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Journal of Taibah University for Science 10 (2016) 329–339

Available online at www.sciencedirect.com

ScienceDirect

FT-IR and Raman spectroscopic studies of ZnF2–ZnO–As2O3–TeO2

glasses

Shaik Kareem Ahmmad a,b,∗, M.A. Samee a, S.M. Taqiullah a,c, Syed Rahman a

a Department of Physics, Osmania University, Hyderabad, Telangana State, Indiab Department of Physics, Muffakahm Jah College of Engineering and Technology, Hyderabad, Telangana State, India

c Department of Physics, Jazan University, Kingdom of Saudi Arabia

Available online 28 January 2015

bstract

The effect of fluorine substitution on the spectral properties of the xZnF2–(20-x)ZnO–40As2O3–40TeO2 (x = 0, 4, 8, 12, 16 and0 mol%) glass system was investigated by FTIR and Raman spectroscopies. The results demonstrate that TeO4 and TeO3 weremong the primary structural units in the investigated glasses in addition to As2O3 pyramids and ZnO4 structural units. The additionf fluorine results in the reduction of Te O Te linkage due to a gradual transformation of trigonal bipyramidal TeO4 through TeO3+1

o trigonal pyramidal TeO , which decreases the connectivity of the tellurite glass former network. The theoretical optical basicity

3

f the studied glasses decreases with increasing ZnF2 content. 2015 The Authors. Production and hosting by Elsevier B.V. on behalf of Taibah University. This is an open access article under

he CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).

eywords: Glasses; EDAX; FTIR; Raman

. Introduction

Tellurium oxide-based glasses have been the subjectf current research due to their interesting electrical,ptical and magnetic properties [1,2]. In addition to hav-ng a unique structure [3,4], telluride glasses also haveood mechanical strength and chemical durability [5–8],

low melting temperature [9], large linear and non-linear

∗ Corresponding author at: Department of Physics, Muffakahm Jahollege of Engineering and Technology, Hyderabad, Telangana State,

ndia. Tel.: +91 9703507860.E-mail address: kareem.physics@gmail.com (S.K. Ahmmad).

eer review under responsibility of Taibah University.

ttp://dx.doi.org/10.1016/j.jtusci.2014.12.008658-3655 © 2015 The Authors. Production and hosting by Elsevier B.V. on

C BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).

refractive indices [10,11] and good optical transmis-sion at infrared [12,13] and visible wavelengths [14–17].These properties make tellurite glasses good candidatesfor the development of optical devices [18]. Furthermore,tellurium oxide-based glasses exhibit higher dielectricconstants and electrical conductivity [19,20].

The basic structural unit of tellurium oxide in binarytellurite glass is the trigonal bipyramid (tbp) with alone pair of electrons, and it forms a Te O Te bondduring glass formation. The physical and structural prop-erties of binary tellurite glasses such as V2O5–TeO2,TeO2–Nb2O5 and TeO2–B2O3 have been investigatedwith ESR spectra [21], X-ray absorption spectroscopy[22] and extended X-ray absorption fine structure [23]

behalf of Taibah University. This is an open access article under the

studies. The change in the coordination of Te from theTeO4 triogonal bipyramid to the TeO3 trigonal pyra-mid (tp) group through the formation of an intermediatepolyhedron TeO3+1 and then to the TeO3 units [24] has

h Univ

330 S.K. Ahmmad et al. / Journal of Taiba

been studied in TeO2 glasses with increasing content ofnetwork modifiers such as alkali and alkaline oxides.Rajendran et al. [4,25] methods the structural and elasticproperties of vanadate bismuth tellurite and TeO2–BaF2glasses employing ultrasonic studies.

Tellurium oxide under normal conditions does nothave the ability to form a glass without a modifiersuch as alkali, alkaline earth oxide and/or other typesof glass formers [7,26,27]. The addition of arsenicoxide (As2O3) to tellurium oxide glasses improves theglass forming ability and the optical transparency inthe blue region. As2O3, a strong glass network former,was being used as a fining agent to remove air bub-bles in glasses. Few studies on As2O3 glasses mixedwith alkali halides, rare earth oxides and some heavymetal oxides were reported [28–30] as having a nar-row glass-forming region. In zinc arsenate glasses,the presence of ZnO improves the mechanical proper-ties as well as the chemical and thermal resistivitiesand reduces the sublimation characteristics of arsenate[31,32]. Recently, Bala Murali Krishna et al. [33–35]studied the optical, structural and dielectric spectro-scopic properties of ZnO–As2O3-based glasses dopedwith chromium and molybdenum ions. In the presentstudy, a strong glass network former, As2O3, has beenchosen for incorporation into the TeO2 glass system.In general, As2O3-mixed glasses possess exception-ally high Raman scattering coefficients and are suitablefor active fibre Raman amplification [36]. Furthermore,the addition of As2O3 into the TeO2 glass system isexpected to affect the far-infrared transmission to a lesserextent than other compounds because the fundamentalmodes of vibration of the As2O3 structural groups liein the region of vibration of the TeO2 structural groups[36].

Binary zinc tellurite glasses have been extensivelystudied [37–41]. Zinc atoms are suggested to play animportant role in forming a glass network and the frac-tion of ZnO in binary zinc tellurite glasses can strengthenthe whole network structure due to its bridging oxygenion. Several studies of infrared and optical absorptionwere published for zinc tellurite glasses [42–45]. It hasbeen reported that absorption properties in TeO2–ZnOglasses exhibited a strong dependence on the ZnO con-tent. A ZnO–TeO2 glass was used as the basis for amulti-component optical system. The addition of modi-fiers such as ZnF2 to the ZnO–TeO2 glass matrix or thesubstitution of fluorine ions for oxide ions is expected

to increase the glass forming range and glass stability,lower the viscosity and improve the transparency sub-stantially in addition to making the glass more moistureresistant [46,47].

ersity for Science 10 (2016) 329–339

Several studies on the introduction of fluorine ionsinto oxide ions were reported for zinc tellurite glasses[48,49]. Because a fluorine ion has nearly the same radiusas an oxygen ion, the probability of substitution of theoxygen ions with fluorine ions is high, but the fluorineions could also occupy interstitial positions. Addition-ally, fluorine has a higher electronegativity than oxygen,and because two fluoride ions would take the place ofone oxide ion, which would cause the breakdown of theglass network structure, the glass transition and deforma-tion temperatures would be expected to decrease with thesubstitution of fluoride ions in place of oxide ions.

To the best of our knowledge, fluorine substitutedzinc arsenic tellurite glasses have not previously beenreported. We recently reported [50] the physical and opti-cal properties of zinc arsenic tellurite glasses based onthe ZnF2–ZnO–As2O3–TeO2 composition. Apart fromthese reported properties, there is a lack of data in the lit-erature on the structural characteristics of these glasses.Therefore, the objective of this research is to characterizethe ZnF2–ZnO–As2O3–TeO2 glass system using FTIRand Raman spectroscopies.

2. Experimental study

In the present study, zinc tellurite glasses of the systemxZnF2–(20-x)ZnO–40As2O3–40TeO2 (x = 0, 4, 8, 12, 16and 20 mol%) were prepared by a melt quench technique.High purity (99.99%) zinc fluoride (ZnF2), zinc oxide(ZnO), tellurium oxide (TeO2) (all Sigma Aldrich) andarsenic oxide (As2O3) (May and Baker) were used asthe starting materials. The detailed experimental pro-cedure for the preparation of the glass samples wasdescribed in our previous paper [50]. The energy disper-sive spectroscopy (EDS) measurements were conductedusing a Thermo instruments model FEI XL30 ESEMattached to a scanning electron microscope (SEM). Thestructure of the glass samples was studied using FTIRand Raman spectroscopies. The FTIR absorption spec-tra were recorded with a Bruker Optics spectrometer(Tensor 27, Germany) using the KBr Pellete technique.Room temperature Micro Raman spectra were recordedusing a Renishaw (UK) spectrometer with a 50 mW inter-nal Argon laser source at an excitation wavelength of514 nm. The spectral resolution was 1 cm−1.

3. Results

3.1. EDS

Energy dispersive X-ray analysis (EDS) is com-monly used to determine the chemical composition of

S.K. Ahmmad et al. / Journal of Taibah University for Science 10 (2016) 329–339 331

Fig. 1. Energy dispersive spectra of the xZnF2–(20-x)ZnO–40As2O3–40TeO2 glasses.

332 S.K. Ahmmad et al. / Journal of Taibah University for Science 10 (2016) 329–339

Table 1EDAX analysis of xZnF2–(20-x) ZnO–40As2O3–40TeO2 glasses.

Basic ingredient taken (wt%) EDAX composition (wt%)

X (mol%) F O Zn As Te F O Zn As Te

0 – 22.10 8.21 37.63 32.06 – 22.41 8.41 37.60 31.584 0.95 21.58 8.16 37.43 31.88 0.72 22.01 8.39 37.35 31.538 1.89 21.01 8.12 37.23 31.69 1.61 21.66 8.45 37.18 31.12

12 2.82 20.56 8.08 37.01 31.53 2.51 20.94 8.44 36.92 31.1931.3631.18

16 3.73 20.05 8.03 36.82

20 4.64 19.57 7.99 36.63

compounds. Fig. 1 presents the EDS pictures of some ofthe studied glass samples. The EDS analysis indicatesthe presence of Te, Zn, O, F and As in the glass samples.Table 1 gives the experimentally and theoretically cal-culated weight per cent (wt%) of the elements present inthe glass samples.

3.2. IR spectra

The IR absorption spectra of the glass sampleswere recorded in the range of 200–2000 cm−1. Fig. 2shows the normalized FTIR absorption spectra of thexZnF2–(20-x)ZnO–40As2O3–40TeO2 glasses. For bet-ter clarity, the spectra are shown in the 400–1000 cm−1

range. Each spectrum was de-convoluted using fiveGaussian functions considering the previously reported

peak assignments [34,51]. An example of the fittingfor 16ZnF2–4ZnO–40As2O3–40TeO2 glass composi-tion is shown in Fig. 3. The de-convolution parametersof the IR bands for the investigated glasses are given in

Fig. 2. FTIR spectra of the xZnF2–(20-x)

3.11 20.44 8.52 36.53 31.40 3.98 19.80 8.30 36.82 31.10

Table 2. The infrared spectra of present glasses show fiveabsorption peaks. The glasses at all compositions presentabsorption peaks at approximately 457, 595, 661, 778and 883 cm−1.

3.3. Raman spectra

To further understand the changes in the glass proper-ties with the addition of ZnF2, Raman spectra of all theglass samples were measured, and the results are shownin Fig. 4. Each spectrum was de-convoluted using threeGaussian functions. The Gaussian de-convolution of theRaman spectra of the 16ZnF2–4ZnO–40As2O3–40TeO2glass is illustrated in Fig. 5. One can see that thereare three Raman bands peaking at approximately 437,645 and 748 cm−1. The de-convolution parameters such

as the band centre and the relative area of the Ramanbands are given in Table 2. The Raman spectra ofthe glass samples are similar to the Raman spectra ofTeO2–ZnO–ZnF2 glasses [46,52].

ZnO–40As2O3–40TeO2 glasses.

S.K. Ahmmad et al. / Journal of Taibah University for Science 10 (2016) 329–339 333

300 450 600 750 900 1050

883

778

661

597

457

Abso

rban

ce (

a.u)

nu mbe-1

ra of 16

4

mwpcarfutatw

TD

X

C

I4567

R8467

C

Wave

Fig. 3. De-convoluted FTIR spect

. Discussion

The FTIR results have been discussed based on theethods provided by Tarte [53] and Condrate [54],hich compare the experimental data of the glass sam-les with data from related crystalline compounds. Theharacteristic absorption bands for the vitreous TeO2nd As2O3 [51] were used as reference points in theesults discussion. The present IR spectra exhibited dif-erent absorption bands due to the various structuralnits of TeO2 and As2O3. The IR spectrum of crys-alline TeO2 is expected to exhibit two absorption bands

t 650 cm−1 and 772 cm−1 due to the symmetrical vibra-ions of the Te Oax and Te Oeq bonds of the TeO4 units,hich are attributed to the TeO4 tetragonal pyramidal

able 2econvoluted parameters of FT-IR and Raman spectra of xZnF2–(20-x)ZnO–

= 0 X = 4 X = 8 X

A C A C A C

R parameters65 0.26 451 0.6 467 1.58 492 1.75 588 0.83 592 7.20 563 6.53 652 17.84 656 25.70 689 9.24 782 25.25 770 36.55 7

aman parameters89 2.58 895 7.33 877 8.58 845 2.63 437 6.64 435 7.98 447 1.17 645 3.01 645 2.97 648 7.74 749 22.04 748 24.78 7

is component band centre (cm−1) and A is relative area (%) of the compone

r (cm )

ZnF2–4ZnO–40As2O3–40TeO2.

structure [55,56]. The introduction of modifier ions suchas Zn2+ destroys the three dimensional network, creatingnon-bridging oxygen (NBO) species and gradually trans-forming the TeO4 units into TeO3+1 and TeO3 [35,57].

Sidek et al. [58] reported a strong IR band located at626 cm−1 and a weak band at 760 cm−1 in a ZnO–TeO2glass system; these are the characteristic of tellurite glassand are attributed to vibrations in the TeO4 tetrago-nal pyramids. In ZnF2–As2O3–TeO2–V2O5 glasses,Gandhi et al. [51] observed a vibrational frequency ofTeO2ax (axial band) located at approximately 643 cm−1,whereas the TeO2eq vibration characteristic (equatorial

band) was missing. In the present IR spectra, the twomajor bands of TeO2 centred at 663 cm−1 and 789 cm−1

are assigned to the symmetrical vibrations of Te Oax

40As2O3–40TeO2 glasses.

= 12 X = 16 X = 20

A C A C A

55 0.68 457 0.919 465 0.2295 3.60 597 5.04 601 3.159 12.13 661 14.75 684 7.276 19.22 778 23.88 808 9.05

83 4.46 883 5.61 897 2.0337 7.75 430 7.41 441 1045 2.74 645 2.15 641 3.1948 25.7 750 21.48 746 35.1

nt band.

334 S.K. Ahmmad et al. / Journal of Taibah University for Science 10 (2016) 329–339

200 300 400 500 600 700 800 900 1000

X=12

X=4

X=16

X=20

X=8X=0

Inte

nsi

ty (

a.u)

enumb-1

2–(20-x

Wav

Fig. 4. Raman spectra of the xZnF

bonds and the symmetric vibrations of Te Oeq bonds inthe TeO4 units, respectively, and are attributed to theTeO4 tetragonal pyramidal structure. It is clear fromFig. 2 that the 663 cm−1 band, which is characteristicof TeO2, shifts to 684 cm−1 with the addition of ZnF2.This may be related to the appearance of TeO3 units, con-comitant with a reduction in the number of TeO4 units[59,60]. The addition of fluorine results in a reduction

of Te O Te linkage due to a gradual transformation oftrigonal bipyramidal TeO4 through TeO3+1 to trigonalpyramidal TeO3, decreasing the connectivity of the tel-lurite glass former network. By increasing the fluorine

200 30 0 40 0 50 0 60 0

430

Inte

nsi

ty (

a.u)

Wavenumb

Fig. 5. De-convoluted Raman spectra of 1

er (cm )

)ZnO–40As2O3–40TeO2 glasses.

ions, three different types of structural units (TeO4,TeO3+1 and TeO3) are presented in the glass structure.

In the present study, the observed IR band at approx-imately 465 cm−1 is attributed to the bending vibrationof the Te O Te or O Te O linkages [61–63], indicat-ing that the vibrations of the Te O Te linkage in thesesamples are due to the transformation of TeO4 groupsinto TeO3 groups.

−1

Mansour [64] reported an IR band at 463 cm inTeO2–Na2O–B2O3 glass and assigned it to the bend-ing vibration of Te O Te linkages. In Nd2O3-dopedTeO2–ZnO–Na2O–Li2O–Nb2O5 glasses, the Te O Te

70 0 80 0 90 0 100 0

750

645

er (cm-1)

6ZnF2–4ZnO–40As2O3–40TeO2.

S.K. Ahmmad et al. / Journal of Taibah University for Science 10 (2016) 329–339 335

Table 3Wavenumbers and band assignments of xZnF2–(20-x)ZnO–40As2O3–40TeO2 glasses.

Wavenumber (cm-1) FI-IR assignments Raman assignments

FT-IR RAMAN

437 Symmetric stretching vibrations of As2O3 pyramidsand ZnO4 units.

465 645 Bending vibrations of Te O Te linkages (or)O Te O linkages

Symmetric stretch of Te O bonds in TeO4 units

592 Symmetric bending vibrations of As O bonds ofAs2O3 groups

663 Symmetrical vibration of TeOax bonds of TeO4 units750 Symmetric stretching vibrations of TeO 3+1 and

TeO3 units789 Symmetrical vibration of TeOeq bonds of TeO4 units889 TeO3 trigonal pyramids

sr

bbpitqZairuTn

AAa1etbsesbtib[fa

ymmetric stretching vibrations were observed in theange of 425–462 cm−1 [40].

Mohamed et al. [44] observed a high-frequency IRand at 893 cm−1 in TeO2–Nb2O5–ZnO glasses. This IRand was assigned to TeO3 trigonal pyramids [9]. In theresent IR spectra, a weak IR band is observed at approx-mately 889 cm−1, which was assigned to the TeO3rigonal pyramidal structure. A shift towards higher fre-uencies was observed for this band position when thenF2 content was increased. This may be related to theppearance of TeO3 units concomitant with a reductionn the number of TeO4 units. The addition of fluorineesults in a reduction of Te O Te linkages due to a grad-al transformation of trigonal bipyramidal TeO4 througheO3+1 to trigonal pyramidal TeO3, decreasing the con-ectivity of the tellurite former network.

As2O3 is a strong network former with corner-sharingsO3 pyramidal units; the normal bond lengths ofs O lie between 1.72 and 1.81 A, and the O As O

nd As O As bond angles range from 90–103◦ and23–135◦, respectively. Four prominent bands arexpected in the IR spectrum of crystalline As2O3 dueo the stretching vibrations υ1 (1050 cm−1), symmetricending vibrations υ 2 (625 cm−1), doubly degeneratedtretching vibrations υ3 (812 cm−1) and doubly degen-rated bending vibrations υ4 (495 cm−1) of the As2O3tructural units [51]. In the present IR spectra, the IRand centred at approximately 592 cm−1 is attributedo the symmetric bending vibrations of As O bondsn the As2O3 groups. When ZnF2 is increased, thisand position shifts to 601 cm−1. Baidoc and Ardelean

65] observed a symmetrical bending vibration IR bandor the As O bonds in ternary boroarsenate glasses atpproximately 606 cm−1.

When As2O3 is present in the TeO2 glass network,cross-linking is likely to occur between some of theTeO4 units and AsO3 units, resulting in the formationof As O Te bonds in the glass network. This is a rea-sonable assumption because the ionic radii of the Te4+

ions and As3+ ions are similar. Additionally, the nearlyequal values of the υs

TeO2ax band and the symmetricalbending vibration (υ2) band of the AsO3 structural unitsalso support this possibility [66]. The assignments ofthe absorption bands as detected in the IR spectra aresummarized in Table 3.

Sidebottom et al. [67] observed two Ramanbands at approximately 740 cm−1 and 670 cm−1 inZnO–ZnF2–TeO2 glasses. The 740 cm−1 Raman bandwas attributed to symmetric stretching of Te O in theTeO3+1 unit, which resembles the TeO4 unit exceptthat one axial Te O bond longer, and 670 cm−1 isassigned to the symmetric stretching of Te O bondsin the TeO4 units. In TeO2–ZnF2–ZnO–Er2O3 glasses,Chillcce et al. [68] observed two Raman bands peak-ing at approximately 670 cm−1 and 744 cm−1, indicatingthe presence of TeO4 units and TeO3+1 and/or TeO3structural units. The proportion of TeO3 and TeO3+1entities within the former network depends on thechemical nature and the concentration of the modifier[69,70].

In the present study, the strong Raman band at approx-imately 750 cm−1 is assigned mainly to the stretchingvibration modes of the TeO3+1 and TeO3 units involvingnon-bridging oxygen (NBO). A shoulder at approxi-mately 645 cm−1 is assigned to asymmetric vibrations of

the Te O Te linkages in TeO4. Fig. 6 shows a normal-ized variation of the intensity ratio, denoted as I746/I641,between the Raman bands located at 746 and 641 cm−1.

336 S.K. Ahmmad et al. / Journal of Taibah University for Science 10 (2016) 329–339

0 4 8 12 16 20

6

7

8

9

10

11

I 746 /

I641

F2 conte

tred at

Zn

Fig. 6. Variation of the intensity ratio between Raman bands cen

As observed, the intensity ratio (I746/I641) increased withincreasing ZnF2 concentration in the glass samples inthis study. This observation mainly indicates the for-mation of more TeO3+1 and/or TeO3 groups causing adecrease in the number of TeO4 units, which means thatstructural changes occurred in the glass. The obviousintensity increase of the Raman band at approximately750 cm−1 confirms the formation of TeO3+1 and TeO3

with non-bridging oxygen. Because the Raman vibra-tions are mainly sensitive to the polarisability of thetellurium entities, the possible formation of oxy-fluoridetellurium entities should cause changes in the Raman

0 4 8

0.7 6

0.7 8

0.8 0

0.8 2

0.8 4

0.8 6

0.8

0.8 27

0.845

Theo

reti

cal

opti

cal

bas

icit

y

ZnF2 conte

Fig. 7. Theoretical optical basicity of the gl

nt (mol%)

approximately 746 and 641 cm−1 as a function of ZnF2 content.

spectrum features. Some O2− atoms might be effectivelyreplaced by F¯ because their ionic radii are the same.Additionally, one oxygen may be replaced by two fluo-rine ions, which would break the Te O Te linkages inthe glass structure and depolymerise the structure net-work accompanied by the formation of more TeO3+1,TeO3 and/or Te(O,F)3+1, Te(O,F)3 groups; their Ramansignatures could be hidden within the broad spectral

−1

bands observed in the wavenumber range from 600 cmto 800 cm−1 [71,72].

In the present spectra, the Raman band at approxi-mately 437 cm−1 is assigned to the symmetric stretching

12 16 20

0.7 63

0.77 8

0.7 94

11

nt ( mol%)

asses as a function of ZnF2 content.

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S.K. Ahmmad et al. / Journal of Taiba

ibrations of As2O3 pyramids and ZnO4 structural units73,74]. Baidoc and Ardelean [65] observed a Ramanand at approximately 490 cm−1 in boroarsenate glasses,hich was assigned to the vibrations of As O bonds.

n ZnO–As2O3–Sb2O3–MoO3 glasses, Bala Muralirishna et al. [34] observed a broad dominant Ramanand at approximately 440 cm−1 and assigned it to theymmetric stretching vibrations of As2O3 pyramids andnO4 structural units. In general, ZnO/ZnF2 is a glassodifier that enters the glass network by breaking up thes O As bonds, and it introduces coordinate defectsnown as dangling bonds in addition to non-bridgingxygen ions. However, ZnO also participates in the glassetwork forming ZnO4 structural units when the zinc ions linked to four oxygens in a covalent bond configuration34].

The theoretical optical basicity (Λth) for the presentlasses has been calculated [75] using the relations inqs. (1) and (2).

For individual oxides such as AOa/2, BOb/2, etc.:

th = Xa/2Λ(AOa/2) + Xb/2Λ(BOb/2)+ (1)

here Λ(AOa/2) and Λ(BOb/2) are optical basicity valuesssigned to the constituent oxides and Xa/2, Xb/2 are thequivalent fractions of the different oxides. Similarly,he optical basicity for the fluoride system composed ofFc, DFd is:

th = XcΛ(CFc) + XdΛ(DFd) + . (2)

For a system composed of oxides AOa/2, BOb/2, etc.nd fluorides CFc, DFd, etc. in the mole ratios NA:NB. . .

r NC:ND. . . the optical basicity is given as the following:

th =[(aNAΛ(AOa/2)/2 + (bNBΛ(BOb/2)/2 + · · ·)+

cNCΛ(CFc) + dNDΛ(DFd) + · · ·)][(aNA/2 + bNB/2 + · · ·) + (cNC + dND + · · ·)]

(3)

The theoretical optical basicity valuesΛ(ZnF2) = 0.46, Λ(ZnO) = 1.08, Λ(TeO2) = 0.97nd Λ(As2O3) = 0.72) are used in this study [76].

Fig. 7 plots the variation of optical basicity as a func-ion of ZnF2. From this plot, it is clear that the opticalasicity decreases with increasing ZnF2 content. The val-es of Λth for the xZnF2–(20-x)ZnO–40As2O3–40TeO2

lass system lie between 0.892 and 0.777. Many physicalnd chemical properties of oxidic media in the vitre-us or molten state have been related to basicity. Theeplacement of ZnF2 has a low polarisability compared

rsity for Science 10 (2016) 329–339 337

with ZnO (high polarisability), which may lead to adecrease in optical basicity with increasing ZnF2 con-tent. Yousef [77] reported a decrease in optical basicitywith the increase of ZnF2 content in TeO2–WO3–ZnF2glasses.

5. Conclusions

From the above results and discussion, the followingconclusions were drawn:

1. Homogeneous glass systems of xZnF2–(20-x)ZnO–40As2O3–40TeO2 (x = 0, 4, 8, 12, 16 and20 mol%) were prepared. The FTIR and Ramanspectra of these glasses were analysed to identifylocal structural variations.

2. De-convoluted IR and Raman spectra of the studiedglasses reveal the presence of five IR bands and threeRaman bands, respectively.

3. The observed IR band at approximately 465 cm−1

was attributed to the bending vibrations of Te O Telinkages.

4. Raman spectral observations indicate the formationof more TeO3+1 and/or TeO3 groups, causing adecrease in TeO4 groups.

5. The IR and Raman spectra reveal the presence of thesymmetric stretching vibration of As2O3 pyramidsand ZnO4 structural units.

6. The theoretical optical basicity of the present glasssystem composed of oxides and fluorides decreaseswith increasing ZnF2 content.

Acknowledgments

One of the authors, Shaik Kareem Ahmmad, wishes tothank Dr. T. R. Ravindran of the Material Science group,IGCAR, Kalpakkam, India for providing the Ramanfacility and Dr. Basheer Ahmed, the Advisor-cum-Director, MJCET, SUES Hyderabad for his financialsupport.

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