Spectroscopic and photoacoustic investigation ofx(V2O5·CuO)(12 x)[3B2O3·K2O] glasses

I. Bratua,* , I. Ardeleanb, A. Barbua, D. Maniub, C. Borsab

aInstitute for Isotopic Molecular Technology, P.O. Box 700, 3400 Cluj 5, Romaniab‘‘Babes-Bolyai’’ University, Faculty of Physics, 3400 Cluj-Napoca, Romania

Received 24 August 1998; accepted 3 December 1998

Abstract

IR and Raman spectra ofx(CuO·V2O5)(1 2 x)[3B2O3·K2O] glasses, with 0# x # 0.5, have been measured and analysed inorder to identify the spectral contribution of each component and to point out the role of V and Cu ions on the structure of theglass network. Thermal diffusivity of these vitreous materials, measured by photoacoustic technique, is sensitive to themicrostructural changes induced by transition metal ions.q 1999 Elsevier Science B.V. All rights reserved.

Keywords:Infrared; Raman; Oxide glasses; Photoacoustics; Transition metal ions

1. Introduction

Many articles deal [1] with the investigation of thespecific physical properties of oxide glasses with tran-sition metal ions, especially because of their abnormalbehaviour [2–5]. The introduction of the transitionmetal in glasses leads to the change of glass structure,metal oxide acting as modifier [6,7]. In this articlethe properties ofx(V2O5·CuO)(1 2 x)[3B2O3·K2O]glasses with 0# x # 0.5 were analysed by IR andRaman spectra, and photoacoustic (PA) technique.

2. Experimental

Glasses of thex(CuO·V2O5)(1 2 x)[3B2O3·K2O]system with 0# x # 0.5 were prepared by usingreagent grade CuO, V2O5, H3BO3 and K2CO3 in

suitable proportions. No crystalline phase wasdetected by X-ray diffraction. All measurementshave been performed at room temperature. Infraredspectra were obtained in the 400–4000 cm21 spectralrange with an UR 20 Carl Zeiss spectrophotometer byusing the KBr pellet technique. The sample wereexcited with a 165 Spectra-Physics Ar ion laser(514.5 nm, 0.5 W) to obtain the Raman spectra. Theback-scattered light was analysed with an 1404 SpexDouble Monochromator having an 9000 SpectraPhotometrics CCD camera detection system cooledat liquid nitrogen temperature. Photoacoustic data –frequency scans – have been recorded by means of theOpen PA Cell (OPC) technique [8] using a homemade experimental set-up [3].

3. Results and discussion

In order to identify the constituent oxides ofx(V2O5·CuO)(12 x)[3B2O3·K2O] system, the absorp-tion IR bands (Fig. 1) were compared with the

Journal of Molecular Structure 482–483 (1999) 675–678

0022-2860/99/$ - see front matterq 1999 Elsevier Science B.V. All rights reserved.PII: S0022-2860(98)00939-9

* Corresponding author. Tel.: 0040 64 185027; fax: 0040 64420042.

E-mail address:ibratu@L30.itim-cj.ro (I. Bratu)

catalogue ones for the vitreous B2O3 [9], for thecrystalline B2O3 [10], CuO [10] and for V2O5 [11].

All the IR absorption bands of vitreous B2O3 werefound (Fig. 1) but shifted towards low wavenumbers.In the matrix spectrum a small band appears att 700 cm21 which probably corresponds to that att 720 cm21 in the vitreous spectrum of the B2O3

and is assigned to B–O–B deformation vibration[12]. At t 920 cm21 a boroxol ring vibration is iden-tified. The band att 1060 cm21 is assigned to theB–O stretching vibrations which includes boronatoms of coordination 4 (BO4 units) [12]. The B–Ostretching vibration for boron of coordination 3 (BO3

units) gives a band att 1265 cm21 [12]. In the spectraof vitreous B2O3 this band appears att 1265 cm21.A broad band att 1370 cm21 is assigned to thestretching vibration of the boroxol ring [13] bycomparison with Na2O·B2O3 [14] glasses where itappears aroundt 1400 cm21 for vitreous B2O3. The

hydroxyls adsorbed by this system are identified bythe broad stretching mode band between 3200 and3600 cm21 and thedOH mode at t 1640 cm21.

The addition of V2O5 and CuO to the 3B2O3·K2Omatrix produces some changes in the spectrum. Theband att 700 cm21 becomes broader because of theappearance of thet 720 cm21 CuO band. Asx isincreased the band att 920 cm21 is shifted towardslow wavenumberst 828 cm21 and broadens. Forx�0.5 this band is centred att 828 cm21 which corre-sponds to V2O5. For x $ 0.2 another band, related toV2O5, appears att 1018 cm21 as a shoulder on thet 1060 cm21 band. The band att 1200 cm21 isbroadened, its intensity increases as the concentrationx is increased, and becomes more intense than theband at t 1060 cm21, at high concentrations thusshowing the domination of the boron atoms of coor-dination 3. IR spectra reveal an increase in number ofBO3 units compared to the number of BO4 units,

I. Bratu et al. / Journal of Molecular Structure 482–483 (1999) 675–678676

Fig. 1. Infrared spectra ofx(CuO·V2O5)·(1 2 x)[3B2O3(K2O] glasses.

which agrees with the formation of orthoborate groupsand the decrease of the number of pentaborate groups[3]. The profile att 1370 cm21 increases in intensityas the concentration of the modifier is increased. Thehydroxyl content diminishes drastically atx � 0.5 asdemonstrated by the disappearance of the broadfeature between 3200 and 3700 cm21. The BO4/BO3

ratio of thexCuO(1 2 x)[3B2O3·K2O] system [7] isdrastically changed when this system is doped withV2O5. For thexCuO(1 2 x)[3B2O3·K2O] system thementioned ratio increases in the 0# x # 0.01

concentration range and decreases forx $ 0.01. Inour case this ratio is approximately equal to 1 forx , 0.05 whereas forx $ 0.05 the boron atoms ofcoordination 3 dominate. The distinct distribution ofthe BO3 and BO4 units in these two systems shows thatthe presence of V2O5 influences the glass structurestronger than the CuO. One can conclude that bothcopper and vanadium oxides play a modifying rolein the [3B2O3·K2O] matrix.

Raman spectrum of vitreous B2O3 is dominated byan intense and narrow band centred att 806 cm21

assigned to the boroxol ring oxygen breathing mode(where the boron atom coordination is 3) [15]. Withthe addition of an alkali oxide, a strong band centredat t 770 cm21 appears and thet 806 cm21 band isshifted to lower wavenumberst 798 cm21 [4]. TheRaman band centred att 770 cm21 was assigned byBril [16] to the symmetric breathing vibration of six-membered rings with one BO4 tetrahedron (i.e. tribo-rate, tetraborate or pentaborate). Addition of K2O tovitreous B2O3 results in a change of the boron coordi-nation number from 3 to 4.

For the glass matrix (x� 0) Raman spectrum (Fig.2) the intensity oft 770 cm21 band is higher than thatat t 798 cm21. The presence of the bands centred att 770 cm21 and att 934 cm21 region can be taken tobe indicative of the presence of pentaborate groups[17].

The increase ofx leads to the rise of thet 934 cm21

intensity band (assigned to orthoborate groups [4,5])as compared to those att 770 andt 798 cm21 bands(Fig. 2). Forx $ 0.03 the band centred att 934 cm21

becomes dominant and a shoulder att 904 cm21

appears. Therefore, the number of nonbridgingoxygens increases with the increasing ofx, and theglass structure becomes more randomised. Forx .0.1 thet 904 cm21 band becomes more intense thanthe t 934 cm21 band, being assigned to the asym-metric vibration of ‘‘loose’’ BO2

4 tetrahedra (i.e.,tetrahedra connecting various segments without parti-cipating in specific borate arrangements) [5]. Theaddition of vanadium and copper ions results in theappearance of ‘‘loose’’ BO24 tetrahedra in the detri-ment of the orthoborate groups�BO32

3 �:For the glasses with 0# x # 0.05 the bands

centred at t 475 and t 1490 cm21 also appear.The t 475 cm21 band is assigned to a ringbending mode (B–O–B) for the borate units

I. Bratu et al. / Journal of Molecular Structure 482–483 (1999) 675–678 677

Fig. 2. Raman spectra ofx(CuO·V2O5)(1 2 x)[3B2O3(K2O] system.

Fig. 3. Composition dependence of thex(CuO·V2O5)·(1 2

x)[3B2O3(K2O] system’s thermal diffusivity coefficient.

[18], which is observed at t 470 cm21 ofpure B2O3 [13]. The very broad band fromt 1490 cm21 is the indication of the chain-type meta-borate groups’ presence [5]. One observes an asym-metric band at t 1225 cm21, which indicates theformation of pyroborate groups�B2O42

5 � [16].The thermal diffusivity coefficienta s of the inves-

tigated glasses and its dependence on the V and Cuoxides content was evaluated (Fig. 3) by taking intoaccount the thermoelastic model applied to the PAsignal phase angle [19].

The thermal diffusivity coefficient of glasses issensitive to microstructural changes, therefore itsbehaviour vs.x shows that the addition even of asmall quantity of Cu and V ions to the glass matrixproduces strong structural changes, evidenced also bythe mentioned spectroscopic measurements. Thesechanges reach saturation aroundx � 0.01, where theorthoborate groups are already formed. This factmeans that the magnitude of the thermal diffusivitlycoefficient depends mainly on the formation of theorthoborate groups.

4. Conclusions

Raman spectra show two effects produced by(V2O5·CuO) addition to the 3B2O3·K2O glass: first,the breaking of the regular structure of the rings(borate and boroxol) and the appearance of orthobo-rate groups forx $ 0.03 and second, the decrease inthe number of these groups and the appearance of‘‘loose’’ BO2

4 , tetrahedra forx . 0.1. Therefore weconclude that the vanadium and copper ions act asnetwork modifiers in the studied glasses. IR spectrareveal an increase in the number of the BO3 unitscompared to the number of BO4 units, in agreement

with the formation of orthoborate groups and thedecrease in number of pentaborate groups.

The thermal diffusivity coefficient of glasses is verysensitive to the increase of the modifiers concentra-tion. The magnitude ofa s closely follows the forma-tion of orthoborate groups.

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