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Materials Chemistry and Physics 143 (2014) 779e787

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Materials Chemistry and Physics

journal homepage: www.elsevier .com/locate/matchemphys

X-ray photoelectron spectroscopy (XPS) and FTIR studies of vanadiumbarium phosphate glasses

Abdelilah Majjane a, Abdelkrim Chahine a,*, Mohamed Et-tabirou a,Bousselham Echchahed b, Trong-On Do c, Peter Mc Breen d

a Laboratoire de Physico-Chimie des Matériaux Vitreux et Cristallisés, Université Ibn Tofail, Faculté des Sciences, Kénitra 14090, Moroccob Laboratoire d’Electrochimie, Corrosion et Environnement, Université Ibn Tofail, Faculté des Sciences, Kénitra, MoroccocDépartement de génie chimique, Université Laval, G1K 7P4, CanadadDépartement de chimie, Université Laval, G1K 7P4, Canada

h i g h l i g h t s

* Corresponding author. Tel.: þ212 537329400; faxE-mail address: abdelkrimchahine@gmail.com (A.

0254-0584/$ e see front matter � 2013 Elsevier B.V.http://dx.doi.org/10.1016/j.matchemphys.2013.10.013

g r a p h i c a l a b s t r a c t

� Bariumevanadiumephosphateglasses.

� Structure has been investigated byXPS and IR spectra.

� Variation in structure and propertieswith substitution of V2O5 for P2O5.

� Conversion of metaphosphate to py-rophosphate and finally toorthophosphate.

� Substitution of PeOeP linkages by PeOeV, PeOeBa and VeOeVlinkages.

a r t i c l e i n f o

Article history:Received 17 April 2013Received in revised form12 September 2013Accepted 5 October 2013

Keywords:GlassesDifferential scanning calorimetry (DSC)Fourier transform infrared spectroscopy(FTIR)X-ray photo-emission spectroscopy (XPS)

a b s t r a c t

Barium vanadophosphate glasses, having composition 50BaOexV2O5e(50 � x)P2O5, (x ¼ 0e50 mol%),were prepared by conventional melt quench method. Density, molar volume and glass transition tem-perature (Tg) were measured as a function of V2O5 content. Structural investigation was done using XPSand FTIR spectroscopy. First, substitution of the P2O5 by the V2O5 in the metaphosphate 50BaOe50P2O5

glass increases the density and Tg and decreases the molar volume. When the amount of V2O5 increases,all these properties show a reverse trend. XPS measurement found in the O1s, P2p, and V2p core levelspectra indicate the presence of primarily PeOeP, PeOeV and VeOeV structural bonds, the asymmetryin the P 2p spectra indeed arises from the spin-orbit splitting of P 2p core level, and more than onevalence state of V ions being present. IR spectroscopy reveals the depolymerization of the phosphateglass network by systematic conversion of metaphosphate chains into pyrophosphate groups and thenorthophosphate groups. Even though metaphosphate to pyrophosphate conversion is taking place due tobreaking of PeOeP linkages, formation of PeOeV and PeOeBa linkages provide cross linking betweenshort P-structural units, which make the glass network more rigid. Above 10e20 mol% V2O5 content,network is highly depolymerized due to the formation of orthophosphate units and VeOeV bridgebonds, resulting in poor cross-linking, making the glass network less rigid.

� 2013 Elsevier B.V. All rights reserved.

: þ212 537329433.Chahine).

All rights reserved.

1. Introduction

Phosphate glasses have been of large interest for a variety oftechnological applications due to several unique properties such ashigh thermal expansion coefficient, low viscosity, UV transmission

A. Majjane et al. / Materials Chemistry and Physics 143 (2014) 779e787780

or electrical conduction [1]. Important biological applications forcalcium phosphate glasses exist, also, as it was demonstrated thatthey are biocompatible as bones and dental implants [2,3].Thestructure of oxide glasses can be expressed by the kind and type ofoxygen coordination polyhedral in the structure and the way theyare interconnected to each other to form the glass network. Glassescontaining transitionmetal (TM) have been studiedmainly becauseof their interested optical, thermal and magnetic properties andpotentials applications [4e6]. The technological importance ofthese glasses requires a detailed understanding of the molecularand structural chemistry in order to determine the relationshipsbetween physical properties and their structural units.

Among transition metal oxides, vanadium pentoxide is one ofthe most studied because it is a network glass modifier and former[7] and its presence in other vitreous matrix determines a networkmodification due to the presence of V4þ ions. Phosphate glassescontaining vanadium pentoxide have also received much attentiondue to the existence of vanadium ions in several oxidation states inthe glass matrix [8]. Some vanadate glasses show a high electroniccondition based on electron-hopping between V4þ and V5þ ions.BaOeP2O5 glasses with high BaO concentration (�50 mol%) havecharacteristics of low photoelastic constant [9], high solubility ofactive ions [10] and good water durability among phosphateglasses. Thermal stability of these glasses is poor due to surfacecrystallization [11], and addition of B2O3 improves significantly itsthermal stability for bulk samples (B2O3 � 3 mol%) [11], andpowdered forms (B2O3 � 7 mol%) [12].

The characterization and understanding of the glasses structureondifferent lengthscales remainsexperimentally difficultmainlydueto the lack of periodicity inherent to glasses. Only the suitable cor-relation of data obtained from several investigations methods allowsthe finding of helpful structural information. Therefore, our interestwas to obtain by means of infrared and X-ray photoelectron spec-troscopy valuable information concerning the structure of the glasseswith thegeneral composition50BaOexV2O5e(50� x)P2O5withx¼0,10, 20, 30, 40 and 50 mol%, and to determine the structural changesthat occur with the substitution of P2O5 with V2O5. Furthermore, theinfluence of this substitution to the evolution of glass transitiontemperature, density and molar volume is also discussed.

2. Experimental details

2.1. Glass preparation

The glass samples were prepared by the melt-quenching tech-nique using analytical grade V2O5, (NH4)2HPO4 and BaCO3. Thefinely mixed powdered materials were preheated in a mufflefurnace at 500 �C for 1 h to evaporate ammonia and water in thebatch. The batches were then melted in air at a constant temper-ature 1000 �C for 30 min. The melt was then quickly quenched andrandom pieces of samples were collected and stored in a desiccatorto prevent from attack by moisture. The glass free vanadium ob-tained is transparent and colorless, and the others become fromlight brown to black with increasing V2O5. The glassy nature of thesamples was confirmed by X-ray diffraction studies.

2.2. Property measurements

Density was measured using the Archimedes method withdiethylorthophtalate as the immersion fluid. The error of the den-sity measurements was not more than �0.03 g cm�3. The molarvolume (Vm) was calculated from the formula:

Vm ¼X

ðniMiÞ=r

Where Mi is the molecular weight for component i, ni the molarfraction of i component, and r the glass density.

The glass transition temperature Tg was measured by a differ-ential scanning calorimeter SETARAM Labsys DSC/ATD/TG at aheating rate of 10 �C min�1 in the range 25e600 �C undercontrolled atmosphere N2. The samples are introduced intoalumina crucibles and the results were corrected by using an emptycell to provide the baseline. The values of the temperatures aregiven with an estimated accuracy of about �5 �C.

2.3. Structure characterization

2.3.1. X-ray photoelectron spectroscopy (XPS) measurementsThe photoelectron spectra were collected on The AXIS-Ultra

from Kratos equipped with a spherical mirror and concentrichemispherical analyzers. All samples spectra were acquired atroom temperature using a monochromatic AlKa (1486 eV) X-rayradiation. The source, operated at 300 W, sensed an approximately5 mm diameter spot on the wafers. Kinetic energies of photoelec-trons were measured using a hemispherical electrostatic analyzerworking in the constant pass energy of 160 eV with a step of 1 eV.The detailed spectra were collected with 20 eV pass energy and aresolution of 0.05 eV. The pressure in the analyzing chamber waskept at 5 � 10�10 Torr. The kinetic energy were referenced todecamped sample of Au 4f7/2: 84.0 eV, Ag 3d5/2: 368.2 eV, Cu 2p3/2:932.6 eV. The C 1s line at 285 eV was used as a reference for allcharge shift corrections as this peak arises from hydrocarboncontamination and its binding energy is generally accepted asremaining constant. The spectra were analyzed and processed withthe use of Casa XPS 2.3.10 software [13]. The background wasapproximated by Shirley algorithm and the detailed spectra werefitted with a GausseLorentz function in Casa XPS software usingMarquard Algorithm. The P 2p curves were fitted taking into ac-count the spin-orbit splitting of 0.85 eV and ratio of 2p1/2:2p3/2components as 0.5.

2.3.2. FTIR spectroscopyThe glass samples were crushed to fine powder. A small amount

of the glass powder was mixed and ground with a relatively largequantity of KBr (3%) which is transparent to IR radiation. Discs formeasurement of IR absorption spectra were formed by pressing themixture at a pressure of 10�15 tons for few minutes. The infraredabsorption spectra of the samples were determined by usingBRUCKER Tensor 27 FTIR spectrometer with 4 cm�1 resolution inthe range of 400e4000 cm�1.

3. Results and discussion

3.1. Density and molar volume

Fig. 1 shows the variation of density and molar volume withrespect to composition. The density of these glasses first increasesand then decreases with the content of V2O5 while correspondingmolar volume first decreases and then increases. In general, thedensity of glass system is explained in terms of a competition be-tween the masses and sizes of the various structural units presentin glass. In other words, the density is related to how tightly theions and ionic groups are packed together in the structure. Thedensity of these glasses should increase continuously due toreplacement of low molecular weight P2O5 by high molecularweight V2O5. But it is found that the density of these glasses de-creases with addition of V2O5 and correspondingly molar volumeincreases, indicating that the vanadium polyhedra form some newinterconnections within the structural network and thus destabi-lize the glass structure. As we reported in the study by IR

Fig. 1. Composition dependence of density, d, and oxygen molar volume, Vm, for50BaOeV2O5e(50 � x)P2O5 glasses.

A. Majjane et al. / Materials Chemistry and Physics 143 (2014) 779e787 781

spectroscopy, for further addition of V2O5 above 10e20 mol%, py-rophosphate groups gets converted into orthophosphate groupsand glass network becomes highly depolymerized, therefore crosslinking is not sufficient to give strength to glass network. The for-mations of weak VeOeV linkages which substitute the PeOePones lead to a great decrease of the network connectivity [14].Furthermore, the incorporation of VO4 tetrahedra reduces theaverage content of bridging oxygen per network-forming poly-hedron and reduces the dimension and interconnection of thestructure units [15].

3.2. Glass transition temperature

Fig. 2 shows the variation of the glass transition temperaturewith V2O5 content in the 50BaOexV2O5e(50� x)P2O5 glass system.From the figure, one sees that the glass transition temperature isvery sensitive to the V2O5 concentrations. The substitution of P2O5by V2O5 from 0 to 10 mol% results in an increase of Tg from 460 to526 �C. Further increase of V2O5 concentration above 10 mol%

Fig. 2. Composition dependence of glass transition temperature Tg, for 50BaOexV2O5e

(50 � x)P2O5 glasses.

shows a decrease in the glass transition temperature. The change inTg indicates a change related to the manner in which V2O5 getsarranged in the glass. The decrease in the glass transition temper-ature implies a decrease in the rigidity of the network. The changesin the type and number of the phosphate and vanadate structuralunits are strongly reflected in XPS and IR spectra.

3.3. X-ray photoelectron spectroscopy

A broad signal for Al 2p was detected within the resolutionlimits in the XPS spectra for all samples. This signal is attributed toaluminum contamination from the crucible.

3.3.1. Barium spectraBa 3d5/2 and Ba 3d3/2 photoelectron peaks for all compositions,

Fig. 3, were recorded and compared to understand the chemicalmodification that occurred as a result of substitution of P2O5 byV2O5. The Ba 3d5/2 photoelectron main peak was observed at780.4 eV for all compositions (except for x¼ 0), whichmatches wellwith the literature value [16e18]. The Ba 3d5/2 peak resulting fromthe fit is shown in Fig. 4 for composition 30% V2O5. The corre-sponding peak positions and the peak width values of Ba 3d5/2 inthe various compositions are shown in Table 1. It was observed thatthe peak width values of Ba 3d5/2 varied from 1.6 to 1.7 eV. Theuncertainty in FWHM is �0.1 eV and the change observed ispractically the same. The Ba 3d5/2 photoelectron peak has threecomponents for all composition (from x¼ 0e50). The component at778.1e778.9 eV with a percentage of 2.7e3.5%, which remainsconstant from x ¼ 0 to x ¼ 50. The main component at 780.4e780.7 eVwhere represents more than 80% (decrease from 93 to 80%when x varies from 0 to 50) indicating a dependence with thecontent of V2O5. The third peak positioned at 781.7e782.4 eVwhere the percentage increase from 5 to 18% indicating a variationwith the V2O5 content. These three components indicate thatbarium is bonded to different units such as (P2O6

2�)N, P2O74�, PO4

3�

and, VO43�.

3.3.2. Phosphore spectraThe evolution of binding energy and relative intensity of P 2p

line components with V2O5 content are shown in Fig. 5. The maincharacteristic was the shift to the low binding energy after theaddition of the V2O5 and the shift is obviously more pronounced at

Fig. 3. Core level Ba 3d3/2 and Ba 3d5/2 for the 50BaOexV2O5e(50 � x)P2O5 glasses.

Fig. 4. High-resolution Ba 3d5/2 spectra for x ¼ 30% V2O5 phosphate glass sample withthe resulting peaks from the least-squares fitting routine. The smooth solid line infigure is the resultant sum of the peaks plus the background. Fig. 5. Core level P 2p for the 50BaOexV2O5e(50 � x)P2O5 glasses.

A. Majjane et al. / Materials Chemistry and Physics 143 (2014) 779e787782

20% V2O5. Simon et al. [19] report, for iron-sodium phosphate basedglasses, that this shift denotes the increase of the electronic statedensity around phosphorous atoms in the iron oxide containingsamples. As the charge distribution in the P]O bond of PO4tetrahedral is displaced towards the oxygen atom, there is a defi-ciency in electron density around the P atom, causing increase inbinding energy of P 2p core level electrons. This approach allowedthem to state that the lower binding energies recorded for ironcontaining glass, indicate a diminished number of P]O bonds andconcluded that the F2O3 addition determines the rupture of P]Olinkages and forms PeOeFe or FeeOeFe bonds. Similarly, weattribute the shift of P 2p photoelectron peaks to the low binding

Table 1Peak positions, FWHM, area and relative abundance from the curve fitting of Ba 3d5/2

core levels for 50BaOexV2O5e(50 � x)P2O5. The uncertainty in the peak positions is�0.1 eV, FWHM �0.1 eV.

CompositionsV2O5 (mol%)

Peak positions (eV) FWHM(eV)

Area % Area

Batch Analyzed Main peak Deconvolutedpeaks

0 0 780.7 782.44 1.60 2717.5 3.5780.73 1.60 73342.5 93.3778.80 1.60 2523.2 3.2

10 13 780.5 781.80 1.55 4023.8 5.5780.50 1.55 65536.5 90.3778.62 1.55 2529.7 3.2

20 19 780.5 781.74 1.70 6155.5 9.1780.45 1.70 58532.3 86.5778.23 1.70 2215.3 3.4

30 31 780.6 781.90 1.70 8143.2 13.2780.60 1.70 51700.5 83.7778.15 1.70 1956.4 3.1

40 39 780.5 781.90 1.70 9230.6 14.3780.50 1.70 53424.6 82.9778.15 1.70 1796.4 2.8

50 47 780.4 781.84 1.70 11066.1 17.6780.40 1.70 49830.3 79.7778.05 1.70 1672.2 2.7

energy to the increase of the electronic state density aroundphosphorus in the vanadium oxide containing samples and for-mation of PeOeV or VeOeV bonds via the rupture of P]Olinkages.

The P 2p3/2/P 2p1/2 doublet was fitted with an energy differenceof 0.9e1.0 eV and a ratio of 0.5. P 2p peaks were deconvoluted intofour components and is shown in Fig. 6 for composition x¼ 30. Thefour components are present in each composition from x¼ 10 to 40but not for x ¼ 0 where only two component are present indicatingthe presence only one type of phosphate group in the surfacebefore V2O5 were added (Table 2).

The main component constitutes 86e91% of total P 2p signal forall compositions. The main component with BE ¼ 133.4e133.7 eV

Fig. 6. High-resolution P 2p spectra for x ¼ 30% V2O5 phosphate glass sample with theresulting peaks from the least-squares fitting routine. The smooth solid line in figure isthe resultant sum of the peaks plus the background.

Table 2Peak positions, FWHM, area and relative abundance from the curve fitting of P 2pcore levels for 50BaOexV2O5e(50 � x)P2O5. The uncertainty in the peak positions is�0.1 eV, FWHM �0.1 eV.

CompositionsV2O5 (mol%)

Peak positions (eV) FWHM(eV)

Area % Area

Batch Analyzed Main peak Deconvolutedpeaks

0 0 134.36 135.14 1.53 2928.0 33.3134.21 1.43 5856.1 66.7

10 13 133.90 135.68 1.36 280.6 4.0134.78 1.36 561.2 8.0134.52 1.36 2040.9 29.4133.68 1.36 4081.8 58.6

20 19 133.58 135.86 1.49 140.3 3.1134.99 1.49 280.5 6.2134.23 1.49 1363.7 30.2133.37 1.49 2727.4 60.5

30 31 133.61 136.02 1.50 132.8 4.3135.12 1.50 265.5 8.5134.29 1.50 907.7 29.0133.39 1.50 1815.3 58.2

40 39 133.68 136.19 1.62 276.7 4.6135.29 1.62 553.4 9.2134.35 1.62 1721.5 28.7133.45 1.62 3442.9 57.5

Fig. 8. High-resolution O 1s spectra for x ¼ 30% V2O5 phosphate glass sample with theresulting peaks from the least-squares fitting routine. The smooth solid line in figure isthe resultant sum of the peaks plus the background.

A. Majjane et al. / Materials Chemistry and Physics 143 (2014) 779e787 783

(P 2p3/2) is attributed to pentavalent tetra coordinated phosphorus(pyrophosphate and orthophosphate) surrounded by differentchemical environment (phosphate-like structure) [20e24]. Thesecond contribution (about 6e9%) observed in P 2p spectrum(134.8e135.3 eV P 2p1/2) should be attributed to remaining meta-phosphate [19] after addition of V2O5. For x ¼ 0 the signal of P 2p(BE ¼ 134.2 eV) can be attributed to phosphate oxide P2O5, theseattribution match well with the literature [21].

3.3.3. Oxygen spectraHigh-resolution XPS spectra for the O1s core level of the studied

glasses are shown in Fig. 7 and an example for the fit is shown inFig. 8. The peaks from x ¼ 10 to 50 were deconvoluted in threecomponents each, while for x ¼ 0 the convolution was made withfour components. The data of the fit was summarized in Table 3.The O1s peak positions for all samples appear to be essentially the

Fig. 7. Core level O 1s and V 2p for the 50BaOexV2O5e(50 � x)P2O5 glasses.

same. While increasing V2O5 (x ¼ 0 to x ¼ 10) content, the peaks athigher energy disappeared, and from x ¼ 20 to x ¼ 50 the spectrashow an asymmetry on the higher binding energy. The appearanceof an asymmetry in the O1s spectra is not unexpected as it is well-known that the O1s peak in glasses can arise from different oxygenbinding sites. Typically a higher energy contribution arises from thepresence of bridging oxygen (BO) atoms and a second lower energypeak results from the non-bridging oxygen (NBO) atoms [25e30].The third peak at a binding energy intermediate to BO and NBOpeaks is owing to asymmetric bridging oxygen (ABO). Conse-quently, for our glasses, a three-peak fit was undertaken as shownin Fig. 8 must be satisfactory for composition from x¼ 10 to 50 witha FWHM varying from 1.4 to 1.6 eV. The resulting peak positions,FWHM, areas under the peaks, and relative abundance of thedifferent oxygen sites are displayed in Table 3. As seen in Table 3

Table 3Peak positions, FWHM, area and relative abundance from the curve fitting of O 1score levels for 50BaOexV2O5e(50 � x)P2O5 glasses. The uncertainty in the peakpositions is �0.1 eV, FWHM �0.1 eV.

CompositionsV2O5 (mol%)

Peak positions (eV) FWHM(eV)

Area % Area

Batch Analyzed Main peak Deconvolutedpeaks

0 0 531.73 533.91 1.47 9761.2 15.7533.19 1.47 17331.6 27.9531.73 1.47 34658.4 55.7529.20 1.47 413.0 0.7

10 13 531.32 533.38 1.40 5442.8 10.5532.42 1.40 20514.2 39.5531.32 1.40 25915.0 50.0

20 19 531.19 533.26 1.58 5024.9 12.2532.17 1.58 8762.8 21.3531.19 1.58 27305.2 66.5

30 31 531.06 533.24 1.63 3983.0 11.2532.02 1.63 10373.4 29.3531.06 1.63 21042.0 59.5

40 39 530.92 532.95 1.45 3803.0 10.5531.72 1.45 11670.7 32.2530.71 1.45 20756.9 57.3

50 47 530.61 532.93 1.43 2503.1 7.7531.66 1.43 7406.3 22.6530.51 1.43 22752.6 69.7

Fig. 9. High-resolution V 2p spectra for x ¼ 30% V2O5 phosphate glass sample with theresulting peaks from the least-squares fitting routine. The smooth solid line in figure isthe resultant sum of the peaks plus the background.

Fig. 10. IR spectra of 50BaOexV2O5e(50 � x)P2O5 glasses.

A. Majjane et al. / Materials Chemistry and Physics 143 (2014) 779e787784

from these fits, the peak positions for O 1s BO and O 1s NBO of 533.2and 531.3 eV, respectively, show a separate dependence on theV2O5 content. The first (BE ¼ 533.2 eV) decrease from 28% forx ¼ 0e10.5% for x ¼ 10 and remain constant for the others com-positions. While the second peak at BE ¼ 531.2 eV varies from 50 to70% depending on V2O5 content. The diminution of NBO number isimposed because in these samples the P atomic concentration de-creases and the relative O/P concentration increases in the sameorder as the BE shift shows (Fig. 8). The concentration of NBO(Be ¼ 532.9e533.2 eV) decrease from 28 to 8% while x varies from0 to 50 (Table 3) indicating a broken in the PO4 chain. The O1s peaksin these glassesmay arise from oxygen atoms existing in some or allof the following structural bonds: PeOeP, PeOeV, VeOeV, PeOeBa, and VeOeBa. Oxygen atoms that are more covalently bonded toglass former atoms on both sides are typically called bridging ox-ygen (PeOeP, VeOeV), while oxygen atoms that are more ionicallybonded to phosphore or vanadium are referred to as non-bridging

Table 4Peak positions, FWHM, area and relative abundance from the curve fitting of V 2pcore levels for 50BaOexV2O5e(50 � x)P2O5 glasses. The uncertainty in the peakpositions is �0.1 eV, FWHM �0.1 eV.

CompositionsV2O5 (mol%)

Peak positions (eV) FWHM(eV)

Area % Area

Batch Analyzed Main peak Deconvolutedpeaks

10 13 518.02 518.90 1.24 290.1 6.2518.11 1.24 2761.0 59.2517.11 1.24 1610.1 34.6

20 19 517.96 519.13 1.38 624.9 7.40517.96 1.38 6628.2 78.3516.84 1.38 1214.1 14.3

30 31 517.91 519.04 1.48 528.8 4.5517.91 1.48 9886.3 82.0516.24 1.48 1633.2 13.5

40 39 517.78 519.05 1.42 2588.2 13.9517.78 1.42 15667.4 83.9516.02 1.42 415.6 2.2

50 47 517.56 518.86 1.40 3760.9 17.1517.56 1.40 17626.1 80.5515.73 1.40 514.1 2.4

oxygen atoms and have lower binding energies (PeOeBa, VeOeBa). The Pauling electronegativity of phosphore (2.19) is greaterthan that of vanadium (1.63) and barium (0.89) and consequentlythe PeOeP bond would be the most covalent, followed by the PeOeV bond, VeOeV bond, PeOeBa bond and then VeOeBa bond.Correspondingly, the binding energy for each structural bondshould be lower. According to Khattak et al. [27], we assigned the O1s peak at 533.2 eV to PeOeP structural bonds and the O 1s peak at531.1 eV to both PeOeV and VeOeV bonds. The O 1s peak at532.0 eV is owing to PeOeBa and VeOeBa bonds.

3.3.4. Vanadium spectraFig. 7 shows the core level spectra of V 2p for the BaOeV2O5e

P2O5 glass samples and the peak positions are in relatively goodagreement with those reported on other vanadate glasses

Fig. 11. (a) Metaphosphate (P2O6)2� contains two PeOeP units. (b) Pyrophosphate(P2O7)4� contains only a single PeOeP bond [44].

A. Majjane et al. / Materials Chemistry and Physics 143 (2014) 779e787 785

[26,31,32]. Although upon more careful inspection of the V 2p3/2spectra, an asymmetry is clearly observable on the lower bindingenergy side of the core level, which is indicative of vanadium ionsexisting in more than one oxidation state [27]. Hence, the mainpeak around 518 eV in each V 2p3/2 spectrum was initially fitted tothree GaussianeLorentzian peaks with the lower binding energypeak (BE ¼ 517 eV) corresponding to V3þ, the second (BE ¼ 518 eV)corresponding to V4þ and the higher binding energy peak

Fig. 12. Schematic representation of the evolution of structure from co

(BE ¼ 519 eV) to V5þ (Fig. 9). Table 4 displays the result of thesethree peaks fits including the peak positions and relative abun-dance of each vanadium oxidation state. The abundance of V3þ

varies from about 35% for the x ¼ 10 to 2% for x ¼ 50 with a sharpdecrease for x ¼ 20. This effect may be explained that the oxidationstate of V3þ is linked to reduction of V4þ upon XPS measurement.This result suggested that even lower oxidation states for vanadiummight be present for smaller V2O5 containing phosphate glasses.

ntinuous phosphate network to the continuous vanadate network.

A. Majjane et al. / Materials Chemistry and Physics 143 (2014) 779e787786

These values are in agreement with those reported for V5þ [33].This indicates that V exists as both V3þ, V4þ and V5þ in this phos-phate glasses.

3.4. Infrared spectroscopy

FTIR absorption spectra of 50BaOexV2O5e(50 � x)P2O5 glasses(0 � x � 50 mol% V2O5) in the frequency range 400e1400 cm�1 areshown in Fig. 10. The spectrum of the glass without V2O5 (x¼ 0 mol%) shows a FTIR pattern typical of metaphosphate NaPO3 glass [34].The characteristics features of 50BaOe50P2O5 glass spectrum arethe PO2 asymmetric stretching vibration band at 1265 cm�1

(nas(PO2)), the PO2 symmetric stretching vibration band at1154 cm�1 (ns(PO2)), the nas(PO3) groups (chain-end groups) at1090 cm�1, the ns of PO3 groups near 1000 cm�1, the nas of POPgroups at 880 cm�1, the ns of PeOeP groups at 770 and 720 cm�1

and the deformation mode of PeOe(PO43�) groups at 520 and

480 cm�1.On the other side, we note that when the vanadium content in

the glass increases up to 10 mol%, the intensities of OePeOasymmetric stretching modes and of the ns of PeOeP bridgesdecrease and the frequency of the nas of the PO2 groups is shiftedfrom 1265 to 1245 cm�1. These changes are due to the decrease ofthe average phosphate chain length [35]. The transformation of thetwo bands at 770e720 cm�1 frequency range, which are attributedto the presence of two PeOeP bridges in metaphosphate chainbased on (P2O6

2�) groups, into a single band at 735 cm�1, assigned toPeOeP linkage in pyrophosphate groups P2O7

4� [36], is anotherconfirmation to the depolymerization of 50BaOe50P2O5 glasswhen V2O5 content increases.

Above 10 mol% V2O5 incorporation, the increase of V2O5 contentchanges the spectrum significantly and shows the disappearance ofall bands between 1245 and 735 cm�1 and development of the newbands around approximate 1130, 1054, 900, 772 and 648 cm�1. Thetwo first bands are characteristics of the isolated ‘P’ tetrahedra(PO4)3� connected to different cations, which suggest that a highlydepolymerized phosphate network is taking place with isolatedorthophosphate. The other bands were assigned to vanadium units.

The band situated at 905e900 cm�1 can be attributed to thevibrations of VO2 groups of the VO4 tetrahedra [37], the band at780e750 cm�1 is assigned to the vibration of VeOeP bridges [38]and finally the band around 648e628 cm�1 is attributed to thebending vibrations of VeO bonds [39e42]. This result reveals thatthe structure changes from the continuous phosphate network tothe continuous vanadate network by the formation of both tetra-hedral VO4 and short phosphate units such as P2O7

4� and (PO4)3�

groups.At this stage, we can provide a structural model to elucidate the

effect of the addition of V2O5 in the 50BaOexV2O5e(50 � x)P2O5glasses. As it was discussed above from FTIR spectra (Fig. 10), thebinary phosphate 50BaOe50P2O5 glass (x ¼ 0) reveals a high de-gree of similarity with those of alkali phosphate glasses based onmetaphosphate composition. This was taken as evidence that thestudied glasses have short range structure resembling to that ofother metaphosphate glasses. Previous studies [43] have inter-preted the FTIR spectra of several metaphosphate glasses on thebasis that the structure consists primarily of numerous PO4 tetra-hedra linked together in infinitely long chains and rings upon twoBOs. The modifier cations (as Ba2þ) are presumed to be located atsites between the NBOs, providing considerably weaker ionic bondsbetween the strong covalent bonds within the chains. 50BaOe50P2O5 glass (x¼ 0) exhibit two bands in the frequency range 770e720 cm�1 which are attributed to the presence of two PeOePbridges in metaphosphate chain based on (P2O6

2�) groups as shownin Fig. 11a [44]. For 10 mol% V2O5 addition, the glass exhibits only a

single band at 735 cm�1 which is assigned to the PeOeP linkage inpyrophosphate group (P2O7

4�) (Fig. 11b) [44]. So we conclude thatwhen V2O5 is added Ba(PO3)2 glass, the skeleton of (P2O6

2�)N chainsis gradually broken into pyrophosphate groups P2O7

4� (Fig. 12).The presence of the band at 1245 cm�1 corresponding to

nas(PO2) in the glass with 20 mol% V2O5 (Fig. 11) and the contri-bution observed in P 2p spectrum at binding energy at 134.8e135.3 eV, P 2p1/2 (Fig. 6) indicating that few chains remain in thisglass compositions, suggesting that the depolymerization is notetotal. Even though this conversion is taking place due to breaking ofPeOeP linkages the formation of PeOeV and PeOeBa linkagesprovide cross linking between shorten ‘P’ structural units whichmakes the glass network more rigid. Therefore the net effect is anincrease in Tg, density and a decrease in molar volume (Fig. 12). Forfurther addition of V2O5 > 20 mol%, pyrophosphate groups getsconverted into orthophosphate groups PO4

3� and glass networkbecomes highly depolymerized, therefore cross linking is not suf-ficient to give strength to glass network. This results in decrease indensity, Tg and an increase in molar volume.

In addition, the vanadium-rich compositions show a structureconsisting mainly of VO4 tetrahedra (Fig. 12). According to Quanand Adams the Ba ions are located probably between vanadatechains and layers [45].

4. Conclusions

XPS and FTIR spectroscopy were used to investigate the struc-tural modifications of vanadiumebariummetaphosphate glasses. Itis argued that the addition of vanadium to barium metaphosphatestructure results in a fast depolymerization of the phosphate chainsbased on (PO3)� units through the pyrophosphate structure basedon dimeric (P2O7)4� units to the orthophosphate structure based onmonomeric (PO4)3�. This conversion is taking place due to breakingof PeOeP linkages and the formation of PeOeV, PeOeBa and VeOeV linkages. The vanadium exists inmultiple valence states in thisstructure. The nonlinear trend of density, molar volume and glasstransition temperature is correlated to the structural evolution.

References

[1] B.C. Sales, Mater. Res. Soc. Bull. 12 (1987) 32.[2] L.L. Hench, R.J. Splinter, W.C. Allen, T.K. Greenlee, J. Biomed. Mater. Res. Symp.

2 (1972) 117.[3] M. Ogino, L.L. Hench, J. Non-Cryst. Sol. 38 & 39 (1980) 673.[4] L.D. Bogomolova, J. Non-Cryst. Sol. 30 (1979) 379.[5] L.D. Bogomolova, M.P. Glassova, J. Non-Cryst. Sol. 37 (1980) 423.[6] R.K.B. Brow, J. Non-Cryst. Sol. 263 (2000) 1.[7] G. Tricot, L. Montagne, L. Delevoye, G. Palavit, V. Kostoj, J. Non-Cryst. Sol. 345

(2004) 56.[8] C. Mercier, G. Palavit, L. Montagne, C. Follet, C.R. Chim. Acad. Sci. 5 (2002) 693.[9] H. In, H. Takebe, K. Morinaga, J. Ceram. Soc. 111 (2003) 426.

[10] S. Jiang, T. Luo, B.-C. Hwang, F. Smekatala, K. Seneschal, J. Lucas,N. Peyghambarian, J. Non-Cryst. Sol. 263 & 264 (2000) 364.

[11] T. Harada, H. In, H. Takebe, K. Morinaga, J. Am. Ceram. Soc. 87 (2004) 408.[12] T. Harada, H. Takebe, M. Kuwabara, J. Am. Ceram. Soc. 89 (2006) 247.[13] N. Fairley, CasaXPS, Version 2.3.9, Casa Software Ltd., Teighnmouth, Devon,

UK, 2003. www.casaxps.comS.[14] N. Kerkouri, M. Ettabirou, A. Chahine, A. Mazzah, M.C. Dhamelincourt,

M. Taibi, J. Optoelectron. Adv. Mater. 12 (2010) 1030.[15] J.M. Stevels, in: S. Flügge (Ed.), Handbuch der Physik, vol. 13, Springer, Berlin,

1962, p. 520.[16] S.M. Mukhopadhyay, Tim C.S. Chen, J. Mater. Res. 10 (6) (1995) 1502.[17] M. Schneider, Wo. Richter, R. Keding, C. Russel, J. Non-Cryst. Sol. 226 (1998) 273.[18] G.Corro, J.L.G. Fierro,R.Montiel, F.Banuelos, J.Mol.Catal. A:Chem.228(2005)275.[19] V. Simon, D. Muresan, A.F. Takács, M. Neumann, S. Simon, Solid State Ionics

178 (2007) 221.[20] H. Jena, V.K. Mittal, S. Bera, S.V. Govindan Kutty, T.R. Kutty, Appl. Surf. Sci. 254

(2008) 7074.[21] A.M. Puziy, O.I. Poddubnaya, R.P. Socha, J. Gurgul, M. Wisniewski, Carbon 46

(2008) 2113.[22] E. Fluck, D.P. Weber, Z. Naturforsch. B29 (1974) 603.

A. Majjane et al. / Materials Chemistry and Physics 143 (2014) 779e787 787

[23] M. Pelavin, D. Hendrickson, J. Hollander, W. Jolly, J. Phys. Chem. 74 (5) (1970)1116.

[24] P.A. Bertrand, J. Vac. Sci. Technol. 18 (1) (1981) 28.[25] G.D. Khattak, M.A. Salim, L.E. Wenger, A.H. Gilani, J. Non-Cryst. Sol. 262

(2000) 66.[26] A. Mekki, G.D. Khattak, L.E. Wenger, J. Non-Cryst. Sol. 330 (2003) 156.[27] G.D. Khattak, A. Mekki, L.E. Wenger, J. Non-Cryst. Sol. 355 (2009) 2148.[28] R.K. Brow, in: R.E. Loehman (Ed.), Characterization of Ceramics, Butterworth-

Heinemann, London, 1993.[29] R.K. Brow, C.M. Arens, X. Yu, E. Day, Phys. Chem. Glasses 35 (1994) 132.[30] B.M.J. Smets, D.M. Krol, Phys. Chem. Glasses 25 (1984) 113.[31] G.D. Khattak, N. Tabet, L.E. Wenger, Phys. Rev. B 72 (2005) 104203.[32] H. Harper, P.W. McMillan, Phys. Chem. Glasses 15 (1974) 148.[33] M.P. Casaletto, S. Kaciulis, L. Lisi, G. Mattogno, A. Mezzi, P. Patrono,

G. Ruoppolo, Appl. Catal. A 218 (2001) 129.[34] L. Montagne, G. Palavit, G. Mairesse, Phys. Chem. Glasses 37 (5) (1996) 206.[35] R.F. Bartholomew, J. Non-Cryst. Sol. 7 (1972) 221.

[36] A. Chahine, M. Et-tabirou, M. Elbenaissi, M Haddad, J.L. Pascal, Chem, Phys. 84(2004) 341.

[37] N. Vedeanu, O. Cozar, I. Ardelean, B. Lendl, J. Optoelectron. Adv. Mater. 8(2006) 78.

[38] R.N. Bhargava, R.A. Condrate Sr., Appl. Spectrosc. 31 (1977) 230.[39] R. Iordanova, Y. Dimitriev, V. Dimitrov, S. Kassabov, D. Klissurski, J. Non-Cryst.

Sol. 204 (1996) 141.[40] T. Gilson, O. Bizri, N. Ceetham, J. Chem. Soc. Dalton Trans. Inorg. Chem. A 291

(1973).[41] L. Abello, E. Husson, Y. Replin, G. Lucazeau, Spectrochim. Acta 39A (1983) 641.[42] Y. Dimitriev, M. Arnaudov, V. Dimitrov, Mh. Chem. 107 (1976) 1335.[43] C.K. Shih, C.J. Su, in: Proceedings of the VIIth International Congress on Glass,

Brussels Belgium, 1965, p. 48.[44] C. Dayanand, G. Bhikshamaiah, V. Jaya Tyagaraju, M. Salagram, A.S.R. Krishna

Murthy, J. Mater. Sci. 31 (1996) 1945.[45] J.T. Quan, C.F. Adams, J. Phys. Chem. 70 (1966) 331.