Structural, Optical and Elastic Properties of Silver oxide incorporated Zinc Tellurite Glass System Doped with Sm3+ ions

Structural, Optical and Elastic Properties of Silver oxide incorporated Zinc Tellurite Glass System Doped with Sm3+ ions

Journal Pre-proof Structural, Optical and Elastic Properties of Silver oxide incorporated Zinc Tellurite Glass System Doped with Sm3+ ions R.A. Tafid...

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Journal Pre-proof Structural, Optical and Elastic Properties of Silver oxide incorporated Zinc Tellurite Glass System Doped with Sm3+ ions

R.A. Tafida, M.K. Halimah, F.D. Muhammad, K.T. Chan, M.Y. Onimisi, A. Usman, A.M. Hamza, S.A. Umar PII:

S0254-0584(20)30180-2

DOI:

https://doi.org/10.1016/j.matchemphys.2020.122801

Reference:

MAC 122801

To appear in:

Materials Chemistry and Physics

Received Date:

22 November 2019

Accepted Date:

12 February 2020

Please cite this article as: R.A. Tafida, M.K. Halimah, F.D. Muhammad, K.T. Chan, M.Y. Onimisi, A. Usman, A.M. Hamza, S.A. Umar, Structural, Optical and Elastic Properties of Silver oxide incorporated Zinc Tellurite Glass System Doped with Sm3+ ions, Materials Chemistry and Physics (2020), https://doi.org/10.1016/j.matchemphys.2020.122801

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Structural, Optical and Elastic Properties of Silver oxide incorporated Zinc Tellurite Glass System Doped with Sm3+ ions R. A. Tafida 1,2., M. K. Halimah 1*., F.D. Muhammad 1., K.T. Chan 1., M.Y. Onimisi2., A.Usman1,3., A.M. Hamza4, 5., S. A. Umar5. 1

Department of physics, Faculty of Science, Universiti Putra Malaysia, Serdang Selangor, UPM

43400. 2

Department of physics, Nigerian Defence Academy, Afaka, PMB 2109, Kaduna, Nigeria.

3

Department of physics, University of Science and Technology, Faculty of Science Wudil, Kano

Nigeria. 4National 5

Agency for Science and Engineering Infrastructure, Idu, Abuja, Nigeria.

Department of Physics, Faculty of Science, Federal University of Lafia, Nigeria.

Abstract Zinc tellurite glasses in the form of [{(TeO2)0.7 (ZnO) 0.3}0.99 (Sm2O3)0.01]1-y (Ag2O) y, y = 0.005. 0.01, 0.015, 0.02 and 0.025 molar fraction is prepared by the method of melt quenching. The molar volume decreases while the density of the glasses increases with an increase in dopant. The indirect and direct band gap increased with an increase in dopant content. Urbach energy, molar refraction, molar polarizability, refractive index, and electronic polarizability are shown to be decreased with an addition of silver oxide. The samples shear and longitudinal velocities are measured at room temperature of 5 MHz frequency.

Poisson ratio (Οƒ), Elastic moduli, hardness (H), Debye

temperature (πœƒπ·), Softening temperature (𝑇𝑆), bond connectivity (d) and fugacity (𝑓𝑔) are calculated to reveal the quantitative analysis concerning the structure of the synthesized glasses. 1

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The obtained results have revealed the adverse effect of silver oxide on the host materials by enhancing the properties and strengthening the glass network. Keywords: Tellurite glasses, Ultrasonic velocities, Elastic moduli, Poisson’s ratio, Softening temperature, Microhardness. 1.

Introduction

Recently, the studies of tellurite base glasses (TeO2) have attracted much attention because of their exceptional properties such as lower melting points, high dielectric constant, great mechanical strength, better durability of chemicals, good infrared transmission capabilities and high refractive indices [1][2]. Tellurium oxide is generally recognized to be a conditional glass former and can form glasses only when modifiers such as alkali, zinc oxide or other transitional metal oxide are added into the glass matrix [3]. A lot of recommendations are recently given to tellurite based glasses due to their unique and encouraging properties [4]. Halimah et al. [5] reported that one of the promising materials especially for nonlinear applications is tellurite glasses because of their low phonon maxima, high refractive index as well as low melting point properties. It has been recently revealed by Mohamed et al. that, zinc tellurite glasses are stable and established abundant interest from a different scientist in the world [6]. This is because the physical and optical properties of tellurite dope glasses are easily changed by zinc oxide since it plays two different important roles as a network modifier and network former in the synthesized glass network respectively [7]. Nazrin et al. reported that ZnO encourages the decrease in melting point and also increases the ability of the glass to form during the glass production process [4].Recently, broad attention is given to the tellurite glasses containing rare-earth ions and this is because of their great potentiality especially in the improvement of lasers and fibers development and for photonics applications such as non-linear optical devices [8]. Hajer et al. (2014) revealed that the rare earth 2

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ions samarium plays the role of a dopant in various crystal hosts as well as glass hosts in the visible region for intense emission [9]. In the present work, samarium oxide is chosen because of its lasing character when doped with TeO2 glasses. Yusoff et al. (2015) have suggested for certain components of the rare earth Sm to be used in photonics and laser devices [10]. The addition of silver oxide in the synthesized glass matrix (𝐴𝑔) is because silver ions are well known for their resistance against humidity, high conductivity and their potentials of being used in a variety of fields such as biomaterials [11]. Silver oxide has also played a vital role as one of the suitable and appropriate elements for the preparation of glass-based materials. Nazrin et al. [4] had reported that the silver addition in the glass system allows the glass samples to be useful in different applications since 𝐴𝑔 has brought plenty of capabilities to induce and augments some phenomena to occur by diffusing of silver into the glass and silver-glass interaction. Most of the technological applications of glass require the knowledge of the glasses elastic, mechanical as well as thermos-physical properties of the glasses[12]. This requires the determination of the elastic moduli, microhardness, softening temperature and so on. Hamid-Reza and coworkers reported on ultrasonic and optical properties of lead bismuth germinate glasses doped with Er3+ /Yb3+ targeted for fiber and laser applications [13]. Elastic properties study using the Ultrasonic non-destructive technique allows in glasses helps in providing details about the glass structure since it has direct connection to the glass’s interatomic potentials. The elastic properties’ study is as well very important as it provide information about interatomic bonding nature as well as some mechanical properties of the studied glasses [14]. The present work reports on the influence of silver oxide on structural, optical and elastic properties of zinc tellurite glass system doped with Sm3+ ions by varying the concentration of 𝐴𝑔 in the order of 0.005, 0.01, 0.015, 0.02 and 0.025 molar fraction respectively. The present study 3

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aims to (i) synthesized Sm3+ glasses doped with 𝐴𝑔 (ii) explore the optical properties of the fabricated samples (iii) to calculate the experimental elastic properties of the prepared glasses to reveal the quantitative analysis for the structure of the synthesized glasses. The hope is that the more silver ions are added to the glass structure, the more the glasses improves in terms of its optical properties and the elastic moduli will decrease with the addition of more silver ions. And from our study, there was no any report of work carried out on the elastic, optical and structural properties of silver oxide doped zinc tellurite glasses incorporated with samarium oxide. 2.

Experimental Procedure

The glasses are prepared using high purity analytical chemicals of TeO2 (Alfa Aesar 99.99%), ZnO (Alfa Aesar 99.99%), Sm2O3 (Alfa Aesar, 99.99%) and Ag2O (Alfa Aesar, 99.99%) with composition of [{(TeO2)0.7 (ZnO) 0.3}0.99 (Sm2O3)0.01]1-y (Ag2O) y, with y = 0.005, 0.01, 0.015, 0.02 and 0.025 molar fraction by means of high temperature melt quenching techniques. The required chemicals of the glass composition of approximately 13g batches were weighted using an electronic balance with an accuracy of (Β±0.0001 g) and thoroughly mixed in an alumina crucible with a glass rod for about 30 minutes to obtain homogeneous mixture for each sample. The mixture was preheated for an hour at 400 Β°C in an alumina crucible to remove moisture from the mixture using an electrical furnace. Another furnace was set at 900oC and was used for melting the powdered mixture for two hours. The melted sample was then quickly poured into a cylindrical stainless steel mold and then transferred into the first furnace set at 400 oC for sample annealing for another one hour. The essence of sample annealing is to avoid thermal stress and enhance the mechanical strength of the glass sample[15][16]. On completing the annealing process, the furnace was then switched off and the samples were left to cool down to room temperature overnight. To obtain a parallel and smooth glass surface, the cylindrical glasses were then cut into different 4

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thicknesses and polished using silicon carbide on both sides and the thickness suitability for optical and elasticity of approximately 5.0 mm and 2.3 mm was measured using Vernier Calipers. The remaining samples were crushed in to powder with a plunger for X-ray diffraction measurement using X-ray diffractometer (X’ pert pro analytical Philips model) and FTIR (Perkin Elmer Spectrum 100 FTIR) spectroscopy analysis at normal room temperature between 20 < 2πœƒ < 80 and 280-4000 cm-1 respectively. The polished bulk glass samples were characterized using UVVis spectrophotometer (Shimadzu UV 1650 PC) at room temperature in the wavelength range of 200 to 2000 nm. The density for all the glass samples was measured based on the Archimedes principle with distilled water as an immersed liquid using electronic densimeter MD- 300S (Alfa Mirage) with an accuracy of (Β±0.001) g/cm3. The measurement of densities was carried out ten (10) times and the average value taken. The density and molar volume of each glass sample was calculated using the following relations [17].

πœŒπ‘ π‘Žπ‘šπ‘π‘™π‘’ =

π‘‰π‘š =

π‘€π‘Žπ‘–π‘Ÿ π‘€π‘€π‘Žπ‘‘π‘’π‘Ÿ

πœŒπ‘€π‘Žπ‘‘π‘’π‘Ÿ

π‘šπ‘€ πœŒπ‘ π‘Žπ‘šπ‘π‘™π‘’

(1)

(2)

Where πœŒπ‘€π‘Žπ‘‘π‘’π‘Ÿ, π‘€π‘Žπ‘–π‘Ÿ,πœŒπ‘ π‘Žπ‘šπ‘π‘™π‘’π‘ , π‘€π‘€π‘Žπ‘‘π‘’π‘Ÿ, and 𝑀𝑀 represent the water density, weight of sample in air, sample density, the weight of sample in water and the molar weight of the sample glasses respectively. 3.

Results

3.1

Density and molar volume

The changes of structure in tellurite doped glasses is obtained via molar volume and density. Furthermore, several properties of the synthesized glass system such as the refractive index, molar 5

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volume, and elastic properties are calculated using the glass density data [18]. The values of density and molar volume are shown in Table 1 and presented in Fig 1. Table 1: Molar volume and density for [{(TeO2)0.7 (ZnO) 0.3}0.99 (Sm2O3)0.01]1-y (Ag2O) y glasses. Molar fraction (Ag) 0.005

Density (g/cm3) [Β± 0.03] 5.19

Molar volume (cm3/mol) [Β± 0.09] 26.67

0.01

5.23

26.61

0.015

5.26

26.50

0.02

5.31

26.36

0.025

5.37

26.15

Density

Molar volume

5.40

26.80

5.38

Density,ρ(g/cm3)

5.34

26.60

5.32 5.30

26.50

5.28

26.40

5.26 26.30

5.24 5.22

Molar volume (cm3/mol)

26.70

5.36

26.20

5.20 5.18 0

0.005

0.01 0.015 0.02 Ag2O(Sm)molar fraction

0.025

26.10 0.03

Fig 1: Density and molar volume variation against Ag2O concentration for [{(TeO2)0.7 (ZnO) 0.3}0.99 (Sm2O3)0.01]1-y (Ag2O) y glasses. 3.2

Spectral analysis of X-ray Diffraction (XRD)

The XRD analysis for [{(TeO2)0.7 (ZnO) 0.3}0.99 (Sm2O3)0.01]1-y (Ag2O) y, glass system is primarily used for phase identification. Therefore, for this glass system, the absence of sharp peaks was obtained and has shown to have a regular glassy character as presented in Fig 2. 6

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0.005 Ag (Sm) 0.02 Ag (Sm)

2000

0.01 Ag (Sm) 0.025 Ag (Sm)

0.015 Ag (Sm)

1800 1600

Counts

1400 1200 1000 800 600 400 200 0 20

30

40

50 Position, 2ΞΈ (0)

60

70

80

Fig 2: XRD pattern for [{(TeO2)0.7 (ZnO) 0.3}0.99 (Sm2O3)0.01]1-y (Ag2O) y glasses. 3.3

Fourier Transform Infrared (FTIR) Spectroscopy

The investigation of FTIR is primarily employed to give details information concerning the local arrangement, structure and the functional groups in both crystalline and non-crystalline materials [19]. The FTIR spectra is presented in Fig 3. The deconvolution of the bands was obtained using Origin 6.0 software. The deconvolution parameter, the band centers and area for each peak with their assignment are recorded in Table 2 and Table 3 respectively. And one of the deconvoluted spectra is shown in Fig 4.

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0.005 Ag2O (Sm)

0.01 Ag2O (Sm)

0.015 Ag2O (Sm)

0.02 Ag2O (Sm)

0.025 Ag2O (Sm)

180

Transmittance (%T)

160 140 120 100 80 60 40 20 0 200

400

600

800

1000

Wavenumbers

1200

1400

1600

(cm-1)

Fig 3: FTIR spectra for [{(TeO2)0.7 (ZnO) 0.3}0.99 (Sm2O3)0.01]1-y (Ag2O) y glasses.

Fig 4: Deconvolution of IR spectra for [{(TeO2)0.7 (ZnO) 0.3}0.99 (Sm2O3)0.01]1-y (Ag2O) y glasses.

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Table 2: Assignment of infrared transmission bands of prepared glass samples with different concentrations of silver oxide. 0.005 molar fraction 604

0.01 molar fraction

cm-1

606

cm-1

0.015 molar fraction 606

0.02 molar fraction

cm-1

608

cm-1

0.025 molar fraction 615

cm-1

Assignment Te-O bonds stretching vibrations in TeO4 units [20].

Table 3: Band area [A (%)], band centre [B (cm-1)] and assignments for [{(TeO2)0.7 (ZnO) 0.3}0.99 (Sm2O3)0.01]1-y (Ag2O) y glass system Molar Stretching mode of Stretching Stretching TeO4 TeO3 trigonal (Sm2O3)[21] fraction mode of mode of trigonal pyramid[22] ZnO[22] Ag2O[23] bipyramid (Ag) [24] 0.005 B 249.64 427.88 595.83 708.97 667.65 0.01 0.015 0.02 0.025

3.4

A

217.50

96.08

72.93

53.67

1.30

B

180.13

437.71

604.71

724.22

725.83

A

440.25

49.10

75.01

20.22

15.93

B

200.23

416.83

529.79

624.19

752.33

A

325.19

21.11

104.01

51.97

14.01

B

171.81

399.99

446.53

620.63

745.70

A

335.05

20.377

123.94

59.458

23.34

B

198.90

437.28

589.54

681.86

735.06

A

10.407

52.77

64.82

63.57

386.99

Oxygen packing density (OPD) and oxygen molar volume (VO)

The amount of rigidity of oxide in a synthesized glass network is achieved using the packing density of oxygen (OPD) as well as the oxygen molar volume (Vo) [25]. The oxygen packing density(0PD) and oxygen molar volume of the synthesized glasses was calculated using the following equations[20]. 9

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𝑂𝑃𝐷 = 𝑛 Γ—

π‘‰π‘œ =

𝜌 Γ— 100 𝑀

(3)

π‘‰π‘š

(4)

βˆ‘π‘₯𝑖𝑛𝑖

Where n represents the amount of oxygen in the composition, ρ is the density of the fabricated samples, M represents the molecular weight of each sample and 𝑛𝑖 is the amount of oxygen of the ith component. The data for the packing density of oxygen and the oxygen molar volume for the fabricated samples are shown in Table 4 and presented in Fig 5. Table 4: Oxygen molar volume and packing density of oxygen for [{(TeO2)0.7 (ZnO) (Sm2O3)0.01]1-y (Ag2O) y glasses. Molar fraction (Ag)

10

0.3}0.99

Oxygen molar volume (Vo) [Β± 0.06]

0.005

The packing density of oxygen (OPD) [Β± 0.07] 101.18

0.01

100.93

9.90

0.015

100.82

9.91

0.02

100.85

9.91

0.025

101.11

9.88

9.88

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Vo, Ag2O (Sm) 9.93

101.15

9.92

101.10

9.92 9.91

101.05

9.91

101.00

9.90

100.95

9.90

100.90

9.89

100.85

9.89

100.80 0

0.005

0.01

0.015

0.02

0.025

Oxygen molar volume

Oxygen packing density

OPD, Ag2O (Sm) 101.20

9.88 0.03

Ag2O (Sm) molar fraction

Fig 5: Variation of Packing density of oxygen and oxygen molar volume against Ag2O concentration for [{(TeO2)0.7 (ZnO) 0.3}0.99 (Sm2O3)0.01]1-y (Ag2O) y glasses. 3.5

Ionic concentration (N) and ionic distance (Ri)

The ionic concentration (N) and ionic distance (Ri) are of significant importance because of their direct relationship regarding the structure of tellurite doped glasses. The values of both ionic concentration and distance are calculated using the following relations [26] .

𝑁=

𝑁 𝐴𝜌 π‘₯ 𝑀𝑀 1/3

()

1 𝑅𝑖 = 𝑁

(5)

(6)

Where 𝑁𝐴, ρ, π‘₯, 𝑀𝑀 represent Avogadro's number, glass sample density, mole fraction and the average molecular weight of the glass system respectively. The calculated values are listed in Table 5 and depicted in Fig 6.

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Table 5: Ionic concentration and ionic distance of [{(TeO2)0.7 (ZnO) 0.3}0.99 (Sm2O3)0.01]1-y (Ag2O) y glasses. Molar fraction (Ag) 0.005

Ionic conc., N(Γ—1020ions/cm3) [Β±0.81] 1.12

Ionic dist., Ri(Γ—10-7) (AO) [Β± 0.27] 2.06

0.01

2.26

2.64

0.015

3.40

1.43

0.02

4.56

1.29

0.025

5.75

1.20

N x 1020 (ions/cm3)

7.00

Ri x10-7

2.50

6.00 5.00 1.50

4.00 3.00

1.00

2.00 0.50

Inter-ionic distance, Ri(Ao)

ionic conc,N(ions/cm3)

2.00

1.00 0.00 0

0.005

0.01 0.015 0.02 Ag2O (Sm) molar fraction

0.025

0.00 0.03

Fig 6: Variation of ionic concentration and inter-ionic distance against Ag2O concentration for [{(TeO2)0.7 (ZnO) 0.3}0.99 (Sm2O3)0.01]1-y (Ag2O) y glasses.

4. Optical Absorption, band gap energy, and Urbach energy To source information regarding the band structures, examine the optically induced transitions and to reveals the band gap energy of non-crystalline, the optical absorption measurement mostly the 12

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absorption edge is of important [20] [27]. The absorption spectra were obtained by UV- Visible Spectrometer (UV-1650 PC, Shimadzu) and were carried out in the wavelength ranges of 2002000 nm. The present glass system optical absorption is presented in Fig 7.

0.005 Ag2O (Sm) 0.02 Ag2O (Sm)

0.01 Ag2O (Sm) 0.025 Ag2O (Sm)

0.015 Ag2O (Sm)

1.40 4F

Absorbance(a.u)

1.20

7/2 6F

1.00 6F

0.80 4I 9/2

0.60

6F

7/2

6F

5/2

6F

3/2

9/2

11/2

0.40 0.20 0.00 200

400

600

800

1000

1200

1400

1600

1800

2000

Wavelength, Ξ» (nm)

Fig 7: UV-Vis absorbance spectra for [{(TeO2)0.7 (ZnO) 0.3}0.99 (Sm2O3)0.01]1-y (Ag2O) y glasses. Davis and Mott [28] revealed that the coefficient of absorption, 𝛼(πœ”), and photon energy, (ћ𝑀) of the incident radiation are associated with one another via the following relation:

𝛼(πœ”) =

𝐡(Ρ›πœ” ― πΈπ‘œπ‘π‘‘)𝑛 Ρ›πœ”

(7)

where n, represents an index that takes the following values, 1/2, 2, 3/2 and 3 subject to the band transitions [29]. These transitions are divided into indirect and direct transitions respectively. B is a constant called the band trailing parameter and is never zero for amorphous materials and πΈπ‘œπ‘π‘‘ represents the optical energy gap of the synthesized glasses. The direct transitions normally take

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place when the momentum of the electron of the atom or molecules is preserved. While in an indirect transition, the electron requires help from a photon for it to move from valence to conduction band [18]. The coefficient of absorption values, 𝛼(πœ”) are generated from the glass samples absorbance at various wavelengths using the following relation:

𝛼(πœ”) = 2.303

𝐴 𝑑

(8)

Where A represents the absorbance and t is the sample thickness respectively. The plot of (π›ΌΡ›πœ”)1/𝑛 Against Ρ›Ο‰ from equation (7) is referred to as Tauc's plot which is used for the estimation of the optical energy band gap of a given transition. This is possible by extrapolating the linear portion of the curve for the Tauc’s plot to meet the Ρ›Ο‰ axis [30]. The indirect optical transition (Ξ±Ρ›Ο‰)1/2, direct optical transition (Ξ±Ρ›Ο‰) 2, band gap energy and Tauc’s plot (π›ΌΡ›πœ”)1/2 = 0 for the present glasses are presented in Fig 8, 9, 10 and 11. Their values are listed in Table 6.

0.005 Ag2O (Sm)

0.01 Ag2O (Sm)

0.02 Ag2O (Sm)

0.025 Ag2O (Sm)

0.015 Ag2O (Sm)

20 18 (Ξ±Ρ›Ο‰)1/2(cm-1eV)1/2

16 14 12 10 8 6 4 2 0 0

1

2

3 Ρ›Ο‰ (eV)

14

4

5

6

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Fig 8: Plot of (Ξ±Ρ›Ο‰)1/2 versus the energy of photon Ρ›Ο‰ for [{(TeO2)0.7 (ZnO) 0.3}0.99 (Sm2O3)0.01]1-y (Ag2O) y glasses. 0.005 Ag2O (Sm)

0.01 Ag2O (Sm)

0.015 Ag2O (Sm)

0.02 Ag2O (Sm)

0.025 Ag2O (Sm)

900 800

(Ξ±Ρ›Ο‰)2(cm-1eV)2

700 600 500 400 300 200 100 0 0

0.5

1

1.5

2

2.5

3

3.5

Ρ›Ο‰ (eV)

Fig 9: Plot of (Ξ±Ρ›Ο‰) 2 versus photon energy Ρ›Ο‰ for [{(TeO2)0.7 (ZnO) 0.3}0.99 (Sm2O3)0.01]1-y (Ag2O) y glasses. Edir

Ein

3.45

3.12

3.44

3.10

E2opt(eV)

3.06

3.42

3.04 3.41

E1opt(eV)

3.08

3.43

3.02

3.40

3.00

3.39

2.98

3.38 0

0.005

0.01

0.015

0.02

0.025

2.96 0.03

Ag2O (Sm) molar fraction

Fig 10: Plot of the indirect and direct energy band gap against Ag2O concentration for [{(TeO2)0.7 (ZnO) 0.3}0.99 (Sm2O3)0.01]1-y (Ag2O) y glasses.

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0.005 Ag2O (Sm)

Tauc's plot indirect band gap

20 18

(Ξ±Ρ›Ο‰)1/2(cm-1eV)1/2

16 14 12 10 8 6 4 2 0 0

1

2

3

4

5

6

Ρ›Ο‰ (eV)

Fig 11: Tauc's plot to determine the indirect optical band gap for [{(TeO2)0.7 (ZnO) (Sm2O3)0.01]1-y (Ag2O) y glasses.

0.3}0.99

Urbach energy (ΔΕ) of glass samples describes the amount of disorderliness in both crystalline and amorphous materials according to [31][24]. The values of Urbach energy Ξ”E in the present glass system are obtained by means of taking the reciprocals of slopes of the linear portion of lnΞ±(𝑣) against Ρ›Ο‰ curves given by the following relations[9].

( )

𝛼(𝑣) = 𝛽𝑒π‘₯𝑝

ћ𝑣 π›₯𝐸

(9)

where 𝛽 is a constant, Ρ› represents the plank constant, v is the photon frequency and Ξ”E is the photon energy of the glass system. The data for Urbach energy are listed in Table 6 and presented in Fig 12 and 13. The sample of Tauc's plot for the determination of Urbach energy is depicted in Fig 14.

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Table 6: Indirect band gap (E1opt), Direct band gap (E2opt) and Urbach energy (ΔΕ) for [{(TeO2)0.7 (ZnO) 0.3}0.99 (Sm2O3)0.01]1-y (Ag2O) y glasses. Molar fraction,

Indirect band gap, E1opt

Direct band gap, E2opt

Urbach energy, ΔΕ

Ag

(eV) [Β±0.02]

(eV) [Β±0.01]

(eV) [Β±0.09]

0.005

2.96

3.38

0.26

0.01

3.05

3.42

0.24

0.015

3.07

3.43

0.23

0.02

3.09

3.44

0.21

0.025

3.10

3.41

0.20

0.005 Ag2O (Sm)

0.01 Ag2O (Sm)

0.02 Ag2O (Sm)

0.025 Ag2O (Sm)

0.015 Ag2O (Sm)

4.50 4.00 3.50 lnΞ±

3.00 2.50 2.00 1.50 1.00 0.50 0.00 0

0.5

1

1.5

2

2.5

3

3.5

4

Π‹Ο‰(eV)

Fig 12: Plot of In (Ξ±) against (Ρ›Ο‰) for [{(TeO2)0.7 (ZnO) 0.3}0.99 (Sm2O3)0.01]1-y (Ag2O) y glasses.

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Urbach Energy 0.27 0.26

ΔΕ(eV)

0.25 0.24 0.23 0.22 0.21 0.20 0

0.005

0.01 0.015 Ag2O (Sm) molar fraction

0.02

0.025

0.03

Fig 13:Variation of Urbach energy for [{(TeO2)0.7 (ZnO) 0.3}0.99 (Sm2O3)0.01]1-y (Ag2O) y glasses against Ag2O concentration.

0.005 Ag2O (Sm)

4.50 4.00 3.50 lnΞ±

3.00 2.50 2.00 1.50 1.00 0.50 0.00 0

1

2

3

4

5

6

Π‹Ο‰(eV)

Fig 14: Tauc’s plot to determine the Urbach energy for [{(TeO2)0.7 (ZnO) 0.3}0.99 (Sm2O3)0.01]1-y (Ag2O) y glasses.

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5. Index of refraction (n), Molar refraction (π‘Ήπ’Ž), Molar polarizability ( ∝ π’Ž) and Electronic polarizability ( ∝ 𝒆) The fabricated glasses index of refraction (n) and molar refraction (π‘…π‘š) depend on the polarizability of the materials. The index of refraction is determined from the optical band gap energy of the synthesized glass system and their data are used to select how suitable the samples are for optical applications, meanwhile, polarizability of glass samples describes the magnitude of the electron response to the electric field [24]. The index of refraction (n), data for silver doped samarium oxide glasses are calculated using the following relations[32]. 𝑛2 ― 1 𝑛2 + 2

πΈπ‘œπ‘π‘‘

=1―

20

(10)

The calculation of molar refractionπ‘…π‘š and molar polarisabilityπ›Όπ‘š are obtained using the LorentzLorentz equation [33] as follows:

π‘…π‘š =

π›Όπ‘š =

( ) 𝑛2 ― 1 𝑛2 + 2

π‘‰π‘š

π‘…π‘š 2.52

(11)

(12)

The values of the electronic polarizability of the glass samples are calculated using the following equation[34].

𝛼𝑒 =

19

3(𝑛2 ― 1) 4πœ‹π‘π΄(𝑛2 + 2)

(13)

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Where n, π‘‰π‘š, 𝑁𝐴, and πΈπ‘œπ‘π‘‘ represent the refractive index, molar volume, Avogadro’s number and the optical energy gap of the samples glasses. Their corresponding values are listed in Table 7 and shown in Fig 15 and 16 respectively. Table 7: Index of refraction (n), molar refraction (Rm), molar polarizability ( ∝ π‘š) and electronic polarizability ( ∝ 𝑒) of [{(TeO2)0.7 (ZnO) 0.3}0.99 (Sm2O3)0.01]1-y (Ag2O) y glasses. Molar fraction Ag

Refractive index (n)[Β± 0.06]

Molar refraction (Rm ) [Β±0.09]cm-3

Molar polarizability, (Ξ±m)[Β±0.03]cm3

Electronic polarizability,(Γ—1025)[Β± 0.06s]cm3

0.005

2.40

16.39

6.50

2.43

0.01

2.38

16.20

6.43

2.41

0.015

2.37

16.11

6.39

2.41

0.02

2.37

15.99

6.34

2.40

0.025

2.36

15.85

6.29

2.40

Ξ±e

2.41

2.44

2.41

2.44

2.40

2.43 2.43

2.40

2.42

2.39

2.42

2.39

2.41

2.38

2.41

2.38

2.40

2.37

2.40

2.37 0

0.005

0.01

0.015

0.02

0.025

2.39 0.03

Electronic Polarizability, Ξ±e x10-25

Refractive index, n

n

Ag2O (Sm) molar fraction

Fig 15: Variation of refractive index and polarizability of [{(TeO2)0.7 (ZnO) 0.3}0.99 (Sm2O3)0.01]1-y (Ag2O) y glasses with Ag2O concentration. 20

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Ξ±m

Rm 16.50 16.40

Molar Polarizability (Ξ±m)

6.51

16.30 6.46

16.20 16.10

6.41

16.00

6.36

15.90 6.31

Molar refraction (Rm) (cm3)

6.56

15.80

6.26 0

0.005

0.01

0.015

0.02

0.025

15.70 0.03

Ag2O (Sm) molar fraction

Fig 16: Variation of molar polarizability and molar refraction of [{(TeO2)0.7 (ZnO) (Sm2O3)0.01]1-y (Ag2O) y glasses with Ag2O concentration.

6.

0.3}0.99

Elastic properties

The elastic properties of synthesized glasses provide details information about the stress-strain relationship in the glass material. Additionally, the strength of a material when force is applied to the material is also studied using the same parameter [35]. Elastic properties are also one of the most significant parameters that are considered while selecting glass samples for a particular application[36]. 6.1

Longitudinal (𝑽𝑳) and Shear ultrasonic velocity (𝑽𝑺)

The two velocities are very important tools for the investigation of elastic properties of a glass material. The values are calculated using the following relation[36].

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𝑉=

2𝑑 π›₯𝑑

(14)

Where d represents the thickness of the sample, V is the ultrasonic wave velocity and Ξ”t represents the time difference for the two measured times of flight respectively. The calculated values of the ultrasonic wave velocities (𝑉𝐿) and (𝑉𝑆) are listed in Table 8 shown in Fig 17. Table 8: Ultrasonic velocities (𝑉𝐿) and (𝑉𝑆) of [{(TeO2)0.7 (ZnO) 0.3}0.99 (Sm2O3)0.01]1-y (Ag2O) y glasses.

22

Molar fraction (Ag) 0.005

VL (Β± m/s)

VS (Β± m/s)

3420

1948

0.01

3352

1833

0.015

3482

1987

0.02

3375

1835

0.025

3682

1913

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VL(m/s)

VS(m/s)

3700

2000

3650

1980

3600

1960

VL(ms-1)

1920

3500

1900

3450

1880

3400

1860

3350

1840

3300 0

0.005

0.01

0.015

0.02

0.025

VS(ms-1)

1940

3550

1820 0.03

Ag2O (Sm) molar fraction

Fig 17: Longitudinal (𝑉𝐿) and shear velocity (𝑉𝑆) of [{(TeO2)0.7 (ZnO) (Ag2O) y glasses against Ag2O concentration. 6.2.1

0.3}0.99

(Sm2O3)0.01]1-y

Poisson’s ratio (Οƒ), Elastic moduli and Micro-hardness (H)

The ratio of Poisson signifies the percentage of a material's resistance to volume [37]. Elastic moduli of glass materials represent the measure of interatomic forces and packing density of the oxides constituents [38]. The quantity of required stress to eliminate free volume in sample glasses are considered by their micro-hardness (H) [5]. The values of the Poisson's ratio, elastic moduli, and micro-hardness of the glass system are calculated using the following equations[5].

𝜎=

(𝐿 ― 2𝐺) 2(𝐿 ― 𝐺)

(15)

𝐿 = 𝑉2𝑙 𝜌

(16)

𝐺 = 𝑉2𝑠 𝜌

(17)

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𝐾=𝐿―

()

4 𝐺 3

(18)

𝐸 = (1 + 𝜎)2𝐺

(19)

(1 ― 2𝜎)𝐸 6(1 + 𝜎)

(20)

𝐻=

where L represents the longitudinal modulus, G is shear modulus, ρ is the density of the glass samples, 𝑉𝑙, is longitudinal velocity, 𝑉𝑠 is shear velocity, K is bulk modulus, E is Young's modulus, H is micro-hardness and Οƒ is the poison's ratio of the glass system. The data for poison’s ratio (Οƒ), elastic moduli and micro-hardness (H) are presented in Table 9 and shown in Fig 18, 19 and 20 respectively. Table 9: Poisson’s ratio (𝜎), elastic moduli and hardness (𝐻) for [{(TeO2)0.7 (ZnO) (Sm2O3)0.01]1-y (Ag2O) y glasses.

0.3}0.99

Molar fraction (Ag) 0.005

(Οƒ)

(H)

L(Gpa)

E(Gpa)

K(Gpa)

G(Gpa)

0.25

3.15

60.80

49.71

34.50

19.72

0.01

0.28

2.49

58.76

45.22

35.33

17.57

0.015

0.25

3.34

63.88

52.36

36.14

20.80

0.02

0.29

2.50

60.54

46.17

36.67

17.89

0.025

0.31

2.42

72.85

51.72

46.63

19.66

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0.32 0.31

Poisons Ratio

0.30 0.29 0.28 0.27 0.26 0.25 0.24 0

0.005

0.01

0.015

0.02

0.025

0.03

Ag2O (Sm) molar fraction

Fig 18: Variation of poisons ratio (𝜎) for [{(TeO2)0.7 (ZnO) 0.3}0.99 (Sm2O3)0.01]1-y (Ag2O) y glasses with Ag2O concentration.

3.60 3.40

H(GPa)

3.20 3.00 2.80 2.60 2.40 2.20 0

0.005

0.01

0.015

0.02

0.025

0.03

Ag2O (Sm) molar fraction

Fig 19: Variation of micro-hardness (𝐻) of glasses with Ag2O concentration.

25

[{(TeO2)0.7 (ZnO) 0.3}0.99 (Sm2O3)0.01]1-y (Ag2O) y

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L (GPa)

E (GPa)

K (GPa)

G (GPa)

70

Elastic modulii (Gpa)

60 50 40 30 20 10 0 0

0.005

0.01

0.015

0.02

0.025

0.03

Ag2O (Sm) molar fraction

Fig 20: Variation of elastic moduli of [{(TeO2)0.7 (ZnO) 0.3}0.99 (Sm2O3)0.01]1-y (Ag2O) y glasses with Ag2O concentration. 6.2.2

Debye temperature (πœ½π‘«) and Softening temperature (𝑻𝑺)

The fabricated samples Debye and softening temperature play a significant role in the present glasses. Debye temperature examines the amount of lattice vibration in solid materials as well as the excitation temperature of vibration in the materials [39]. Softening temperature (𝑇𝑆) as the name implies signifies the variation of temperature from viscous to plastic flow. The temperature stability of glass materials is also decided by their softening temperatures [3]. The calculated data of the two temperatures are obtained using the following relation[40].

𝑇𝑠 =

𝑀𝑣2𝑠

( )

(20)

𝑐2𝑛

1/3

( )

β„Ž 3πœ‘π‘π΄ πœƒπ· = π‘˜ 4πœ‹π‘‰π‘š

26

π‘£π‘š

(21)

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where M represents the glass molecular weight, c is constant, k is the Boltzmann’s constant, h is plank constant, 𝑁𝐴 is the Avogadro’s number, πœ‘ is the number of atoms in the chemical formula, π‘‰π‘š is molar volume and π‘£π‘š is the mean ultrasonic velocity. The data’s of Softening and Debye temperature are listed in Table 10 and shown in Fig 21 and 22 respectively. Table 10: Debye temperature (πœƒπ·), Softening temperature (𝑇𝑆), bond connectivity (d) and fugacity (𝑓𝑔) for[{(TeO2)0.7 (ZnO) 0.3}0.99 (Sm2O3)0.01]1-y (Ag2O) y glasses. Molar fraction (Ag) 0.005

πœƒπ·(K)

𝑇𝑆(K)

d

𝑓𝑔

295

731

2.28

0.09

0.01

298

737

1.98

0.07

0.015

301

741

2.30

0.09

0.02

300

732

1.95

0.06

0.025

315

782

1.68

0.05

320

Debye Temperature, ΞΈD (K)

315

310

305

300

295

290

0

0.005

0.01 0.015 Ag2O (Sm) molar fraction

0.02

Fig 21: Variation of Debye temperature for [{(TeO2)0.7 (ZnO) glasses with Ag2O concentration 27

0.3}0.99

0.025

0.03

(Sm2O3)0.01]1-y (Ag2O)

y

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790

Softening Temprature,TS (K)

780 770 760 750 740 730 720 0

0.005

0.01 0.015 Ag2O (Sm) molar fraction

0.02

0.025

0.03

Fig 22: Plot of softening temperature for [{(TeO2)0.7 (ZnO) 0.3}0.99 (Sm2O3)0.01]1-y (Ag2O) y glasses. 6.2.3

Fractal bond connectivity (𝒅) and fugacity (π’‡π’ˆ)

Fractal bond connectivity of a glass sample (d) is a suitable parameter and provides information about the dimensionality of the glass arrangement [39]. An additional significant parameter in the current study is fugacity (𝑓𝑔) which is also called the fluctuation free volume in sample glasses, describes the amount of rigidity of the synthesized glass system [41]. The two parameters are calculated using the following relation[42].

𝑑=

4𝐺 𝐾 1 (1 ― 2𝜎)2 = 𝑓𝑔 2(1 + 𝜎)

()

𝑓𝑔𝐼𝑛

28

(22)

(23)

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Where K represents the bulk modulus, G is the shear modulus and 𝜎 is the Poisson's ratio of the glass samples. The data of fractal bond connectivity and fugacity are listed in Table 10 and presented in Fig 23.

d

fg 0.10

2.30

0.09

2.20 0.08

2.10

0.07

2.00 1.90

0.06

Fugacity, (fg)

Fractal bond conectivity, (d)

2.40

1.80 0.05

1.70 1.60 0

0.005

0.01

0.015

0.02

0.025

0.04 0.03

Ag2O (Sm) molar fraction

Fig 23: Variation of fractal bond connectivity and fugacity for [{(TeO2)0.7 (ZnO) (Sm2O3)0.01]1-y (Ag2O) y glasses with Ag2O concentration. 7.

0.3}0.99

Discussion

The graph of molar volume and density are presented in Fig 1 while their data are shown in Table 1. The behavior of density revealed a steady increasing trend while molar volume shows a generally decreasing trend with an increase in silver oxide content which has obeyed its inversely proportional relationship with density. The increasing density values are associated with the lower molecular weight replacement of TeO2 (atomic mass =159.60 g/mol) by the upper molecular weight of Ag2O (atomic mass 231.735 g/mol) in the glass system [43]. Theoretically, the molar 29

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volume has inverse proportionality relation with the density of glass materials and direct proportionality relation to the molecular weight of the fabricated samples. Therefore, the decreasing molar volume reflects the reduction in the free volume of the synthesized glasses. The graph of X-ray diffraction at various dopant content of Ag is presented in Fig 2. The presence of a broad hump exists at the lower angle of scattering with the nonappearance of sharp absorption peaks in the spectra demonstrating the existence of short-range order in the structure of the fabricated samples [44]. Fig 3 has presented the graph of FTIR spectra of the fabricated samples while Tables 2 and 3 show the assignment and the deconvolution data of the transmission bands at various dopant concentrations. It can be observed that there exists only one broad absorption band in the spectra at 604-615 cm-1 which has corresponded to the stretching vibration of the TeO4 structural unit and this has confirmed the presence of the TeO4 group in all tellurite containing glasses[20]. The ZnO absorption band does not surface which has established the broken down of zinc lattice in the spectra. The deconvolution result revealed the existence of five different absorption bands in the IR spectra which are assigned to TeO4, TeO3, ZnO, Sm2O3 and Ag2O structural units respectively. Generally, the areas for TeO4 and TeO3 structural units increases after the process. The areas for Sm2O3 and ZnO structural units decreases while the Ag2O structural unit’s increases. This can be related to the structural rearrangement process and bond breaking that occur in the fabricated samples[45]. As well as the ionization and atomic displacement process that occurs in the glass system. The oxygen packing density OPD and oxygen molar volume (Vo) of the synthesized glasses are presented in Fig 5 and listed in Table 4. The calculated values of OPD decrease from 0.005 to 0.015 molar fraction and then increases at 0.02 and 0.025 molar fraction when more silver oxide content is added into the glass system. The data for oxygen molar volume (Vo) increases from 30

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0.005 to 0.015 molar fraction and then decreases at 0.02 and 0.025 molar fraction with dopant content increase respectively. The decreasing OPD can be associated with the existence of NBOs in the sample glasses and an increase in the interstitial space of the glass network [46]. The increasing values of OPD with an increase in the concentration of more Ag2O shows that the NBO is not formed at those concentrations and the interstitial space of the glass network decreases [20]. The oxygen molar volume reduction has contributed to the decrease in the molar volume of the glass system. This has also indicated the reduction in the creation of NBO and excess volume of the glass system which has contributed to a tightly packed arrangement in the glass system [47]. Ionic concentration N and ionic distance 𝑅𝑖 of the sample glasses are presented in Fig 6 and their data are listed in Table 5. The increasing trend of ionic concentration is observed from (1.128 to 5.755) Γ— 1020 ions/cm3 while the ionic distance (𝑅𝑖) decreases from (2.069 to 1.202) Γ— 10-7 𝐴° with an increase in silver oxide concentration respectively. According to literature, higher ionic concentration in the glass network resulted in the lesser ionic distance and hence the higher the glass network connectivity and rigidity [48]. The optical absorption spectra of the synthesized glasses are depicted in Fig 7. The spectral absorption of the fabricated samples shows the presence of seven absorption bands as a result of f-f transitions which are located at the following wavelength: [ 405, 482, 962, 1091, 1241, 1390 and 1498 nm] respectively. The bands are initiated from ground state 6H5/2 to excited states: 4F7/2, 4I , 6F 6 6 6 9/2 11/2, F9/2, F7/2, F5/2,

and 6F3/2 transition respectively. There exists the strongest absorption

peak at 1241 and 1390 nm which are assigned to 6H5/2 β†’ 6F7/2 and 6H5/2β†’6F5/2. The edge of absorption is shifted to the higher wavelength with an increase of more dopant and this behavior may be due to the less rigidity in the sample glasses [49]. The amorphous nature of the sample glasses has contributed to the not sharply define of the optical absorption edge. Fig 10 and 11 have 31

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presented the indirect and direct optical band gap, Tauc's plot indirect band gap with glass composition of [{(TeO2)0.7 (ZnO) 0.3}0.99 (Sm2O3)0.01]1-y (Ag2O) y at different Ag2O content. As listed in Table 6, the data for the indirect band gap increases from 2.969 eV until 3.105 eV while that of direct band gap increases from 0.005 to 0.02 molar fraction with a slight decrease at 0.025 molar fraction respectively as the dopant content increases. The increasing band gap energy has reflected the creation of (BO) in the glass matrix [50]. According to [4], silver oxide addition in the fabricated samples can lead to the transformation of the trigonal pyramid into trigonal bipyramid and supports the manifestation of more (BO) in the synthesized glasses. However, decreasing values of Eopt as observed at 0.025 molar fraction for direct band gap with an increase in silver oxide may be related to the structural changes that happen when more silver oxide content is added in the glass network as testified by [51]. Furthermore, the reduction in direct optical band gap is credited to the formation of NBO in the glass system and this has supported in the less order of the fabricated samples [49]. From Table 6 and Fig 13, the Urbach energy values reduces from 0.260 eV until 0.209 eV as dopant content increases from 0.005 until 0.025 molar fraction. The decrease in defects concentration has contributed to the decreasing Urbach energy values which in turn causes the fragility nature of the glass to decrease as well and produces glasses with great stability and connectivity [52]. The Urbach energy data of the present glasses are within the ranges of 0.045 eV to 0.66 eV as reported for values of amorphous semi-conductors Urbach energy [53] and one of the Tauc's plots on how the data was obtained is presented in Fig 14. The graph of index of refraction and polarizability against molar fraction of silver oxide are presented in Fig 15, while Table 7 displays the values of index of refraction, molar refraction, molar polarizability and electronic polarizability for [{(TeO2)0.7 (ZnO) 0.3}0.99 (Sm2O3)0.01]1-y (Ag2O) y glasses. The index of 32

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refraction decreases from 2.405 to 2.369 while electronic polarizability values decrease from 2.436 Γ…3 to 2.401 Γ…3 with an increase in dopant content. The reduction in refractive index and polarizability of the present glasses might be due to the incorporation of modifier Ag2O which has contributed to the decrease in the amount of (NBO) in the glass system [54]. Molar polarizability and molar refraction against dopant concentration are presented in Fig 16. It can be observed that these two parameters are found to be strongly related to one another as they exhibit a similar pattern in behavior. The molar refraction decreases gradually from 16.399 cm3 to 15.851 cm3 while molar polarizability decreases from 6.507 Γ…3 to 6.290 Γ…3 respectively with dopant content increase. According to [55], non-bridging oxygen has high possibilities to polarize when compared to the BO and therefore, the decrease in NBO causes the reduction in molar refraction and molar polarizability as the concentration of the dopant increases. The assessment of elastic properties is another important feature that can give details explanations concerning the stress-strain relationship in glass samples. In the present glass systems, the measurement of ultrasonic velocities was observed in the uncertainty range of Β± 5 m/s. Fig 17 presents the graph of shear (𝑉𝑆) and longitudinal velocity(𝑉𝐿) against the dopant concentration while Table 8 lists the ultrasonic velocity values. It can be seen that the two velocities have a similar behavioral pattern with an increase of dopant. At y = 0.005 molar fraction the two velocities experience an anomalous reduction from 3420 m/s to 3352 m/s and 1948 m/s to 1833 m/s respectively. With the addition of more dopant concentration, the ultrasonic velocities increase in both longitudinal and shear velocities at y =0.015 molar fraction. The decreasing and increasing behavior of the two velocities is also observed at y =0.02 and y = 0.025 molar fraction with silver oxide content addition in the glass system. Meanwhile, the fluctuation of the two velocities is based on the rigidity change and the glass elastic properties. The two velocities decrease as a result of 33

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the decrease in glass hardness and rigidity as well as the creation of more NBOs in the glass network [38]. The addition of more dopant concentration causes a further decrease in NBO concentration and an increase in the glass rigidity. This has caused a massive increment in the glass ultrasonic velocities [48]. Furthermore, according to Nazrin et al. (2018), an increase in the ultrasonic velocities leads to an increase in the packing density because of the conversion of coordination in the glass system [44]. The data for Poisson's ratio, micro-hardness and glass elastic moduli are presented in Table 9. The graph of Poisson's ratio against the concentration of dopant is depicted in Fig 18. It can be observed that Poisson's ratio has an increasing trend from 0.259 at y = 0.005 molar fraction to 0.315 at y = 0.025 molar fraction. Meanwhile, a slight decrease is observed for Poisson's ratio at y = 0.015 molar fraction respectively. Poisson's ratio always relies on the dimensionality of the glass network as well as the density of cross-link. Therefore, according to [45] the ratio of poison between the ranges of 0.1 to 0.2 indicate that the fabricated samples possess a high cross-link density while the ranges between 0.3 to 0.5 reflected a lower density of cross-link. In the present study, the presence of rare earth Sm and silver oxide has caused more ions to expand in the system network. This process has weakened the structure of the glasses (loose packing) which further breaks down the TeO2 and ZnO as well as the transformation of BO to NBO. This leads to the discontinuity in the structure of the glasses and hence decreases the glass rigidity and supports a reduction in the velocity by causing an increasing Poisson's ratio values of the glass network [5]. The decrease in the value observed when y = 0.015 molar fraction for poisons ratio can be related to the gradual rise in the average crosslink density of the synthesized glasses [49]. The microhardness (H) as shown in Fig 19 decreases from 3.158 GPa to 2.49 GPa when y = 0.005 to y =0.01 molar fraction. The value increases at y =0.015 molar fraction with an increase of dopant. 34

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However, further addition of dopant changes the micro-hardness (H) where it exhibits a steady decrease until 2.423 GPa at y = 0.025 molar fraction. The changes of the structural unit in the glass network from TeO3 to TeO4 forming BO atoms have resulted in increasing the glass compactness and can be the reason behind the decreasing microhardness [46]. Furthermore, decreasing rigidity of the fabricated samples also contributed to the reduction of the microhardness of the synthesized glasses [45]. At y = 0.015 molar fraction the hardness increases and this can be due to the increase in glass samples rigidity according to [48]. This is expected as the elastic moduli of the glass network also increases. Additionally, the elevation of microhardness can be related to the decreasing NBOs which has resulted in a stronger network [45]. The graph of elastic moduli is depicted in Fig 20 and listed in Table 9. It can be seen that the longitudinal modulus, L, ranges from 60.809 to 72.856 GPa, young modulus, E, from 49.711 to 51.728 GPa, bulk modulus, K, from 34.504 to 46.634 GPa and shear modulus, G, from 19.728 to 19.666 respectively. The elastic moduli values increase with an increase in dopant content as a result of the increase in glass rigidity which can be credited to the addition of more dopant in the synthesized glass network [46]. However, in the present glasses, the increase in the strength of the materials has also contributed to the observed increase in elastic moduli of the fabricated glasses [38]. Table 10 tabulates the data of Debye temperature, softening temperature, fractal bond connectivity and fugacity of the present glass system. Fig 21 and 22 present the graph of Debye temperature and softening temperature against silver oxide content. Both Debye and softening temperatures exhibit an increasing trend with only a decrease when y= 0.02 molar fraction with an increase in silver oxide content. The decreasing Debye and softening temperatures of the synthesized glasses are assigned to the changes in the number of atoms per unit volume as well as the presence of NBOs in the glass system [40]. The reduction in bond strength is also one of the significant features 35

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that lead to a decrease in the Debye and softening temperatures respectively [48]. The elevation of the two parameters as observed signifies the increase in the glass rigidity which can be related to the increase in the number of atoms in the chemical formula and increase in the mean ultrasonic velocity of the glass system [49]. Additionally, the increasing values of Debye and softening temperature can be predicted as a result of the strengthening of the glass structure which is attributed to the generation of BO in the fabricated samples [41]. Fig 23 illustrates the graph of fractal bond connectivity (d) and fugacity (𝑓𝑔) of the synthesized glasses. The two parameters show a similar pattern in behavior and exhibit a generally decreasing trend from 2.287 to 1.686 and 0.091 to 0.052 respectively with an increase in silver oxide content. The fractal bind connectivity and fugacity values only increase when y = 0.015 molar fraction and therefore, the decreasing values for the two parameters can be associated with the increase in the amount of BOs and decrease in glass rigidity respectively. The increase in the number of NBOs and rigidity is predicted to the reason behind an increase in fugacity and the bond connectivity of the fabricated glasses respectively [42]. 8.

Conclusion

In conclusion, the zinc tellurite glass system with a composition of [{(TeO2)0.7 (ZnO) (Sm2O3)0.01]1-y (Ag2O)

y

0.3}0.99

where y =0.005, 0.01, 0.015, 0.02 and 0.025 molar fraction were

synthesized using melt quenching techniques. The fabricated glass samples are amorphous because of the absence of sharp absorption peaks in the XRD. FTIR analysis revealed the presence of TeO4 structural units. Molar volume and density obey the theoretical relationship of opposite behavior with molar volume decreasing and density increases with an increase in dopant concentration. Lower molecular weight replacement of TeO2 by the higher molecular weight of Ag2O in the glass system has contributed to the increasing values of density. The packing density of oxygen, ionic 36

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concentration, oxygen molar volume, and ionic distance were calculated for structural analysis of the glass system. The amorphous nature of the fabricated glasses has also been confirmed by the absence of sharp peaks in the absorption spectra of the synthesized glasses. The indirect and direct energy band gap increases from 2.969 eV to 3.105 eV and 3.388 eV to 3.410 eV with an increase in dopant which can be related to the formation of BO in the glass matrix. Urbach energy, molar refraction, molar polarizability, refractive index and electronic polarizability decrease with an increase in the silver oxide. The Urbach energy decreases from 0.260 eV to 0.209 eV while the index of refraction decreases from 2.405 to 2.369 respectively. The decreasing Urbach energy reflects the decrease in defects concentration in the glass network while the decrease in refractive index and polarizability can be ascribed to the formation of NBO due to the introduction of the modifier oxide in the glass samples. The pulse-echo overlap method was used to obtain the glass elastic properties at 5MHz. The longitudinal and shear velocity were examined and their results signify an unstable trend as previously anticipated. The generation of BO in the glass system produces glasses with strong connectivity. The data of the related parameters such as the ultrasonic velocities, Poisson's ratio Debye temperature, softening temperature, fractal bond connectivity, fugacity hardness, and elastic moduli increase with an increase in dopant content respectively. Where the elastic properties decrease can be attributed to the transformation of BO to NBO which are regarded to be the reason behind the distraction in the fabricated samples network and hence reduces the glass connectivity and rigidity as well. Structural changes always affect elastic properties of glass materials which have corresponded to the deviation of the molar fraction of the glass system. In the present study, based on the obtained result of the elastic moduli of the glass system, the connectivity and rigidity of the fabricated for the studied glass system proved to be good when compared to other studies. This can be justified by the increase in the values of

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ultrasonic velocity as well as the decrease in fractal bond connectivity of the synthesized glasses. Although we initially expected increase in refractive index, polarizability and some other parameter as well as decrease in value in elastic moduli micro-hardness and some others with increase in Ag+ composition, the results obtained showed a non-uniform pattern of increase and decrease in values, suggesting that at some points more bonds are form and broken at some other points. Acknowledgment The research was reinforced by the Ministry of Higher Education Malaysia and Universiti Putra Malaysia (UPM), Malaysia using Geran Putra Berimpak (vot no. 9597200). References [1]

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Declaration of interests β˜’ The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper. ☐The authors declare the following financial interests/personal relationships which may be considered as potential competing interests:

Journal Pre-proof Highlight ο‚·

Zinc tellurite glass system was synthesized via melt quenching method

ο‚·

The indirect and direct band gap is found to be increased with silver content

ο‚·

Elastic moduli is found to be increased and this show that the rigidity of the glass system is increased also

ο‚·

Debye and softening temperature exhibit similar trend with increase in dopant as the glass system become more rigid