 × 10−3

9.9 × 10−4 2.0 × 10−5 1.0 × 10−2 1.0 × 10−3 5.5 × 10−5 2.0 × 10−3 2.9 × 10−3

Table 6 (b) DC conductivity values of x ZnO-(30-x) Li2O-10 TeO2–60 B2O3 glass system. Temperature(o C)

100 °C 150 °C 200 °C 250 °C 300 °C 350 °C 400 °C

DC conductivity (σdc) at various temperatures in (Ω−1 cm−1) ZL 1

ZL 2

ZL 3

ZL 4

ZL 5

7.5 × 10−9 4.6 × 10−9 2.7 × 10−8 8.5 × 10−8 1.2 × 10−7 3.7 × 10−7 1.6 × 10−6

6.0 × 10−10 2.9 × 10−8 1.8 × 10−7 2.1 × 10−7 2.2 × 10−7 2.8 × 10−7 3.5 × 10−7

2.3 × 10−8 1.4 × 10−7 6.6 × 10−8 2.3 × 10−8 4.5 × 10−8 5.3 × 10−7 1.9 × 10−6

3.6 × 10−8 3.4 × 10−9 1.8 × 10−8 8.4 × 10−9 1.6 × 10−8 3.6 × 10−9 7.7 × 10−8

4.0 × 10−10 5 × 10−9 7.2 × 10−9 2.1 × 10−8 1.1 × 10−8 7.0 × 10−8 7.1 × 10−8

frequency dispersion of the conductivity is due to the fact that inhomogeneities in the amorphous glass materials may be microscopic in nature with a distribution of the relaxation processes through a distribution of energy barriers [49]. The conductivity values are increased up to the maximum phonon energies of the glass system [50]. Finally, AC conductivity of the glass system increases with the frequency and temperature. The non-linear variation of density and OPD influences the AC Conductivity in the present study. Addition of ZnO causes the creation of non-bridging oxygens which may be the reason for fluctuation in the conductivity values. Presence of three modifiers with various structural changes also influences the conductivity [51]. However AC and DC both the conductivities of the glass system are increased with temperature and frequency. The AC conductivity varied from 10−5 -10−2 Ω−1 cm−1 and DC conductivity is varied from 10−10–10−6 Ω−1 cm−1 with different mole percentage of ZnO at

are responsible for the variation of intensity of most prominent Raman peaks near 737 cm−1 -790 cm−1 for the glass system with different ZnO contents. Therefore adding network modifier ZnO to the glass network the structural changes were observed. 4.7. AC conductivity and dielectric studies The frequency dependent AC conductivity mainly arises from the interfacial polarization, grain boundaries and other inhomogeneities present in the disordered materials such as polymers and glasses. Region-I is attributed to polarization effects between sample and electrode interface. Region-II is observed at intermediate frequencies in which AC conductivity is almost independent of frequency. This domain is also treated as DC conductivity region. In the third domain σac is found to increase to a maximum value and conductivity converge (merge) into a single value for all the glass samples. The strong 42

Journal of Non-Crystalline Solids 514 (2019) 35–45

P. Naresh, et al.

6

8.0x10

5

6.0x10

5

4.0x10

5

2.0x10

5

300 C 0 350 C

1.0x10

7

8.0x10

6

6.0x10

6

4.0x10

6

2.0x10

6

200 C 0 250 C

II

1.0x10

0

Z (ohm)

1.2x10

II

Z (ohm)

0

6

0.0

0.0 5

0.0

5

5

5

6

2.0x10 4.0x10 6.0x10 8.0x10 1.0x10 1.2x10

0.0

6

2.0x10

6

I

Z (ohm)

4.0x10

6

6.0x10

6

8.0x10

6

1.0x10

7

I

Z (ohm)

Fig. 10. Z/ (Vs) Z// plots ZL1 sample at various temperatures.

1.0x10

7

4.0x10

6

3.5x10

6

3.0x10

6

2.5x10

6

2.0x10

6

1.5x10

6

1.0x10

6

5.0x10

5

0

300 C 0 350 C

o

6

II

6.0x10

Z"

8.0x10

6

Z (ohm)

200 C o 250 C

4.0x10

6

2.0x10

6

0.0

0.0 6

0

6

1x10

6

2x10

6

3x10

6

4x10

5x10

0.0

5.0x10

5

1.0x10

6

1.5x10 I

6

2.0x10

6

2.5x10

/

Fig. 11. Z (Vs) Z

//

6.0x10

6

4.0x10

6

2.0x10

6

II

8.0x10

6

Z (ohm)

7

200 C 0 250 C

II

Z (ohm)

1.0x10

6

plots ZL2 sample at various temperatures.

7x10

6

6x10

6

5x10

6

4x10

6

3x10

6

2x10

6

1x10

6

0

0

1.2x10

3.0x10

Z (ohm)

Z'

7

6

0.0

300 C 0 350 C

0 0.0

2.0x10

6

4.0x10

6

6.0x10

6

8.0x10

6

1.0x10

7

1.2x10

7

-1x10

6

0

1x10

6

2x10

6

3x10

6

4x10

6

5x10

6

6x10

6

7x10

6

I

I

Z (ohm)

Z (ohm) Fig. 12. Z/ (Vs) Z// plots ZL3 sample at various temperatures.

effects. At high temperatures the impedance plots of high lithium containing glasses, shows two depressed semicircles combined each other [49]. The radius of the semicircle is decreasing with increase of temperature for all the glass samples containing high lithium content i,e for ZL 1,ZL2 and ZL3 samples. This behaviour is not observed for ZL 4 and ZL 5 samples in which lithium content is below 20 mol percentages. Appearance of semicircle below the real axis indicates that the sampleelectrode system in which the relaxation time distributes continuously and it is not single valued.

various temperatures. The ionic conductivity plays a significant role in conductivity. 4.8. Cole-Cole plots At the temperatures 30 °C and 50 °C impedance Cole-Cole plots do not give good results for the present glass system due to the inhomogeneities in the glass samples. At 100 °C all the glass samples show single semicircle in the impedance plots which may be due to bulk 43

Journal of Non-Crystalline Solids 514 (2019) 35–45

P. Naresh, et al.

1.2x10

7 0

300 C 0 350 C

0

6.0x10

6

Z (ohm)

6

I

I

Z (ohm)

8.0x10

200 C 0 250 C

4.0x10

2.0x10

1.0x10

7

8.0x10

6

6.0x10

6

4.0x10

6

2.0x10

6

6

6

0.0 0.0 0.0

2.0x10

6

4.0x10

6

6.0x10

6

8.0x10

0.0

6

6

6

I

Fig. 13. Z (Vs) Z

0

7

8.0x10

6

6.0x10

6

4.0x10

6

2.0x10

6

200 C 0 250 C

0

8.0x10

6

6.0x10

6

4.0x10

6

2.0x10

6

300 C 0 350 C

II

1.0x10

7

plots ZL4 sample at various temperatures.

Z (ohm)

II

Z (ohm)

//

7

7

7

Z (ohm) /

1.2x10

6

I

Z (ohm)

1.4x10

6

2.0x10 4.0x10 6.0x10 8.0x10 1.0x10 1.2x10

0.0

0.0

0.0

3.0x10

6

6.0x10

6

9.0x10

6

1.2x10

7

1.5x10

7

0.0

2.0x10

I

6

4.0x10

6

6.0x10

6

8.0x10

6

I

Z (ohm)

Z (ohm)

Fig. 14. Z/ (Vs) Z// plots ZL5 sample at various temperatures.

ac

6.0x10

-3

5.0x10

-3

4.0x10

-3

3.0x10

-3

2.0x10

-3

1.0x10

-3

resistance. Most of the semicircles could be fitted to R-C circuits with R and C in parallel combination. In the Cole-Cole plots the resistance decreased with increasing temperature. The prominent semicircles appeared below glass transition temperature indicate that resistance(R) and capacitance(C) are in parallel combination. The behaviour of Cole-Cole plots are in good agreement with the earlier reports [49,52].

ZL 1 ZL 2 ZL 3 ZL 4 ZL 5

5. Conclusions

0.0 -1.0x10

Glass composition is synthesized through melt quench technique. XRD spectra revealed short range order with a broad hump which is the characteristic nature of glass materials. Glass transition temperature is increased due to addition of modifier oxide ZnO. Structure related physical properties like density and OPD were observed with non-linear variation. Study of mechanical properties revealed that structural changes and type of bonding between the atoms. The range of Poisson's ratio (0.19–0.22) suggests that the glass network having high cross link density. FTIR and Raman studies confirmed the existence and conversion of basic structural units such as BO3 and BO4 along with modifier units and no common peak is observed. The AC conductivity varied from 10−5 -10−2 Ω−1 cm−1 and DC conductivity is varied from 10−10–10−6 Ω−1 cm−1 with different mole percentage of ZnO at various temperatures. The ionic conductivity plays a significant role in

-3

2

3

4

5

6

7

8

9

10

11

-1

1000/T in (K ) Fig. 15. Variation of σac with reciprocal of temperature.

According to the literature [52] ionic conductors show spikes at low frequency and semicircle at high frequency. The electrode-sample interface dispersion is more pronounced in the low frequency region, and in the high frequency region the depressed semicircle may be due to the dispersive behaviour of the glass bulk resistance or the sample bulk 44

Journal of Non-Crystalline Solids 514 (2019) 35–45

P. Naresh, et al.

conductivity. The highest AC conductivity (10−2 Ω−1 cm−1) of ZL3 sample suggests that the present glass samples are very useful in solid state battery applications. Impedance plots show a single semicircle at low frequency and temperature whereas two depressed semicircles observed at high frequency and temperatures. In the earlier reports AC conductivity is varied from 10−5–10−3 Ω−1 cm−1order. The present reported AC conductivity values are in higher order 10−2 Ω−1 cm−1. Therefore, the AC conductivity is enhanced with the addition of ZnO.

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Acknowledgements The authors are thankful to Prof. M.V.N. Ambika Prasad, Gulbarga University, Kalaburagi, India for providing AC conductivity measurements. First author P. Naresh is thankful to Dr. V. Ganesan, Centre director, UGC-DAE Consortium for Scientific Research, Indore, India for providing TM-DSC, FTIR and Raman experimental facilities. References [1] B.N. Meera, J. Ramakrishna, J. Non-Cryst. Solids 159 (1993) 1–21. [2] P. Gayathri Pavani, K. Sadhana, V. Chandra Mouli, Physica B 406 (2011) 1242–1247. [3] S.L. Meena, B. Bhatia, J. Pure Appl. Ind. Phys. 6 (10) (2016) 75–83. [4] S. Thirumaran, K. Sathish, Res. J. Chem. Environ. 18 (10) (2015) 77–82. [5] K.A. Matori, M. Hafiz, M. Zaid, H.J. Quah, S. Hj, A. Aziz, Adv. Mater. Sci. Eng. (2015) 596361, , https://doi.org/10.1155/2015/596361. [6] L. Hwa, K. Hsieh, L. Liu, Mater. Chem. Phys. 78 (2002) 105. [7] R. El Mallawany, N. El Khoshkhany, H. Afifi, Mater. Chem. Phys. 95 (2006) 321. [8] Ghada El. Falaky, W.Guirguis Osiris, J. Non-Cryst. Solids 358 (2012) 1746–1752. [9] Y.B. Saddeek, K.A. Aly, K.S. Shaaban, Atif Mossad Ali, Moteb M. Alqhtani, Ali M. Alshehri, M.A. Sayed, E.A. Abdel Wahab, J. Non-Cryst. Solids 498 (2018) 82–88. [10] Y. Saddeek, H. Mohamed, M. Azzoz, Phys. Status Solidi A 201 (9) (2004) 2053. [11] G. Lakshminarayana, S.O. Baki, M.I. Sayyed, M.G. Dong, A. Lira, A.S.M. Noor, I.V. Kityk, M.A. Mahdi, J. Non-Cryst. Solids 481 (2018) 568–578. [12] N. Elkhoshkhany, Samir Y. Marzouk, Nourhan Moataz, Sherif H. Kandil, J. NonCryst. Solids 500 (2018) 289–301. [13] S. Rani, N. Ahlawat, R. Parmar, S. Dhankhar, R.S. Kundu, Indian J. Phy. 92 (7) (2018) 901–909. [14] Makishima-Mackenzie, J. Non-Cryst. Solids 17 (1975) 147. [15] A.K. Jonscher, Dielectric Relaxation in Solids, Chelsea Dielectrics, London, 1983. [16] S. Dahiya, R. Punia, S. Murugavel, A.S. Maan, Indian J. Phy. 88 (11) (2014) 1169. [17] H.A.A. Sidek, S. Rosmawati, Z.A. Talib, M.K. Halimah, W.M. Daud, Am. J. Appl. Sci.

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