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Vibrational Spectroscopy 48 (2008) 259–262 www.elsevier.com/locate/vibspec
Raman spectroscopic study of CuO–V2O5–P2O5–CaO glass system N. Vedeanu a,*, O. Cozar b, I. Ardelean b, B. Lendl c, D.A. Magdas d a
Iuliu Hatieganu University of Medicine and Pharmacy, Faculty of Pharmacy, Department of Physics-Biophysics, 400023 Cluj-Napoca, Romania b Babes-Bolyai University, Faculty of Physics, Department of Biomedical Physics, 400084 Cluj-Napoca, Romania c Institute of Chemical Technologies and Analytics, Vienna University of Technology, A-1060 Vienna, Austria d National Institute for Research and Development of Isotopic and Molecular Technologies, RO-400293 Cluj-Napoca, Romania Received 21 July 2007; received in revised form 23 December 2007; accepted 4 January 2008 Available online 31 January 2008
Abstract In order to evidence the structural changes induced by CuO and V2O5 in the phosphate glass network and their modifier or former role, x(CuOV2O5)(100 x)[P2O5CaO] glass system was prepared and investigated using Raman spectroscopy (0 x 40 mol%). Raman spectra of the studied glasses present the specific bands of the phosphate glasses at low concentration of transition metal (TM) ions, but at higher concentration (x > 7 mol%) a strong depolymerization of the phosphate network appears; non-bridging oxygen atoms are involved in V– O–P and Cu–O–P bonds and new short units are formed. For a high concentration of V2O5 (x > 10 mol%) the Raman bands of V2O5 prevail in the spectra; this fact suggests that vanadium oxide imposes its structural units in the network acting thus as a network glass former. 2D correlation analysis was also applied for the concentration-dependent Raman spectra in order to verify the assignments of the vibration modes and to find correlations in the changes induced by TM ions content. 2D correlation maps indicate a good correlation between the bands at 705 cm 1 assigned to P–O–P stretching vibration and at 1175 cm 1 assigned to PO2 groups which suggest the depolymerization of the phosphate network. The correlation between the 1270 cm 1 and 930 cm 1 bands also suggests that V2O5 oxide is responsible for P O bonds breaking and P–O–V formation. # 2008 Elsevier B.V. All rights reserved. Keywords: Raman spectroscopy; Phosphate glasses; V2O5 oxide
1. Introduction Phosphate glasses containing TM oxides present superior physical properties such as high thermal expansion coefficient, low melting temperature and high UV transmission in comparison with silicate or borate glasses. For this reason phosphate glasses have a great potential application in solidstate lasers and as optical fibres for communication devices [1– 3]. Important biological applications for calcium phosphate glasses also exist as it was demonstrated that they are biocompatible as bones and dental implants [4,5]. Vanadium and copper ions are very suitable to be used in glasses because they are characterized by a partially filled d shell which can exist in at least two valence states [6]; the technological importance of these glasses requires a detailed understanding of the molecular and structural chemistry in * Corresponding author. E-mail address:
[email protected] (N. Vedeanu). 0924-2031/$ – see front matter # 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.vibspec.2008.01.003
order to determine a relationship between properties and structure [7]. The addition of TM oxides leads to the depolymerization of the phosphate chains and to the formation of new P–O–TM bonds which can change the electrical, optical or magnetic properties of these glasses. A recent problem related to phosphate glasses concerns the double role of some oxides as network modifiers and formers, oxides that traditionally are considered only network modifiers. It was reported that WO3 oxide in xWO3 (100 x)[2P2O5PbO] glass system acts as a network former for x 30 mol% using deconvolution method [8]. IR spectra of Fe2O3–PbO–P2O5 glasses revealed that both PbO and Fe2O3 play dual role as network formers and modifiers depending on their content. Beyond the critical content of Fe2O3 in phosphate glasses the addition of PbO and Fe2O3 leads to the breakdown of the P O bonds and to the formation of P–O–Pb and P–O–Fe instead of P–O–P ones [9]. The present work wants to identify the specific structural units that appear in x(CuOV2O5)(100 x)[P2O5CaO] glass
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Fig. 1. XRD spectra of x(CuOV2O5)(1
x)[P2O5CaO] glasses.
system and to prove that V2O5 has a dual role as network modifier and former for specific concentrations. 2. Experimental In order to prepare x(CuOV2O5)(1 x)[P2O5CaO] glasses with 0 x 40 mol% we used (NH4)H2PO4, CuO, V2O5 and CaO of reagent grade purity. The samples were prepared by weighting suitable amounts of these components, powder mixing and mixture melting in a sintered corundum crucibles at 1250 8C for half an hour. The mixture was put into the furnace directly at this temperature. The melts were poured then on stainless steel plates. XRD spectra of the studied glasses have shown that all the samples are vitreous samples and they do not present any crystalline phase (Fig. 1). Raman spectra were measured with a Horiba Jobin Yvon Micro-Raman spectrometer (LabRam-HR) equipped with an integral Olympus BX 41 microscope and Peltier-cooled CCD detection, using the 632.8 nm line of a He–Ne laser (1.5 mW) for excitation. The spectra were recorded in the 1400–200 cm 1 range of Raman shifts at 1.3 cm 1 spectral resolution. 3. Results and discussions 3.1. Raman spectra Raman spectra of x(CuOV2O5)(1 x)[P2O5CaO] glasses with 0 x 40 mol% are shown in Fig. 2. The most important bands and their assignments are given in Table 1. It is known that V2O5 have usually a network modifier effect [10] when added to phosphate glasses which consist in the depolymerization of the long phosphate chains and in a local reorganization of the structural units in which only the short range phosphate units or ring structure appear. Recently it was suggested that for high concentration of V2O5 it can also act as a network former and it is possible to evolve from a phosphate network to a pure vanadate network in which PO4 tetrahedra are
Fig. 2. Raman experimental spectra of x(CuOV2O5)(1 glasses.
x)[P2O5CaO]
isolated [11,1]. It can be seen in this respect that for high content of V2O5 (x > 7 mol%) new bands occur in the spectra: a band at 640 cm 1 due to the vibration of P–O–P in-chain [2,12–15], a band at 750 cm 1 assigned to in-chain P–O–P asymmetric stretching vibration [12–15], a shoulder at 870 cm 1, another one at 905 cm 1 both due to V–O stretching vibration [12–15] and a band at 930 cm 1 attributed to V O vibration in the tetragonal pyramid of V2O5 [13]. These last two bands are clearly observed in the spectra of the glasses for x 20 mol%. The two bands that appeared in the spectra at 870 cm 1 and at 930 cm 1 are assigned to O–V–O and V–O–V groups but they are also attributed to the very short phosphate chain units [13,8]. Furthermore the increasing intensity of the band at 905 cm 1 assigned to O–V–O and V–O–V groups underline the breaking of the phosphate chains and V2O5 tendency to act as a network former, as these two last bands dominates the spectra for x 40 mol%. An important remark regards the bands at 705 cm 1 and 1175 cm 1. These two bands are assigned to in-chain P–O–P symmetric stretching vibration and to PO2 symmetric stretching groups of the corner sharing PO4 tetrahedra. Both bands decrease in intensity and disappear from the spectra for x 20 mol%; other bands appear at 640 cm 1 and 750 cm 1. Table 1 Raman bands and band assignment for x(CuOV2O5)(1 with 0 x 40 mol% Wavenumber (cm 1) 330 640 705–750 870–905 980 1030 1175 1270
x)[P2O5CaO] glasses
Band assignment Bending vibrations of phosphate polyhedra Combination of low energy vibrations of V–O–V chains and P–O–P symmetric stretching vibrations In-chain P–O–P asymmetric stretching vibrations Stretching vibrations of O–V–O in metavanadate chains V O vibrations in VO5 tetragonal pyramid PO3 symmetric stretching bands PO2 symmetric stretching, symmetric stretching vibrations in O–P–O groups of corner sharing PO4 tetrahedra P O symmetric stretching vibrations
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The first one is related with the shorter chains formation or ring structures of phosphate units [8] and the other one is due to PO4 isolated polyhedra as the content of PO4 groups increase when the phosphate chains are breaking [8,16]. The shift of the band at 750 cm 1 is also due to the CuO effect [3]. Finally the band at 1270 cm 1 attributed to P O bonds decrease in intensity up to disappearance because of the formation of M–O–P (M = V4+ and Cu2+) bonds which makes weaker the initial P O bond [10]. 3.2. Two dimension correlation spectroscopy (2D-COS) The aim of using 2D-COS [17] in this paper is that to verify the assignments of the vibration modes and to elucidate the sequence of structural transformations in the phosphate network by introducing TM oxides. We applied 2D-COS to the V2O5 and CuO concentrationdependent Raman spectra. The obtained synchronous and asynchronous maps for Raman spectra are shown in Fig. 3(a) and (b). Raman synchronous spectrum indicates that the cross-peaks at (1270, 1175) cm 1 and (1175, 705) cm 1 decrease with the increasing of TM ions and the cross-peaks at (1175, 930) cm 1, (1175, 640) cm 1, (1175, 425) cm 1, (1175, 320) cm 1 and (930, 705) cm 1 increase with the increasing of TM ions. Compared with the experimental spectra, the synchronous map indicates clearly that the symmetric stretching vibration of V– O–V chains (the band at 640 cm 1) and V O vibrations in VO5 tetragonal pyramids (the band at 930 cm 1) increase in intensity when V2O5 and CuO content increase [2,13,18]. Raman asynchronous spectrum shows the following important cross-peaks: (1270, 1175) cm 1, (1270, 1 1 705) cm , (1175, 1000) cm , (1175, 980) cm 1, (1175, 750) cm 1, (1000, 705) cm 1, (930, 550) cm 1 and (930, 355) cm 1. This information may suggest that the bands at 980 cm 1 and 1000 cm 1 are not new bands, they are only shifts of the 1030 cm 1 band. The shift of this band is consistent with the depolymerization of the phosphate network and with the formation of isolated VO5 groups for high content of V2O5 (x 20 mol%). This conclusion is sustained also by the fact that at high concentration (x = 20 mol%) a band at 905 cm 1 that appeared in asynchronous map is attributed to the vibration of O–V–O or V–O–V metavanadate bonds [13]. These types of bonds which are more stable from the chemical point of view partially replace the P–O–P chains. Compared with experimental spectra it can be observed that this bands dominate the spectra at 40 mol%; this fact demonstrates the former role of V2O5 oxide if it is in high concentration (x 20 mol%). The asynchronous spectrum indicates also that there is no correlation between the band at 1175 cm 1 attributed to symmetric stretching vibration in PO2 groups of corner sharing tetrahedral and the band at 1270 cm 1 attributed to P O bonds. There is also no correlation between the band at 1175 cm 1 and 1000 cm 1, the last one being attributed to stretching vibrations in PO3 groups [18]. Both synchronous and asynchronous spectra [19] indicate a good correlation between the band at 1270 cm 1 and 930 cm 1
Fig. 3. (a and b) Raman 2D correlation spectra of x(CuOV2O5)(1 x)[P2O5CaF2] glasses for 0 x 40 mol%; (a) synchronous spectrum and (b) asynchronous spectrum.
suggesting that the breaking of P O bonds is due to V2O5 oxide in high concentration (x 20 mol%). There is also a correlation between the bands at 1175 cm 1 and 705 cm 1 indicating that the decreasing of these two bands up to their disappearance are related to each other, so the number of inchain P–O–P bonds and PO2 groups are diminishing with the increase of V2O5 content. 2D-COS results imply that there is a strong correlation between the changes in the corner and edge structures with the increasing content of vanadium oxide and that P–O–P bonds are partially replaced by V–O–Vor O–V–O bonds proving that this oxide acts as a network former at high content (x 20 mol%). 4. Conclusions The shape of Raman spectra of the studied glasses is influenced by the presence of vanadium oxide. The phosphate chain is depolymerized with the increasing of vanadium oxide
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content so in consequence its characteristic bands strongly decrease in intensity except the specific bands for short phosphate chain or ring structures. For x = 40 mol% the O–V– O and V–O–V bands dominate the spectra and demonstrate the former role of V2O5 oxide if it is in high concentration. 2D-COS was successfully applied in this study helping in a better vibration bands assignment and in clarifying the structural changing induced by the TM oxides. Both synchronous and asynchronous spectra indicate a good correlation between the breaking of P O bonds and vanadium content and between the diminishing of in-chain P–O–P bonds and PO2 groups and vanadium content. Acknowledgements Nicoleta Vedeanu acknowledges financial support from the European Union Marie Curie Training Site on Advanced and Applied Vibrational Spectroscopy (Contract no. HPMT-CT2000-00059). References [1] G. Tricot, L. Montagne, L. Delevoye, G. Palavit, V. Kostoj, J. Non-Cryst. Solids 345–346 (2004) 56. [2] J.J. Hudgens, R.K. Brow, D.R. Tallant, S.W. Martin, J. Non-Cryst. Solids 223 (1998) 21.
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