The modifier/former role of MoO 3 in some calcium-phosphate glasses D. Toloman a , R. Ciceo-Lucacel b , D.A. Magdas a,⇑ , A. Regos b , A.R. Biris a , C. Leostean a , I. Ardelean b a National Institute for Research and Development of Isotopic and Molecular Technologies, 65-103 Donath Street, 400293 Cluj-Napoca, Romania b Faculty of Physics, ‘‘Babes-Bolyai’’ University, 400084 Cluj-Napoca, Romania article info Article history: Received 9 October 2012 Received in revised form 20 December 2012 Accepted 21 December 2012 Available online 29 December 2012 Keywords: Calcium-phosphate glasses Molybdenum oxide EPR Raman spectroscopy Dual role abstract This paper report the results obtained by EPR and Raman investigations of xMoO 3 (100  x)[P 2 O 5 CaO] with 0 6 x 6 50 mol% glass system. From EPR spectroscopy were evidenced the local symmetry and the interaction between Mo 5+ ions. Depending on the content of MoO 3 were highlighted the EPR spectra modifications. By Raman spectroscopy were identified and analyzed the modification which appear on the characteristic bands of these glasses. At low concentration of molybdenum oxide the specific Raman bands of long phosphate chains (Q 2 ) dominate the spectra meanwhile for high molybdenum content the most intense bands are those specific to MoO 3 and short phosphate groups. From both techniques we can conclude that at low concentration of molybdenum oxide, it acts as a very strong network modifier while for high concentrations it plays the role of network co-former. Ó 2012 Elsevier B.V. All rights reserved. 1. Introduction Glasses containing transition metal ions offer much interest be- cause of their potential application in electrochemical, electronic and electro-optical devices [1–4]. The properties of glasses are mainly determined by the degree of local order/disorder, therefore the investigations giving information about the local and molecu- lar structure are important in order to understand the correlation between the corresponding properties and structure. The category of materials called glass network formers cover a large diversity of substances which are able to form glasses by themselves. Following both, structural and kinetic theories which give the properties needed by a substance to be able to vitrify it selves, it was noticed that the most common oxides used as glass network formers are: SiO 2 ,B 2 O 3 and P 2 O 5 [5]. The structure of phosphate glasses is formed by PO 4 tetrahedra connected by corners similar to the silica structure. Vitreous P 2 O 5 has a three-dimensional network build up with PO 4 tetrahedra connected by three of their four corners. The fourth one is occupied by terminal double-bonded oxygen. By introducing the glass net- work modifiers a depolymerization of P 2 O 5 vitreous skeleton ap- pears conducting to the breaking of PAOAP bond and formation of terminal oxygens [6]. Depending on the number of the bridging oxygen the phosphate tetrahedra can be described in Q n formalism, where n 0 represents the number of the bridging oxygens and can have a value of 0, 1, 2, 3. Such notation was first used by Lippma et al. [7], and is widely accepted in the literature for describing structures of phosphate network. A framework built up with Q 3 denotes a fully polymerized structure, while Q 2 unit gives only a two-dimensional structure based on chains or rings, specific to methaphosphate structure. Q 1 mean two tetrahedral connected by a corner and Q 0 means isolated tetrahedra. Q 1 and Q 0 units are characteristic for pyrophosphate and orthophosphate struc- tures [8]. Electron paramagnetic resonance (EPR) is one of the most effi- cient methods for characterization of the local order and magnetic interactions in glasses [9]. The molybdenum ions exist in at least two valence states as Mo 5+ and Mo 6+ . Independent of the nature of the alkaline ion, the r e conductivity in these glasses was as- sumed to be due to electronic hopping from the lower valence state Mo 5+ (donor level) to higher valence state Mo 6+ (acceptor le- vel). It is also well known that the Mo 5+ ion is a sensitive indicator for the structural changes of the local symmetry in oxide glasses [10–13]. Thus, the presence of octahedrally coordinated Mo 5+ ions were identified in the case of phosphate glasses, the octahedron being trigonally distorted [10]. Raman scattering spectra have been used for investigation of the molecular structure of phosphate glasses [14–16]. In the Ra- man spectra of methaphosphate glasses, there are band at 695 cm 1 for the (POP) sym stretching vibration, at 1173 cm 1 for the (PO 2 ) sym stretching vibration, and a band at 1270 cm 1 for the (P@O) sym vibration. The position and shape of these bands have been found to be sensitive to the phosphate chain length and the network modifier species. This paper aims to present our results concerning the structural details of the xMoO 3 (1  x)[P 2 O 5 CaO] with 0 6 x 6 50 mol% glasses investigated by EPR and Raman spectroscopy. Distribution 0925-8388/$ - see front matter Ó 2012 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.jallcom.2012.12.112 ⇑ Corresponding author. Tel.: +40 0264 584037; fax: +40 0264 420042. E-mail address: Alina.Magdas@itim-cj.ro (D.A. Magdas). Journal of Alloys and Compounds 556 (2013) 67–70 Contents lists available at SciVerse ScienceDirect Journal of Alloys and Compounds journal homepage: www.elsevier.com/locate/jalcom